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During the time of the deposition of the Niobrara Chalk, much life inhabited the seas of the Western Interior Seaway. By this time in the Late Cretaceous many new lifeforms appeared such as mosasaurs, which were to be some of the last of the aquatic lifeforms to evolve before the end of the Mesozoic. Life of the Niobrara Chalk is comparable to that of the Dakota Formation, although the Dakota Formation, which was deposited during the Cenomanian, predates the chalk by about 10 million years.

Table key

Bony fish

Pycnodontiformes

Semionotiformes

Pachycormiformes

Genus	Species	Member	Abundance	Notes	Images
Protosphyraena	P. bentonianum			A swordfish-like pachycormid
	P. nitida	Smoky Hill Chalk
	P. perniciosa	Smoky Hill Chalk
	P. tenuis	Smoky Hill Chalk
	P. gladius	Smoky Hill Chalk		Named as a new genus, Bonnerichthys
Bonnerichthys	B. gladius	Smoky Hill Chalk		A filter feeding pachycormid

Crossognathiformes

Genus	Species	Member	Abundance	Notes	Images
Apsopelix	A. anglicus	Smoky Hill Chalk		A crossognathid.
Pachyrhizodus	P. caninus	Smoky Hill Chalk		A pachyrhizodontid
	P. leptopsis	Smoky Hill Chalk
	P. minimus	Smoky Hill Chalk

Ichthyodectiformes

Genus	Species	Member	Abundance	Notes	Images
Xiphactinus	X. audax	Smoky Hill Chalk		A large ichthyodectid
Ichthyodectes	I. ctenodon	Smoky Hill Chalk		An ichthyodectid
Gillicus	G. arcuantus	Smoky Hill Chalk		A saurodontid
Saurodon	S. leanus	Smoky Hill Chalk		A saurodontid
Saurocephalus	S. lanciformis	Smoky Hill Chalk		A saurodontid

Tselfatiiformes

Genus	Species	Member	Abundance	Notes	Images
Thryptodus	T. zitteli	Smoky Hill Chalk		A plethodid
Pentanogmius	P. evolutus	Smoky Hill Chalk		A plethodid
Martinichthys	M. brevis	Smoky Hill Chalk		A plethodid
	M. xiphoides	Smoky Hill Chalk
Niobrara	N. encarsia	Smoky Hill Chalk		A plethodid
Zanclites	Z. xenurus	Smoky Hill Chalk		A plethodid

Aulopiformes

Genus	Species	Member	Abundance	Notes	Images
Cimolichthys	C. nepaholica	Smoky Hill Chalk		A cimolichthyid
Enchodus	E. dirus	Smoky Hill Chalk		An enchodontid
	E. gladiolus	Smoky Hill Chalk
	E. petrosus	Smoky Hill Chalk
	E. shumardi	Smoky Hill Chalk
Apateodus	Indeterminate	Smoky Hill Chalk		An alepisauriform actinopterygiian related to the modern lancetfish and lizardfish
Stratodus	S. apicalis	Smoky Hill Chalk		An alepisauriform actinopterygiian
Leptecodon	L. rectus			An alepisauriform actinopterygiian

Beryciformes

Other bony fish

Cartilaginous fish

Fish are by far the most common fossils found from the formation, with remains of prehistoric sharks, ray-finned fishes, and lobe-finned fishes in abundance. As well as smaller fish, many large predatory fish were present in the seas at that time, most notably Xiphactinus. Several fish were of close relation to modern day fish including primitive coelacanths, slime heads, lancetfish, gars, swordfish, and salmonids.

Sharks

Genus	Species	State	Member	Abundance	Notes	Images
Cretoxyrhina	C. mantelli		Smoky Hill Chalk		A large lamniform shark
Cretalamna	C. appendiculata		Smoky Hill Chalk		A lamniform shark
Cretolamna	C. appendiculata	N/A	N/A	N/A	An extremely widely used lapsus calami for Cretalamna.
Johnlongia	Indeterminate		Smoky Hill Chalk		An odontaspidid lamniform shark
Pseudocorax	P. laevis		Smoky Hill Chalk		A lamniform shark smaller than Cretoxyrhina
Squalicorax	S. falcatus		Smoky Hill Chalk		A lamniform
	S. kaupi		Smoky Hill Chalk
	S. pristodontus		Smoky Hill Chalk
Scapanorhynchus	S. raphiodon		Smoky Hill Chalk		A mitsukurinid shark similar in appearance to the modern day goblin shark
Ptychodus	P. anonymus		Smoky Hill Chalk		A ptychodontid lamniform shark
	P. martini		Smoky Hill Chalk
	P. mortoni		Smoky Hill Chalk
	P. occidentalis		Smoky Hill Chalk
	P. polygyrus		Smoky Hill Chalk

Other cartilaginous fish

Genus	Species	State	Member	Abundance	Notes	Images
Edaphodon	E. laqueatus				A callorhinchid chimaeriform related to the modern ratfish
Rhinobatos	R. incertus		Smoky Hill Chalk

Dinosaurs

Nonavian dinosaurs have been found in the Niobrara Chalk despite it being located hundreds of miles out to sea at the time. The most reasonable theory is that the carcasses drifted out to sea. It is unlikely that the bodies were carried out by outgoing tides along the shorelines where they died, but rather it is more probable that the dinosaurs were carried offshore by floodwaters during a storm. In the shallow waters the bodies would have begun to decompose and bacteria within the carcass would have produced gasses that would have accumulated in the gut, thereby making the body buoyant. Next, the prevailing winds and currents would have carried it out to sea, where it would eventually settle to the bottom and be buried in sediment.

A few caudal vertebrae from a hadrosaur have been found with bite marks and have been eroded, suggesting at one point they were digested. A single tooth belonging to Squalicorax was found in situ under the vertebrae. This suggested the shark consumed the posterior end of the tail of a floating hadrosaur carcass and had partially digested it before fossilization. Most dinosaurs in the chalk were nodosaurs. The dinosaurs found here were endemic to Appalachia.

Non-avian

Genus	Species	State	Member	Material	Notes	Images
Claosaurus	C. agilis	Kansas	Smoky Hill Chalk	"Single articulated postcranial skeleton with associated skull fragments."	A small hadrosaurid
Indeterminate hadrosaurid					A hadrosaurid of indeterminate classification. Possibly Corythosaurus.
Niobrarasaurus	N. coleii	Kansas	Smoky Hill Chalk	"Partial skeleton."	A nodosaurid ankylosaur.
Hierosaurus	H. sternbergi	Kansas	Smoky Hill Chalk	"Osteoderms."	A nodosaurid ankylosaur.

Birds

Three genre of birds are present in the formation, although rare. They were unrelated to modern birds, as they still retained teeth. Baptornis and Hesperornis were large flightless aquatic birds suited for diving. Ichthyornis was a seabird that resembled the gulls and petrels of today. Both probably preyed on small fish and were preyed upon by sharks, large bony fish such as Xiphactinus, and mosasaurs.

Genus	Species	State	Member	Material	Notes	Images
Apatornis	A. celer	Kansas Nebraska	Smoky Hill Chalk	"Postcranial elements."
Baptornis	B. advenus		Smoky Hill Chalk	"Fragmentary skull nearly complete postcranium."	A baptornithid hesperornithiform
Guildavis	G. tener		Smoky Hill Chalk
Hesperornis	H. crassipes	Kansas		"Partial postcranial skeleton."
	H. gracilis	Kansas		"Tarsometatarsus."
	H. regalis	Kansas	Smoky Hill Chalk		A large hesperornithid hesperornithiform
Iaceornis	I. marshi		Smoky Hill Chalk
Ichthyornis	I. agilis	Kansas			Junior synonym of I. dispar.
	I. anceps	Kansas			Junior synonym of I. dispar.
	I. dispar	Kansas	Smoky Hill Chalk		An ichthyornithid
	I. lentus	Kansas
	I. tener	Kansas
	I. validus	Kansas			Junior synonym of I. dispar.
	I. victor	Kansas			Junior synonym of I. dispar.
Parahesperornis	P. alexi	Kansas	Smoky Hill Chalk	"Partial skull complete postcranium."

Invertebrates

Clams, oysters, crinoids, ammonites, and squid are all common in the Niobrara Chalk and must have constituted the majority of life at the time. Evidence of sponges, annelid worms, and crustaceans are less common and are usually found as trace fossils.

Bivalves

Genus	Species	Member	Abundance	Notes	Images
Cladoceramus	C. undulatoplicatus	Smoky Hill Chalk
Durania	D. maxima	Smoky Hill Chalk
Haploscapha		Fort Hays Limestone
Inoceramus		Fort Hays Limestone
Ostrea		Fort Hays Limestone
Platyceramus	P. platinus	Smoky Hill Chalk
Pseudoperna	P. congesta	Smoky Hill Chalk
Volviceramus	V. grandis	Smoky Hill Chalk

Cephalopods

Genus	Species	Member	Abundance	Notes	Images
Baculites		Smoky Hill Chalk
Clioscaphites		Smoky Hill Chalk
Rugaptychus		Smoky Hill Chalk
Spinaptychus		Smoky Hill Chalk
Tusoteuthis	T. longa	Smoky Hill Chalk		A nomen dubium.
Enchoteuthis	E. melanae	Smoky Hill Chalk		Most material formerly referred to Tusoteuthis now belongs to this taxon.
	E. cobbani	Smoky Hill Chalk
Niobrarateuthis	N. bonneri	Smoky Hill Chalk

Echinoderms

Mosasaurs

Mosasaurs are the most common marine reptiles in the Niobrara Chalk and the most successful ones in the sea at the time. Several different genera representing the four different subfamilies of Mosasauridae: the Tylosaurinae, Plioplatecarpinae, Mosasaurinae, and Halisaurinae, were present in Niobrara. They were the dominant carnivorous marine reptiles and ate cephalopods, fish, turtles, pterosaurs, birds, and even plesiosaurs. There is evidence of them consuming other smaller mosasaurs. Despite this, mosasaurs often fell prey to some of the large sharks at the time, such as Cretoxyrhina.

The presence of young mosasaurs in the formation suggests that mosasaurs were viviparous and gave birth hundreds of miles out to sea, as Niobrara was in the middle of the Western Interior Seaway at the time. Juveniles would likely have been vulnerable to predation by the many large mid-ocean predators present in the ecosystem.

Genus	Species	Member	Abundance	Notes	Images
Clidastes	C. liodontus	Smoky Hill Chalk
	C. prophython	Smoky Hill Chalk
Ectenosaurus	E. clidastoides	Smoky Hill Chalk
	E. everhartorum	Smoky Hill Chalk
	E. tlemonectes	Smoky Hill Chalk
Eonatator	E. sternbergii	Smoky Hill Chalk		A small halisaurine
Platecarpus	P. tympaniticus	Smoky Hill Chalk		A plioplatecarpine
Plesioplatecarpus	P. planifrons	Smoky Hill Chalk
Tylosaurus	T. nepaeolicus	Smoky Hill Chalk		A large tylosaurine, with the largest T. proriger reaching about 13 metres in length.
	T. proriger	Smoky Hill Chalk
Selmasaurus	S. johnsoni	Smoky Hill Chalk

Plesiosaurs

Plesiosaurs are present from two different families within Plesiosauroidea in the Niobrara Chalk: the Polycotylidae, or short-necked plesiosaurs, and the Elasmosauridae, or long-necked plesiosaurs. Polycotylids superficially resemble pliosaurs, which are not present within the formation, but are unrelated. They were fast swimmers, unlike the Elasmosaurs that used their long necks to catch fish. Plesiosaurs are rare in the formation and were therefore likely uncommon in the Western Interior Seaway at the time. Specimens become much more numerous in the Pierre Shale situated above the chalk.

Genus	Species	State	Member	Time span	Notes	Images
Polycotylus	P. latipinnis		Smoky Hill Chalk	84.5-81.5 Ma ago	A polycotylid.
Dolichorhynchops	D. osborni		Smoky Hill Chalk	84.5-81.5 Ma ago	A polycotylid. also present in the Pierre Shale Formation
Brimosaurus	B. grandis	Kansas	Fort Hays Limestone		A nomen dubium.
Styxosaurus	S. snowii		Smoky Hill Chalk	85-81.5 Ma ago	A large elasmosaurid, also present in the Pierre Shale Formation
Elasmosaurus	"E." sternbergi		Smoky Hill Chalk	84.5-81.5 Ma ago	Most likely not referable to Elasmosaurus.

Pterosaurs

Two genre of pterosaurs are present in the formation, both within Pterodactyloidea: the pteranodontid Pteranodon (sometimes broken into several genera like Geosternbergia and Dawndraco, though this is dubious) and the nyctosaurid Nyctosaurus. They are large pterosaurs with elongated cranial crests. The pterosaurs of Niobrara probably spent most of their time at sea and rarely went on land, with Nyctosaurus being a probably fully pelagic animal. Pteranodon probably foraged on the ocean surface, while Nyctosaurus was a frigatebird-like aerial predator.

Genus	Species	Member	Time span	Notes	Images
Nyctosaurus	N. gracilis	Smoky Hill Chalk	85–84.5 Ma ago	A nyctosaurid ornithocheiroid.
Pteranodon	P. longiceps	Smoky Hill Chalk	86–84.5 Ma ago	A large and very abundant pteranodontid ornithocheiroid.
Geosternbergia	G. sternbergi	Smoky Hill Chalk	86–84.5 Ma ago	A species of Pterosaur that is regarded by a few Paleontologists to be a species of Pteranodon, though most regard it as a distinct species.

Turtles

Sea turtles have been found from the Niobrara Chalk that reached large sizes. The biggest, Archelon, was considerably larger than its distant relative, the leatherback sea turtle, which is the largest of the sea turtles alive today. The sea turtles most likely fed on ammonites, squid, and other cephalopods.

Genus	Species	Member	Abundance	Notes	Images
Bothremys	B. barberi	Smoky Hill Chalk
Chelosphargis	C. advena	Smoky Hill Chalk
Ctenochelys	C. stenopora	Smoky Hill Chalk
Porthochelys	P. laticeps	Smoky Hill Chalk		A toxichelid cryptodire
Protostega	P. gigas	Smoky Hill Chalk		A protostegid cryptodire
Toxochelys	T. latiremis	Smoky Hill Chalk		A chelonioid cryptodire

Footnotes

1. ^ "Table 13.1: Bony Fish", Everhart (2005), page 244.
2. Viegas, Jennifer (18 February 2010), SUV-Sized Fish Were Earliest Filter-Feeders, Discovery News, retrieved 1 April 2010
3. ^ "Table 13.1: Bony Fish", Everhart (2005), page 245.
4. Fielitz, C.; Stewart, J. D.; & Wiffen, J. 1999. Aethocephalichthys hyainarhinos gen. et sp. nov., a new and enigmatic Late Cretaceous actinopterygian from North America and New Zealand. Mesozoic Fishes 2 – Systematics and Fossil Record, G. Arratia & H.-P. Schultze (eds.): pp. 95-106, 7 figs.
5. ^ "Table 13.1: Sharks/Rays", Everhart (2005), page 244
6. ^ "Table 13.1: Sharks/Rays," Everhart (2005), page 244. Note that Cretalamna is listed here under the widely used lapsus calami Cretolamna.
7. "Introduction", in "Skeletal and Dental Anatomy..." Shimada (2007), page 584
8. "Niobrarasaurus". Oceansofkansas.com. Retrieved 2016-04-13.
9. "Shark bit dino". Oceansofkansas.com. Retrieved 2016-04-13.
10. Everhart, M. J. and K. Ewell. 2006. Shark-bitten dinosaur (Hadrosauridae) vertebrae from the Niobrara Chalk (Upper Coniacian) of western Kansas. Kansas Academy of Science, Transactions, 109 (1-2):27-35.
11. Brownstein, Chase D. (February 2018). "The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia". Palaeontologia Electronica. 21 (1.5A): 1–56. doi:10.26879/801. Retrieved 21 March 2021.
12. ^ "Table 13.1: Dinosaurs", Everhart (2005), page 246.
13. ^ "Dinosaur distribution (Late Cretaceous; North America; Kansas; Niobrara Chalk Formation)." Weishampel, et al. (2004). Pp. 582.
14. "Table 20.1," in Weishampel, et al. (2004). Page 439.
15. ^ Everhart, Michael J.; Ewell, Keith (April 2006). "Shark-bitten dinosaur (Hadrosauridae) caudal vertebrae from the Niobrara Chalk (Upper Coniacian) of western Kansas". Transactions of the Kansas Academy of Science. 109 (1 & 2): 27–35. doi:10.1660/0022-8443(2006)109[27:sdhcvf]2.0.co;2. ISSN 0022-8443. S2CID 86366930.
16. "Table 17.1," in Weishampel, et al. (2004). Page 367.
17. "Table 17.1," in Weishampel, et al. (2004). Page 368.
18. ^ "Table 13.1: Birds," Everhart (2005), page 246.
19. "Dinosaur distribution (Late Cretaceous; North America; Nebraska; Niobrara Chalk Formation)." Weishampel, et al. (2004). Pp. 586.
20. "Table 11.1," in Weishampel, et al. (2004). Page 214.
21. ^ "Table 11.1," in Weishampel, et al. (2004). Page 215.
22. ^ "Table 13.1: Invertebrates," Everhart (2005), page 244.
23. ^ "Material: YPM 1640," in "The Occurrence of Elasmosaurids..." Everhart (2006), page 172.
24. ^ Fuchs, D.; Iba, Y.; Heyng, A.; Iijima, M.; Klug, C.; Larson, N.; Schweigert, G. (28 June 2019). "The Muensterelloidea: phylogeny and character evolution of Mesozoic stem octopods". Papers in Palaeontology. 6 (1): 31–92. doi:10.1002/spp2.1254. S2CID 198256507.
25. "Tylosaur food". Oceansofkansas.com. 2004-09-26. Retrieved 2016-04-13.
26. Everhart, M. J. 2002. New data on plesiosaur remains found as stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas. (Abstract) Transactions of the Kansas Academy of Science
27. Everhart, M. J. 2004. Late Cretaceous interaction between predators and prey. Evidence of feeding by two species of shark on a mosasaur. PalArch, vertebrate palaeontology series 1(1):1-7.
28. Everhart, M. J. 2002. Remains of immature mosasaurs (Squamata; Mosasauridae) from the Niobrara Chalk (Late Cretaceous) argue against nearshore nurseries. (Abstract) Journal of Vertebrate Paleontology 22(suppl. to 3):52A.
29. ^ "Table 13.1: Mosasaurs", Everhart (2005), page 245.
30. ^ "Table 13.1: Mosasaurs", Everhart (2005), page 246.
31. Willman, A.J.; Konishi, T.; Caldwell, M.W. (2021). "A new species of Ectenosaurus (Mosasauridae: Plioplatecarpinae) from western Kansas, USA, reveals a novel suite of osteological characters for the genus". Canadian Journal of Earth Sciences. 58 (9): 741–755. doi:10.1139/cjes-2020-0175.
32. Kiernan, Caitlin R.; Ebersole, Jun A. (2023). "Two new plioplatecarpine mosasaurs (Mosasauridae; Plioplatecarpinae) of the genus Ectenosaurus from the Upper Cretaceous of North America". PaleoBios. 40 (13). doi:10.5070/P9401362375. ISSN 0031-0298.
33. Bardet N, Suberbiola P, Iarochene M, Bouya B, Amaghzaz M (2005). "A new species of Halisaurus from the Late Cretaceous phosphates of Morocco, and the phylogenetical relationships of the Halisaurinae (Squamata: Mosasauridae)". Zoological Journal of the Linnean Society. 143 (3): 447–472. doi:10.1111/j.1096-3642.2005.00152.x.
34. Polcyn, M. J., and Everhart, M. J., 2008, Description and phylogenetic analysis of a new species of Selmasaurus (Mosasauridae: Plioplatecarpinae) from the Niobrara Chalk of western Kansas: In: Proceedings of the Second Mosasaur Meeting, edited by Everhart, M. J, Fort Hays Studies, Special Issue number 3, p. 13-28.
35. "Field Guide, Part 3; Marine reptiles". Oceansofkansas.com. 2011-01-25. Retrieved 2016-04-13.
36. ^ "Table 13.1: Plesiosaurs," Everhart (2005), page 245.
37. ^ Carpenter, K. (2003). "Vertebrate Biostratigraphy of the Smoky Hill Chalk (Niobrara Formation) and the Sharon Springs Member (Pierre Shale)." High-Resolution Approaches in Stratigraphic Paleontology, 21: 421-437. doi:10.1007/978-1-4020-9053-0
38. ^ "Material: YPM 1640," in "The Occurrence of Elasmosaurids..." Everhart (2006), page 173.
39. Wilton, Mark P. (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press. ISBN 0691150613.
40. ^ "Table 13.1: Pterosaurs," Everhart (2005), page 246.
41. "Geosternbergia". Pteros. Pteros. Retrieved 28 August 2022.
42. ^ "Table 13.1: Turtles," Everhart (2005), page 245.

References

• Everhart, Michael J. Oceans Of Kansas: A Natural History Of The Western Interior Sea (Life of the Past). Bloomington: Indiana University Press, 2005. 322 pp.
• Everhart, Michael J. 2006. "The Occurrence of Elasmosaurids (Reptilia: Plesiosauria) in the Niobrara Chalk of Western Kansas"; Paludicila; 5(4) pp. 170–183
• Shimada, K. 2007. "Skeletal and dental anatomy of lamniform shark, Cretalamna appendiculata from Upper Cretaceous Niobrara Chalk of Kansas". Journal of Vertebrate Paleontology, 27(3):584–602.
• Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.

• Geology of Kansas
• Upper Cretaceous Series of North America
• Prehistoric fauna by locality
• Mesozoic paleobiotas