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			{{Short description|Fossil flora and fauna of North American site}}
	{{underconstruction}}
			This is an overview of the fossil flora and fauna of the Maastrichtian-Danian ].
	==Theropods==		== Invertebrates ==
			===Insects===
			Insects from the groups ], ], and possibly ] have been unearthed in Hell Creek in amber.<ref name="depalma">{{cite journal |last1=DePalma |first1=Robert |last2=Cichocki |first2=Frederich |last3=Dierick |first3=Manuel |last4=Feeney |first4=Robert |title=Preliminary Notes on the First Recorded Amber Insects from the Hell Creek Formation |journal=The Journal of Paleontological Sciences |date=2010 |volume=10 |pages=1–7 |url=https://aaps-journal.org/pdf/JPS-C-10-0001.pdf |access-date=16 November 2020}}</ref><ref name="nel">{{cite journal |last1=Nel |first1=André |last2=DePalma |first2=Robert A. |last3=Engel |first3=Michael S. |title=A possible hemiphlebiid damselfly in Late Cretaceous amber from South Dakota (Odonata: Zygoptera) |journal=Transactions of the Kansas Academy of Science |date=2010 |volume=113 |issue=3/4 |pages=231–234 |doi=10.1660/062.113.0312 |jstor=41309615|s2cid=84827761 }}</ref> Fossils found in the Hell Creek Formation and the ] of these insects went extinct during the ].<ref>{{cite web |last1=Messer |first1=A'ndrea Eluse |title=Leaf-mining insects destroyed with the dinosaurs, others quickly appeared |url=https://news.psu.edu/story/321434/2014/07/24/research/leaf-mining-insects-destroyed-dinosaurs-others-quickly-appeared |website=Penn State News |publisher=Pennsylvania State University |access-date=20 August 2014}}</ref><ref>{{cite web |title=North Dakota site shows wreckage from same object that killed the dinosaurs |url=https://www.washington.edu/news/2019/03/29/north-dakota-site-shows-wreckage-from-same-object-that-killed-the-dinosaurs/ |website=UW News |publisher=University of Washington |access-date=29 March 2019}}</ref><ref>{{cite magazine |last1=Peterson |first1=Douglas |title=The Day the Dinosaurs Died |url=https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died |magazine=The New Yorker}}</ref>
			{{Paleobiota-key-compact}}
			{| class="wikitable sortable mw-collapsible" style="margin:auto; width:100%
			! Genus
			! Species
			! Location
			! Stratigraphic position
			! Material
			! Notes
			! Images
			|-
			|style="background:#FEF6E4;"|
			'']''
			|style="background:#FEF6E4;"|
			'']''
			|style="background:#FEF6E4;"|
			|style="background:#FEF6E4;"|
			|style="background:#FEF6E4;"|
			|style="background:#FEF6E4;"|
			Possible hispine beetle herbivory on '']''
			|style="background:#FEF6E4;"|
			|-
			|-
			|
			]<ref name="nel"/>
			|
			Indeterminate
			|
			|
			|
			|
			Possible ] ]
			|
			|-
			|-
			|
			]<ref name="depalma"/>
			|
			Indeterminate
			|
			|
			|
			|
			Undescribed ]n ]
			|
			|-
			|-
			|
			]<ref name="depalma"/>
			|
			Indeterminate
			|
			|
			|
			|
			Undescribed ]n ]
			|
			|-
			|-
			|
			]<ref>{{cite journal |last1=Nel |first1=André |title=Maastrichtian representatives of the dragonfly family Aeschnidiidae question the entomofaunal turnover of the early Late Cretaceous |url=https://www.biotaxa.org/pe/article/view/palaeoentomology.4.3.5 |journal=Palaeoentomology |date=2021 |volume=4 |issue=3 |doi=10.11646/palaeoentomology.4.3.5 |access-date=17 Feb 2024 }}</ref>
			|
			Indeterminate
			|
			|
			|
			|
			Indeterminate ] ]
			|
			|-
			|}
	===Other theropods===		===Molluscs===
	{| class="wikitable" align="center" width="100%"		{| class="wikitable sortable mw-collapsible" style="margin:auto; width:100%
			! Genus
			! Species
			! Location
			! Stratigraphic position
			! Material
			! Notes
			! Images
	|-		|-
			| rowspan=3 | '']''
	! colspan="6" align="center" |'''Miscellaneous ] ]s of the Hell Creek Formation'''
			|
			'']''
			|
			|
			|
			|
			Freshwater ]s
			|
	|-		|-
			|
			'']''
			|
			|
			|
			|
			Freshwater ]s
			|
			|-
			|
			'']''
			|
			|
			|
			|
			Freshwater ]s
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			| ] of family ].<ref name="mussel">{{cite web |last1=Graf |first1=Dan |last2 = Cummings |first2=Kevin |title=The Mussel Project |url=http://mussel-project.uwsp.edu/fmuotwaolcb/ |website=UWSP Mussel Project |publisher=The University of Wisconsin-Stevens Point |access-date=7 June 2021}}</ref>
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			| ] of family ].<ref name=mussel />
			|
			|-
			| rowspan=2 | '']''
			| '']''
			|
			|
			|
			| ] of family ].<ref name=mussel />
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			| ] of family ].<ref name=mussel />
			|
			|-
			| rowspan=9 | '']''
			| '']''
			|
			|
			|
			| ] of family ].<ref name=mussel />
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			|
			|
			|
			|
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			|
			|
			|-
			| rowspan=2 | '']''
			| '']''
			|
			|
			|
			|
			|
			|-
			| ''C. sp''
			| South Dakota
			|
			|
			| From a marine facies ("tongue"). Modern members of the genus live in fresh water
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			| "]". "]". "]". "]". Family ].
			|
			|-
			| '']''
			| Indeterminate
			|
			|
			|
			|
			|
			|-
			| '']''
			| ''C. sp''
			|
			|
			|
			| ]
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			| Bivalve. Family ]. From a marine facies ("tongue") in South Dakota.
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			| ]. Family ]. Collected from a marine facies ("tongue") in South Dakota.
			|
			|-
			| '']''
			| ''G. sp''
			|
			|
			|
			| Bivalve. Family Cardiidae (]). Collected from a marine facies ("tongue") in South Dakota.
			|
			|-
			| '']''
			| ''?H. sp''
			|
			|
			|
			| Bivalve. Present members of this genus are ]. Collected from a marine facies ("tongue") in South Dakota.
			|
			|-
			| '']''
			| indeterminate
			|
			|
			|
			| Bivalve. Family ]. Collected from a marine facies ("tongue") in South Dakota.
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			| ]. From a marine facies ("tongue") in South Dakota.
			|
			|-
			| '']''
			| '']''
			|
			|
			|
			| Microconch of an ammonite. From a marine facies ("tongue") in South Dakota.
			|
			|-
			| ]
			| indeterminate
			|
			|
			|
			| Ammonite. From a marine facies ("tongue") in South Dakota. Other attributes: specimen has hooks on its shell.
			|
			|-
			|}
			== Amphibians ==
			{{Paleobiota-key-compact}}
			{| class="wikitable sortable mw-collapsible" style="margin:auto; width:100%
	! Genus		! Genus
	! Species		! Species
			! Location
	! Presence
			! Stratigraphic position
	! Description
			! Material
			! Notes
			! Images
	|-		|-
	|		|
			Anura (])<ref name="parsons">Pearson ''et al.'' (2002) p. 154</ref>
	'']''
	|		|
			indeterminate<ref name="parsons"/>
	''A. archibaldi''
	|		|
			* North Dakota<ref name="parsons2">Pearson ''et al.'' (2002) pp. 145–167</ref>
			* South Dakota<ref name="parsons2"/>
			|
			Middle to upper Hell Creek Formation<ref name="parsons3">Pearson ''et al.'' (2002) p. 155</ref>
			|
			3 unassigned specimens<ref name="parsons4">Pearson ''et al.'' (2002) pp. 156</ref>
			|
			Anura indet. consists of material not currently assigned to any genus of frog.<ref name="parsons"/>
			|
			|-
			|
			'']''<ref name="eb1970-amphibians-barb">Listed as "cf. ''Barbourula'' sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.</ref>
			|
			Indeterminate<ref name="eb1970-amphibians">"Class Amphibia," in Estes and Berberian, (1970). Page 4.</ref>
			|
			* Montana<ref name="eb1970-amphibians-montana">"Class Amphibia," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.</ref>
			|
			|
			|
			|
			|-
			|
			Caudata (])<ref name="parsons"/>
			|
			indeterminate<ref name="parsons"/>
			|
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			Lower to uppermost Hell Creek Formation<ref name="parsons3"/>
			|
			149 unassigned specimens<ref name="parsons4"/>
			|
			Material of Caudata indet. is not currently assigned to any genus.<ref name="parsons"/>
			|
			|-
			|
			'']''<ref name="eb1970-amphibians-eopel">Listed as "''Eopelobates''? sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.</ref>
			|
			Indeterminate<ref name="eb1970-amphibians" />
			|
			* Montana<ref name="eb1970-amphibians-montana" />
			|
			|
			|
			|
			|-
			|
			'']''<ref name="parsons"/><ref name="eb1970-amphibians" />
			|
			''H. dilatus''<ref name="parsons"/><ref name="eb1970-amphibians" />
			|
			* Montana<ref name="eb1970-amphibians-montana" />
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			Middle to upper Hell Creek Formation<ref name="parsons3"/>
			|
			6 specimens<ref name="parsons4"/>
			|
			''Habrosaurus'' is a ] ].<ref name="parsons"/>
			|
			|-
			|
			'']''<ref name="eb1970-amphibians" />
			|
			''L. bairdi''<ref name="eb1970-amphibians" />
			|
			* Montana<ref name="eb1970-amphibians-montana" />
			|
			|
			|
			|
			|-
			|
			'']''<ref name="parsons"/><ref name="eb1970-amphibians" />
			|
			''O. kayi''<ref name="parsons"/><ref name="eb1970-amphibians" />
			|
			* Montana<ref name="eb1970-amphibians-montana" />
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			Lower to upper Hell Creek Formation<ref name="parsons3"/>
			|
			22 specimens<ref name="parsons4"/>
			|
			''Opisthotriton'' is classified as a ].<ref name="parsons"/>
			|
			|-
			|
			'']''<ref name=Paranecturus>{{cite journal |author=David G. Demar Jr. |year=2013 |title=A new fossil salamander (Caudata, Proteidae) from the Upper Cretaceous (Maastrichtian) Hell Creek Formation, Montana, U.S.A |journal=Journal of Vertebrate Paleontology |volume=33 |issue=3 |pages=588–598 |doi=10.1080/02724634.2013.734887 |bibcode=2013JVPal..33..588D |s2cid=128532897 }}</ref>
			|
			''P. garbanii''<ref name=Paranecturus />
			|
			* Montana<ref name=Paranecturus />
			|
			|
			|
			A member of ].<ref name=Paranecturus />
			|
			|-
			|
			'']''<ref name="eb1970-amphibians" />
			|
			''P. cretacica''<ref name="eb1970-amphibians" />
			|
			* Montana<ref name="eb1970-amphibians-montana" />
			|
			|
			|
			|
			|-
			|
			'']''<ref name="eb1970-amphibians" />
			|
			''P. copei''<ref name="eb1970-amphibians" />
			|
			* Montana<ref name="eb1970-amphibians-montana" />
			|
			|
			|
			|
			|-
			|
			'']''<ref name="parsons"/><ref name="eb1970-amphibians" />
			|
			''S. tectum''<ref name="parsons"/><ref name="eb1970-amphibians" />
			|
			* Montana<ref name="eb1970-amphibians-montana" />
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			Lower to upper Hell Creek Formation<ref name="parsons3"/>
			|
			144 specimens<ref name="parsons4"/>
			|
			''Scapherpeton'' is a ] that is very common in the Hell Creek Formation.<ref name="parsons"/>
			|
			|-
			|
			'']''<ref name="eb1970-amphibians" />
			|
			''S. pustulosa''<ref name="eb1970-amphibians" />
			|
			* Montana<ref name="eb1970-amphibians-montana" />
			|
			|
			|
			A small frog
			|
			|}
			== Fish ==
			=== Bony fish ===
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="7" style="text-align:center;" | ''']'''
			|-
			! Genus !! Species !! Location !! Stratigraphic position !! Material !! Notes !! Images
			|-
			| rowspan=5 | '']''<ref name="parsons"/><ref name="eb1970-bonyfish">"Class Osteichthyes," in Estes and Berberian, (1970). Page 3.</ref><ref name=":3">{{Cite journal |last1=Hilton |first1=Eric J. |last2=Grande |first2=Lance |date=2022-10-03 |title=Late Cretaceous sturgeons (Acipenseridae) from North America, with two new species from the Tanis site in the Hell Creek Formation of North Dakota |journal=Journal of Paleontology |volume=97 |issue=1 |pages=189–217 |doi=10.1017/jpa.2022.81 |s2cid=252702937 |doi-access=free }}</ref>
			| '']''<ref name=":3" />
			|
			* North Dakota (])<ref name=":3" />
			|
			|
			| rowspan=4 | A ]
	|		|
	An ].
	|-		|-
			| '']''<ref name="eb1970-bonyfish" />
			|
			* Montana<ref name="eb1970-bonyfish-montana">"Class Osteichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1.</ref>
	|		|
	'']''
	|		|
			|
	''P. lacustris''
			|-
			| '']''<ref name=":3" />
			|
			* North Dakota (Tanis)<ref name=":3" />
			|
	|		|
	|		|
	A common ], possibly ]. Also found in the ], ], ], and ]s.
	|-		|-
			| ''A.'' cf. ''A. amnisinferos''<ref name=":3" />
	|		|
			* North Dakota (Tanis)<ref name=":3" />
	'']''
	|		|
	''R. gilmorei''
	|		|
	|		|
			|-
	A common coelurosaur, possibly synonymous with ''Paronychodon''. Also found in the ], ], ], ], and ]s.
			|
			cf. ''A.'' sp.<ref name="parsons"/>
			|
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			Lower to upper Hell Creek Formation<ref name="parsons3"/>
			|
			18 specimens are tentatively assigned to ''Acipenser'' sp.<ref name="parsons4"/>
			|
			''Acipenser'' sp. is tentatively referred to the genus.<ref name="parsons"/>
			|
			|-
			| '']''<ref name=":4">{{cite journal |last1=Sato |first1=Hiroki |last2=Murray |first2=Alison M. |last3=Vernygora |first3=Oksana |last4=Currie |first4=Philip J. |title=A rare, articulated sturgeon (Chondrostei: Acipenseriformes) from the Upper Cretaceous of Dinosaur Provincial Park, Alberta, Canada |journal=Journal of Vertebrate Paleontology |date=4 July 2018 |volume=38 |issue=4 |pages=(1)-(15) |doi=10.1080/02724634.2018.1488137 |s2cid=92574712 }}</ref>
			| ''A. acanthaspis''<ref name=":4" />
			|
			* Montana<ref name=":4" />
			|
			|
			| A sturgeon, originally considered as indeterminate material<ref name=":4" />
			|
			|-
			| '']''<ref name="parsons"/><ref name="eb1970-bonyfish" />
			| '']''<ref name="parsons"/><ref name="eb1970-bonyfish" />
			|
			* Montana<ref name="eb1970-bonyfish-montana" />
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			| Lower to upper Hell Creek Formation<ref name="parsons3"/>
			| 28 specimens<ref name="parsons4"/>
			| A long-snouted slender fish classified as an ].<ref name="parsons"/>
			|
			|-
			| '']''<ref name="eb1970-bonyfish-4">"Class Osteichthyes," in Estes and Berberian, (1970). Page 4.</ref>
			| ''C. amnicolus''<ref name="eb1970-bonyfish-4" />
			|
			* Montana<ref name="eb1970-bonyfish-montana-4" />
			|
			|
			|
			|
			|-
			|
			'']''<ref name="eb1970-bonyfish" />
			|
			''C. fragosus''<ref name="eb1970-bonyfish" />
			|
			* Montana<ref name="eb1970-bonyfish-montana" />
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			|
			|
			A small ] fish (ubiquitous). Previously known as ''Amia fragosa'' or ''Kindleia fragosa''.<ref>{{cite journal |last1=Grande |first1=Lance |last2=Bemis |first2=William E. |title=A Comprehensive Phylogenetic Study of Amiid Fishes (Amiidae) Based on Comparative Skeletal Anatomy. an Empirical Search for Interconnected Patterns of Natural History |journal=Journal of Vertebrate Paleontology |date=10 April 1998 |volume=18 |issue=sup1 |pages=1–696 |doi=10.1080/02724634.1998.10011114 |bibcode=1998JVPal..18S...1G }}</ref> 2610 specimens have been assigned to ''Kindleia'', making it an extremely common genus.<ref name="parsons4"/>
			|], species within same genus as ''C. fragosus'']]
			|
			|-
			| "'']''"<ref name="parsons"/><ref name="eb1970-bonyfish" />
			| "''L. occidentalis''"<ref name="parsons"/><ref name="eb1970-bonyfish" />
			|
			* Montana<ref name="eb1970-bonyfish-montana" />
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			| Lower to uppermost Hell Creek Formation<ref name="parsons3"/>
			| 938 specimens are assigned to ''Lepidosteus''<ref name="parsons4"/>
			| A ] that is very common in the Hell Creek Formation.<ref name="parsons"/> '']''.<ref>{{cite journal |last1=Grande |first1=Lance |title=An Empirical Synthetic Pattern Study of Gars (lepisosteiformes) and Closely Related Species, Based Mostly on Skeletal Anatomy. the Resurrection of Holostei |journal=Copeia |date=2010 |volume=2010 |issue=2A |pages=iii–871 |jstor=20787269 }}</ref>
			| ]
			|-
			| '']''<ref name="parsons"/>
			| ''M. thomasi''<ref name="parsons"/>
			|
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			| Lower to upper Hell Creek Formation<ref name="parsons3"/>
			| 6 specimens are assigned to ''Melvius''<ref name="parsons4"/>
			| A large ] ].<ref name="parsons"/>
			|
			|-
			| '']''
			| ''P. paulkatoi''
			|
			|
			|
			| Fish with columnar teeth
			|
			|-
			| '']''<ref name="eb1970-bonyfish" />
			| ''P. montanensis''<ref name="eb1970-bonyfish" />
			|
			* Montana<ref name="eb1970-bonyfish-montana" />
			|
			|
			|
			|
			|-
			| '']''<ref name="eb1970-bonyfish" />
			| ''P. wilsoni''<ref name="eb1970-bonyfish" />
			|
			* Montana<ref name="eb1970-bonyfish-montana" />
			|
			|
			| A ]
			|
			|-
			| '']''<ref name="eb1970-bonyfish-para">Listed as "cf. ''Paralbula casei''" in "Class Osteichthyes," Estes and Berberian, (1970). Page 4.</ref>
			| ''P. casei''<ref name="eb1970-bonyfish-para" />
			|
			* Montana<ref name="eb1970-bonyfish-montana-4">"Class Osteichthyes," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.</ref>
			|
			|
			|
			|
			|-
			| '']''<ref name=":2">{{cite journal |last1=Hilton |first1=Eric J. |last2=During |first2=Melanie A.D. |last3=Grande |first3=Lance |last4=Ahlberg |first4=Per E. |title=New paddlefishes (Acipenseriformes, Polyodontidae) from the Late Cretaceous Tanis Site of the Hell Creek Formation in North Dakota, USA |journal=Journal of Paleontology |date=May 2023 |volume=97 |issue=3 |pages=675–692 |doi=10.1017/jpa.2023.19 |bibcode=2023JPal...97..675H |s2cid=258095684 |doi-access=free }}</ref>
			| ''P. willybemisi''<ref name=":2" />
			|
			* North Dakota (Tanis)<ref name=":2" />
			|
			|
			| A paddlefish
			| ]
			|-
			| '']''<ref name="eb1970-bonyfish-4" />
			| ''P. nanus''<ref name="eb1970-bonyfish-4" />
			|
			* Montana<ref name="eb1970-bonyfish-montana-4" />
			|
			|
			| Small ]
			|
			|-
			| '']''<ref name="eb1970-bonyfish" />
			| Indeterminate<ref name="eb1970-bonyfish" />
			|
			* Montana<ref name="eb1970-bonyfish-montana" />
			|
			|
			|
			|
			|-
			| ]
			| Indeterminate
			|
			|
			|
			| Fish
			|
			|-
			| ]<ref name=":5">{{cite journal |last1=Grande |first1=Lance |last2=Bemis |first2=William E. |title=Osteology and Phylogenetic Relationships of Fossil and Recent Paddlefishes (Polyodontidae) with Comments on the Interrelationships of Acipenseriformes |journal=Memoir |publisher=Society of Vertebrate Paleontology |date=1991 |volume=1 |pages=ii–121 |doi=10.2307/3889328 |jstor=3889328 }}</ref>
			| Indeterminate<ref name=":5" />
			|
			* Montana<ref name=":5" />
			|
			|
			| Paddlefish
			|
			|-
			| '']''<ref name="eb1970-bonyfish" />
			| ''P. squamosus''<ref name="eb1970-bonyfish" />
			|
			* Montana<ref name="eb1970-bonyfish-montana" />
			|
			|
			| A sturgeon
			|
			|-
			| '']''<ref name=":2" />
			| ''P. inundatus''<ref name=":2" />
			|
			* North Dakota (Tanis)<ref name=":2" />
			|
			|
			| A paddlefish
			|
	|-		|-
	|}		|}
	====Deinonychosaurs====		=== Cartilaginous fish ===
	{| class="wikitable" align="center" width="100%"
			{| class="wikitable sortable mw-collapsible"
	|-		|-
	! colspan="6" align="center" |'''] ]s of the Hell Creek Formation'''		! colspan="7" style="text-align:center;"|'''] reported from the Hell Creek Formation'''
	|-		|-
	! Genus		! Genus
	! Species		! Species
			! Location
	! Presence
			! Stratigraphic position
	! Description
			! Material
			! Notes
	! Images		! Images
	|-		|-
			|
			'']''<ref name=GSAeuselachians />
			|
			''C.'' sp.<ref name=GSAeuselachians />
			|
			* ]<ref name=GSAeuselachians />
			|
			|
			|
			A member of ].<ref name=GSAeuselachians />
			|
			]
			|-
			|
			'']''<ref name=Galagadon>{{cite journal |author1=Terry A. Gates |author2=Eric Gorscak |author3=Peter J. Makovicky |year=2019 |title=New sharks and other chondrichthyans from the latest Maastrichtian (Late Cretaceous) of North America |journal=Journal of Paleontology |volume= 93|issue= 3|pages=512–530 |doi=10.1017/jpa.2018.92 |bibcode=2019JPal...93..512G |doi-access=free }}</ref>
			|
			''G. nordquistae''
			|
			* South Dakota
			|
			|
			Isolated teeth
			|
			A ]
			|
			|-
			|
			'']''<ref name="eb1970-cartfish">"Class Chondrichthyes," in Estes and Berberian, (1970). Page 3.</ref>
			|
			''L. selachos''<ref name="eb1970-cartfish" />
			|
			* Montana<ref name="eb1970-cartfish-montana">"Class Chondrichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1.</ref>
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			Lower to upper Hell Creek Formation<ref name="parsons3"/>
			|
			40 specimens<ref name="parsons4"/>
			|
			A genus of prehistoric ]s in the family ]. It makes up 0.4% of the remains of the vertebrates of the Hell Creek Formation.<ref name="parsons"/>
			|
			|-
			|
			'']''<ref name=GSAeuselachians />
			|
			''M. pustulosus''<ref name=GSAeuselachians >{{Cite book |author1=Todd D. Cook |author2=Michael G. Newbrey |author3=Donald B. Brinkman |author4=James I. Kirkland |year=2014 |chapter=Euselachians from the freshwater deposits of the Hell Creek Formation of Montana |title=Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas |volume=503 |pages=229–246 |doi=10.1130/2014.2503(08) |series=Geological Society of America Special Papers |isbn=978-0-8137-2503-1 }}</ref>
			|
			* ]<ref name=GSAeuselachians />
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			Lower to upper Hell Creek Formation.<ref name="parsons3"/>
			|
			1677 specimens<ref name="parsons4"/> previously assigned to ''M. bipartitus''.<ref name=GSAeuselachians />
			|
			Is an ] ]<ref name="parsons"/> ] related to ]es.<ref name=GSAeuselachians /> Described on the basis of teeth formerly assigned to the species ''M. bipartitus''.<ref name=GSAeuselachians /> The material assigned to ''Myledaphus bipartitus'' and makes up 16.5% of the vertebrate remains.<ref name="parsons"/>
			|
			|-
			|
			'']''<ref name=GSAeuselachians />
			|
			''P. estesi''<ref name=GSAeuselachians />
			|
			* ]<ref name=GSAeuselachians />
			|
			|
			|
			A member of ].<ref name=GSAeuselachians /> Formerly assigned to the genus '']''.
			|
			|-
			|
			'']''<ref name=GSAeuselachians />
			|
			''R. americana''<ref name=GSAeuselachians />
			|
			* ]<ref name=GSAeuselachians />
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/>
			|
			Middle Hell Creek Formation<ref name="parsons3"/>
			|
			5 specimens previously assigned to ''Squatirhina''<ref name="parsons4"/>
			|
			A ]-like shark.<ref name=GSAeuselachians /> Formerly assigned to ''Squatirhina''. The remains consist of 0.05% of the vertebrates.<ref name="parsons4"/> Also known from the ].<ref name=GSAeuselachians />
	|		|
			|-
	]
	|		|
			] indet.<ref name=Galagadon />
	cf. '']'' sp.
			|
			Indeterminate
			|
			* South Dakota
			|
			|
			An isolated tooth.
	|		|
	|		|
	| rowspan="99" |
	]'']]
	|-		|-
	|		|
			]<ref>{{cite journal |title=Stratigraphy and paleontology of the Cretaceous Hell Creek Formation, Stumpf site, Morton County, North Dakota |journal=Proceedings of the North Dakota Academy of Sciences |date=1994 |volume=48}}</ref>
	'']''
	|		|
			.sp.
	'']'' sp.
	|		|
			* North Dakota
	A very common dromaeosaurid.
			|
			|
			|
			|
			|-
			|}
			== Dinosaurs ==
			A paleo-population study is one of the most difficult of analyses to conduct in field paleontology. Here is the most recent estimate of the proportions of the eight most common dinosaurian families in the Hell Creek Formation, based on detailed field studies by White, Fastovsky and Sheehan.<ref>{{cite journal |last1=White |first1=Paul |last2=Fastovsky |first2=David |last3=Sheehan |first3=Peter |title=Taphonomy and suggested structure of the dinosaurian assemblage of the Hell Creek Formation (Maastrichtian), eastern Montana and western North Dakota |journal=PALAIOS |date=1998 |volume=13 |issue=1 |page=41 |doi=10.2307/3515280 |jstor=3515280 |bibcode=1998Palai..13...41W |url=https://digitalcommons.uri.edu/cgi/viewcontent.cgi?article=1080&context=cels_past_depts_facpubs }}</ref>
			* '''Ceratopsidae''' 61%
			* '''Hadrosauridae''' 23%
			* '''Ornithomimidae''' 5%
			* '''Tyrannosauridae''' 4%
			* '''Hypsilophodontidae''' 3%
			* '''Dromaeosauridae''' 2%
			* '''Pachycephalosauridae''' 1%
			* '''Troodontidae''' 1% (represented only by teeth)
			]
			Outcrops sampled by the Hell Creek Project were divided into three sections: lower, middle and upper slices. The top and bottom sections were the focus of the PLoS One report, and within each portion many remains of '']'', '']'', and '']'' were found. ''Triceratops'' was the most common in each section, but, surprisingly, ''Tyrannosaurus'' was just as common, if not slightly more common, than the hadrosaur ''Edmontosaurus''. In the upper Hell Creek section, for example, the census included twenty two ''Triceratops'', five ''Tyrannosaurus'', and five ''Edmontosaurus''.
			The dinosaurs '']'', '']'', '']'' and '']'' were also included in the breakdown, but were relatively rare. Other dinosaurs, such as ''Sphaerotholus'', ''Denversaurus'', ''Torosaurus'', ''Struthiomimus'', ''Acheroraptor'', ''Dakotaraptor'', ''Pectinodon,'' ''Richardoestesia'', ''Paronychodon'', ''Anzu'', ''Leptorhynchos'' and ''Troodon (more likely Pectinodon)'', were reported as being rare and are not included in the breakdown.
			The dinosaur collections made over the past decade during the Hell Creek Project yielded new information from an improved genus-level collecting schema and robust data set that revealed relative dinosaur abundances that were unexpected, and ontogenetic age classes previously considered rare. We recognize a much higher percentage of ''Tyrannosaurus'' than previous surveys. ''Tyrannosaurus'' equals ''Edmontosaurus'' in U3 and in L3 comprises a greater percentage of the large dinosaur fauna as the second-most abundant taxon after ''Triceratops'', followed by ''Edmontosaurus''. This is surprisingly consistent in (1) the two major lag deposits (MOR loc. HC-530 and HC-312) in the Apex sandstone and Jen-rex sand where individual bones were counted and (2) in two thirds of the formation reflected in L3 and U3 records of dinosaur skeletons only.
			''Triceratops'' is by far the most common dinosaur at 40% (n = 72), ''Tyrannosaurus'' is second at 24% (n = 44), ''Edmontosaurus'' is third at 20% (n = 36), followed by ''Thescelosaurus'' at 8% (n = 15), ''Ornithomimus'' at 5% (n = 9), and ''Pachycephalosaurus'' and ''Ankylosaurus'' both at 1% (n = 2) are relatively rare.
			Fossil footprints of dinosaurs from the Hell Creek Formation are very rare. As of 2017, there is only one find of a possible ''Tyrannosaurus rex'' footprint, dating from 2007 and described a year later.<ref>{{cite journal | last1 = Manning | first1 = P. L. | last2 = Ott | first2 = C. | last3 = Falkingham | first3 = P. L. | year = 2008 | title = The first tyrannosaurid track from the Hell Creek Formation (Late Cretaceous), Montana, U.S.A | journal = PALAIOS | volume = 23 | issue = 10| pages = 645–647 | doi = 10.2110/palo.2008.p08-030r | bibcode = 2008Palai..23..645M | s2cid = 129985735 }}</ref> A trackway made by mid-sized theropod, possibly a small tyrannosaurid individual, was discovered in South Dakota in 1997, and in 2014 these footprints were named '']''.<ref name="styxi">{{cite journal |last1=Lockley |first1=M. |last2=Triebold |first2=M. |last3=Janke |first3=P. R. |year=2014 |title=Dinosaur Tracks from the Hell Creek Formation (Upper Cretaceous, Maastrichtian), South Dakota |journal=Fossil Footprints of Western North America: New Mexico Museum of Natural History and Science, Bulletin |volume=62 |pages=459–468 |url=https://econtent.unm.edu/digital/collection/bulletins/id/7309}}</ref>
			=== Ornithischians ===
			==== Ankylosaurs ====
			Indeterminate nodosaur remains have been unearthed in the Hell Creek Formation and other nearby areas.<ref name="Carpenter Breithaupt 1986">{{cite journal |last1=Carpenter |first1=Kenneth |last2=Breithaupt |first2=Brent |title=Latest Cretaceous occurrence of nodosaurid ankylosaurs (Dinosauria, Ornithischia) in Western North America and the gradual extinction of the dinosaurs |journal=Journal of Vertebrate Paleontology |date=2 September 1986 |volume=6 |issue=3 |pages=251–257 |doi=10.1080/02724634.1986.10011619 |bibcode=1986JVPal...6..251C }}</ref><ref>{{cite journal |last1=Carpenter |first1=K. |title=Late Cretaceous dinosaurs from the Denver Basin, Colorado |journal=Rocky Mountain Geology |date=November 2002 |volume=37 |issue=2 |pages=237–254 |doi=10.2113/11 |bibcode=2002RMGeo..37..237C |url=http://doc.rero.ch/record/14415/files/PAL_E1598.pdf }}</ref>
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="7" style="text-align:center;"|'''] reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
			|-
			|
			'']''<ref name="cretaceous-distribution-montana" />
			|
			''A. magniventris''<ref name="cretaceous-distribution-montana" />
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			| Upper
			|A partial skull, teeth, cervical vertebrae, dorsal vertebrae, caudal vertebrae, right scapulocoracoid, otic capsule, maxilla fragment, right jugal, left jugal and quadratojugal, sacral centra, additional fragments of the cervical half rings and a partial tail club handle.
			|
			An ]. Also found in the ], ], ] and ]s.
			|
			]
			|-
			|
			'']''<ref name="cretaceous-distribution-montana" />
			|
			''D. schlessmani''<ref name="cretaceous-distribution-montana" />
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			* South Dakota<ref name="cretaceous-distribution-southdakota" />
	|		|
			|Skull roof, pelvis and osteoderms.
			|
			A ] ankylosaur whose remains have been found in the ] and ].<ref name="Carpenter Breithaupt 1986"/>
			|
			]
			|-
			|}
			==== Pachycephalosaurs ====
			An undescribed and unnamed pachycephalosaur is present in North Dakota.<ref name="cretaceous-distribution-northdakota" /> Pachycephalosaur remains have been unearthed in Montana as in the case of '']'' and the now invalid genus ''Stenotholus kohleri'', which is now a junior synonym of ''Pachycephalosaurus''.<ref>{{cite journal |last1=Giffin |first1=Emily B. |last2=Gabriel |first2=Diane L. |last3=Johnson |first3=Rolf E. |title=A New Pachycephalosaurid Hell Creek Formation of Montana |journal=Journal of Vertebrate Paleontology |date=22 January 1988 |volume=7 |issue=4 |pages=398–407 |doi=10.1080/02724634.1988.10011672 |jstor=4523163 }}</ref>
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="7" style="text-align:center;"|''']s reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
	|-		|-
	|		|
			'']''<ref name="bakkeretal2006">Bakker et al. (2006)</ref>
	'']''
	|		|
			''D. hogwartsia''<ref name="bakkeretal2006" />
	''Troodon'' sp.
	|		|
			* South Dakota<ref name="bakkeretal2006" />
	| A ].
			|
			* Middle<ref name="bakkeretal2006" />
			|
			|
			A ], possibly synonymous with '']''.
			|
			]
			|-
			|
			'']''<ref name="cretaceous-distribution-montana" />
			|
			''P. wyomingensis''<ref name="cretaceous-distribution-montana" />
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			* South Dakota<ref name="cretaceous-distribution-southdakota" />
			|
			|
			|
			A pachycephalosaur. Also found in the ].
			|
			]
			|-
			|'']''<ref name="Platytholus">{{cite journal |last1=Horner |first1=John R. |last2=Goodwin |first2=Mark B. |last3=Evans |first3=David C. |title=A new pachycephalosaurid from the Hell Creek Formation, Garfield County, Montana, U.S.A. |journal=Journal of Vertebrate Paleontology |date=28 October 2022 |volume=42 |issue=4 |doi=10.1080/02724634.2023.2190369 |bibcode=2022JVPal..42E0369H |s2cid=258154892 }}</ref>
			|''P. clemensi<ref name="Platytholus" />''
			|
			* Montana<ref name="Platytholus" />
			|
			* Lower<ref name="Platytholus" />
			|A partial skull<ref name="Platytholus" />
			|A medium-sized pachycephalosaurine closely related to '']'' and '']''
			|
			]
			|-
			|rowspan=2 |
			'']''<ref name="cretaceous-distribution-montana" />
			|
			''S. buchholtzae''<ref name="cretaceous-distribution-montana" />
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			|
			* Lower to upper<ref>{{cite journal |last1=Williamson |first1=Thomas E. |last2=Carr |first2=Thomas D. |title=A new genus of derived pachycephalosaurian from western North America |journal=Journal of Vertebrate Paleontology |date=2003 |volume=22 |issue=4 |pages=779–801 |doi=10.1671/0272-4634(2002)0222.0.CO;2 |s2cid=86112901 }}</ref><ref name="Woodruff23" />
			|
			"Skull material."<ref name="table-21-1-465">"Table 21.1," in Weishampel, et al. (2004). Page 465.</ref>
			|
			A pachycephalosaur whose remains have also been found in the ]. Genus also known from the ], ] and the ].
			|rowspan=2 |
			]
			|-
			|
			''S. triregnum''<ref name="Woodruff23">{{cite journal |last1=Woodruff |first1=D. Cary |last2=Schott |first2=Ryan K. |last3=Evans |first3=David C. |title=Two new species of small-bodied pachycephalosaurine (Dinosauria, Marginocephalia) from the uppermost Cretaceous of North America suggest hidden diversity in well-sampled formations |journal=Papers in Palaeontology |date=November 2023 |volume=9 |issue=6 |doi=10.1002/spp2.1535 |bibcode=2023PPal....9E1535W |s2cid=265261709 }}</ref>
			|
			* Montana<ref name="Woodruff23" />
			|
			* Middle<ref name="Woodruff23" />
			|
			A left squamosal.<ref name="Woodruff23" />
			|
			A pachycephalosaur distinguished from ''S. buchholtzae'' by its more ornamented squamosal.<ref name="Woodruff23" />
			|-
			|
			'']''<ref name="cretaceous-distribution-montana" />
			|
			''S. spinifer''<ref name="cretaceous-distribution-montana" />
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			* South Dakota
			* North Dakota
			|
			|
			|
			A pachycephalosaur, possibly synonymous with '']''. Also found in the ] and the ].
			|
			]
	|-		|-
	|}		|}
	===Oviraptorosaurs===		==== Ceratopsians ====
			Indeterminate ceratopsid teeth and some identifiable bones from ''Triceratops'' can be extremely common.<ref>{{cite book |last1=Carpenter |first1=Kenneth |title=Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs |date=2006 |publisher=Indiana University Press |id={{Project MUSE|49401|type=book}} |isbn=978-0-253-02795-5 }}{{page needed|date=January 2024}}</ref><ref>{{cite book |last1=Ryan |first1=Michael J. |last2=Chinnery-Allgeier |first2=Brenda J. |last3=Eberth |first3=David A. |title=New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium |date=2010 |publisher=Indiana University Press |isbn=978-0-253-35358-0 |jstor=j.ctt16gzgng }}</ref><ref>{{cite journal |last1=Scannella |first1=John B. |last2=Fowler |first2=Denver W. |title=A stratigraphic survey of Triceratops localities in the Hell Creek Formation, northeastern Montana (2006–2010) |journal=Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas |date=2014 |doi=10.1130/2014.2503(12) }}</ref><ref>{{cite report|doi=10.7934/p1099 |title=Evolutionary Trends in Triceratops from the Hell Creek Formation, Montana (Project) |year=2014 |last1=Scannella |first1=B. |last2=Fowler |first2=W. |last3=Goodwin |first3=B. |last4=Horner |first4=R. }}</ref><ref>{{cite journal |last1=Scannella |first1=John |title=A chasmosaurine ceratopsid premaxilla from the basal sandstone of the Hell Creek Formation, Montana |journal=Vertebrate Anatomy Morphology Palaeontology |date=10 November 2020 |volume=8 |pages=154–169 |doi=10.18435/vamp29366 |s2cid=228888356 |doi-access=free }}</ref> 8.31% of all vertebrate remains from the Hell Creek Formation are unassigned ceratopsids.<ref name="parsons4"/> In 2012, a new unidentified species of chasmosaur ceratopsian with noticeable differences from ''Triceratops'' was unearthed in South Dakota by a fossil hunter named John Carter.<ref>{{cite web|last1=Biles|first1=Jan|title=Rare dinosaur skull being prepared for exhibition|url=http://cjonline.com/news-local/2015-09-07/rare-dinosaur-skull-being-prepared-exhibition|website=Topeka Capital-Journal.com|publisher=Topeka Capital-Journal|access-date=7 September 2015}}</ref><ref>{{cite web|title=Super-sized Ceratopsian Skull Might be New Species|url=https://blog.everythingdinosaur.co.uk/blog/_archives/2015/08/29/super-sized-ceratopsian-skull-might-be-new-species.html|website=Everything Dinosaur|date=29 August 2015 |access-date=29 August 2015}}</ref><ref>{{cite web|last1=O' Connell|first1=Max|title=Dinosaur skull found in Buffalo likely a new species|url=http://rapidcityjournal.com/news/local/dinosaur-skull-found-in-buffalo-likely-a-new-species/article_b33d3375-b74c-5941-aa0b-281ad59b430a.html|website=Rapid City Journal|date=27 August 2015 |access-date=27 August 2015}}</ref>
	{| class="wikitable" align="center" width="100%"
			{{Paleobiota-key-compact}}
			{| class="wikitable sortable mw-collapsible"
	|-		|-
	! colspan="5" align="center" |'''] ]s of the Hell Creek Formation'''		! colspan="8" style="text-align:center;"|''']s reported from the Hell Creek Formation'''
	|-		|-
	! Genus		! Genus
	! Species		! Species
			! Synonyms
	! Presence
			! State
	! Description
			! Stratigraphic position
			! Material
			! Notes
	! Images		! Images
	|-		|-
	|		|
			'']''<ref name="cretaceous-distribution-montana" />
	* '']''
	|		|
			''L. gracilis''<ref name="cretaceous-distribution-montana" />
	# ''Chirostenotes'' sp.
	|		|
			|
	| A large ].
			* Montana<ref name="cretaceous-distribution-montana" />
	| rowspan="99" |
			|
	] sp.'']]
			|
			|
			A small primitive-looking ]n. Fossils have also been found in the ] in Wyoming.<ref>{{cite journal |last1=Ostrom |first1=John H. |title=Leptoceratops gracilis from the 'Lance' Formation of Wyoming |journal=Journal of Paleontology |date=May 1978 |volume=52 |issue=3 |pages=697–704 |jstor=1303974 }}</ref>
			|
			]
	|-		|-
	|		|
			'']''<ref name="OttLarson">Christopher J. Ott and Peter L. Larson, 2010, "A New, Small Ceratopsian Dinosaur from the Latest Cretaceous Hell Creek Formation, Northwest South Dakota, United States: A Preliminary Description", In: Ryan, M.J., Chinnery-Allgeier, B.J., and Eberth, D.A. (eds.) ''New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium'', Bloomington, Indiana University Press, 656 pp.</ref>
	* '']''
	|		|
			''T. sacrisonorum''<ref name="OttLarson">Christopher J. Ott and Peter L. Larson, 2010, "A New, Small Ceratopsian Dinosaur from the Latest Cretaceous Hell Creek Formation, Northwest South Dakota, United States: A Preliminary Description", In: Ryan, M.J., Chinnery-Allgeier, B.J., and Eberth, D.A. (eds.) ''New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium'', Bloomington, Indiana University Press, 656 pp.</ref>
	# ''Chirostenotes'' sp.
	|		|
			|
	| A large ].
			* South Dakota<ref name="OttLarson">Christopher J. Ott and Peter L. Larson, 2010, "A New, Small Ceratopsian Dinosaur from the Latest Cretaceous Hell Creek Formation, Northwest South Dakota, United States: A Preliminary Description", In: Ryan, M.J., Chinnery-Allgeier, B.J., and Eberth, D.A. (eds.) ''New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium'', Bloomington, Indiana University Press, 656 pp.</ref>
			|
			|
			|
			A controversial ceratopsian possibly synonymous with ''Triceratops''<ref name="Longrich">{{Cite journal|author=Nicholas R. Longrich |year=2011 |title=''Titanoceratops ouranous'', a giant horned dinosaur from the Late Campanian of New Mexico|journal=Cretaceous Research |volume=32 |issue= 3|pages= 264–276|doi=10.1016/j.cretres.2010.12.007|bibcode=2011CrRes..32..264L }}</ref>
			|
			]
			|-
			|
			'']''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|
			''T. latus''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			*North Dakota<ref name="parsons2" /><ref name="cretaceous-distribution-northdakota" />
			* South Dakota<ref name="parsons2"/><ref name="cretaceous-distribution-southdakota" />
			|
			Upper Hell Creek Formation<ref name="parsons3"/>
			|
			|
			A ceratopsian that was once proposed to be synonymous with ''Triceratops'',<ref name="scannella&horner2010">{{cite journal | last1 = Scannella | first1 = J. | last2 = Horner | first2 = J.R. | year = 2010 | title = ''Torosaurus'' Marsh, 1891, is ''Triceratops'' Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny | journal = Journal of Vertebrate Paleontology | volume = 30 | issue = 4| pages = 1157–1168 | doi = 10.1080/02724634.2010.483632 | bibcode = 2010JVPal..30.1157S | s2cid = 86767957 }}</ref> but is now regarded as a valid and distinct ceratopsian.<ref>{{cite journal |last1=Mallon |first1=Jordan C |last2=Holmes |first2=Robert B |last3=Bamforth |first3=Emily L |last4=Schumann |first4=Dirk |title=The record of Torosaurus (Ornithischia: Ceratopsidae) in Canada and its taxonomic implications |journal=Zoological Journal of the Linnean Society |date=7 May 2022 |volume=195 |issue=1 |pages=157–171 |doi=10.1093/zoolinnean/zlab120 |doi-access=free }}</ref> A rare ceratopsid.<ref name="parsons3" /> Fossils have been in the ], ], ], ], ], ] and ].
			|
			]
			|-
			| rowspan="2" |
			'']''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|
			''T. horridus''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|
			*''T. serratus''<ref name="cretaceous-distribution-montana" />
			*''Ugrosaurus olsoni''<ref name="Forster2016">{{cite journal |last1=Forster |first1=Catherine A. |title=Taxomomic validity of the ceratopsid dinosaur Ugrosaurus olsoni (Cobabe and Fastovsky) |journal=Journal of Paleontology |date=March 1993 |volume=67 |issue=2 |pages=316–318 |doi=10.1017/S0022336000032273 |bibcode=1993JPal...67..316F |s2cid=133184183 }}</ref>
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			* North Dakota<ref name="parsons2"/><ref name="cretaceous-distribution-northdakota" />
			*Wyoming
			* South Dakota<ref name="parsons2"/><ref name="cretaceous-distribution-southdakota" />
			|
			Lowermost to the middle Hell Creek Formation<ref name=":0">{{cite journal |last1=Scannella |first1=John B. |last2=Fowler |first2=Denver W. |last3=Goodwin |first3=Mark B. |last4=Horner |first4=John R. |title=Evolutionary trends in Triceratops from the Hell Creek Formation, Montana |journal=Proceedings of the National Academy of Sciences |date=15 July 2014 |volume=111 |issue=28 |pages=10245–10250 |doi=10.1073/pnas.1313334111 |doi-access=free |pmid=24982159 |pmc=4104892 |bibcode=2014PNAS..11110245S }}</ref>
			|
			Four specimens are assigned to ''Triceratops horridus'' from the Hell Creek Formation.<ref name="parsons4"/> Isolated, shed ceratopsid teeth are incredibly common in the Hell Creek and Lance Formations, being by most collectors, with some being nothing more than worn down fragments up to superb teeth containing complete, preserved roots. Because the teeth of different ceratopsians are so similar to one another, its hard to differentiate between genera/species, but based on the abundance of identifiable bones belonging to ''Triceratops'' in Lancian-aged North American formations, especially the Hell Creek, isolated ceratopsid teeth from the lower and middle Hell Creek Formation have a high likelihood of originating from ''T''. ''horridus''.
			|
			A ceratopsian.<ref name="parsons"/> Also found in the ], ], ], ], and ]s.
			|
			]
			|-
			|
			''T. prorsus''<ref name="cretaceous-distribution-montana" />
			|
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			*South Dakota
			|Upper 1/3 of the Hell Creek Formation<ref name=":0" />
			|
			Very common.{{Citation needed|date=October 2009}} Because the teeth of different ceratopsians are so similar to one another, its hard to differentiate between genera/species, but based on the abundance of identifiable bones belonging to ''Triceratops'' in Lancian-aged North American formations, especially the Hell Creek, isolated ceratopsid teeth from the upper 1/3 of the Hell Creek Formation have a high likelihood of originating from ''T''. ''prorsus''.
			|
			Also found in the ] and ]s.
			|
			]
			|-
			|}
			==== Ornithopods and relatives ====
			Indeterminate hadrosaurid remains are very common in the Hell Creek Formation.<ref name="parsons"/>
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="8" style="text-align:center;"|'''] and ] reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! Synonyms
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
	|-		|-
	|		|
	* '']''		'']''
	|		|
			''E. annectens''
	# ''Elmisaurus elegans''
	|		|
			* ''Anatosaurus annectens''<ref name=campioneevens2011>{{cite journal | last1 = Campione | first1 = N.E. | last2 = Evans | first2 = D.C. | year = 2011 | title = Cranial Growth and Variation in Edmontosaurs (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous Megaherbivore Diversity in North America | journal = PLOS ONE | volume = 6 | issue = 9| page = e25186 | doi = 10.1371/journal.pone.0025186 | pmid = 21969872 | pmc=3182183| bibcode = 2011PLoSO...625186C | doi-access = free }}</ref>
	| An oviraptorosaur, possibly a species of '']''. Also found in the ].
			* ''Anatotitan copei''<ref name=campioneevens2011/>
			|
			* Montana<ref name="cretaceous-distribution-montana" />
			* South Dakota<ref name="cretaceous-distribution-southdakota" />
			* North Dakota(Mummy Fossil)<ref>{{cite journal |last1=Manning |first1=Phillip L. |last2=Morris |first2=Peter M. |last3=McMahon |first3=Adam |last4=Jones |first4=Emrys |last5=Gize |first5=Andy |last6=Macquaker |first6=Joe H. S. |last7=Wolff |first7=George |last8=Thompson |first8=Anu |last9=Marshall |first9=Jim |last10=Taylor |first10=Kevin G. |last11=Lyson |first11=Tyler |last12=Gaskell |first12=Simon |last13=Reamtong |first13=Onrapak |last14=Sellers |first14=William I. |last15=van Dongen |first15=Bart E. |last16=Buckley |first16=Mike |last17=Wogelius |first17=Roy A. |title=Mineralized Soft-Tissue Structure and Chemistry in a Mummified Hadrosaur from the Hell Creek Formation, North Dakota (USA) |journal=Proceedings: Biological Sciences |date=7 October 2009 |volume=276 |issue=1672 |pages=3429–3437 |doi=10.1098/rspb.2009.0812 |jstor=30244137|pmid=19570788 |pmc=2817188 }}</ref><ref>{{cite journal |last1=Vajda |first1=Vivi |last2=Lyson |first2=Tyler R. |last3=Bercovici |first3=Antonie |last4=Doman |first4=Jessman H. |last5=Pearson |first5=Dean A. |title=A snapshot into the terrestrial ecosystem of an exceptionally well-preserved dinosaur (Hadrosauridae) from the Upper Cretaceous of North Dakota, USA |journal=Cretaceous Research |date=November 2013 |volume=46 |pages=114–122 |doi=10.1016/j.cretres.2013.08.010|bibcode=2013CrRes..46..114V |url=http://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-1409 }}</ref>
			|
			|
			Very common.
			|
			A hadrosaur. Also found in the ], ], ], ], and ]s.<ref>{{cite journal |last1=Rohrer |first1=W. L. |last2=Konizeski |first2=R. |title=On the Occurrence of Edmontosaurus in the Hell Creek Formation of Montana |journal=34 |date=May 1960 |volume=34 |issue=3 |pages=464–466 |jstor=1300943 }}</ref><ref name="Wosik Goodwin Evans 2017">{{cite journal |last1=Wosik |first1=Mateusz |last2=Goodwin |first2=Mark B. |last3=Evans |first3=David C. |title=A nestling-sized skeleton of Edmontosaurus (Ornithischia, Hadrosauridae) from the Hell Creek Formation of northeastern Montana, U.S.A., with an analysis of ontogenetic limb allometry |journal=Journal of Vertebrate Paleontology |date=2 November 2017 |volume=37 |issue=6 |pages=e1398168 |doi=10.1080/02724634.2017.1398168 |bibcode=2017JVPal..37E8168W |s2cid=90735967 |url=https://figshare.com/articles/journal_contribution/5899300 }}</ref> Hatchlings have also been unearthed.<ref name="Wosik Goodwin Evans 2017"/>
			|
			]
			|-
			| rowspan="4" |
			'']''<ref name="cretaceous-distribution-southdakota" />
			|
			''T. garbanii''<ref name="cretaceous-distribution-montana-thesgarb" /><ref name="Boyd etal">{{cite journal |last1=Boyd |first1=Clint A. |last2=Brown |first2=Caleb Marshal |last3=Scheetz |first3=Rodney D. |last4=Clarke |first4=Julia A. |title=Taxonomic Revision of the Basal Neornithischian Taxa Thescelosaurus and Bugenasaura |date=12 September 2009 |volume=29 |issue=3 |pages=758–770 |jstor=20627088 |journal=Journal of Vertebrate Paleontology|doi=10.1671/039.029.0328 |bibcode=2009JVPal..29..758B |s2cid=84273584 }}</ref>
			|
			*''Bugenasaura garbanii''<ref name="Boyd etal" />
			|
			* Montana<ref name="cretaceous-distribution-montana-thesgarb">Listed as "?'']''" in "Dinosaur distribution (Late Cretaceous; North America; Montana)." Weishampel, et al. (2004). Page 584.</ref>
			* South Dakota<ref name="cretaceous-distribution-southdakota-thesgarb">Noted as being present, although misspelled as "'']'', in " "Dinosaur distribution (Late Cretaceous; North America; South Dakota)." Weishampel, et al. (2004). Page 586.</ref>
			|
			|
			|
			|
			|-
			|
			''T. neglectus''<ref name="parsons"/><ref name="cretaceous-distribution-southdakota" />
			|
			|
			* North Dakota<ref name="parsons2"/>
			* South Dakota<ref name="parsons2"/><ref name="cretaceous-distribution-southdakota" />
			|
			Lower to upper Hell Creek Formation<ref name="parsons3"/>
			|
			50 specimens<ref name="parsons4"/>
			|
			A small ]. Also found in the ], ], ], and ]s.<ref name=CABetal09>Boyd, Brown, et al. (2009)</ref> Two species are known from Hell Creek; ''T. neglectus'' and ''T. garbanii''.<ref>{{cite journal |last1=Galton |first1=Peter M. |title=Notes on Thescelosaurus, a Conservative Ornithopod Dinosaur from the Upper Cretaceous of North America, with Comments on Ornithopod Classification |journal=Journal of Paleontology |date=September 1974 |volume=48 |issue=5 |pages=1048–1067 |jstor=1303302 }}</ref>
			|
			]
	|-		|-
	|}		|}
	===Tyrannosaurids===		=== Theropods ===
			Theropod tracks have been found in South Dakota.<ref name="cretaceous-distribution-southdakota" /> A trackway from South Dakota, named ''Wakinyantanka'', was made by a mid-sized theropod with three slender toes, possibly a small tyrannosaurid.<ref name="styxi"/> A second footprint that may have been made by a specimen of '']'' was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation of Montana.<ref>{{cite journal |last1=Manning |first1=Phillip L. |last2=Ott |first2=Christopher |last3=Falkingham |first3=Peter L. |title=A Probable Tyrannosaurid Track from the Hell Creek Formation (Upper Cretaceous), Montana, United States |journal=PALAIOS |date=September–October 2008 |volume=23 |issue=9/10 |pages=645–647 |doi=10.2110/palo.2008.p08-030r |jstor=27670550 |bibcode=2008Palai..23..645M |s2cid=129985735 }}</ref> This second track measures {{Convert|72|cm|sp=us}} long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by ''Tyrannosaurus'' is unclear, though ''Tyrannosaurus'' is the only large theropod known to have existed in the Hell Creek Formation, though in past ] remains have described here but its most likely that they are the remains of ''Tyrannosaurus rex''.<ref>{{cite journal |last1=Dalman |first1=S.G. |last2=Lucas |first2=S.G. |title=A new large Tyrannosaurid ''Alamotyrannus brinkmani'', n. gen., n. sp. (Theropoda: Tyrannosauridae), from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico |journal=New Mexico Museum of Natural History and Science Bulletin}}</ref><ref>{{cite journal |last1=Molnar |first1=R.E. |title=An Albertosaur from the Hell Creek Formation of Montana |journal=Journal of Paleontology |date=January 1980 |volume=54 |issue=1 |pages=102–108 |jstor=1304167}}</ref> Theropod remains are very common in Hell Creek, some of which belong to indeterminate species on ].<ref>{{cite journal |last1=Molnar |first1=R. E. |title=A New Theropod Dinosaur from the Upper Cretaceous of Central Montana |journal=Journal of Paleontology |date=January 1978 |volume=52 |issue=1 |pages=73–82 |jstor=1303791 }}</ref>
	{| class="wikitable" align="center" width="100%"
			==== Alvarezsaurs ====
			{| class="wikitable sortable mw-collapsible"
	|-		|-
	! colspan="8" align="center" |'''] ]s of the Hell Creek Formation'''		! colspan="8" style="text-align:center;"|''']s reported from the Hell Creek Formation'''
	|-		|-
	! Genus		! Genus
	! Species		! Species
			! Synonyms
	! State		! State
	! Stratigraphic position		! Stratigraphic position
			! Material
	! Abundance
			! Notes
	! Description
	! Images		! Images
	|-		|-
			|"''Ornithomimus"''
			|''"O." minutus''
	|		|
	'']''
	|		|
	''A. megagracilis''
	|		|
	|		|
	|		|
			|
			|-
			|
			'']''<ref name=Fowler2020>{{cite journal |author1=Denver W. Fowler |author2=John P. Wilson |author3=Elizabeth A. Freedman Fowler |author4=Christopher R. Noto |author5=Daniel Anduza |author6=John R. Horner |year=2020 |title=''Trierarchuncus prairiensis'' gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana |journal=Cretaceous Research |volume=116 |pages=Article 104560 |doi=10.1016/j.cretres.2020.104560 |s2cid=225630913 |doi-access=free |bibcode=2020CrRes.11604560F }}</ref>
			|
			''T. prairiensis''<ref name=Fowler2020/>
			|
			|
			* Montana<ref name="cretaceous-distribution-montana">"Dinosaur distribution (Late Cretaceous; North America; Montana)." Weishampel, et al. (2004). Page 584.</ref>
			|
			upper Hell Creek Formation.
			|
			|
			An alvarezsaur known from a partial post-cranial skeleton.<ref>Hutchinson and Chiappe, 1998. The first known alvarezsaurid (Theropoda: Aves) from North America. Journal of Vertebrate ]. 18(3), 447–450.</ref>
			|
			|-
			|}
			==== Tyrannosaurids ====
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="8" style="text-align:center;"|''']s reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! Synonyms
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
			|-
			|
			'']''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|
			''T. rex''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|
			*''Albertosaurus megagracilis''<ref name="cretaceous-distribution-montana" />
			*''Aublysodon molnari''<ref name="cretaceous-distribution-montana" />
			*''Dinotyrannus megagracilis''<ref name="cretaceous-distribution-montana" />
			*'']''
			|
			* Montana<ref name="cretaceous-distribution-montana">"Dinosaur distribution (Late Cretaceous; North America; Montana)." Weishampel, et al. (2004). Page 584.</ref>
			* North Dakota<ref name="parsons2"/><ref name="cretaceous-distribution-northdakota">"Dinosaur distribution (Late Cretaceous; North America; North Dakota)." Weishampel, et al. (2004). Page 585.</ref>
			* South Dakota<ref name="parsons2"/><ref name="cretaceous-distribution-southdakota">"Dinosaur distribution (Late Cretaceous; North America; South Dakota)." Weishampel, et al. (2004). Page 586.</ref>
			|
			Lower to upper Hell Creek Formation.
			|
			|
			A tyrannosaur, known from several specimens including a juvenile nicknamed "]".<ref>{{cite journal |last1=Horner |first1=John R. |last2=Goodwin |first2=Mark B. |last3=Myhrvold |first3=Nathan |title=Dinosaur Census Reveals Abundant Tyrannosaurus and Rare Ontogenetic Stages in the Upper Cretaceous Hell Creek Formation (Maastrichtian), Montana, USA |journal=PLOS ONE |date=9 February 2011 |volume=6 |issue=2 |pages=e16574 |doi=10.1371/journal.pone.0016574 |doi-access=free |pmid=21347420 |pmc=3036655 |bibcode=2011PLoSO...616574H }}</ref> Also found in the ], ], ], ], ], ], ], ], ], ], ], and also found in ]s. Isolated teeth in the Hell Creek are common enough to be dug commercially by collectors, but rare enough that they are often sold for very high prices with fragmentary teeth usually beginning at least in the hundreds of USD, and complete teeth in the thousands of USD. Perhaps the best known iconic dinosaur.
			|
			]
			|-
			|style="background:#E6E6E6;"|
			'']?''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|style="background:#E6E6E6;"|
			''N.lancensis''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|style="background:#E6E6E6;"|
			*''Stygivenator?''
			*''Deinodon lancensis''
			*''Albertosaurus lancensis''<ref name="cretaceous-distribution-montana" />
			*''Tyrannosaurus lancensis?''
			|style="background:#E6E6E6;"|
			*Montana
			*Wyoming
			|style="background:#E6E6E6;"|
			Lower to upper Hell Creek Formation.
			|style="background:#E6E6E6;"|
			A few specimens are known
			|style="background:#E6E6E6;"|
			Invalid genus, now recognised as juvenile ''T. rex.''
			|style="background:#E6E6E6;"|
			]
			|}
			==== Ornithomimosaurs ====
			Ornithomimid remains are not uncommon in the Hell Creek Formation.<ref name="parsons"/> Fifteen specimens from the Hell Creek Formation are undetermined ornithomimids<ref name="parsons4"/>
			{{Paleobiota-key-compact}}
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="8" style="text-align:center;"|''']s reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
			|-
			|
			"]"
			|
			unnamed
			|
			* South Dakota<ref>Triebold, 1997. The Sandy Site: Small Dinosaurs from the Hell Creek Formation of South Dakota. in Wolberg, Stump and Rosenberg (eds). Dinofest International: Proceedings of a Symposium sponsored by Arizona</ref>
			|
			|
			One partial skeleton.
			|
			An ]; '']''.
			|
			|-
			|
			'']''<ref name="cretaceous-distribution-southdakota" />
			|
			''S. sedens''<ref name="longrich2008"/>
			|
			* Montana
			|
			|
			* AMNH 975, a foot claw
			* UCMP 154569, a partial skeleton
			|
			A large ornithomimid similar to '']'' in size. Also found in the ].<ref name="longrich2008">Longrich (2008), pages 983–996.</ref>
			|
			]
			|-
			|
			'']''
			|
			''O. velox''<ref name="longrich2008"/>
			|
			* Montana
			* South Dakota
			* North Dakota
			|
			|
			Fragmentary specimens
			|
			An ornithomimid which was also found in the ].
			|
			]
			|-
			|}
			==== Oviraptorosaurs ====
			Oviraptorosaur fossils have been found at the Hell Creek Formation for many years, most notably from isolated elements until the discovery of ''Anzu''. In the past, oviraptorosaur fossils found were thought to have belonged to '']'', '']'', and '']''.<ref name="cretaceous-distribution-montana" /><ref name=anzu>{{Cite journal | doi = 10.1371/journal.pone.0092022| title = A New Large-Bodied Oviraptorosaurian Theropod Dinosaur from the Latest Cretaceous of Western North America| journal = PLOS ONE| volume = 9| issue = 3| pages = e92022| year = 2014| last1 = Lamanna | first1 = M. C. | last2 = Sues | first2 = H. D. | last3 = Schachner | first3 = E. R. | last4 = Lyson | first4 = T. R. | pmid=24647078 | pmc=3960162| bibcode = 2014PLoSO...992022L| doi-access = free}}</ref><ref>{{cite journal |last1=Stein |first1=Walter W. |title=TAKING COUNT: A Census of Dinosaur Fossils Recovered From the Hell Creek and Lance Formations (Maastrichtian). |journal=The Journal of Paleontological Sciences |date=2019 |volume=8 |pages=1–42 |url=https://www.aaps-journal.org/pdf/JPS.C.2019.01a.pdf }}</ref><ref>{{cite report |last1=Schachner |first1=Emma |last2=Larson |first2=Tyler |last3=Hanks |first3=Harold |title=A preliminary report of a new specimen of Chirostenotes (Oviraptorosauria: Theropoda) from the Hell Creek Formation of North Dakota }} in {{cite journal |doi=10.1080/02724634.2006.10010069 |title=Abstracts of Papers |journal=Journal of Vertebrate Paleontology |year=2006 |volume=26 |pages=1–152 |bibcode=2006JVPal..26S...1. }}</ref><ref>{{cite journal |last1=Russel |first1=Dale A. |last2=Manabe |first2=Makoto |title=Synopsis of the Hell Creek (uppermost Cretaceous) dinosaur assemblage. |journal=Geological Society of America Special Papers |date=2002 |volume=361 |pages=169–176 |isbn=9780813723617 |url=https://books.google.com/books?id=cHvcIeh2f84C&dq=Hell+Creek+Chirostenotes&pg=PA169 |access-date=18 October 2020}}</ref> In 2016, an undescribed large-bodied caenagnathid was unearthed in Montana.<ref>{{cite journal |last1=Benner |first1=Elizabeth K. C. |last2=Cullen |first2=T. M. |last3=Evans |first3=D. C. |title=MORPHOLOGICAL AND HISTOLOGICAL ANALYSIS OF A NEW LARGE-BODIED 10 CAENAGNATHID SPECIMEN (THEROPODA: OVIRAPTOROSAURIA) FROM THE HELL CREEK FORMATION (MONTANA) |journal=Canadian Society of Vertebrate Paleontology |date=May 18–21, 2016 |pages=17–18 |url=https://cansvp.files.wordpress.com/2013/08/csvp-2016-abstract-book-compressed.pdf |access-date=17 November 2020}}</ref>
			{{Paleobiota-key-compact}}
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="8" style="text-align:center;"|''']s reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
			|-
			|
			'']''<ref name="cretaceous-distribution-montana" /><ref name=anzu>{{Cite journal | doi = 10.1371/journal.pone.0092022| title = A New Large-Bodied Oviraptorosaurian Theropod Dinosaur from the Latest Cretaceous of Western North America| journal = PLOS ONE| volume = 9| issue = 3| pages = e92022| year = 2014| last1 = Lamanna | first1 = M. C. | last2 = Sues | first2 = H. D. | last3 = Schachner | first3 = E. R. | last4 = Lyson | first4 = T. R. | pmid=24647078 | pmc=3960162| bibcode = 2014PLoSO...992022L| doi-access = free}}</ref>
			|
			''A. wyliei''<ref name=anzu/>
			|
			* North Dakota<ref name="parsons2"/><ref name=anzu/>
			* South Dakota<ref name="parsons2"/><ref name=anzu/>
			|
			Lower to upper Hell Creek Formation<ref name="parsons4"/>
			|
			12 well-preserved specimens<ref name="parsons3"/>
			|
			One of the largest known ], and the largest known from North America. Material previously assigned to ] ''indet.'' is now placed in the genus ''Anzu''.<ref name=anzu/>
			|
			]
			|-
			|
			]
			|
			Indeterminate
			|
			* Montana
			|
			|
			|
			Similar to '']'' and ''].''
			|
			|-
			|'']''
			|''E. infernalis''
			|
			* South Dakota<ref name="Eoneophron">{{Cite journal |last1=Atkins-Weltman |first1=K. L. |last2=Simon |first2=D. J. |last3=Woodward |first3=H. N. |last4=Funston |first4=G. F. |last5=Snively |first5=E. |year=2024 |title=A new oviraptorosaur (Dinosauria: Theropoda) from the end-Maastrichtian Hell Creek Formation of North America |journal=PLOS ONE |volume=19 |issue=1 |at=e0294901 |doi=10.1371/journal.pone.0294901 |doi-access=free|pmid=38266012 |pmc=10807829 |bibcode=2024PLoSO..1994901A }}</ref>
			|
			|A partial right hindlimb<ref name="Eoneophron" />
			|Closely related to '']'' and ''].<ref name="Eoneophron" />''
			|]
			|-
			|}
			==== Eumaniraptorans ====
			Historically, numerous teeth have been attributed to various dromaeosaurid and troodontid taxa with known body fossils from only older formations, including '']'', '']'', '']'', '']'', and '']''. However, in a 2013 study, Evans ''et al.'' concluded that there is little evidence for more than a single dromaeosaurid taxon, '']'', in the Hell Creek-Lance assemblages, which would render these taxa invalid for this formation. This was disproved in a 2015 study, DePalma ''et al.'', when they described the new genus '']'', a large species of dromaeosaur.<ref name="acheroraptor" /> Fossilized teeth of various troodontids and coelurosaurs are common throughout the Hell Creek Formation; the best known examples include '']'', '']'' and '']'', respectively. Teeth belonging to possible intermediate species of ''Dromaeosaurus''<ref>{{cite journal |last1=Russel |first1=Dale A. |last2=Manabe |first2=Makoto |title=Synopsis of the Hell Creek (uppermost Cretaceous) dinosaur assemblage. |journal=Geological Society of America Special Papers |date=2002 |volume=361 |pages=169–176 |isbn=9780813723617 |url=https://books.google.com/books?id=cHvcIeh2f84C&dq=Hell+Creek+Dromaeosaurus&pg=PA169 |access-date=23 October 2020}}</ref> and ''Saurornitholestes''<ref name=weishampel>''Dinosaur distribution (Late Cretaceous; North America; North Dakota).'' Weishampel, ''et al.'' (2004). Page '''585'''</ref> have been unearthed at the Hell Creek Formation and the nearby Lance Formation.
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="8" style="text-align:center;"|''']ns reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
			|-
			|
			'']''<ref name="acheroraptor">{{Cite journal | last1 = Evans | first1 = D. C. | last2 = Larson | first2 = D. W. | last3 = Currie | first3 = P. J. | doi = 10.1007/s00114-013-1107-5 | title = A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America | journal = Naturwissenschaften | year = 2013 | pmid = 24248432| volume=100 | issue = 11 | pages=1041–9| bibcode = 2013NW....100.1041E | s2cid = 14978813 }}</ref>
			|
			''A. temertyorum ''<ref name="acheroraptor"/>
			|
			* Montana<ref name="acheroraptor"/>
			* North Dakota?<ref name="parsons"/>
			* South Dakota?<ref name="parsons"/>
			|
			Lower? to upper Hell Creek Formation<ref name="parsons"/>
			|
			* ROM 63777, a maxilla and tooth<ref name="acheroraptor"/>
			* ROM 63778, a partial dentary<ref name="acheroraptor"/>
			* isolated teeth<ref name="acheroraptor"/>
			|
			A ] ]. Teeth previously referred to various Campanian dromaeosaurids ''Saurornitholestes'' and ''Dromaeosaurus'', frequently found throughout the formation, probably belong to this one species. Evans et al. conclude that there is little evidence for the former two taxa being present in the Hell Creek-Lance assemblages.<ref name="acheroraptor"/>
			|
			]
			|-
			| rowspan="4" |
			'']''<ref name="parsons"/>
			|
			''A. archibaldi''<ref name="parsons"/><ref name="cretaceous-distribution-montana" />
			|
			* Montana<ref name="parsons"/>
			|
			Middle Hell Creek Formation<ref name="parsons3"/>
			|
			* UCMP 117600, ], a tarsometatarsus
			* PU 17324, a tarsometatarsus
			|
			An ].<ref name="parsons"/>
			|
			]
			|-
			|
			cf. ''A. archibaldi''<ref name=longrichetal2011/>
			|
			* Montana<ref name=longrichetal2011/>
			|
			Uppermost Hell Creek Formation<ref name=longrichetal2011/>
			|
			* YPM 57235, a coracoid
			|
			An avisaurid tentatively referred to ''A. archibaldi'' based on its size.<ref name=longrichetal2011/>
			|
			|-
			|''A. darwini''<ref name="Magnusavis" />
			|
			* Montana
			|
			|
			* DDM 1577.730, a right tarsometatarsus
			|
			|
			|-
			|
			''A.'' sp.<ref name="stidham1999">Stidham, 1999. North American avisaurids (Aves: Enantiornithes): New data on morphology and phylogeny. VII International Symposium on Mesozoic Terrestrial Ecosystems, abstracts.</ref>
			|
			* Montana<ref name="stidham1999" />
			|
			|
			* distal tarsals, metatarsus (juvenile)<ref name="stidham1999" />
			* MOR3070, a partial right tarsometatarsus
			|
			|
			|-
			|
			'']''<ref name=Brodavis>{{cite journal |author1=Larry D. Martin |author2=Evgeny N. Kurochkin |author3=Tim T. Tokaryk |year=2012 |title=A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia |journal=] |volume=21 |pages= 59–63|doi=10.1016/j.palwor.2012.02.005}}</ref>
			|
			''B. baileyi''<ref name=Brodavis />
			|
			* South Dakota<ref name=Brodavis />
			|
			|
			* UNSM 50665, a left tarsometatarsus missing proximal end, trochleae II and III.<ref name=Brodavis />
			|
			A primitive ].<ref name=Brodavis />
			|
			|-
			|
			'']''<ref name="DePalma et al.">{{Cite journal|title=The first giant raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation|first1=Robert T.|last1=Bakker|first2=Peter L.|last2=Larson|first3=Larry D.|last3=Martin|first4=David A.|last4=Burnham|first5=Robert A.|last5=DePalma|date=30 October 2015|doi=10.17161/paleo.1808.18764|journal=Paleontological Contributions|volume= 14: 1–16|doi-access=free|hdl=1808/18764|hdl-access=free}}</ref>
			|
			''D. steini ''<ref name="DePalma et al."/>
			|
			* South Dakota<ref name="DePalma et al."/>
			|
			Upper Hell Creek Formation<ref name="DePalma et al."/>
			|
			* PBMNH.P.10.113.T, a partial skeleton.<ref name="DePalma et al."/>
			* PBMNH.P.10.115.T, a tibia.<ref name="DePalma et al."/>
			* PBMNH.P.10.118.T, an astragalocalcaneum.<ref name="DePalma et al."/>
			* isolated teeth.<ref name="DePalma et al."/>
			|
			A large ].<ref name="acheroraptor"/>
			|
			]
			|-
			|'']''<ref name="Magnusavis">{{Cite journal |last1=Clark |first1=Alexander D. |last2=Atterholt |first2=Jessie |last3=Scannella |first3=John B. |last4=Carroll |first4=Nathan |last5=O'Connor |first5=Jingmai K. |author-link5=Jingmai O'Connor |date=2024-10-09 |editor-last=Pinheiro |editor-first=Felipe Lima |title=New enantiornithine diversity in the Hell Creek Formation and the functional morphology of the avisaurid tarsometatarsus |journal=] |language=en |volume=19 |issue=10 |pages=e0310686 |doi=10.1371/journal.pone.0310686 |issn=1932-6203 |pmid=39383133 |doi-access=free|pmc=11463745 }}</ref>
			|''M. ekalakaensis''
			|
			*Montana
			|
			|
			* CCM V2019.5.1, partial right tarsometatarsus and toe bone
			|A large enantiornithine closely related to avisaurids.
			|
			|-
			|
			'']''<ref name="Olshevsky, G. 1991, pp 196">Olshevsky, G., 1991, ''A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia. Mesozoic Meanderings 2'' pp 196</ref>
			|
			''P. caperatus''<ref name="Olshevsky, G. 1991, pp 196"/>
			|
			*North Dakota, South Dakota, and Montana.
			|
			|
			*YPM 10624, a fossilized tooth. Teeth of this genus have been found too.
			|
			A troodontid theropod who is known from fossil teeth. Fossils have also been found in the ] in ].
			|
			]
			|-
			|
			'']''<ref name=carpenter1982>{{cite journal|last=Carpenter|first=K.|year=1982|title=Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod|journal=Contributions to Geology, University of Wyoming|volume=20|issue=2|pages=123–134|url=http://doc.rero.ch/record/232469/files/PAL_E4465.pdf}}</ref><ref name="Olshevsky, G. 1991, pp 196"/>
			|
			''P. bakkeri''<ref name=carpenter1982>{{cite journal|last=Carpenter|first=K.|year=1982|title=Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod|journal=Contributions to Geology, University of Wyoming|volume=20|issue=2|pages=123–134|url=http://doc.rero.ch/record/232469/files/PAL_E4465.pdf}}</ref><ref name="Olshevsky, G. 1991, pp 196"/>
			|
			*Montana
			|
			|
			*UCM 38445, a fossilized tooth. Teeth of this genus have been found too.
			|
			*A troodontid theropod who is known from fossil teeth. Fossils have also been found in the ] in ].
			|
			]
			|-
			|'']''<ref name="Brodavis"/>
			|
			''P. skutchi ''<ref name=Potamornis>{{cite journal | last1 = Elzanowski | first1 = A. | last2 = Paul | first2 = G.S. | last3 = Stidham | first3 = T.A. | year = 2001 | title = An avian quadrate from the Late Cretaceous Lance Formation of Wyoming | journal = Journal of Vertebrate Paleontology | volume = 20 | issue = 4| pages = 712–719 | doi=10.1671/0272-4634(2000)0202.0.co;2| s2cid = 86292770 }}</ref>
			|
			* Montana<ref name=Potamornis />
			|
			|
			*UCMP 117605, a tarsometatarsus
			|
			A ] also found in the ].<ref name=Potamornis/>
			|
			|-
			|
			'']''<ref name="Estes, R. 1964">{{cite book |last1=Estes |first1=Richard |title=Fossil vertebrates from the late Cretaceous Lance formation, eastern Wyoming |date=1964 |publisher=University of California Press |oclc=3753287 }}{{page needed|date=December 2022}}</ref><ref name="Larson & Currie 2013">{{cite journal |last1=Larson |first1=Derek W. |last2=Currie |first2=Philip J. |title=Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time |journal=PLOS ONE |date=23 January 2013 |volume=8 |issue=1 |pages=e54329 |doi=10.1371/journal.pone.0054329 |pmid=23372708 |pmc=3553132 |bibcode=2013PLoSO...854329L |doi-access=free }}</ref>
			|
			''R. sp.''<ref name="Estes, R. 1964"/><ref name="Larson & Currie 2013"/>
			|
			*Montana.
			|
			|
			*Teeth.
			|
			A coelurosaur that is known from teeth and from two species ''Richardoestesia gilmorei'' and ''Richardestesia isosceles'', which have also been unearthed in the ] in ].
			|
			]
			|-
			|]<ref>{{cite thesis |last1=Stidham |first1=Thomas Allen |title=The origin and ecological diversification of modern birds: Evidence from the extinct wading ducks, Presbyornithidae (Neornithes: Anseriformes) |year=2001 |id={{ProQuest|304684225}} |oclc=892837810 }}</ref>
			|"''S. lofgreni.''"
			|
			* Montana.
			|
			|
			|A ], it is notable for being one of the few birds known to have survived the ].
			|
			|-
			|
			"Unnamed enantiornithine B"<ref name=longrichetal2011/>
			|
			Unnamed
			|
			* Montana<ref name=longrichetal2011/>
			|
			|
			* YPM 57823, a partial coracoid<ref name=longrichetal2011/>
			|
			An unnamed ].<ref name=longrichetal2011/>
			|
			|-
			|
			"Unnamed hesperornithiform A"<ref name=longrichetal2011/>
			|
			Unnamed
			|
			* Montana
			|
			|
			* UCMP 13355, a tarsometatarsus
			|
			A primitive ].<ref name=Brodavis /> The Hell Creek specimen was referred to the same unnamed taxon as RSM P 2315.1 from the Canadian ].<ref name=longrichetal2011/> RSM P 2315.1 was later made the holotype of ''Brodavis americanus''.<ref name=Brodavis /> May be a synonym of '']''.<ref name=longrichetal2011/>
			|
			|-
			|
			"Unnamed ornithurine B"<ref name=longrichetal2011>{{cite journal | last1 = Longrich | first1 = N.R. | last2 = Tokaryk | first2 = T. | last3 = Field | first3 = D.J. | year = 2011 | title = Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary | journal = Proceedings of the National Academy of Sciences | volume = 108 | issue = 37| pages = 15253–15257 | doi = 10.1073/pnas.1110395108 | bibcode=2011PNAS..10815253L | pmid=21914849 | pmc=3174646| doi-access = free }}</ref>
			|
			Unnamed<ref name="eb1970-aves" />
			|
			* Montana<ref name="eb1970-aves-montana">"Class Aves," in Estes and Berberian, (1970). Page 7. All taxa listed occur in Montana, see page 1.</ref>
			|
			|
			* UCMP 129143, a partial coracoid<ref name=longrichetal2011/>
			|
			An ] possibly similar to '']''<ref name=longrichetal2011/><ref name="eb1970-aves">"Class Aves," in Estes and Berberian, (1970). Page 7.</ref>
			|
			|-
			|
			"Unnamed ornithurine C"<ref name=longrichetal2011/>
			|
			Unnamed
			|
			* Montana<ref name=longrichetal2011/>
			* South Dakota<ref name=longrichetal2011/>
			|
			|
			* SDSM 64281A, a partial coracoid<ref name=longrichetal2011/>
			* SDSM 64281B, a partial coracoid<ref name=longrichetal2011/>
			* UCMP 175251, a partial coracoid<ref name=longrichetal2011/>
			* MOR 2918, a partial coracoid<ref name=longrichetal2011/>
			|
			An ornithurine, also present in the ] and ], one of the few individual bird species known to have survived the Cretaceous–Paleogene extinction<ref name=longrichetal2011/>
			|
			|-
			|
			"Unnamed ornithurine D"<ref name=longrichetal2011/>
			|
			Unnamed
			|
			* Montana<ref name=longrichetal2011/>
			|
			|
			* UCMP 187207, a partial coracoid<ref name=longrichetal2011/>
			|
			An ] also present in the ]<ref name=longrichetal2011/>
			|
			|}
			== Pterosaurs ==
			Undescribed pterosaur remains were reported from ].<ref name="Henderson & Peterson 2006"/> A specimen of an ] pterosaur from ] likely belongs to '']'', though it is not diagnostic to the species level.<ref name="Henderson & Peterson 2006">{{cite journal |last1=Henderson |first1=Michael |last2=Peterson |first2=Joseph |title=An Azhdarchid Pterosaur Cervical Vertebra from the Hell Creek Formation (Maastrichtian) of Southeastern Montana |journal=Journal of Vertebrate Paleontology |date=30 March 2006 |volume=26 |issue=1 |pages=192–195 |doi=10.1671/0272-4634(2006)262.0.CO;2 |jstor=4524549 |s2cid=130751879 |url=http://doc.rero.ch/record/15687/files/PAL_E2073.pdf }}</ref>
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="8" style="text-align:center;"|''']s of the Hell Creek Formation'''
			|-
			! Taxa
			! Species
			! State
			! Stratigraphic location
			! Material
			! Notes
			! Images
			|-
			|
			] '']''<ref name="Henderson & Peterson 2006"/>
			|
			Indeterminate
			|Montana<ref name="Henderson & Peterson 2006"/>
			|
			|
			|A single ] neck bone which may belong to the genus '']''.<ref name="Henderson & Peterson 2006"/>
			|
			]
			|-
			|}
			== Crocodylomorphs ==
			{{Paleobiota-key-compact}}
			{| class="wikitable sortable mw-collapsible"
			|-
			! colspan="8" style="text-align:center;"|'''] reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! State
			! Stratigraphic&nbsp;position
			! Material
			! Notes
			! Images
			|-
			|
			'']''<ref name=JIG362>{{Cite journal |author1=R. Matsumoto |author2=S. E. Evans |year=2010 |title=Choristoderes and the freshwater assemblages of Laurasia |journal=] |volume=36 |issue=2 |pages=253–274 |url=http://revistas.ucm.es/index.php/JIGE/article/view/33860 |doi=10.5209/rev_jige.2010.v36.n2.11|doi-access=free |bibcode=2010JIbG...36..253M }}</ref>
			|
			* ''B. sternbergii''<ref name=JIG362 />
			|
			* Montana
			* North Dakota
			* South Dakota
			|
			|
			|
			] genus of ] that lived from the ] to the ] in ].
			|
			]
			]
			|-
			|
			'']''<ref name=JIG362 />
			|
			* ''B. montana''<ref name=JIG362 />
			|
			* Montana
			* South Dakota
			* North Dakota
			|
			|
			|
			] genus of ].
			|
			]
			]
			|-
			|
			'']''<ref name=JIG362 />
			|
			* ''T. neocesariensis''<ref name=JIG362 />
			|
			* Montana
			|
			|
			|
			] genus of ] ] which existed during the ] and early ].
	|		|
			]
			]
			|}
			== Turtles ==
	| rowspan="99" |
			{{Paleobiota-key-compact}}
	]'']]
			{| class="wikitable sortable mw-collapsible"
	]'']]
			|-
			! colspan="8" style="text-align:center;"|''']s reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
	|-		|-
	| rowspan="2" |
	'']''
	|		|
			'']''<ref name="eb1970-turtles">"Order Testudinata," in Estes and Berberian, (1970). Page 5.</ref>
	''A. mirandus''
	|		|
			Indeterminate<ref name="eb1970-turtles" />
	|		|
			* Montana<ref name="eb1970-turtles-montana">"Order Testudinata," in Estes and Berberian, (1970). Page 5. All taxa listed occur in Montana, see page 1.</ref>
	|		|
			|
			|
			Extinct genus of aquatic ]s belonging to the family ].
	|		|
			]
	|-		|-
	|		|
			'']''<ref name=PEinfernalis>{{cite journal |author1=Walter G. Joyce |author2=Donald B. Brinkman |author3=Tyler R. Lyson |year=2019 |title=A new species of trionychid turtle, ''Axestemys infernalis'' sp. nov., from the Late Cretaceous (Maastrichtian) Hell Creek and Lance formations of the Northern Great Plains, USA |journal=Palaeontologia Electronica |volume=22 |issue=3 |pages=Article number 22.3.72 |doi=10.26879/949 |doi-access=free }}</ref>
	''A. molnari''
			|
			''A. infernalis''<ref name=PEinfernalis />
			|
			* Montana
			* North Dakota
			* South Dakota
			* Wyoming
			|
			|
			|
			A ] belonging to the family ]. Its fossils from the Hell Creek Formation were formerly assigned to the late ] species ''Axestemys splendidus''.<ref>{{cite journal |last1=Arbour |first1=Victoria M. |last2=Zanno |first2=Lindsay E. |last3=Larson |first3=Derek W. |last4=Evans |first4=David C. |last5=Sues |first5=Hans-Dieter |title=The furculae of the dromaeosaurid dinosaur Dakotaraptor steini are trionychid turtle entoplastra |journal=PeerJ |date=9 February 2016 |volume=4 |pages=e1691 |doi=10.7717/peerj.1691 |pmid=26893972 |pmc=4756751 |doi-access=free }}</ref><ref name=PEinfernalis />
			|
			|-
			|
			'']''<ref name="eb1970-turtles" />
			|
			''C. victa''<ref name="eb1970-turtles" />
			|
			* Montana<ref name="eb1970-turtles-montana" />
			|
			|
			|
			A relative of ].
			|
			|-
			|
			'']''
			|
			''P. brinkman''
			|
			* Montana
			* North Dakota
	|		|
	|		|
			|
			A relative of ].
			|
	|-		|-
	|		|
	'']''		'']''
			|
			''E. cretacea''
			|
			* Montana
	|		|
	''N. lancensis''
	|		|
	|		|
			A relative of ].<ref name=Hoplochelysclark />
	|		|
	| A small ], possibly synonymous with '']''.
	|-		|-
	|		|
			'']''<ref name="eb1970-turtles" />
	'']''<ref name="cretaceous-distribution-montana">"Dinosaur distribution (Late Jurassic; North America; Montana)." Weishampel, et al. (2004). Pp. 584.</ref>
	|		|
			''E. cephalica''<ref name="eb1970-turtles" />
	''T. rex''
	|		|
			* Montana<ref name="eb1970-turtles-montana" />
	|		|
	|		|
			|
	| A tyrannosaur, known from several specimens including a juvenile nicknamed "]". Also found in the ], ], ], ], ], ], ], ], ], and ]s.
			] ]
			|
	|-		|-
			|
			'']''
			|
			''G. sonsalla''
			|
			* North Dakota
			|
			|
			|
			Extinct genus of ] ].
			|
			|-
			|
			'']''
			|
			''P. cohen''
			|
			* North Dakota
			|
			|
			|
			A relative of extinct family of ] ].
			|
			|-
			|
			'']''
			|
			''C. putorius''
			|
			* South Dakota
			* North Dakota
			|
			|
			|
			A relative of ].
			|
			|-
			|
			'']''
			|
			''G. lancensis''
			|
			* Montana
			* North Dakota
			|
			|
			|
			] related to the ].
			|
			|-
			|
			'']''<ref name=Hoplochelysclark>{{Cite journal |author1=Georgia E. Knauss |author2=Walter G. Joyce |author3=Tyler R. Lyson |author4=Dean Pearson |year=2011 |title=A new kinosternoid from the Late Cretaceous Hell Creek Formation of North Dakota and Montana and the origin of the ''Dermatemys mawii'' lineage |journal=Paläontologische Zeitschrift |volume=85 |issue=2 |pages=124–142 |doi=10.1007/s12542-010-0081-x |bibcode=2011PalZ...85..125K |s2cid=129123961 }}</ref>
			|
			''H. clark''<ref name=Hoplochelysclark />
			|
			* North Dakota<ref name=Hoplochelysclark />
			|
			|
			|
			A ] related to the ].<ref name=Hoplochelysclark />
			|
			|-
			|]<ref name=":1">{{Cite web |title=Cretaceous-Period Softshell Turtle Lived alongside Giant Dinosaurs {{!}} Sci-News.com |url=http://www.sci-news.com/paleontology/hutchemys-walkerorum-10616.html |access-date=2022-03-15 |website=Breaking Science News {{!}} Sci-News.com |date=14 March 2022 |language=en-US}}</ref>
			|''H. walkerorum<ref name=":1" />''
			|
			* North Dakota<ref name=":1" />
			|
			|A ]<ref name=":1" />
			|A ] related to the ].<ref name=":1" />
			|
			|-
			|
			'']''
			|
			''P. sp''
			|
			|
			|
			|
			] ].
			|
			|-
			|
			'']''
			|
			''B. sinuosa''
			|
			|
			|
			|
			Largest ] land ].
			|
			|-
			|
			'']''<ref name="eb1970-turtles" />
			|
			Indeterminate<ref name="eb1970-turtles" />
			|
			* Montana<ref name="eb1970-turtles-montana" />
			|
			|
			|
			A ] of ]s belonging to the family ].
			|
			]
			|-
			|
			'']''
			|
			''A. foveatus''
			|
			|
			|
			|
			] ].
			|]
			|-
			|
			'']''
			|
			''H. distincta''
			|
			|
			|
			|
			] ].
			|
			|-
			|
			'']''
			|
			''J. backmani''
			|
			|
			|
			|
			Thin-shelled macrobaenid ].
			|
			|-
			|
			'']''
			|
			''P. antiqua''
			|
			|
			|
			|
			] ].
			|
			|-
			|
			'']''
			|
			''S. estesi''
			|
			|
			|
			|
			] ].
			|
			|-
			|
			'']''
			|
			''N. eximius''
			|
			|
			|
			|
			Largest ] ] in Hell Creek Formation.
			|
			]
			|-
			|
			'']''<ref>{{Cite journal|author1=Tyler R. Lyson |author2=Jacob L. Sayler |author3=Walter G. Joyce |year=2019 |title=A new baenid turtle, ''Saxochelys gilberti'', gen. et sp. nov., from the uppermost Cretaceous (Maastrichtian) Hell Creek Formation: sexual dimorphism and spatial niche partitioning within the most speciose group of Late Cretaceous turtles |journal=Journal of Vertebrate Paleontology |volume=39 |issue=4 |pages=e1662428 |doi=10.1080/02724634.2019.1662428 |bibcode=2019JVPal..39E2428L |s2cid=208587902 |url=https://figshare.com/articles/dataset/A_new_baenid_turtle_i_Saxochelys_gilberti_i_gen_et_sp_nov_from_the_uppermost_Cretaceous_Maastrichtian_Hell_Creek_Formation_sexual_dimorphism_and_spatial_niche_partitioning_within_the_most_speciose_group_of_Late_Cretaceous_turtles/9944129 }}</ref>
			|
			''S. gilberti''
			|
			* North Dakota
			|
			|
			* A population of over 30 individual skeletons
			|
			A member of the family ].
			|
			|-
			|
			'']''
			|
			''T. insiliens''
			|
			|
			|
			|
			] ].
			|
			|-
			|
			]
			|
			Indeterminate
			|
			|
			|
			|
			]-like ].
			|
	|}		|}
			== Squamata ==
	===Ornithomimmosaurs===
			{{Paleobiota-key-compact}}
	{| class="wikitable" align="center" width="100%"
			{| class="wikitable sortable mw-collapsible"
	|-		|-
	! colspan="5" align="center" |'''] ]s of the Hell Creek Formation'''		! colspan="8" style="text-align:center;"|'''] reported from the Hell Creek Formation'''
	|-		|-
	! Genus		! Genus
	! Species		! Species
			! State
	! Presence
			! Stratigraphic position
	! Description
			! Material
			! Notes
	! Images		! Images
	|-		|-
	|		|
			'']''<ref name=PNASsquamates>{{Cite journal|author1=Nicholas R. Longrich |author2=Bhart-Anjan S. Bhullar |author3=Jacques A. Gauthier |year=2012 |title=Mass extinction of lizards and snakes at the Cretaceous–Paleogene boundary |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=52 |pages=21396–21401 |doi=10.1073/pnas.1211526110 |pmid=23236177 |pmc=3535637|bibcode=2012PNAS..10921396L |doi-access=free }}</ref><ref name=PNASsquamatescorrection>{{Cite journal|author1=Nicholas R. Longrich |author2=Bhart-Anjan S. Bhullar |author3=Jacques A. Gauthier |year=2013 |title=Correction for "Mass extinction of lizards and snakes at the Cretaceous–Paleogene boundary," by Nicholas R. Longrich, Bhart-Anjan S. Bhullar, and Jacques A. Gauthier, which appeared in issue 52, December 26, 2012, of Proc Natl Acad Sci USA (109:21396–21401; first published December 10, 2012; 10.1073/pnas.1211526110) |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=110 |issue=16 |page=6608 |doi=10.1073/pnas.1303907110|bibcode=2013PNAS..110Q6608. |pmc=3631639 |doi-access=free }}</ref>
	* '']''
	|		|
			''C. monstrosus''<ref name=PNASsquamates /><ref name=PNASsquamatescorrection />
	# ''Ornithomimus'' sp.
			|
			* Montana<ref name=PNASsquamates />
			|
			|
			|
			A ]n lizard of uncertain phylogenetic placement, also known from the ].<ref name=PNASsquamates />
	|		|
	| An ].
	| rowspan="99" |
	]]]
	|-		|-
	|		|
			'']''<ref name=PNASsquamates /><ref name=PNASsquamatescorrection />
	* '']''
			|
			''C. robustus''<ref name=PNASsquamates /><ref name=PNASsquamatescorrection />
			|
			* Montana<ref name=PNASsquamates />
			|
			|
			|
			An ]n ] of uncertain phylogenetic placement.<ref name=PNASsquamates />
			|
			|-
			|
			'']''<ref name=PNASsquamates /><ref name=PNASsquamatescorrection />
			|
			''O. gracilis''<ref name=PNASsquamates /><ref name=PNASsquamatescorrection />
			|
			* Montana<ref name=PNASsquamates />
			|
			|
			|
			A ]n lizard of uncertain phylogenetic placement. Also known from the ].<ref name=PNASsquamates />
			|
			|-
			|
			'']''<ref name=PNASsquamates />
			|
			''P. aquilonius''<ref name=PNASsquamates />
			|
			* Montana<ref name=PNASsquamates />
			|
			|
			|
			A ] ]n lizard.<ref name=PNASsquamates />
			|
			|-
			|
			'']''
			|
			''H. placodon''
			|
			|
			|
			|
			] ].
			|
			]
			|-
			|
			'']''
			|
			''L. denticulatus''
			|
			|
			|
			|
			Small ] ].
			|
			|-
			|
			'']''
			|
			''C. segnis''
			|
			|
			|
			|
			Largest ] ] in Hell Creek Formation
			|
			|-
			|
			'']''
			|
			''C. sloani''
			|
			|
			|
			|
			]? ].
			|
			|-
			|
			'']''
			|
			''E. lancensis''
			|
			|
			|
			|
			] ].
			|
			]
			|-
			|
			'']''
			|
			''P. jepseni''
			|
			|
			|
			|
			] ].
			|
			|-
			|
			'']''
			|
			''P. wyomingensis''
			|
			|
			|
			|
			Necrosaurid ].
			|
			|-
			|
			'']''
			|
			''P. bogerti''
			|
			|
			|
			|
			]? ].
			|
			|-
			|
			'']''
			|
			''P. canadensis''
			|
			|
			|
			|
			A large ] ], closely related to today's ] ]. It was the largest lizard in the Hell Creek formation.
			|
			|-
			|
			]
			|
			Indeterminate
			|
			|
			|
			|
			]. Earliest-known ].
			|
			]
			|
			|-
			|
			]
			|
			Indeterminate
			|
			|
			|
			|
			Indeterminate ] remains have been unearthed in North Dakota; they may belong to a mosasaur measuring {{cvt|11|m|ft}} in length.<ref>{{Cite web|date=2019-03-31|title=Fossils may capture the day the dinosaurs died. Here's what you should know.|url=https://www.nationalgeographic.com/science/article/fossils-found-from-day-dinosaurs-died-chicxulub-tanis-cretaceous-extinction|archive-url=https://web.archive.org/web/20210305093325/https://www.nationalgeographic.com/science/article/fossils-found-from-day-dinosaurs-died-chicxulub-tanis-cretaceous-extinction|url-status=dead|archive-date=March 5, 2021|access-date=2021-08-20|website=Science|language=en}}</ref><ref>{{cite journal |last1=Van Vranken |first1=Nathan E. |last2=Boyd |first2=Clint A. |title=The first in situ collection of a mosasaurine from the marine Breien Member of the Hell Creek Formation in south-central North Dakota, USA |journal=PaleoBios |date=21 August 2021 |volume=38 |issue=1 |doi=10.5070/P938054460 |doi-access=free }}</ref>
	|		|
			]
	# ''Struthiomimus sedens''
	|		|
	| A large ornithomimid.<ref name="longrich2008">Longrich, N. (2008). "A new, large ornithomimid from the Cretaceous Dinosaur Park Formation of Alberta, Canada: Implications for the study of dissociated dinosaur remains." ''Palaeontology, '''54'''(1): 983-996.</ref>
	|-		|-
	|}		|}
			== Choristoderans ==
	==Ornithischians==
			{{Paleobiota-key-compact}}
	{| class="wikitable" align="center" width="100%"
			{| class="wikitable sortable mw-collapsible"
	|-		|-
	! colspan="5" align="center" |''']n ]s of the Hell Creek Formation'''		! colspan="8" style="text-align:center;"|''']ns reported from the Hell Creek Formation'''
	|-		|-
	! Taxa		! Genus
			! Species
	! Presence
			! State
	! Description
			! Stratigraphic&nbsp;position
			! Material
			! Notes
	! Images		! Images
	|-		|-
	|		|
			'']''<ref name=JIG362 />
	'''Genus:'''
	*'']''
	# ''Ankylosaurus magniventris''
	|		|
			''C. sp.''<ref name=JIG362 />
	| An ]. Also found in the ] and ]s.
			|
	| rowspan="99" |
			* Montana
	]'']]
			|
	]'']]
			|
	]'']]
			|
			A&nbsp;].
			|
			]<br />
			]
			|}
			== Mammals ==
			=== Multituberculates ===
			{{Paleobiota-key-compact}}
			{| class="wikitable sortable mw-collapsible"
	|-		|-
			! colspan="7" style="text-align:center;"|'''] reported from the Hell Creek Formation'''
			|-
			! Genus
			! Species
			! State
			! Stratigraphic position
			! Material
			! Notes
			! Images
			|-
			|
			'']''<ref name=KielanJaworowska9899>], Richard L. Cifelli, and Zhe-Xi Luo, ''Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure'', Columbia University Press, New York, 2004 {{ISBN|0-231-11918-6}}, p. 98-99</ref>
			|
			''C. minor''<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
	|		|
			A multituberculate of uncertain phylogenetic placement.
	'''Genus:'''
	* '']''
	# '']''
	|		|
			]
	| A ], possibly synonymous with '']''.
	|-		|-
			|rowspan=3|
			'']''<ref name=KielanJaworowska9899 />
	|		|
	'''Genus:'''		''C. nitidus''
			|
	*'']''
			* Montana
	# ''Edmontonia'' sp.
			* North Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
	|		|
	| An ankylosaur.
	|-		|-
	|		|
			''C.'' cf. ''nitidus''<ref name=KielanJaworowska9899 />
	'''Family:'''
	* ]
	# cf. '']'' sp.
	|		|
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
	|		|
	# A primitive ]n.
	|-		|-
	|		|
			''C.'' sp.<ref name=KielanJaworowska9899 />
	'''Genus:'''
			|
	*'']''
			* North Dakota<ref name=KielanJaworowska9899 />
	# ''Pachycephalosaurus wyomingensis''
			|
			|
			|
			A ] multituberculate.
	|		|
	| A pachycephalosaur. Also found in the ] and ]s.
	|-		|-
			|rowspan =2|
			'']''<ref name=KielanJaworowska9899 />
	|		|
	'''Genus:'''		''C. gracilis''
	* '']''
	# ''Sphaerotholus bucholtzae''
	|		|
			* Montana<ref name=KielanJaworowska9899 />
	| A pachycephalosaur, possibly synonymous with '']''.
			|
			|
			|
			A ] multituberculate.
			|
			]
	|-		|-
	|		|
			* ''C.'' cf. ''gracilis''<ref name=KielanJaworowska9899 />
	'''Genus:'''
			|
	* '']''
			* South Dakota<ref name=KielanJaworowska9899 />
	# ''Stygimoloch spinifer''
			|
			|
			|
			A ] multituberculate.
	|		|
	| A pachycephalosaur, possibly synonymous with '']''. Also found in the ].
	|-		|-
	|		|
			'']''<ref name=KielanJaworowska9899 />
	'''Genus:'''
			|
	*'']''
			''E. browni''<ref name=KielanJaworowska9899 />
	# ''Torosaurus latus''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
	|		|
	| A ceratopsian. Also found in the ], ], ], ], and ]s.
	|-		|-
			|rowspan=5|
			'']''<ref name=KielanJaworowska9899 />
	|		|
	'''Genus:'''		''M. conquistus''
	* '']''
	# ''Triceratops horridus''
	# ''Triceratops prorsus''
	|		|
			* South Dakota<ref name=KielanJaworowska9899 />
	# Very common.
			|
	# Very common.
			|
			|
			A ] multituberculate.
			|
			]
			|-
			|
			''M. robustus''
			|
			* Montana
			* North Dakota
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			]
			|-
			|
			''M.'' cf. ''robustus''
			|
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			''M.'' sp.
			|
			* North Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			?''M.'' sp.<ref name=KielanJaworowska9899 />
			|
			* North Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|rowspan=8|
			'']''<ref name=KielanJaworowska9899 />
			|
			''M. formosa''
			|
			* Montana
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			''M.'' cf. ''formosa''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			''M. hensleighi''
			|
			* Montana
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			''M.'' cf. ''hensleighi''
			|
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			''M. thompsoni''
			|
			* Montana
			* North Dakota
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			''M.'' cf. ''thompsoni''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			''M'' sp.<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			?''M'' sp.<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			?'']''<ref name=KielanJaworowska9899 />
			|
			?''N. burgessi''<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			'']''<ref name=KielanJaworowska9899 />
			|
			''P. priscus''<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A multituberculate of uncertain phylogenetic placement.
			|
			|-
			|
			'']''<ref name=Paleobiology393 />
			|
			''P. nelsoni''<ref name=Paleobiology393 />
			|
			|
			|
			|
			A ] multituberculate.
			|
			|-
			|
			'']''
			|
			''S. kuszmauli''
			|
			* Montana
			|
			|
			|
			It was a member of the extinct order ].
	|		|
	# A ceratopsian, very common. Also found in the ], ], ], ], ], and ]s.
	# A ceratopsian, possibly be synonymous with '']'', very common. Also found in the ] and ]s.
	|-		|-
	|}		|}
	====Ornithopods====		=== Metatherians ===
			{{Paleobiota-key-compact}}
	{| class="wikitable" align="center" width="100%"
			{| class="wikitable sortable mw-collapsible"
	|-		|-
	! colspan="5" align="center" |''']n ]s of the Hell Creek Formation'''		! colspan="7" style="text-align:center;"|''']ns reported from the Hell Creek Formation'''
	|-		|-
	! Taxa		! Genus
			! Species
	! Presence
			! State
	! Description
			! Stratigraphic position
			! Material
			! Notes
	! Images		! Images
	|-		|-
			|rowspan=5|
			'']''<ref name=KielanJaworowska9899 />
	|		|
	'''Genus:'''		''A. marshi''
			|
	*'']''
			* Montana
	# ''Anatotitan copei''
			* North Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			An ]. genus of small, ] mammal that was a member of the ], a group of mammals that includes modern-day ].
	|		|
	| A "duck-billed" ], possibly synonymous with '']''.
	| rowspan="99" |
	]'']]
	|-		|-
	|		|
	'''Genus:'''		''A.'' cf. ''marshi''
	*'']''
	# ''Edmontosaurus annectens''
	# ''Edmontosaurus regalis''
	|		|
			* Montana
	# Very common.
			* South Dakota<ref name=KielanJaworowska9899 />
	# Very common.
			|
			|
			|
			An ].
	|		|
	# A hadrosaur. Also found in the ], ], ], ], and ]s.
	# A hadrosaur, very common. Also found in the ], ], ], ], and ]s.
	|-		|-
	|		|
	'''Genus:'''		''A. wilsoni''
			|
	* '']''?
			* Montana<ref name=KielanJaworowska9899 />
	# ''Parasaurolophus walkeri''?
			|
			|
			|
			An ].
	|		|
	| A crested lambeosaurine hadrosaur. Also found in the ].
	|-		|-
	|		|
	'''Genus:'''		''A.'' cf. ''wilsoni''
			|
	*'']''
			* Montana<ref name=KielanJaworowska9899 />
	# ''Thescelosaurus garbanii''
			|
	# ''Thescelosaurus neglectus''
			|
			|
			An ].
	|		|
	| A small ]. Also found in the ], ], ], and ]s. Includes ''Bugenasaura''.<ref name=CABetal09>{{cite journal|last=Boyd|first=Clint A.|coauthors=Brown, Caleb M.; Scheetz, Rodney D.; and Clarke, Julia A.|date=2009|title=Taxonomic revision of the basal neornithischian taxa ''Thescelosaurus'' and ''Bugenasaura''|journal=Journal of Vertebrate Paleontology|volume=29|issue=3|pages=758–770}}</ref>
	|-		|-
			|
			''A.'' sp.<ref name=KielanJaworowska9899 />
			|
			* North Dakota
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			An ].
			|
			]
			|-
			|rowspan=5|
			'']''<ref name=KielanJaworowska9899 />
			|
			''D. padanicus''
			|
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|
			''D. vorax''
			|
			* Montana
			* North Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ]. genus of ] ] from the Late Cretaceous of North America.
			|
			]<br />
			]
			|-
			|
			''D.'' cf. ''vorax''
			|
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			]
			|-
			|
			''D.'' sp.
			|
			* North Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|
			cf. ''D.'' sp.<ref name=KielanJaworowska9899 />
			|
			* North Dakota
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|rowspan=2|
			'']''<ref name=KielanJaworowska9899 />
			|
			''G. twitchelli''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|
			''G.'' cf. ''twitchelli''<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|rowspan=2|
			'']''<ref name=JMEProtungulatum>{{cite journal |author1=J. David Archibald |author2=Yue Zhang |author3=Tony Harper |author4=Richard L. Cifelli |title=''Protungulatum'', confirmed Cretaceous occurrence of an otherwise Paleocene eutherian (placental?) mammal |journal=Journal of Mammalian Evolution |volume=18 |issue=3 |pages=153–161 |year=2011 |doi=10.1007/s10914-011-9162-1 |s2cid=16724836 }}
			</ref>
			|
			''L. cooki''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|
			''L. krejcii''<ref name=JMEProtungulatum />
			|
			* Montana
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|
			'']''<ref name=Paleobiology393 />
			|
			''N. improvida''<ref name=Paleobiology393 />
			|
			|
			|
			|
			A ].
			|
			|-
			|
			'']''
			|
			''N. jasoni'' (= ''N. intermedius'')<ref name=Paleobiology393>{{cite journal |author=Gregory P. Wilson|title=Mammals across the K/Pg boundary in northeastern Montana, U.S.A.: dental morphology and body-size patterns reveal extinction selectivity and immigrant-fueled ecospace filling |journal=Paleobiology |volume=39 |issue=3 |pages=429–469 |year=2013 |doi=10.1666/12041 |bibcode=2013Pbio...39..429W |s2cid=36025237 }}</ref><ref>{{cite journal |author1=Thomas E. Williamson |author2=Stephen L. Brusatte |author3=Thomas D. Carr |author4=Anne Weil |author5=Barbara R. Standhardt |title=The phylogeny and evolution of Cretaceous–Palaeogene metatherians: cladistic analysis and description of new early Palaeocene specimens from the Nacimiento Formation, New Mexico |journal=Journal of Systematic Palaeontology |volume=10 |issue=4 |pages=625–651 |year=2012 |doi=10.1080/14772019.2011.631592 |bibcode=2012JSPal..10..625W |s2cid=83996185 }}</ref>
			|
			* Montana
			* South Dakota
			|
			|
			|
			A ].
			|
			|-
			|
			'']''<ref name=KielanJaworowska9899 />
			|
			''P. elegans''<ref name=KielanJaworowska9899 />
			|
			* Montana
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|rowspan=2|
			'']''<ref name=KielanJaworowska9899 />
			|
			''P. foxi''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			An ].
			|
			|-
			|
			''P. lulli''<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			An ].
			|-
			|rowspan=3|'']''<ref name=JMEProtungulatum /><ref name=D07>{{cite journal |last1=Davis |first1=B. M. |title=A revision of 'pediomyid' marsupials from the Late Cretaceous of North America |journal=Acta Palaeontologica Polonica |date=2007 |volume=52 |issue=2 |pages=217–256 |url=https://www.app.pan.pl/archive/published/app52/app52-217.pdf }}</ref>
			|
			''P. florencae''<ref name=JMEProtungulatum /><ref name=D07/>
			|
			* Montana
			* North Dakota
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|''P. hatcheri''<ref name=JMEProtungulatum /><ref name=D07/>
			|
			* Montana
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A ].
			|
			|-
			|''P. mcgilli''<ref name=K14>{{Cite journal|last1=Kelly |first1=T.S. |year=2014 |title=Preliminary report on the mammals from Lane's Little Jaw Site Quarry: a latest Cretaceous (earliest Puercan?) local fauna, Hell Creek Formation, southeastern Montana |journal=Paludicola |volume=10 |issue=1 |pages=50–91 |url=https://paludicolavertpaleo.files.wordpress.com/2018/05/10-1-kelly-2014.pdf }}</ref>
			|
			* Montana<ref name=K14/>
			|
			|
			|
			A ].
			|
			|-
			|
			'']''<ref name=KielanJaworowska9899 />
			|
			''T. rhaister''<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			An ].
			|
	|}		|}
	==Plants==		=== Eutherians ===
			{{Paleobiota-key-compact}}
	{| class="wikitable" align="center" width="100%"
			{| class="wikitable sortable mw-collapsible"
	|-		|-
	! colspan="5" align="center" |''']s of the Hell Creek Formation'''		! colspan="7" style="text-align:center;"|''']ns reported from the Hell Creek Formation'''
	|-		|-
	! Taxa		! Genus
			! Species
	! Presence
			! State
	! Description
			! Stratigraphic position
			! Material
			! Notes
	! Images		! Images
	|-		|-
	|		|
	'''Genus:'''		'']''
			|
	* '']''
			''A. magnus''
	# ''Metasequoia'' sp.
			|
			* Montana
			* North Dakota
			|
			|
			|
			a possible ], formerly a species of ]<ref>{{cite journal |last1=Fox |first1=Richard C. |title=A revision of the Late Cretaceous–Paleocene eutherian mammal Cimolestes Marsh, 1889 |journal=Canadian Journal of Earth Sciences |date=December 2015 |volume=52 |issue=12 |pages=1137–1149 |doi=10.1139/cjes-2015-0113 |bibcode=2015CaJES..52.1137F }}</ref>
	|		|
	| Casts of Dawn Redwood seed cones are known from the Hell Creek.
	|-		|-
	|		|
			'']''<ref name=KielanJaworowska9899 />
	'''Genus:'''
			|
	* '']''
			''A. saskatchewanensis''<ref name=KielanJaworowska9899 />
	# ''Cobbania corrugata''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A eutherian of uncertain phylogenetic placement.
	|		|
	| A prehistoric species of water lettuce, previously assigned to the genus '']''.
	|-		|-
			|
			'']''
			|
			A. cerberoides
			|
			* Montana
			|
			|
			|
			A eutherian of uncertain classification, formally a species of ]
			|
			|-
			|
			'']''<ref name=KielanJaworowska9899 />
			|
			''B. tenuis''<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A cimolestid eutherian.
			|
			|-
			|rowspan=2|
			'']''<ref name=KielanJaworowska9899 />
			|
			''C. incisus''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A cimolestid eutherian.
			|-
			|
			''C. stirtoni''<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A cimolestid eutherian.
			|
			|-
			|rowspan=4|
			'']''<ref name=KielanJaworowska9899 />
			|
			''G. hypoconus''
			|
			* Montana
			* South Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A gypsonictopsid eutherian.
			|
			|-
			|
			''G. illuminatus''
			|
			* Montana
			* North Dakota<ref name=KielanJaworowska9899 />
			|
			|
			|
			A gypsonictopsid eutherian.
			|
			|-
			|
			''G.'' cf. ''illuminatus''
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A gypsonictopsid eutherian.
			|
			|-
			|
			''G.'' sp.<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A gypsonictopsid eutherian.
			|
			|-
			|
			cf. '']''<ref name=KielanJaworowska9899 />
			|
			cf. ''Paranyctoides'' sp.<ref name=KielanJaworowska9899 />
			|
			* Montana<ref name=KielanJaworowska9899 />
			|
			|
			|
			A nyctitheriid eutherian.
			|
			|-
			|
			'']''<ref name=JMEProtungulatum />
			|
			''P. coombsi''<ref name=JMEProtungulatum />
			|
			* Montana<ref name=JMEProtungulatum />
			|
			|
			|
			A stem-placental.
			|
			]
			|-
			|
			'']''
			|
			''P. ceratops''
			|
			* Montana
			|
			|
			|
			A genus with four species believed to be either ]-]s or stem-].
			|
			]
			|-
			|
			'']''
			|
			''S. propalaeoryctes''
			|
			* Montana
			|
			|
			|
			A eutherian of uncertain classification, formally a species of ]
			|
	|}		|}
	==Pterosaurs==		== Flora ==
			] at ] is represented by angiosperm-dominated ]. ]]
	{| class="wikitable" align="center" width="100%"
			The Hell Creek Formation was a low ] at the time before the sea retreated, and in the wet ground of the dense ], the diversity of ] and ]s were present. An endless diversity of ], ]s and ] grew in the forest understory. On the exposed point bars of large ], there were ]s and ]s. The evidence of the forested environment is overwhelmingly supported by ], rooted gley ]s,<ref>{{cite journal |last1=Fastovsky |first1=David E. |last2=McSWEENEY |first2=Kevin |title=Paleosols spanning the Cretaceous-Paleogene transition, eastern Montana and western North Dakota |journal=Geological Society of America Bulletin |date=1987 |volume=99 |issue=1 |pages=66 |doi=10.1130/0016-7606(1987)99<66:PSTCTE>2.0.CO;2 |bibcode=1987GSAB...99...66F }}</ref> and ubiquitous tree leaves. The presence of the simple and lobed leaves, combined with an extremely high ] diversity, extinct ] '']'', '']'', many types of ], and several types of ]s is different from any modern plant community. There are numerous types of leaves, seeds, flowers and other structures from ], or flowering plants. The Hell Creek Formation of this layer contains over 300 tablets, of which ] are by far the most diverse and dominant flora of the entire population, about 90 percent, followed by about 5% of ]s, 4% of ]s, and others. Compared to today Hell Creek's flora which is ], then Hell Creek's flora was ] mixed with ] and ] forest. In sharp contrast to the ] today, the presence of many ] taxa such as ] and ]s meant the climate was warmer and wetter then.
			]), closely related to the genus '']''.]]
			The plants of the Hell Creek Formation generally represent angiosperm-dominated ]s of variable diversity, depending on ] position and ]. There appears to be floral transitions visible on a ] range from the lower to the upper Hell Creek Formation. For this reason, ] and Leo Hickey divided it into five zones and described them as HCIa, HCIb, HCIIa, HCIIb, and HCIII as a reflection of floral change through time.<ref>{{cite book |doi=10.1130/SPE247-p433 |chapter=Megafloral change across the Cretaceous/Tertiary boundary in the northern Great Plains and Rocky Mountains, U.S.A. |title=Global Catastrophes in Earth History; an Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality |series=Geological Society of America Special Papers |date=1990 |last1=Johnson |first1=Kirk R. |last2=Hickey |first2=Leo J. |volume=247 |pages=433–444 |isbn=0-8137-2247-0 }}</ref> For example, the HCIa zone is dominated by '']'', ''],'' '']'', and '']'', and is located 55 to 105 meters below the ]. Although the HCIb zone is a very thin layer, about 5 meters of rock, it bears unusually high diversity of ] and ]by plants, including ], ], ], and ].<ref name=":6" /><ref name="Megaflora2002">{{cite book |doi=10.1130/0-8137-2361-2.329 |chapter=Megaflora of the Hell Creek and lower Fort Union Formations in the western Dakotas: Vegetational response to climate change, the Cretaceous-Tertiary boundary event, and rapid marine transgression |title=The Hell Creek Formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An Integrated continental record of the end of the Cretaceous |date=2002 |last1=Johnson |first1=Kirk R. |isbn=978-0-8137-2361-7 }}</ref>
			]'' is one of the common fossil leaf species in the HCIII zone.]]
			There is evidence of transitional floras in the middle of the Hell Creek Formation as shown by HCII and HCIII zones. The HCII flora represents a transitional period where taxa from the lower Hell Creek are replaced by the HCIII flora. The diversity of the HCIII zone is very high, and its composition is more uniform than that of HCII, many of which were rare or absent from the zones below, and some others that used to be common below became rarer in the HCIII zone. These forms include '']'', '']'', '']'', and many members of the ] including '']'', '']'', and '']'', while '']'', '']'', and many ] became rarer. This phenomenon suggests that the ] was warming during the last 300,000-500,000 years of the ].<ref name=":6" /><ref name="Megaflora2002"/><ref>{{cite journal |last1=Johnson |first1=Kirk R. |last2=Nichols |first2=Douglas J. |last3=Attrep |first3=Moses |last4=Orth |first4=Charles J. |title=High-resolution leaf-fossil record spanning the Cretaceous/Tertiary boundary |journal=Nature |date=August 1989 |volume=340 |issue=6236 |pages=708–711 |doi=10.1038/340708a0 |bibcode=1989Natur.340..708J |s2cid=4302433 }}</ref><ref>{{cite journal |last1=Barnet |first1=James S.K. |last2=Littler |first2=Kate |last3=Kroon |first3=Dick |last4=Leng |first4=Melanie J. |last5=Westerhold |first5=Thomas |last6=Röhl |first6=Ursula |last7=Zachos |first7=James C. |title=A new high-resolution chronology for the late Maastrichtian warming event: Establishing robust temporal links with the onset of Deccan volcanism |journal=Geology |date=1 February 2018 |volume=46 |issue=2 |pages=147–150 |doi=10.1130/G39771.1 |bibcode=2018Geo....46..147B |hdl=10871/30937 |hdl-access=free }}</ref>
			Johnson claims that there are no ], ]s, ]s, ]es, ], or ]s in the Hell Creek Formation. There is no evidence of fern prairie either.<ref>{{cite journal |last1=Retallack |first1=Gregory J. |title=A pedotype approach to latest Cretaceous and earliest Tertiary paleosols in eastern Montana |journal=Geological Society of America Bulletin |date=November 1994 |volume=106 |issue=11 |pages=1377–1397 |doi=10.1130/0016-7606(1994)106<1377:APATLC>2.3.CO;2 |bibcode=1994GSAB..106.1377R }}</ref> However, there was an extremely high angiosperm diversity — common ], '']'', '']'', and ] — along with extinct ] '']'', '']'', ], ], and ] ]s. This represents the ] as the Hell Creek landscape. The nature of these forests is uncertain because Johnson found that the majority of the ] and ] genera are now extinct. He also believes that, very roughly 80% of the terrestrial plant taxa died out in what is now ] at the ]. On other hand, there is a great increase in the abundance of fossil ] in the two centimeters of rock that directly overlies the impact fallout layer (the famous ]). This increase in ] abundance is commonly referred as "]" (meaning that if the abundance of ]s as a function of ] position were plotted out, the graph would show a spike just above the impact fallout layer).
			Many of the modern plant affinities in the Hell Creek Formation (e.g., those with the prefix "]" or with quotes around the genus name) may not in reality belong to these genera; instead they could be entirely different plants that resemble modern genera. Therefore, there is some question regarding whether the modern '']'' or '']'', as two examples, actually lived in the ].
			Compared to the rich Hell Creek Formation fossil plant localities of the ], relatively few plant specimens have been collected from Montana. A few taxa were collected at Brownie Butte Montana by Shoemaker, but most plants were collected from ] (]) and from ]. Among the localities, the Mud Buttes, located in ], ], is probably the richest megaflora assemblage known and the most diverse leaf quarry from the Hell Creek Formation.<ref name="Megaflora2002"/> "TYPE" after the binomial means that it is represented by a type specimen found in the ] collections. "YPM" is the prefix for the ] specimen number; "DMNH" is for the ]; "USNM" is for ]; and so on. The majority of Hell Creek megafloral specimens are collected at the ].
			===Overview (from Johnson, 2002)===
			'''302 plant morphotypes based on leaf only, including''':
			*1 bryophyte (mosses and liverworts)
			*11 ferns
			*1 sphenopsid
			*10 conifers
			*1 ginkgo (uncommon)
			*278 angiosperms (roughly 92% of all taxa found)
			===Paleoflora===
			{{paleobiota-key-compact}}
			====Liverworts====
			{| class="wikitable sortable" style="margin:auto; width:100%;"
	|-		|-
			! Genus
	! colspan="5" align="center" |''']s of the Hell Creek Formation'''
			! Species
			! Location
			! Stratigraphic position
			! Abundance
			! Notes
			! Images
	|-		|-
			|
	! Taxa
			'']''
	! Presence
			|
	! Description
			'']''
			|
			|
			|
			|
			Only known ] in Hell Creek.
			|
			]
			|-
			|}
			====Ferns====
			{| class="wikitable sortable" style="margin:auto; width:100%;"
			|-
			! Genus
			! Species
			! Location
			! Stratigraphic position
			! Abundance
			! Notes
	! Images		! Images
	|-		|-
	|		|
	'''Family:'''		'']''
	* ]
	# cf. '']'' sp.
	|		|
			''E.'' sp
	| A single ] neck bone may belong to the genus ''Quetzalcoatlus''.<ref name="henderson&peterson2006">Henderson, M.D. and Peterson, J.E. "An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana." ''Journal of Vertebrate Paleontology'', '''26'''(1): 192–195.</ref>
			|
	| rowspan="99" |
			|
	]'']]
			|
			|
			Rare in the Hell Creek Formation.
			|
			]
			|-
			|
			]?
			|
			indeterminate
			|
			|
			|
			|
			|
			|-
			|
			'']''
			|
			''S.'' sp
			|
			|
			|
			|
			Floating aquatic plant.
			|
			]
	|-		|-
	|}		|}
			====Cycadophytes====
	==Footnotes==
			{| class="wikitable sortable" style="margin:auto; width:100%;"
	{{Reflist}}
			|-
			! Genus
			! Species
			! Location
			! Stratigraphic position
			! Abundance
			! Notes
			! Images
			|-
			| rowspan="2" |'']''
			|
			''N. comtula''
			|
			|
			|
			|Unlike ''N. yukonensis'', its leaves are {{plantgloss|pinnatisect}} pinnules. Common.
			|
			|-
			|
			''N. yukonensis''
			|
			|
			|
			|
			The only Hell Creek Formation ]. A simple leaf. Common.
			|
			]
			|-
			|}
			====Ginkgoales====
			{| class="wikitable sortable" style="margin:auto; width:100%;"
			|-
			! Genus
			! Species
			! Location
			! Stratigraphic position
			! Abundance
			! Notes
			! Images
			|-
			|
			'']''
			|
			'']''
			|
			|
			|
			|
			The only ] in the Hell Creek Formation; uncommon
			|
			]
			|-
			|}
			====Conifers====
			{| class="wikitable sortable" style="margin:auto; width:100%;"
			|-
			! Genus
			! Species
			! Location
			! Stratigraphic position
			! Abundance
			! Notes
			! Images
			|-
			|
			'']''?
			|
			indeterminate<ref name="Megaflora2002"/>
			|
			|
			|
			|
			Casts of ] leaves.
			|
			|-
			|
			'']''
			|
			'']''
			|
			|
			|
			|
			Casts of ] foliage. Uncommon
			|
			|-
			|
			'']''
			|
			''D.'' sp
			|
			|
			|
			|A conifer seed cone. It's likely to belong to ''].''
			|
			|-
			|
			'']''
			|
			'']''
			|
			|
			|
			|
			A ] conifer closely related to '']''. Common.
			|
			]
			|-
			|
			'']''
			|
			''Elatocladus'' sp,<ref name="Megaflora2002"/>
			|
			|
			|
			|
			A ] leaf morphogenus<ref name="Megaflora2002"/>
			|
			|-
			|
			'']''
			|
			'']''
			|
			|
			|
			|
			]-like or ]-like conifer.<br/> Less common in the lower 2/3 but more common in the upper 1/3 of the Hell Creek Formation.<ref name="Megaflora2002"/>
			|
			]
			|-
			|'']''
			|
			'']''
			|
			|
			|
			|Uncommon conifer.
			|
			]
			|-
			|
			'']''
			|
			'']''
			|
			|
			|
			|
			''M. occidentalis'' seed cones are known from the Hell Creek.
			|
			|-
			|
			'']''
			|
			''Platyspiroxylon'' sp.<ref name="Megaflora2002"/>
			|
			|
			|
			|
			A ]ous wood morphogenus
			|
			|-
			|
			'']''
			|
			''Podocarpoxylon'' sp.<ref name="Megaflora2002"/>
			|
			|
			|
			|
			A possibly ] wood morphogenus
			|
			|-
			|
			'']''
			|
			''Sequoiaxylon'' sp.<ref name="Megaflora2002"/>
			|
			|
			|
			|
			A ]ous wood morphogenus
			|
			|-
			|
			'']''
			|
			''Taxodioxylon'' sp.<ref name="Megaflora2002"/>
			|
			|
			|
			|
			A ]ous wood morphogenus
			|
			|-
			|
			'']''
			|
			'']''
			|
			|
			|
			|
			Related to today's ].
			|
			|-
			|
			Unidentified
			|
			Unidentified<ref name="Megaflora2002"/>
			|
			|
			|
			|
			Unspecified ] fossils<ref name="Megaflora2002"/>
			|
			|-
			|}
			====Angiosperms====
			{| class="wikitable sortable" style="margin:auto; width:100%;"
			|-
			! Genus
			! Species
			! Location
			! Stratigraphic position
			! Abundance
			! Notes
			! Images
			|-
			|
			''"]"''
			|
			''"A." lessigiana''
			|
			|
			|
			|
			Abundant at Brownie Butte, ].
			|
			]
			|-
			|
			'']?''
			|
			''A?. robusta''
			|
			|
			|
			|
			Abundant at Brownie Butte, Montana.
			|
			]
			|-
			|'']''
			|
			''A. polevoi''
			|
			|
			|
			|A lobed leaf. Closely relating to ''Bisonia''. Fairly common.
			|
			|-
			|'']''
			|cf. ''A. affinis''
			|
			|
			|
			|An uncommon taxon with compound leaves.
			|]
			|-
			|'']''
			|
			''B. niemi''
			|
			|
			|
			|
			A broad leaf, probably in the ].<br/> A common taxon. Type specimen was found in South Dakota.
			|]
			|-
			|'']''
			|''B. serrata''
			|
			|
			|
			|In the ], closely relating to extant ''].'' Less common.
			|
			|-
			|]?
			|
			indeterminate
			|
			|
			|
			|''Incertae sedis''. It's not likely in the ].<ref>{{Cite web |title=Cruisin' the fossil freeway : an epoch tale of a scientist and an artist on the ultimate 5,000-mile paleo road trip {{!}} WorldCat.org |url=https://search.worldcat.org/title/125404857 |access-date=2024-01-27 |website=search.worldcat.org |language=en}}</ref>
			|
			]
			|-
			|'']''
			|''C. ulmiformis''
			|
			|
			|
			|Though this fossil fruit is abundant in the ], it's also found in Hell Creek. It may belong to ].<ref>{{Cite journal |last1=Manchester |first1=Steven R. |last2=O'Leary |first2=Elizabeth L. |date=2010 |title=Phylogenetic Distribution and Identification of Fin-winged Fruits |journal=Botanical Review |volume=76 |issue=1 |pages=1–82 |doi=10.1007/s12229-010-9041-0 |jstor=40792810 |bibcode=2010BotRv..76....1M |s2cid=8207808 }}</ref>
			|
			|-
			|
			''"]"''
			|
			''"C." taurenensis''
			|
			|
			|
			|
			''Incertae sedis''. It's common in the lowermost to the middle Hell Creek Formation, but less common in the upper 1/3 Hell Creek Formation.<ref name="Megaflora2002"/>
			|
			]
			|-
			|
			''"]"''
			|
			''"C." lineafolia''
			|
			|
			|
			|
			Included in ''] affinis'' by L. Hickey.<br/> Belongs in Rhamnaceae (modern ]s and '']'').{{citation needed|date=February 2024}} Some other specimens referred to '']''(?) sp.), a real cinnamon bush. Its affinity is questionable.
			|
			]
			|-
			| rowspan="4" |''Cissites''
			|cf. ''C. acerifolia''
			|
			|
			|
			|This morphotype was first described from the ].<ref name=":6">{{cite thesis |last1=Johnson |first1=Kirk Richard |date=1989 |title=A high-resolution megafloral biostratigraphy spanning the Cretaceous-Tertiary boundary in the northern Great Plains |url=https://www.proquest.com/openview/26466332bf1f90e5d5e952eee5a81147/1 }}{{page needed|date=January 2024}}</ref>
			|
			|-
			|
			''C. insignis''
			|
			|
			|
			|
			This form represents of the group of ] leaves from ].<ref name=":6" />
			|
			|-
			|
			''C. lobata''
			|
			|
			|
			|A lobed leaf with half-naked basal lateral veins. Common in the upper 1/3 of the Hell Creek Formation.
			|
			|-
			|
			''C. puilasokensis''
			|
			|
			|
			|A palmately lobed leaf with 5 primary veins. Common in the upper 1/3 of the Hell Creek Formation.
			|]
			|-
			| rowspan="2" |
			'']''
			|
			''C. corrugata''
			|
			|
			|
			|
			A prehistoric species of water lettuce, previously assigned to the genus '']''.
			| rowspan="2" |
			]
			|-
			|''C. hickeyi''
			|
			|
			|
			|Another Cobbania species from pond sediments known as "Licking Leaves."<ref>{{Cite journal |last1=Stockey |first1=Ruth A. |last2=Rothwell |first2=Gar W. |last3=Johnson |first3=Kirk R. |date=October 2016 |title=Evaluating Relationships among Floating Aquatic Monocots: A New Species of Cobbania (Araceae) from the Upper Maastrichtian of South Dakota |journal=International Journal of Plant Sciences |language=en |volume=177 |issue=8 |pages=706–725 |doi=10.1086/688285 |s2cid=89477112 }}</ref>
			|-
			|'']''
			|''C. newberryi''
			|
			|
			|
			|The majority of leaves are entire-margined but some may develop a few teeth.<ref name=":6" />
			|
			|-
			|''"]"''
			|''"C." sp''
			|
			|
			|
			|A reed-type plant.
			|]
			|-
			| rowspan="3" |'']''
			|
			'']''
			|
			|
			|
			|
			This taxon is extremely common in the Hell Creek Formation, but is rare in Paleocene sediments.<br/> It is believed to be in ], closely related to the living '']''.<ref name=":6" /><ref>{{Cite journal |last1=Peppe |first1=Daniel J. |last2=Hickey |first2=Leo J. |date=October 2014 |title=Fort Union Formation Fossil Leaves (Paleocene, Williston Basin, North Dakota, USA) Indicate Evolutionary Relationships Between Paleocene and Eocene Plant Species |journal=Bulletin of the Peabody Museum of Natural History |volume=55 |issue=2 |pages=171–189 |doi=10.3374/014.055.0209 |s2cid=129724520 }}</ref>
			|
			]
			|-
			|
			''aff. "Dryophyllum" subfalcatum''
			|
			|
			|
			|
			see above.
			|
			|-
			|
			''"D." tenneseensis''
			|
			|
			|
			|This taxon is similar to ''D. subfalcatum]]'' but with extremely high L/W ratio and craspedodromous venation.<ref name=":6" />
			|
			|-
			|'']''
			|
			''E. montana''
			|
			|
			|
			|
			Johnson, 1996. In the ] (related to today's Sycamore). A very common taxon.
			|]
			|-
			|
			"'']''"
			|
			"''F.''" ''planicostata''
			|
			|
			|
			|Despite the genus name, it's in ].
			|
			]
			|-
			|
			'']''
			|
			''G.'' ''saportana''
			|
			|
			|
			|
			Another generic ].
			|]
			|-
			|
			'']''
			|
			''H. hydrocotyloidea''
			|
			|
			|
			|''Incertae sedis.'' May be related to ]. An uncommon taxon.
			|
			|-
			|
			'']?''
			|
			aff. ''Humulus sp.''
			|
			|
			|
			| May be related to the extant genus '']''.
			|]
			|-
			|
			'']''
			|
			''H. pinnata''
			|
			|
			|
			|
			Floating aquatic fern
			|]
			|-
			|'']''
			|
			''L. scutatum''
			|
			|
			|
			|Floating aquatic ], closely related to ''].''
			|]
			|-
			|
			'']''
			|
			''L. bradacii''
			|
			|
			|
			|
			Johnson, 1996. In the ]: a common taxon.
			|]
			|-
			|
			''"]"''
			|
			''"L." laramiense''
			|
			|
			|
			|Unlobed leaf. May be related to today's ] (yellow poplar). An uncommon taxon.
			|]
			|-
			|
			'']''
			|
			''L. sp''
			|
			|
			|
			|
			Four-lobed leaf. May be related to today's ] (yellow poplar). An uncommon taxon.
			|
			]
			|-
			|
			'']''
			|
			''L. preartocarpoides''
			|
			|
			|
			|
			''Incertae sedis'' but possibly in Proteales. Johnson, 1996.
			|]
			|-
			|'']''
			|
			''L. wardiana''
			|
			|
			|
			|Large leaves. Closely related to ''"Dryophyllum" subfalcatum''.
			|
			|-
			|''"]"''
			|
			''M. pulchra''
			|
			|
			|
			|
			Occurs in southern the ] flora,<Br/> Leo Hickey claims it is found further north in ] and the ].{{citation needed|date=February 2024}}
			|
			]
			|-
			| rowspan="3" |'']''
			|
			''M. johnsonii''
			|
			|
			|
			|A new Marmarthia species described in Peppe et al. 2007.<ref>{{Cite journal |last1=Peppe |first1=Daniel J. |last2=Erickson |first2=J. Mark |last3=Hickey |first3=Leo J. |date=May 2007 |title=Fossil leaf species from the Fox Hills Formation (Upper Cretaceous: North Dakota, USA) and their paleogeographic significance |journal=Journal of Paleontology |volume=81 |issue=3 |pages=550–567 |doi=10.1666/05067.1 |bibcode=2007JPal...81..550P |s2cid=129967389 }}</ref>
			|
			|-
			|
			''M. pearsonii''
			|
			|
			|
			|
			Johnson, 1996. In the ]: a very common taxon.
			|
			]
			|-
			|
			''M. trivialis''
			|
			|
			|
			|
			Johnson, 1996. In the ]: a very common taxon.
			|
			|-
			|
			"'']''"
			|
			"''Myrica''" ''torreyi''
			|
			|
			|
			|''Incertae sedis''. Not actually a ].
			|
			]
			|-
			|
			'']''
			|
			''N. sp''
			|
			|
			|
			|One of the most common aquatic plants in Hell Creek.
			|]
			|-
			|'']''
			|
			''N. montanum''
			|
			|
			|
			| An aquatic angiosperm, closely related to ]. Uncommon.
			|
			|-
			|'']''
			|
			''N. borealis''
			|
			|
			|
			|
			A fossil fruit likely to belonging to ''].''<ref>{{Cite journal |last1=Crane |first1=Peter R. |last2=Manchester |first2=Steven R. |last3=Dilcher |first3=David L. |date=October 1991 |title=Reproductive and Vegetative Structure of Nordenskioldia (Trochodendraceae), A Vesselless Dicotyledon from the Early Tertiary of the Northern Hemisphere |journal=American Journal of Botany |volume=78 |issue=10 |pages=1311–1334 |doi=10.1002/j.1537-2197.1991.tb12599.x }}</ref>
			|
			|-
			|
			'']''
			|
			''P. hastata''
			|
			|
			|
			|Despite the name, it's not related to extant genus ''].''
			|
			|-
			|'']''
			|
			''P. porosia''
			|
			|
			|
			|
			A ] with fruits and seeds visually similar to '']'' though it's dubious.{{citation needed|date=February 2024}}
			|
			]
			|-
			|
			'']''
			|
			''P. cordatum''
			|
			|
			|
			|May be related to ]. A common taxon.
			|
			|-
			| rowspan="2" |
			'']''
			|
			''P. marginata''
			|
			|
			|
			|
			Johnson, 1996. In the ]. A common taxon.
			|]
			|-
			|
			''P. raynoldsii''
			|
			|
			|
			|An uncommon taxon.
			|
			|-
			|
			'']''
			|
			''P. verrucosa''
			|
			|
			|
			|A fossil fruit that may belong to ].<ref>{{cite journal |last1=Manchester |first1=Steven R. |last2=Kodrul |first2=Tatyana M. |title=Morphology, affinities and phytogeographic history of Porosia Hickey in the Cretaceous and Paleocene of North America and Asia |journal=Acta Palaeobotanica |date=June 2014 |volume=54 |issue=1 |pages=77–99 |doi=10.2478/acpa-2014-0002 |doi-access=free }}</ref>
			|
			|-
			|
			'']''
			|
			''R. cleburnii''
			|
			|
			|
			|
			''Incertae sedis.'' A '']'' look-alike leaf.<ref name=":6" />
			|]
			|-
			|
			'']''
			|
			''S.'' sp
			|
			|
			|
			|
			] palm tree. Very common.
			|]
			|-
			|
			'']''
			|
			''S. antiquus''
			|
			|
			|
			|
			A fruit seed that may belong to the palm family (]), closely related to the genus '']''.<ref>{{cite journal |last1=McIver |first1=Elisabeth E |title=The paleoenvironment of ''Tyrannosaurus rex'' from southwestern Saskatchewan, Canada |journal=Canadian Journal of Earth Sciences |date=February 2002 |volume=39 |issue=2 |pages=207–221 |doi=10.1139/e01-073 |bibcode=2002CaJES..39..207M }}</ref>
			|]
			|-
			|
			'']''
			|
			''T. angulata''
			|
			|
			|
			|
			A water caltrop look-alike.
			|]
			|-
			| rowspan="4" |
			'']''
			|
			''T. arctica''
			|
			|
			|
			|A fossil fruit that may belong to '']''.
			|
			|-
			|''T. ellipticum''
			|
			|
			|
			|A ] look-alike. An uncommon taxon.
			|
			|-
			|''T. genetrix''
			|
			|
			|
			|A ] look-alike. A common taxon.
			|
			|-
			|
			''T. nebrascensis''
			|
			|
			|
			|A very common taxon.
			|]
			|-
			|
			''"]"''
			|
			''"V." stantonii''
			|
			|
			|
			|
			Possibly a member of the ] rather than ]<ref name="Megaflora2002"/><ref>{{cite book |last1=Arens |first1=Nan Crystal |last2=Allen |first2=Sarah E. |title=Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas |chapter=A florule from the base of the Hell Creek Formation in the type area of eastern Montana: Implications for vegetation and climate |date=1 January 2014 |doi=10.1130/2014.2503(06) |isbn=9780813725031 }}</ref>
			|]
			|-
			|
			''"]"''
			|
			''"Z." fibrillosus''
			|
			|
			|
			|A common taxon.
			|
			]
			|-
			| rowspan="2" |
			'']''
			|
			''Z. attenuata''
			|
			|
			|
			|
			Related to today's ] plant. Its closest living relative is the Asian genus '']''.<br/> Some Hell Creek Formation specimens show damage from hispine ] ("leaf beetles" (Wilf et al., 2000)).
			|
			]
			|-
			|''Z. magnifolia''
			|
			|
			|
			|Another '']'' species, previously assigned to '']? magnifolia''.
			|
			|-
			|
			'']''
			|
			''Z. flabella''
			|
			|
			|
			| An uncommon taxon.
			|
			|}
			===Palynology===
			{| class="wikitable sortable" style="margin:auto; width:100%;"
			|-
			! Genus
			! Species
			! Location
			! Stratigraphic position
			! Abundance
			! Notes
			! Images
			|-
			|rowspan=3|'']''
			|
			'']''<ref name="NortonHall1969">{{cite journal |last1=Norton |first1=N.J. |last2=Hall |first2=J.H. |year=1969 |title=Palynology of the Upper Cretaceous and Lower Tertiary in the type locality of the Hell Creek Formation, Montana, USA |journal=Palaeontographica Abteilung B |volume=125 |pages=1–64}}</ref>
			|
			Montana
			|
			|
			|
			A conifer palynomorph
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			A conifer palynomorph
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			A conifer palynomorph
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=16|'']''
			|
			''Aquilapollenites amplus''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites attenuatus''
			|
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites collaris''
			|
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites conatus''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites delicatus''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites marmarthensis''
			|
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites polaris''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites pulvinus''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites pyriformis''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites quadricretaeus''
			|
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites quadrilobus''
			|
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites reductus''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites reticulatus''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites senonicus''
			|
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites turbidus''
			|
			|
			|
			|
			|
			|-
			|
			''Aquilapollenites striatus''
			|
			|
			|
			|
			|
			]
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			A ] palynomorph
			|
			|-
			|
			'']''
			|
			''Balmeisporites'' ''sp.''
			|
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			''Converrucosisporites'' sp.<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			A ] palynomorph
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana<br/>South Dakota
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			A fern spore palynomorph
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			A fern spore palynomorph
			|
			|-
			|
			'']''
			|
			'']''
			|
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			''Interpollis'' cf. ''I. supplingensis''
			|
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=4|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Liliacidites'' sp.<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=5|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Monosulcites'' sp.<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana<br/>South Dakota
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=3|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=8|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=5|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			''Tricolpopollenites'' sp1, sp2<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=6|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|rowspan=2|'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|]
			|-
			|
			'']''
			|
			'']''<ref name="NortonHall1969"/>
			|
			Montana
			|
			|
			|
			|
			|-
			|}
			== See also ==
			* ] ''(with link directory)''
			* ]
			* ]
			* ]
			* ]
			** ], Spain
			** ], Spain
			** ], Argentina
			** ], Antarctica
			{{clear}}
			== References ==
			{{Reflist|2}}
			=== Bibliography ===
			;General
			* {{citation |last1=Broad |first1=William J. |last2=Chang |first2=Kenneth |title=Fossil Site Reveals Day That Meteor Hit Earth and, Maybe, Wiped Out Dinosaurs |url=https://www.nytimes.com/2019/03/29/science/dinosaurs-extinction-asteroid.html |work=The New York Times |date=29 March 2019 }}
			* {{citation |first=Douglas |last=Preston |year=2019 |title=The Day the Dinosaurs Died |url=https://newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died |magazine=The New Yorker |pages=1 |access-date=2019-04-01}}
			* {{citation |last=U.S. National |first=Park Service |year=1966 |title=National Natural Landmarks - National Natural Landmarks (U.S. National Park Service) |url=https://www.nps.gov/subjects/nnlandmarks/site.htm?Site=HECR-MT |publisher=www.nps.gov |pages=1 |access-date=2019-03-22}}
			;Geology
			<!--Most recent first-->
			* {{citation | last=DePalma | first=Robert A. | last2=Smit | first2=Jan | last3=Burnham | first3=David A. | last4=Kuiper | first4=Klaudia | last5=Manning | first5=Phillip L. | last6=Oleinik | first6=Anton | last7=Larson | first7=Peter | last8=Maurrasse | first8=Florentin J. | last9=Vellekoop | first9=Johan | last10=Richards | first10=Mark A. | last11=Gurche | first11=Loren | last12=Alvarez | first12=Walter |year=2019 |title=A seismically induced onshore surge deposit at the K-Pg boundary, North Dakota |journal=] |volume=116 |issue=17 |pages=8190–8199 |doi=10.1073/pnas.1817407116 |doi-access=free |pmid=30936306 |pmc=6486721|bibcode=2019PNAS..116.8190D }} {{bibcode|2019PNAS..116.8190D}}
			* {{citation |last1=Evans |first1=D.C. |last2=Larson |first2=D.W. |last3=Currie |first3=P.J. |year=2013 |title=A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America |journal=] |volume=100 |issue=11 |pages=1041–1049 |doi=10.1007/s00114-013-1107-5|pmid=24248432 |bibcode=2013NW....100.1041E }} {{bibcode|2013NW....100.1041E |pmid=24248432}}
			* {{citation |last1=Husson |first1=D. |last2=Galbrun |first2=B. |last3=Laskar |first3=J. |last4=Hinnov |first4=L.A. |last5=Thibault |first5=N. |last6=Gardin |first6=S. |last7=Locklair |first7=R.E. |year=2011 |title=Astronomical calibration of the Maastrichtian (late Cretaceous) |journal=] |volume=305 |issue=3 |pages=328–340 |doi=10.1016/j.epsl.2011.03.008|bibcode=2011E&PSL.305..328H }} {{bibcode|2011E&PSL.305..328H}}
			* {{citation |last=LeCain |first=Rebecca |year=2010 |title=Magnetostratigraphy of the Hell Creek and lower Fort Union formations in northeast Montana |url=https://scholars.unh.edu/thesis/552 |publisher=Master's Theses and Capstones |pages=1 |access-date=2020-03-30}}
			* {{citation |last1=Johnson |first1=K.R. |last2=Nichols |first2=D.J. |last3=Hartman |first3=J.H. |year=2002 |title=Hell Creek Formation: A 2001 synthesis. The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the northern Great Plains |journal=] |volume=361 |pages=503–510}}
			;Paleontology
			<!--Most recent first-->
			* {{citation |last=DePalma |first=Robert |year=2010 |title=Preliminary Notes on the First Recorded Amber Insects from the Hell Creek Formation |url=https://www.researchgate.net/publication/228474031 |journal=] |access-date=2019-02-21}}
			* {{citation |last1=Boyd |first1=Clint A. |last2=Brown |first2=Caleb M. |last3=Scheetz |first3=Rodney D. |last4=Clarke |first4=Julia A. |year=2009 |title=Taxonomic revision of the basal neornithischian taxa ''Thescelosaurus'' and ''Bugenasaura'' |journal=] |volume=29 |issue=3 |pages=758–770 |doi=10.1671/039.029.0328|bibcode=2009JVPal..29..758B }}
			* {{citation |last=Longrich |first=N |year=2008 |title=A new, large ornithomimid from the Cretaceous Dinosaur Park Formation of Alberta, Canada: Implications for the study of dissociated dinosaur remains |journal=] |volume=54 |issue=1 |pages=983–996 |doi=10.1111/j.1475-4983.2008.00791.x|bibcode=2008Palgy..51..983L }}
			* {{citation |last1=Manning |first1=P.L. |last2=Ott |first2=C. |last3=Falkingham |first3=P.L. |year=2008 |title=The first tyrannosaurid track from the Hell Creek Formation (Late Cretaceous), Montana, U.S.A |journal=] |volume=23 |issue=10 |pages=645–647 |doi=10.2110/palo.2008.p08-030r|bibcode=2008Palai..23..645M }} {{bibcode|2008Palai..23..645M}}
			* {{citation |last1=Bakker |first1=R.T. |last2=Sullivan |first2=R.M. |last3=Porter |first3=V. |last4=Larson |first4=P. |last5=Saulsbury |first5=S.J. |year=2006 |title=''Dracorex hogwartsia'', n. gen., n. sp., a spiked, flat-headed pachycephalosaurid dinosaur from the Upper Cretaceous Hell Creek Formation of South Dakota in Lucas, S. G. and Sullivan, R. M., eds., Late Cretaceous vertebrates from the Western Interior |url=http://www.childrensmuseum.org/themuseum/dinosphere/draco_rex/dracorex_hogwartsia.pdf |archive-url=https://web.archive.org/web/20110717174743/http://www.childrensmuseum.org/themuseum/dinosphere/draco_rex/dracorex_hogwartsia.pdf |archive-date=2011-07-17 |journal=] |volume=35 |pages=331–354 |author1-link=Robert Bakker }}
			* {{citation |last1=Henderson |first1=M.D. |last2=Peterson |first2=J.E. |year=2006 |title=An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana |journal=] |volume=26 |issue=1 |pages=192–195 |doi=10.1671/0272-4634(2006)262.0.CO;2 |jstor=4524549 |s2cid=130751879 |url=http://doc.rero.ch/record/15687/files/PAL_E2073.pdf }}
			* {{citation |last1=Weishampel |first1=David B. |author2-link=Peter Dodson |last2=Dodson |first2=Peter |author3-link=Halszka Osmólska |last3=Osmólska |first3=Halszka |year=2004 |title=The Dinosauria, 2nd edition |url=https://books.google.com/books?id=vtZFDb_iw40C |publisher=Berkeley: University of California Press |pages=1–880 |access-date=2019-02-21 |isbn=0-520-24209-2 |author1-link=David B. Weishampel }}
			* {{citation |last1=Pearson |first1=D.A. |last2=Schaefer |first2=T. |last3=Johnson |first3=K.R. |last4=Nichols |first4=D.J. |last5=Hunter |first5=J.P. |year=2002 |title=The Hell Creek Formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An integrated continental record of the end of the Cretaceous |url=https://books.google.com/books?id=cHvcIeh2f84C&pg=PA145 |journal=Vertebrate Biostratigraphy of the Hell Creek Formation in Southwestern North Dakota and Northwestern South Dakota, Geological Society of America |volume=Special Paper 361 |pages=145–167 |access-date=2019-03-22 |isbn=9780813723617}}
			* {{citation |last=Varricchio |first=D.J |year=2001 |title=Late Cretaceous oviraptorosaur (Theropoda) dinosaurs from Montana |publisher=D. H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life. Indiana University Press, Indianapolis, Indiana |pages=42–57}}
			* {{citation |last1=Currie |first1=P.J. |last2=Padian |first2=K. |year=1997 |title=The Encyclopedia of Dinosaurs |url=https://archive.org/details/encyclopediadino00curr_075 |publisher=Academic Press |pages=1–901 |access-date=2020-03-30 |isbn=978-0-122-26810-6}}
			** {{cite book |last=Eberth |first=D.A. |year=1997 |title=Edmonton Group |url=https://archive.org/details/encyclopediadino00curr_075 |url-access=registration |location=San Diego|publisher=Academic Press|pages=–204 |isbn=978-0-122-26810-6}}
			** {{cite book |last=Lofgren |first=D.F. |year=1997 |title=Hell Creek Formation |url=https://archive.org/details/encyclopediadino00curr_075 |url-access=registration |location=San Diego|publisher=Academic Press|pages=–303 |isbn=978-0-122-26810-6}}
			** {{cite book |last=Breithaupt |first=B.H |year=1997 |title=Lance Formation |url=https://archive.org/details/encyclopediadino00curr_075 |url-access=registration |location=San Diego|publisher=Academic Press|pages=–395 |isbn=978-0-122-26810-6}}
			* {{citation |last=Christophel |first=D.C. |year=1976 |title=Fossil floras from the Smoky Tower locality, Alberta, Canada |journal=Palaeontographica, Abt. B |volume=157 }}
			* {{citation |last=Chandrasekharam |first=A. |year=1974 |title=Megafossil flora from the Genesee locality, Alberta, Canada |journal=Palaeontographica, Abt. A |volume=174 }}
			* {{citation |last1=Estes |first1=R. |first2=P. |last2=Berberian |year=1970 |title=Paleoecology of a late Cretaceous vertebrate community from Montana |journal=] |volume=343 |pages=1}}
			== External links ==<!-- Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 402 -->
			* provides a faunal list
			*
			*
			{{authority control}}
			]
	==References==
			]
	* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp.&nbsp;ISBN 0-520-24209-2.
			]
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Latest revision as of 06:26, 16 December 2024

Fossil flora and fauna of North American site

This is an overview of the fossil flora and fauna of the Maastrichtian-Danian Hell Creek Formation.

Invertebrates

Insects

Insects from the groups Diptera, Zygoptera, and possibly Hemiphlebiidae have been unearthed in Hell Creek in amber. Fossils found in the Hell Creek Formation and the Fort Union Formation of these insects went extinct during the K-T Event.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Cephaloleichnites	Cephaloleichnites strongi				Possible hispine beetle herbivory on Zingiberopsis attenuta
?Hemiphlebiidae	Indeterminate				Possible Hemiphlebiid damselflies
Brachycera	Indeterminate				Undescribed brachyceran flies
Nematocera	Indeterminate				Undescribed nematoceran flies
Aeschnidiidae	Indeterminate				Indeterminate aeschnidiid dragonflies

Molluscs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Plesielliptio	P. postbiplicatus				Freshwater Unionid river mussels
	P. gibbosoides				Freshwater Unionid river mussels
	P. whitfieldi				Freshwater Unionid river mussels
Rhabdotophorus	R. aldrichi				Freshwater mussel of family Unionidae.
Pleurobema	P. cryptorhynchus				Freshwater mussel of family Unionidae.
Plethobasus	P. aesopiformis				Freshwater mussel of family Unionidae.
	P. biesopoides
Quadrula	Q. cylindricoides				Freshwater mussel of family Unionidae.
Proparreysia	P. verrucosiformis				Freshwater mussel of family Unionidae.
	P. holmesiana
	P. barnumi
	P. percorrugata
	P. pyramidatoides
	P. letsoni
	P. retusoides
	P. corbiculoides
	P. paucinodosa
?Obovaria	?O. pyramidella
Corbicula	C. cf. subelliptica
	C. sp	South Dakota			From a marine facies ("tongue"). Modern members of the genus live in fresh water
Sphaerium	S. beckmani				"Pill clam". "Nut clam". "Fingernail clam". "Pea clam". Family Sphaeriidae.
Pleiodon	Indeterminate
Campeloma	C. sp				Freshwater snail
Anomia	A. gryphorhyncha				Bivalve. Family Anomiidae. From a marine facies ("tongue") in South Dakota.
Crassostrea	C. subtrigonalis				Oyster. Family Ostreidae. Collected from a marine facies ("tongue") in South Dakota.
Granocardium	G. sp				Bivalve. Family Cardiidae (cockle). Collected from a marine facies ("tongue") in South Dakota.
?Hiatella	?H. sp				Bivalve. Present members of this genus are rock borers. Collected from a marine facies ("tongue") in South Dakota.
Leptosolen	indeterminate				Bivalve. Family Cultellidae. Collected from a marine facies ("tongue") in South Dakota.
Sphenodiscus	S. lenticularis				Ammonite. From a marine facies ("tongue") in South Dakota.
Discoscaphites	D. rossi				Microconch of an ammonite. From a marine facies ("tongue") in South Dakota.
Scaphitidae	indeterminate				Ammonite. From a marine facies ("tongue") in South Dakota. Other attributes: specimen has hooks on its shell.

Amphibians

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Anura (frog)	indeterminate	North Dakota South Dakota	Middle to upper Hell Creek Formation	3 unassigned specimens	Anura indet. consists of material not currently assigned to any genus of frog.
Barbourula	Indeterminate	Montana
Caudata (salamander)	indeterminate	North Dakota South Dakota	Lower to uppermost Hell Creek Formation	149 unassigned specimens	Material of Caudata indet. is not currently assigned to any genus.
Eopelobates	Indeterminate	Montana
Habrosaurus	H. dilatus	Montana North Dakota South Dakota	Middle to upper Hell Creek Formation	6 specimens	Habrosaurus is a sirenid amphibian.
Lisserpeton	L. bairdi	Montana
Opisthotriton	O. kayi	Montana North Dakota South Dakota	Lower to upper Hell Creek Formation	22 specimens	Opisthotriton is classified as a Batrachosauroididae.
Paranecturus	P. garbanii	Montana			A member of Proteidae.
Proamphiuma	P. cretacica	Montana
Prodesmodon	P. copei	Montana
Scapherpeton	S. tectum	Montana North Dakota South Dakota	Lower to upper Hell Creek Formation	144 specimens	Scapherpeton is a scapherpetonid that is very common in the Hell Creek Formation.
Scotiophryne	S. pustulosa	Montana			A small frog

Fish

Bony fish

Bony fishes
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Acipenser	A. amnisinferos	North Dakota (Tanis)			A sturgeon
	A. eruciferus	Montana
	A. praeparatorum	North Dakota (Tanis)
	A. cf. A. amnisinferos	North Dakota (Tanis)
	cf. A. sp.	North Dakota South Dakota	Lower to upper Hell Creek Formation	18 specimens are tentatively assigned to Acipenser sp.	Acipenser sp. is tentatively referred to the genus.
Anchiacipencer	A. acanthaspis	Montana			A sturgeon, originally considered as indeterminate material
Belonostomus	B. longirostris	Montana North Dakota South Dakota	Lower to upper Hell Creek Formation	28 specimens	A long-snouted slender fish classified as an aspidorhynchid.
Coriops	C. amnicolus	Montana
Cyclurus	C. fragosus	Montana North Dakota South Dakota			A small amiid fish (ubiquitous). Previously known as Amia fragosa or Kindleia fragosa. 2610 specimens have been assigned to Kindleia, making it an extremely common genus.
"Lepisosteus"	"L. occidentalis"	Montana North Dakota South Dakota	Lower to uppermost Hell Creek Formation	938 specimens are assigned to Lepidosteus	A lepidosteid that is very common in the Hell Creek Formation. Nomen dubium.
Melvius	M. thomasi	North Dakota South Dakota	Lower to upper Hell Creek Formation	6 specimens are assigned to Melvius	A large amiid fish.
Phyllodus	P. paulkatoi				Fish with columnar teeth
Palaeolabrus	P. montanensis	Montana
Paleopsephurus	P. wilsoni	Montana			A paddlefish
Paralbula	P. casei	Montana
Parapsephurus	P. willybemisi	North Dakota (Tanis)			A paddlefish
Platacodon	P. nanus	Montana			Small teleost fish
Protamia	Indeterminate	Montana
Pachyrhizodontoidei	Indeterminate				Fish
Polyodontidae	Indeterminate	Montana			Paddlefish
Protoscaphirhynchus	P. squamosus	Montana			A sturgeon
Pugiopsephurus	P. inundatus	North Dakota (Tanis)			A paddlefish

Cartilaginous fish

Chondrichthyes reported from the Hell Creek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Chiloscyllium	C. sp.	Montana			A member of Hemiscylliidae.
Galagadon	G. nordquistae	South Dakota		Isolated teeth	A carpet shark
Lonchidion	L. selachos	Montana North Dakota South Dakota	Lower to upper Hell Creek Formation	40 specimens	A genus of prehistoric sharks in the family Hybodontidae. It makes up 0.4% of the remains of the vertebrates of the Hell Creek Formation.
Myledaphus	M. pustulosus	Montana North Dakota South Dakota	Lower to upper Hell Creek Formation.	1677 specimens previously assigned to M. bipartitus.	Is an anacoracid batoid rajiform related to guitarfishes. Described on the basis of teeth formerly assigned to the species M. bipartitus. The material assigned to Myledaphus bipartitus and makes up 16.5% of the vertebrate remains.
Protoginglymostoma	P. estesi	Montana			A member of Ginglymostomatidae. Formerly assigned to the genus Brachaelurus.
Restesia	R. americana	Montana North Dakota South Dakota	Middle Hell Creek Formation	5 specimens previously assigned to Squatirhina	A wobbegong-like shark. Formerly assigned to Squatirhina. The remains consist of 0.05% of the vertebrates. Also known from the Lance Formation.
Carcharhinidae indet.	Indeterminate	South Dakota		An isolated tooth.
Scapanorhynchus	.sp.	North Dakota

Dinosaurs

A paleo-population study is one of the most difficult of analyses to conduct in field paleontology. Here is the most recent estimate of the proportions of the eight most common dinosaurian families in the Hell Creek Formation, based on detailed field studies by White, Fastovsky and Sheehan.

• Ceratopsidae 61%
• Hadrosauridae 23%
• Ornithomimidae 5%
• Tyrannosauridae 4%
• Hypsilophodontidae 3%
• Dromaeosauridae 2%
• Pachycephalosauridae 1%
• Troodontidae 1% (represented only by teeth)

Outcrops sampled by the Hell Creek Project were divided into three sections: lower, middle and upper slices. The top and bottom sections were the focus of the PLoS One report, and within each portion many remains of Triceratops, Edmontosaurus, and Tyrannosaurus were found. Triceratops was the most common in each section, but, surprisingly, Tyrannosaurus was just as common, if not slightly more common, than the hadrosaur Edmontosaurus. In the upper Hell Creek section, for example, the census included twenty two Triceratops, five Tyrannosaurus, and five Edmontosaurus.

The dinosaurs Thescelosaurus, Ornithomimus, Pachycephalosaurus and Ankylosaurus were also included in the breakdown, but were relatively rare. Other dinosaurs, such as Sphaerotholus, Denversaurus, Torosaurus, Struthiomimus, Acheroraptor, Dakotaraptor, Pectinodon, Richardoestesia, Paronychodon, Anzu, Leptorhynchos and Troodon (more likely Pectinodon), were reported as being rare and are not included in the breakdown.

The dinosaur collections made over the past decade during the Hell Creek Project yielded new information from an improved genus-level collecting schema and robust data set that revealed relative dinosaur abundances that were unexpected, and ontogenetic age classes previously considered rare. We recognize a much higher percentage of Tyrannosaurus than previous surveys. Tyrannosaurus equals Edmontosaurus in U3 and in L3 comprises a greater percentage of the large dinosaur fauna as the second-most abundant taxon after Triceratops, followed by Edmontosaurus. This is surprisingly consistent in (1) the two major lag deposits (MOR loc. HC-530 and HC-312) in the Apex sandstone and Jen-rex sand where individual bones were counted and (2) in two thirds of the formation reflected in L3 and U3 records of dinosaur skeletons only.

Triceratops is by far the most common dinosaur at 40% (n = 72), Tyrannosaurus is second at 24% (n = 44), Edmontosaurus is third at 20% (n = 36), followed by Thescelosaurus at 8% (n = 15), Ornithomimus at 5% (n = 9), and Pachycephalosaurus and Ankylosaurus both at 1% (n = 2) are relatively rare.

Fossil footprints of dinosaurs from the Hell Creek Formation are very rare. As of 2017, there is only one find of a possible Tyrannosaurus rex footprint, dating from 2007 and described a year later. A trackway made by mid-sized theropod, possibly a small tyrannosaurid individual, was discovered in South Dakota in 1997, and in 2014 these footprints were named Wakinyantanka styxi.

Ornithischians

Ankylosaurs

Indeterminate nodosaur remains have been unearthed in the Hell Creek Formation and other nearby areas.

Ankylosauria reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Ankylosaurus	A. magniventris	Montana	Upper	A partial skull, teeth, cervical vertebrae, dorsal vertebrae, caudal vertebrae, right scapulocoracoid, otic capsule, maxilla fragment, right jugal, left jugal and quadratojugal, sacral centra, additional fragments of the cervical half rings and a partial tail club handle.	An ankylosaur. Also found in the Lance, Frenchman, Ferris and Scollard Formations.
Denversaurus	D. schlessmani	Montana South Dakota		Skull roof, pelvis and osteoderms.	A nodosaurid ankylosaur whose remains have been found in the Lance and Laramie Formation.

Pachycephalosaurs

An undescribed and unnamed pachycephalosaur is present in North Dakota. Pachycephalosaur remains have been unearthed in Montana as in the case of Platytholus and the now invalid genus Stenotholus kohleri, which is now a junior synonym of Pachycephalosaurus.

Pachycephalosaurs reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Dracorex	D. hogwartsia	South Dakota	Middle		A pachycephalosaur, possibly synonymous with Pachycephalosaurus.
Pachycephalosaurus	P. wyomingensis	Montana South Dakota			A pachycephalosaur. Also found in the Lance Formation.
Platytholus	P. clemensi	Montana	Lower	A partial skull	A medium-sized pachycephalosaurine closely related to Acrotholus and Prenocephale
Sphaerotholus	S. buchholtzae	Montana	Lower to upper	"Skull material."	A pachycephalosaur whose remains have also been found in the Frenchman Formation. Genus also known from the Kirtland Formation, Dinosaur Park Formation and the Horseshoe Canyon Formation.
	S. triregnum	Montana	Middle	A left squamosal.	A pachycephalosaur distinguished from S. buchholtzae by its more ornamented squamosal.
Stygimoloch	S. spinifer	Montana South Dakota North Dakota			A pachycephalosaur, possibly synonymous with Pachycephalosaurus. Also found in the Ferris Formation and the Lance Formation.

Ceratopsians

Indeterminate ceratopsid teeth and some identifiable bones from Triceratops can be extremely common. 8.31% of all vertebrate remains from the Hell Creek Formation are unassigned ceratopsids. In 2012, a new unidentified species of chasmosaur ceratopsian with noticeable differences from Triceratops was unearthed in South Dakota by a fossil hunter named John Carter.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Ceratopsians reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Leptoceratops	L. gracilis		Montana			A small primitive-looking ceratopsian. Fossils have also been found in the Lance Formation in Wyoming.
Tatankaceratops	T. sacrisonorum		South Dakota			A controversial ceratopsian possibly synonymous with Triceratops
Torosaurus	T. latus		Montana North Dakota South Dakota	Upper Hell Creek Formation		A ceratopsian that was once proposed to be synonymous with Triceratops, but is now regarded as a valid and distinct ceratopsian. A rare ceratopsid. Fossils have been in the Lance Formation, Javelina Formation, North Horn Formation, Laramie Formation, El Picacho Formation, Frenchman Formation and Scollard Formation.
Triceratops	T. horridus	T. serratus Ugrosaurus olsoni	Montana North Dakota Wyoming South Dakota	Lowermost to the middle Hell Creek Formation	Four specimens are assigned to Triceratops horridus from the Hell Creek Formation. Isolated, shed ceratopsid teeth are incredibly common in the Hell Creek and Lance Formations, being by most collectors, with some being nothing more than worn down fragments up to superb teeth containing complete, preserved roots. Because the teeth of different ceratopsians are so similar to one another, its hard to differentiate between genera/species, but based on the abundance of identifiable bones belonging to Triceratops in Lancian-aged North American formations, especially the Hell Creek, isolated ceratopsid teeth from the lower and middle Hell Creek Formation have a high likelihood of originating from T. horridus.	A ceratopsian. Also found in the Evanston, Frenchman, Lance, Laramie, and Scollard Formations.
	T. prorsus		Montana South Dakota	Upper 1/3 of the Hell Creek Formation	Very common. Because the teeth of different ceratopsians are so similar to one another, its hard to differentiate between genera/species, but based on the abundance of identifiable bones belonging to Triceratops in Lancian-aged North American formations, especially the Hell Creek, isolated ceratopsid teeth from the upper 1/3 of the Hell Creek Formation have a high likelihood of originating from T. prorsus.	Also found in the Frenchman and Lance Formations.

Ornithopods and relatives

Indeterminate hadrosaurid remains are very common in the Hell Creek Formation.

Ornithopods and Thescelosaurs reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Edmontosaurus	E. annectens	Anatosaurus annectens Anatotitan copei	Montana South Dakota North Dakota(Mummy Fossil)		Very common.	A hadrosaur. Also found in the Denver, Frenchman, Lance, Laramie, and Scollard Formations. Hatchlings have also been unearthed.
Thescelosaurus	T. garbanii	Bugenasaura garbanii	Montana South Dakota
	T. neglectus		North Dakota South Dakota	Lower to upper Hell Creek Formation	50 specimens	A small thescelosaurine. Also found in the Frenchman, Lance, Laramie, and Scollard Formations. Two species are known from Hell Creek; T. neglectus and T. garbanii.

Theropods

Theropod tracks have been found in South Dakota. A trackway from South Dakota, named Wakinyantanka, was made by a mid-sized theropod with three slender toes, possibly a small tyrannosaurid. A second footprint that may have been made by a specimen of Tyrannosaurus was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation of Montana. This second track measures 72 centimeters (28 in) long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by Tyrannosaurus is unclear, though Tyrannosaurus is the only large theropod known to have existed in the Hell Creek Formation, though in past albertosaurine remains have described here but its most likely that they are the remains of Tyrannosaurus rex. Theropod remains are very common in Hell Creek, some of which belong to indeterminate species on maniraptorans.

Alvarezsaurs

Alvarezsaurs reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
"Ornithomimus"	"O." minutus
Trierarchuncus	T. prairiensis		Montana	upper Hell Creek Formation.		An alvarezsaur known from a partial post-cranial skeleton.

Tyrannosaurids

Tyrannosaurids reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Tyrannosaurus	T. rex	Albertosaurus megagracilis Aublysodon molnari Dinotyrannus megagracilis Nanotyrannus lancensis?	Montana North Dakota South Dakota	Lower to upper Hell Creek Formation.		A tyrannosaur, known from several specimens including a juvenile nicknamed "Jane". Also found in the Denver, Frenchman, Hill Creek South, Javelina, Lance, Ferris, Livingston, McRae, North Horn, Scollard, Willow Creek Formation, and also found in Lomas Coloradas Formations. Isolated teeth in the Hell Creek are common enough to be dug commercially by collectors, but rare enough that they are often sold for very high prices with fragmentary teeth usually beginning at least in the hundreds of USD, and complete teeth in the thousands of USD. Perhaps the best known iconic dinosaur.
Nanotyrannus?	N.lancensis	Stygivenator? Deinodon lancensis Albertosaurus lancensis Tyrannosaurus lancensis?	Montana Wyoming	Lower to upper Hell Creek Formation.	A few specimens are known	Invalid genus, now recognised as juvenile T. rex.

Ornithomimosaurs

Ornithomimid remains are not uncommon in the Hell Creek Formation. Fifteen specimens from the Hell Creek Formation are undetermined ornithomimids

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Ornithomimids reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
"Orcomimus"	unnamed	South Dakota		One partial skeleton.	An ornithomimid; nomen nudum.
Struthiomimus	S. sedens	Montana		AMNH 975, a foot claw UCMP 154569, a partial skeleton	A large ornithomimid similar to Gallimimus in size. Also found in the Lance Formation.
Ornithomimus	O. velox	Montana South Dakota North Dakota		Fragmentary specimens	An ornithomimid which was also found in the Denver Formation.

Oviraptorosaurs

Oviraptorosaur fossils have been found at the Hell Creek Formation for many years, most notably from isolated elements until the discovery of Anzu. In the past, oviraptorosaur fossils found were thought to have belonged to Caenagnathus, Chirostenotes, and Elmisaurus. In 2016, an undescribed large-bodied caenagnathid was unearthed in Montana.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Oviraptorosaurs reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Anzu	A. wyliei	North Dakota South Dakota	Lower to upper Hell Creek Formation	12 well-preserved specimens	One of the largest known oviraptorosaurs, and the largest known from North America. Material previously assigned to Caenagnathidae indet. is now placed in the genus Anzu.
Caenagnathidae	Indeterminate	Montana			Similar to Citipes and Elmisaurus.
Eoneophron	E. infernalis	South Dakota		A partial right hindlimb	Closely related to Citipes and Elmisaurus.

Eumaniraptorans

Historically, numerous teeth have been attributed to various dromaeosaurid and troodontid taxa with known body fossils from only older formations, including Saurornithoides, Zapsalis, Dromaeosaurus, Saurornitholestes, and Troodon. However, in a 2013 study, Evans et al. concluded that there is little evidence for more than a single dromaeosaurid taxon, Acheroraptor, in the Hell Creek-Lance assemblages, which would render these taxa invalid for this formation. This was disproved in a 2015 study, DePalma et al., when they described the new genus Dakotaraptor, a large species of dromaeosaur. Fossilized teeth of various troodontids and coelurosaurs are common throughout the Hell Creek Formation; the best known examples include Paronychodon, Pectinodon and Richardoestesia, respectively. Teeth belonging to possible intermediate species of Dromaeosaurus and Saurornitholestes have been unearthed at the Hell Creek Formation and the nearby Lance Formation.

Eumaniraptorans reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Acheroraptor	A. temertyorum	Montana North Dakota? South Dakota?	Lower? to upper Hell Creek Formation	ROM 63777, a maxilla and tooth ROM 63778, a partial dentary isolated teeth	A velociraptorine dromaeosaurid. Teeth previously referred to various Campanian dromaeosaurids Saurornitholestes and Dromaeosaurus, frequently found throughout the formation, probably belong to this one species. Evans et al. conclude that there is little evidence for the former two taxa being present in the Hell Creek-Lance assemblages.
Avisaurus	A. archibaldi	Montana	Middle Hell Creek Formation	UCMP 117600, holotype, a tarsometatarsus PU 17324, a tarsometatarsus	An avisaurid.
	cf. A. archibaldi	Montana	Uppermost Hell Creek Formation	YPM 57235, a coracoid	An avisaurid tentatively referred to A. archibaldi based on its size.
	A. darwini	Montana		DDM 1577.730, a right tarsometatarsus
	A. sp.	Montana		distal tarsals, metatarsus (juvenile) MOR3070, a partial right tarsometatarsus
Brodavis	B. baileyi	South Dakota		UNSM 50665, a left tarsometatarsus missing proximal end, trochleae II and III.	A primitive hesperornithiform.
Dakotaraptor	D. steini	South Dakota	Upper Hell Creek Formation	PBMNH.P.10.113.T, a partial skeleton. PBMNH.P.10.115.T, a tibia. PBMNH.P.10.118.T, an astragalocalcaneum. isolated teeth.	A large dromaeosaurid.
Magnusavis	M. ekalakaensis	Montana		CCM V2019.5.1, partial right tarsometatarsus and toe bone	A large enantiornithine closely related to avisaurids.
Paronychodon	P. caperatus	North Dakota, South Dakota, and Montana.		YPM 10624, a fossilized tooth. Teeth of this genus have been found too.	A troodontid theropod who is known from fossil teeth. Fossils have also been found in the Lance Formation in Wyoming.
Pectinodon	P. bakkeri	Montana		UCM 38445, a fossilized tooth. Teeth of this genus have been found too.	A troodontid theropod who is known from fossil teeth. Fossils have also been found in the Lance Formation in Wyoming.
Potamornis	P. skutchi	Montana		UCMP 117605, a tarsometatarsus	A hesperornithiform also found in the Lance Formation.
Richardoestesia	R. sp.	Montana.		Teeth.	A coelurosaur that is known from teeth and from two species Richardoestesia gilmorei and Richardestesia isosceles, which have also been unearthed in the Lance Formation in Wyoming.
"Styginetta"	"S. lofgreni."	Montana.			A Presbyornithid, it is notable for being one of the few birds known to have survived the Cretaceous–Paleogene extinction event.
"Unnamed enantiornithine B"	Unnamed	Montana		YPM 57823, a partial coracoid	An unnamed enantiornithean.
"Unnamed hesperornithiform A"	Unnamed	Montana		UCMP 13355, a tarsometatarsus	A primitive hesperornithiform. The Hell Creek specimen was referred to the same unnamed taxon as RSM P 2315.1 from the Canadian Frenchman Formation. RSM P 2315.1 was later made the holotype of Brodavis americanus. May be a synonym of Potamornis.
"Unnamed ornithurine B"	Unnamed	Montana		UCMP 129143, a partial coracoid	An ornithurine possibly similar to Cimolopteryx
"Unnamed ornithurine C"	Unnamed	Montana South Dakota		SDSM 64281A, a partial coracoid SDSM 64281B, a partial coracoid UCMP 175251, a partial coracoid MOR 2918, a partial coracoid	An ornithurine, also present in the Lance Formation and Fort Union Formation, one of the few individual bird species known to have survived the Cretaceous–Paleogene extinction
"Unnamed ornithurine D"	Unnamed	Montana		UCMP 187207, a partial coracoid	An ichthyornithean also present in the Frenchman Formation

Pterosaurs

Undescribed pterosaur remains were reported from North Dakota. A specimen of an azhdarchid pterosaur from Montana likely belongs to Quetzalcoatlus, though it is not diagnostic to the species level.

Pterosaurs of the Hell Creek Formation
Taxa	Species	State	Stratigraphic location	Material	Notes	Images
cf. Quetzalcoatlus	Indeterminate	Montana			A single azhdarchid neck bone which may belong to the genus Quetzalcoatlus.

Crocodylomorphs

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Crocodylomorphs reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Borealosuchus	B. sternbergii	Montana North Dakota South Dakota			Extinct genus of crocodylians that lived from the Late Cretaceous to the Eocene in North America.
Brachychampsa	B. montana	Montana South Dakota North Dakota			Extinct genus of alligatoroid.
Thoracosaurus	T. neocesariensis	Montana			Extinct genus of gavialoid crocodilian which existed during the Late Cretaceous and early Paleocene.

Turtles

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Turtles reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Adocus	Indeterminate	Montana			Extinct genus of aquatic turtles belonging to the family Adocidae.
Axestemys	A. infernalis	Montana North Dakota South Dakota Wyoming			A turtle belonging to the family Trionychidae. Its fossils from the Hell Creek Formation were formerly assigned to the late Campanian species Axestemys splendidus.
Compsemys	C. victa	Montana			A relative of Dermatemydidae.
Peckemys	P. brinkman	Montana North Dakota			A relative of Baenidae.
Emarginachelys	E. cretacea	Montana			A relative of chelydrids.
Eubaena	E. cephalica	Montana			Baenid turtle
Gamerabaena	G. sonsalla	North Dakota			Extinct genus of baenid turtle.
Palatobaena	P. cohen	North Dakota			A relative of extinct family of cryptodiran turtles.
Cedrobaena	C. putorius	South Dakota North Dakota			A relative of Baenidae.
Gilmoremys	G. lancensis	Montana North Dakota			Trionychidae related to the softshell turtle.
Hoplochelys	H. clark	North Dakota			A kinosternoid related to the Central American river turtle.
Hutchemys	H. walkerorum	North Dakota		A shell	A Plastomeninae related to the softshell turtle.
Plastomenus	P. sp				Trionychidae turtle.
Basilemys	B. sinuosa				Largest dermatemydid land tortoise.
Trionyx	Indeterminate	Montana			A genus of softshell turtles belonging to the family Trionychidae.
Aspideretoides	A. foveatus				Trionychidae turtle.
Helopanoplia	H. distincta				Trionychidae turtle.
Judithemys	J. backmani				Thin-shelled macrobaenid turtle.
Plesiobaena	P. antiqua				Baenid turtle.
Stygiochelys	S. estesi				Baenid turtle.
Neurankylus	N. eximius				Largest baenid turtle in Hell Creek Formation.
Saxochelys	S. gilberti	North Dakota		A population of over 30 individual skeletons	A member of the family Baenidae.
Thescelus	T. insiliens				Baenid turtle.
Chelydridae	Indeterminate				Chelydrids-like turtle.

Squamata

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Squamates reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Cemeterius	C. monstrosus	Montana			A platynotan lizard of uncertain phylogenetic placement, also known from the Lance Formation.
Cerberophis	C. robustus	Montana			An alethinophidian snake of uncertain phylogenetic placement.
Obamadon	O. gracilis	Montana			A polyglyphanodontian lizard of uncertain phylogenetic placement. Also known from the Lance Formation.
Peneteius	P. aquilonius	Montana			A chamopsiid polyglyphanodontian lizard.
Haptosphenus	H. placodon				Teiidae lizard.
Leptochamops	L. denticulatus				Small Teiidae lizard.
Chamops	C. segnis				Largest Teiidae lizard in Hell Creek Formation
Contogenys	C. sloani				Scincidae? lizard.
Exostinus	E. lancensis				xenosaurid lizard.
Proxestops	P. jepseni				Anguidae lizard.
Parasaniwa	P. wyomingensis				Necrosaurid lizard.
Paraderma	P. bogerti				Helodermatidae? lizard.
Palaeosaniwa	P. canadensis				A large Monstersauria lizard, closely related to today's varanid lizards. It was the largest lizard in the Hell Creek formation.
Boidae	Indeterminate				Snake. Earliest-known boid.
Mosasauridae	Indeterminate				Indeterminate mosasaur remains have been unearthed in North Dakota; they may belong to a mosasaur measuring 11 m (36 ft) in length.

Choristoderans

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Choristoderans reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Champsosaurus	C. sp.	Montana			A champsosaur.

Mammals

Multituberculates

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Multituberculates reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Cimexomys	C. minor	Montana			A multituberculate of uncertain phylogenetic placement.
Cimolodon	C. nitidus	Montana North Dakota			A cimolodontid multituberculate.
	C. cf. nitidus	South Dakota			A cimolodontid multituberculate.
	C. sp.	North Dakota			A cimolodontid multituberculate.
Cimolomys	C. gracilis	Montana			A cimolomyid multituberculate.
	C. cf. gracilis	South Dakota			A cimolomyid multituberculate.
Essonodon	E. browni	Montana			A cimolomyid multituberculate.
Meniscoessus	M. conquistus	South Dakota			A cimolomyid multituberculate.
	M. robustus	Montana North Dakota South Dakota			A cimolomyid multituberculate.
	M. cf. robustus	South Dakota			A cimolomyid multituberculate.
	M. sp.	North Dakota			A cimolomyid multituberculate.
	?M. sp.	North Dakota			A cimolomyid multituberculate.
Mesodma	M. formosa	Montana South Dakota			A neoplagiaulacid multituberculate.
	M. cf. formosa	Montana			A neoplagiaulacid multituberculate.
	M. hensleighi	Montana South Dakota			A neoplagiaulacid multituberculate.
	M. cf. hensleighi	South Dakota			A neoplagiaulacid multituberculate.
	M. thompsoni	Montana North Dakota South Dakota			A neoplagiaulacid multituberculate.
	M. cf. thompsoni	Montana			A neoplagiaulacid multituberculate.
	M sp.	Montana			A neoplagiaulacid multituberculate.
	?M sp.	Montana			A neoplagiaulacid multituberculate.
?Neoplagiaulax	?N. burgessi	Montana			A neoplagiaulacid multituberculate.
Paracimexomys	P. priscus	Montana			A multituberculate of uncertain phylogenetic placement.
Paressonodon	P. nelsoni				A cimolomyid multituberculate.
Stygimys	S. kuszmauli	Montana			It was a member of the extinct order Multituberculata.

Metatherians

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Metatherians reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Alphadon	A. marshi	Montana North Dakota			An alphadontid. genus of small, primitive mammal that was a member of the Metatheria, a group of mammals that includes modern-day marsupials.
	A. cf. marshi	Montana South Dakota			An alphadontid.
	A. wilsoni	Montana			An alphadontid.
	A. cf. wilsoni	Montana			An alphadontid.
	A. sp.	North Dakota South Dakota			An alphadontid.
Didelphodon	D. padanicus	South Dakota			A stagodontid.
	D. vorax	Montana North Dakota			A stagodontid. genus of Stagodontidae marsupials from the Late Cretaceous of North America.
	D. cf. vorax	South Dakota			A stagodontid.
	D. sp.	North Dakota			A stagodontid.
	cf. D. sp.	North Dakota South Dakota			A stagodontid.
Glasbius	G. twitchelli	Montana			A glasbiid.
	G. cf. twitchelli	Montana			A glasbiid.
Leptalestes	L. cooki	Montana			A pediomyid.
	L. krejcii	Montana South Dakota			A pediomyid.
Nanocuris	N. improvida				A deltatheridiid.
Nortedelphys	N. jasoni (= N. intermedius)	Montana South Dakota			A herpetotheriid.
Pediomys	P. elegans	Montana South Dakota			A pediomyid.
Protalphadon	P. foxi	Montana			An alphadontid.
	P. lulli	Montana			An alphadontid.
Protolambda	P. florencae	Montana North Dakota South Dakota			A pediomyid.
	P. hatcheri	Montana South Dakota			A pediomyid.
	P. mcgilli	Montana			A pediomyid.
Turgidodon	T. rhaister	Montana			An alphadontid.

Eutherians

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Eutherians reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Altacreodus	A. magnus	Montana North Dakota			a possible creodont, formerly a species of Cimolestes
Alostera	A. saskatchewanensis	Montana			A eutherian of uncertain phylogenetic placement.
Ambilestes	A. cerberoides	Montana			A eutherian of uncertain classification, formally a species of Cimolestes
Batodon	B. tenuis	Montana			A cimolestid eutherian.
Cimolestes	C. incisus	Montana			A cimolestid eutherian.
	C. stirtoni	Montana			A cimolestid eutherian.
Gypsonictops	G. hypoconus	Montana South Dakota			A gypsonictopsid eutherian.
	G. illuminatus	Montana North Dakota			A gypsonictopsid eutherian.
	G. cf. illuminatus	Montana			A gypsonictopsid eutherian.
	G. sp.	Montana			A gypsonictopsid eutherian.
cf. Paranyctoides	cf. Paranyctoides sp.	Montana			A nyctitheriid eutherian.
Protungulatum	P. coombsi	Montana			A stem-placental.
Purgatorius	P. ceratops	Montana			A genus with four species believed to be either stem-placentals or stem-primates.
Scollardius	S. propalaeoryctes	Montana			A eutherian of uncertain classification, formally a species of Cimolestes

Flora

The Hell Creek Formation was a low floodplain at the time before the sea retreated, and in the wet ground of the dense woodland, the diversity of angiosperms and conifers were present. An endless diversity of herbaceous flowering plants, ferns and moss grew in the forest understory. On the exposed point bars of large river systems, there were shrubs and vines. The evidence of the forested environment is overwhelmingly supported by petrified wood, rooted gley paleosols, and ubiquitous tree leaves. The presence of the simple and lobed leaves, combined with an extremely high dicot diversity, extinct cycadeoid Nilssoniocladus, Ginkgo, many types of monocots, and several types of conifers is different from any modern plant community. There are numerous types of leaves, seeds, flowers and other structures from Angiosperms, or flowering plants. The Hell Creek Formation of this layer contains over 300 tablets, of which angiosperms are by far the most diverse and dominant flora of the entire population, about 90 percent, followed by about 5% of conifers, 4% of ferns, and others. Compared to today Hell Creek's flora which is prairie, then Hell Creek's flora was hardwood forest mixed with deciduous and evergreen forest. In sharp contrast to the Great Plains today, the presence of many thermophilous taxa such as palm trees and gingers meant the climate was warmer and wetter then.

The plants of the Hell Creek Formation generally represent angiosperm-dominated riparian forests of variable diversity, depending on stratigraphic position and sedimentary environment. There appears to be floral transitions visible on a stratigraphic range from the lower to the upper Hell Creek Formation. For this reason, Kirk Johnson and Leo Hickey divided it into five zones and described them as HCIa, HCIb, HCIIa, HCIIb, and HCIII as a reflection of floral change through time. For example, the HCIa zone is dominated by "Dryophyllum" subfalcatum, Leepierceia preartocarpoides, "Vitis" stantonii, and "Celastrus" taurenensis, and is located 55 to 105 meters below the K-Pg boundary layer. Although the HCIb zone is a very thin layer, about 5 meters of rock, it bears unusually high diversity of herbaceous and shrubby plants, including Urticaceae, Ranunculaceae, Rosaceae, and Cannabaceae.

There is evidence of transitional floras in the middle of the Hell Creek Formation as shown by HCII and HCIII zones. The HCII flora represents a transitional period where taxa from the lower Hell Creek are replaced by the HCIII flora. The diversity of the HCIII zone is very high, and its composition is more uniform than that of HCII, many of which were rare or absent from the zones below, and some others that used to be common below became rarer in the HCIII zone. These forms include Elatides longifolia, "Dryophyllum" tennessensis, Liriodendrites bradacii, and many members of the Laurales including Bisonia niemii, "Ficus" planicostata, and Marmarthia trivialis, while "Celastrus" taurenensis, Leepierceia preartocarpoides, and many cupressaceous conifers became rarer. This phenomenon suggests that the global temperature was warming during the last 300,000-500,000 years of the Cretaceous period.

Johnson claims that there are no grasses, oaks, maples, beeches, figs, or willows in the Hell Creek Formation. There is no evidence of fern prairie either. However, there was an extremely high angiosperm diversity — common plane trees, "Dryophyllum" subfalcatum, Leepierceia preartocarpoides, and palm trees — along with extinct cycadeoid Nilssoniocladus, Ginkgo, araucariaceous, podocarpaceous, and cupressaceous conifers. This represents the mixed deciduous and evergreen broad-leaved forest as the Hell Creek landscape. The nature of these forests is uncertain because Johnson found that the majority of the angiosperm and conifer genera are now extinct. He also believes that, very roughly 80% of the terrestrial plant taxa died out in what is now Great Plains at the K-Pg boundary. On other hand, there is a great increase in the abundance of fossil fern spores in the two centimeters of rock that directly overlies the impact fallout layer (the famous K-Pg boundary layer). This increase in fern spore abundance is commonly referred as "the fern spike" (meaning that if the abundance of spores as a function of stratigraphic position were plotted out, the graph would show a spike just above the impact fallout layer).

Many of the modern plant affinities in the Hell Creek Formation (e.g., those with the prefix "aff." or with quotes around the genus name) may not in reality belong to these genera; instead they could be entirely different plants that resemble modern genera. Therefore, there is some question regarding whether the modern Ficus or Juglans, as two examples, actually lived in the Late Cretaceous.

Compared to the rich Hell Creek Formation fossil plant localities of the Dakotas, relatively few plant specimens have been collected from Montana. A few taxa were collected at Brownie Butte Montana by Shoemaker, but most plants were collected from North Dakota (Slope County) and from South Dakota. Among the localities, the Mud Buttes, located in Bowman County, North Dakota, is probably the richest megaflora assemblage known and the most diverse leaf quarry from the Hell Creek Formation. "TYPE" after the binomial means that it is represented by a type specimen found in the Yale-Peabody Museum collections. "YPM" is the prefix for the Yale-Peabody Museum specimen number; "DMNH" is for the Denver Museum of Nature & Science; "USNM" is for Smithsonian National Museum of Natural History; and so on. The majority of Hell Creek megafloral specimens are collected at the Denver Museum of Nature & Science.

Overview (from Johnson, 2002)

302 plant morphotypes based on leaf only, including:

• 1 bryophyte (mosses and liverworts)
• 11 ferns
• 1 sphenopsid
• 10 conifers
• 1 ginkgo (uncommon)
• 278 angiosperms (roughly 92% of all taxa found)

Paleoflora

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Liverworts

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Marchantia	M. pealii				Only known liverwort in Hell Creek.

Ferns

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Equisetum	E. sp				Rare in the Hell Creek Formation.
Polypodiaceae?	indeterminate
Salvinia	S. sp				Floating aquatic plant.

Cycadophytes

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Nilssoniocladus	N. comtula				Unlike N. yukonensis, its leaves are pinnatisect pinnules. Common.
	N. yukonensis				The only Hell Creek Formation cycadophyte. A simple leaf. Common.

Ginkgoales

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Ginkgo	G. adiantoides				The only ginkgoalean in the Hell Creek Formation; uncommon

Conifers

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Araucaria?	indeterminate				Casts of Monkey-puzzle leaves.
Cupressinocladus	C. interruptus				Casts of cupressaceae foliage. Uncommon
Dammarites	D. sp				A conifer seed cone. It's likely to belong to Elatides longifolia.
Ditaxocladus	D. catenulata				A cupressaceous conifer closely related to Cupressinocladus. Common.
Elatocladus	Elatocladus sp,				A taxodioid leaf morphogenus
Elatides	E. longifolia				Araucaria-like or Cunninghamia-like conifer. Less common in the lower 2/3 but more common in the upper 1/3 of the Hell Creek Formation.
Glyptostrobus	G. europaeus				Uncommon conifer.
Metasequoia	M. occidentalis				M. occidentalis seed cones are known from the Hell Creek.
Platyspiroxylon	Platyspiroxylon sp.				A cupressaceaeous wood morphogenus
Podocarpoxylon	Podocarpoxylon sp.				A possibly podocarpaceous wood morphogenus
Sequoiaxylon	Sequoiaxylon sp.				A cupressaceaeous wood morphogenus
Taxodioxylon	Taxodioxylon sp.				A cupressaceaeous wood morphogenus
Taxodium	T. olrikii				Related to today's bald cypress.
Unidentified	Unidentified				Unspecified cheirolepidiacous fossils

Angiosperms

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
"Artocarpus"	"A." lessigiana				Abundant at Brownie Butte, Montana.
Annona?	A?. robusta				Abundant at Brownie Butte, Montana.
Araliaephyllum	A. polevoi				A lobed leaf. Closely relating to Bisonia. Fairly common.
Averrhoites	cf. A. affinis				An uncommon taxon with compound leaves.
Bisonia	B. niemi				A broad leaf, probably in the Laurales. A common taxon. Type specimen was found in South Dakota.
Browniea	B. serrata				In the Nyssaceae, closely relating to extant Camptotheca. Less common.
Cannabaceae?	indeterminate				Incertae sedis. It's not likely in the Cannabaceae.
Carpites	C. ulmiformis				Though this fossil fruit is abundant in the Early Paleocene, it's also found in Hell Creek. It may belong to Apiaceae.
"Celastrus"	"C." taurenensis				Incertae sedis. It's common in the lowermost to the middle Hell Creek Formation, but less common in the upper 1/3 Hell Creek Formation.
"Cinnamomum"	"C." lineafolia				Included in Ficus affinis by L. Hickey. Belongs in Rhamnaceae (modern buckthorns and Ceanothus). Some other specimens referred to Cinnamomum sezanensis(?) sp.), a real cinnamon bush. Its affinity is questionable.
Cissites	cf. C. acerifolia				This morphotype was first described from the Cenomanian Dakota Group.
	C. insignis				This form represents of the group of Cenomanian leaves from Dakota Formation.
	C. lobata				A lobed leaf with half-naked basal lateral veins. Common in the upper 1/3 of the Hell Creek Formation.
	C. puilasokensis				A palmately lobed leaf with 5 primary veins. Common in the upper 1/3 of the Hell Creek Formation.
Cobbania	C. corrugata				A prehistoric species of water lettuce, previously assigned to the genus Pistia.
	C. hickeyi				Another Cobbania species from pond sediments known as "Licking Leaves."
Cornophyllum	C. newberryi				The majority of leaves are entire-margined but some may develop a few teeth.
"Cypercites"	"C." sp				A reed-type plant.
Dryophyllum	D. subfalcatum				This taxon is extremely common in the Hell Creek Formation, but is rare in Paleocene sediments. It is believed to be in Sabiaceae, closely related to the living Meliosma.
	aff. "Dryophyllum" subfalcatum				see above.
	"D." tenneseensis				This taxon is similar to D. subfalcatum]] but with extremely high L/W ratio and craspedodromous venation.
Erlingdorfia	E. montana				Johnson, 1996. In the Platanaceae (related to today's Sycamore). A very common taxon.
"Ficus"	"F." planicostata				Despite the genus name, it's in Lauraceae.
Grewiopsis	G. saportana				Another generic Platanaceae.
Harmsia	H. hydrocotyloidea				Incertae sedis. May be related to lotus. An uncommon taxon.
Humulus?	aff. Humulus sp.				May be related to the extant genus Humulus.
Hydropteris	H. pinnata				Floating aquatic fern
Limnobiophyllum	L. scutatum				Floating aquatic monocot, closely related to Pistia.
Liriodendrites	L. bradacii				Johnson, 1996. In the Magnoliidae: a common taxon.
"Liriodendron"	"L." laramiense				Unlobed leaf. May be related to today's tulip tree (yellow poplar). An uncommon taxon.
Liriodendron	L. sp				Four-lobed leaf. May be related to today's tulip tree (yellow poplar). An uncommon taxon.
Leepierceia	L. preartocarpoides				Incertae sedis but possibly in Proteales. Johnson, 1996.
Laurophyllum	L. wardiana				Large leaves. Closely related to "Dryophyllum" subfalcatum.
"Magnolia"	M. pulchra				Occurs in southern the Wyoming flora, Leo Hickey claims it is found further north in Montana and the Dakotas.
Marmarthia	M. johnsonii				A new Marmarthia species described in Peppe et al. 2007.
	M. pearsonii				Johnson, 1996. In the Lauraceae: a very common taxon.
	M. trivialis				Johnson, 1996. In the Lauraceae: a very common taxon.
"Myrica"	"Myrica" torreyi				Incertae sedis. Not actually a bayberry.
Nelumbo	N. sp				One of the most common aquatic plants in Hell Creek.
Nelumbium	N. montanum				An aquatic angiosperm, closely related to lotus. Uncommon.
Nordenskioldia	N. borealis				A fossil fruit likely to belonging to Zizyphoides flabella.
Paranymphaea	P. hastata				Despite the name, it's not related to extant genus Nymphaea.
Palaeoaster	P. porosia				A papaveraceous with fruits and seeds visually similar to Romneya though it's dubious.
Penosphyllum	P. cordatum				May be related to Sterculioideae. A common taxon.
Platanites	P. marginata				Johnson, 1996. In the Platanaceae. A common taxon.
	P. raynoldsii				An uncommon taxon.
Porosia	P. verrucosa				A fossil fruit that may belong to Rutaceae.
Rhamnica	R. cleburnii				Incertae sedis. A Tetracera look-alike leaf.
Sabalites	S. sp				Coryphoid palm tree. Very common.
Spinifructus	S. antiquus				A fruit seed that may belong to the palm family (Arecaceae), closely related to the genus Astrocaryum.
Trapago	T. angulata				A water caltrop look-alike.
Trochodendroides	T. arctica				A fossil fruit that may belong to Trochodendroides nebrascensis.
	T. ellipticum				A katsura look-alike. An uncommon taxon.
	T. genetrix				A katsura look-alike. A common taxon.
	T. nebrascensis				A very common taxon.
"Vitis"	"V." stantonii				Possibly a member of the Platanaceae rather than Vitaceae
"Ziziphus"	"Z." fibrillosus				A common taxon.
Zingiberopsis	Z. attenuata				Related to today's ginger plant. Its closest living relative is the Asian genus Alpinia. Some Hell Creek Formation specimens show damage from hispine beetles ("leaf beetles" (Wilf et al., 2000)).
	Z. magnifolia				Another Zinigberopsis species, previously assigned to Canna? magnifolia.
Zizyphoides	Z. flabella				An uncommon taxon.

Palynology

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Abietineaepollenites	Abietineaepollenites foveoreticulatus	Montana			A conifer palynomorph
	Abietineaepollenites microalatus	Montana			A conifer palynomorph
	Abietineaepollenites varius	Montana			A conifer palynomorph
Acanthotriletes	Acanthotriletes levidensis	Montana
Alnipollenites	Alnipollenites verus	Montana
Appendicisporites	Appendicisporites tricornitatus	Montana
Aquilapollenites	Aquilapollenites amplus	Montana
	Aquilapollenites attenuatus
	Aquilapollenites collaris
	Aquilapollenites conatus	Montana
	Aquilapollenites delicatus	Montana
	Aquilapollenites marmarthensis
	Aquilapollenites polaris	Montana
	Aquilapollenites pulvinus	Montana
	Aquilapollenites pyriformis	Montana
	Aquilapollenites quadricretaeus
	Aquilapollenites quadrilobus
	Aquilapollenites reductus	Montana
	Aquilapollenites reticulatus	Montana
	Aquilapollenites senonicus
	Aquilapollenites turbidus
	Aquilapollenites striatus
Azolla	Azolla cretacea	Montana			A mosquito fern palynomorph
Balmeisporites	Balmeisporites sp.
Calamospora	Calamospora mesozoica	Montana
Camarozonosporites	Camarozonosporites heskemensis	Montana
Cicatricosisporites	Cicatricosisporites carlylensis	Montana
	Cicatricosisporites dorogensis	Montana
Cingulatisporites	Cingulatisporites dakotaensis	Montana
	Cingulatisporites scabratus	Montana
Clavatricolpites	Clavatricolpites prolatus	Montana
Concavisporites	Concavisporites rugulatus	Montana
	Concavisporites rugulatus	Montana
Converrucosisporites	Converrucosisporites sp.	Montana
Corylus	Corylus granilabratus	Montana			A hazelnut palynomorph
Cupanieidites	Cupanieidites major	Montana
Cyathidites	Cyathidites foveolatus	Montana
	Cyathidites minor	Montana
Cycadopites	Cycadopites scabratus	Montana
Deltoidospora	Deltoidospora diaphana	Montana
Dicotetradites	Dicotetradites granulatus	Montana
Ephedripites	Ephedripites ovatus	Montana
	Ephedripites undulatus	Montana
Erdtmanipollis	Erdtmanipollis cretaceus	Montana South Dakota
Gleicheniidites	Gleicheniidites excelsus	Montana
	Gleicheniidites senonicus	Montana
Gnetaceaepollenites	Gnetaceaepollenites eocenipites	Montana
Haloragacidites	Haloragacidites quadratus	Montana
Hamulatisporis	Hamulatisporis hamulatis	Montana
Hymenophyllumsporites	Hymenophyllumsporites parvus	Montana			A fern spore palynomorph
	Hymenophyllumsporites pseudomaximus	Montana			A fern spore palynomorph
Ilexpollenites	Ilexpollenites compactus
Inaperturopollenites	Inaperturopollenites rugulatus	Montana
Interpollis	Interpollis cf. I. supplingensis
Kurtzipites	Kurtzipites trispissatus	Montana
	Kurtzipites trispissatus	Montana
Laevigatosporites	Laevigatosporites anomalus	Montana
	Laevigatosporites discordatus	Montana
	Laevigatosporites gracilis	Montana
	Laevigatosporites ovatus	Montana
Liliacidites	Liliacidites variegatus	Montana
	Liliacidites sp.	Montana
Lycopodiumsporites	Lycopodiumsporites austroclavatidites	Montana
Momipites	Momipites circularis	Montana
	Momipites parvus	Montana
Monosulcites	Monosulcites carpentieri	Montana
	Monosulcites crescentus	Montana
	Monosulcites latus	Montana
	Monosulcites tectatus	Montana
	Monosulcites sp.	Montana
Myrtipites	Myrtipites granulatus	Montana
	Myrtipites scabratus	Montana
Nyssapollenites	Nyssapollenites analepticus	Montana
	Nyssapollenites pseudocruciatus	Montana
Osmundacidites	Osmundacidites wellmanii	Montana
Pachysandra	Pachysandra cretaceae	Montana South Dakota
Palmidites	Palmidites maximus	Montana
Peromonolites	Peromonolites granulatus	Montana
Phyllocladidites	Phyllocladidites mawsonii	Montana
	Phyllocladidites ruei	Montana
Podocarpidites	Podocarpidites otagoensis	Montana
Polyadopollenites	Polyadopollenites psilatus	Montana
Polycolpites	Polycolpites granulatus	Montana
Polypodiidites	Polypodiidites inangahuensis	Montana
Proteacidites	Proteacidites retusus	Montana
	Proteacidites retusus	Montana
	Proteacidites thalmannii	Montana
Psilatricolporites	Psilatricolporites prolatus	Montana
Pterocaryapollenites	Pterocaryapollenites stellatus	Montana
Reticuloidosporites	Reticuloidosporites dentatus	Montana
Schizosporis	Schizosporis complexus	Montana
	Schizosporis parvus	Montana
Spheripollenites	Spheripollenites subgranulatus	Montana
Spinamonoporites	Spinamonoporites typicus	Montana
Stereisporites	Stereisporites antiquasporites	Montana
	Stereisporites psilatus	Montana
Striainaperturites	Striainaperturites ovatus	Montana
Styx	Styx major	Montana
	Styx minor	Montana
Taxodiaceaepollenites	Taxodiaceaepollenites hiatus	Montana
Triatriopollenites	Triatriopollenites granilabratus	Montana
Tricolpites	Tricolpites bacustriatus	Montana
	Tricolpites delicatulus	Montana
	Tricolpites foveolatus	Montana
	Tricolpites interangulus
	Tricolpites parvistriatus	Montana
	Tricolpites psilascabratus	Montana
	Tricolpites reticulatus	Montana
	Tricolpites striatus	Montana
Tricolpopollenites	Tricolpopollenites clavireticulatus	Montana
	Tricolpopollenites megaexactus	Montana
	Tricolpopollenites microreticulatus	Montana
	Tricolpopollenites microscabratus	Montana
	Tricolpopollenites sp1, sp2	Montana
Tricolporopollenites	Tricolporopollenites elongatus	Montana
	Tricolporopollenites foveotectatus	Montana
	Tricolporopollenites granustriatus	Montana
	Tricolporopollenites megaexactus	Montana
	Tricolporopollenites prolatus	Montana
	Tricolporopollenites striatus	Montana
Triplanosporites	Triplanosporites sinuosus	Montana
Triporopollenites	Triporopollenites rugatus	Montana
Ulmipollenites	Ulmipollenites undulosus	Montana
	Ulmipollenites verrucatus	Montana
Ulmoideipites	Ulmoideipites tricostatus	Montana
Wodehouseia	Wodehouseia spinata	Montana
Zlivisporis	Zlivisporis blanensis	Montana

See also

• List of fossil sites (with link directory)
• Lists of dinosaur-bearing stratigraphic units
• Paleobiota of the Morrison Formation
• Lance fauna
• Cretaceous-Paleogene formations
  • Tremp Formation, Spain
  • Tremp Formation, Spain
  • Lefipán Formation, Argentina
  • Lopez de Bertodano Formation, Antarctica

References

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10. ^ Pearson et al. (2002) p. 155
11. ^ Pearson et al. (2002) pp. 156
12. Listed as "cf. Barbourula sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.
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15. Listed as "Eopelobates? sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.
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External links

• Cretaceous Hell Creek Faunal Facies provides a faunal list
• Phillip Bigelow, "Hell Creek life: Fossil Flora & Fauna, a Paleoecosystem"
• Paleobiology Database: MPM locality 3850 (Hell Creek Formation): Maastrichtian, Montana

Categories:

• Maastrichtian life
• Cretaceous–Paleogene boundary
• Danian life
• Natural history of Montana
• Natural history of North Dakota
• Natural history of South Dakota
• Natural history of Wyoming
• Paleontology in the United States
• National Natural Landmarks in Montana
• Hell Creek Formation
• Hell Creek fauna
• Late Cretaceous animals of North America
• Fauna of the Western United States
• Cretaceous fossil record
• Lists of prehistoric animals
• Mesozoic paleobiotas
• Dinosaur-related lists