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Arundel Formation
Stratigraphic range: late Aptian or early Albian PreꞒ Ꞓ O S D C P T J K Pg N ↓
Outdoor excavation on an exposed portion of the Arundel clays at Dinosaur Park at Laurel, Maryland, USA
Type	Geological Formation
Unit of	Potomac Group
Underlies	Patapsco Formation (Unconformity)
Overlies	Patuxent Formation
Thickness	up to 125 feet (40 m)
Lithology
Primary	Claystone, mudstone
Other	Siderite nodules
Location
Region	Maryland, Washington D. C.
Country	United States
Type section
Named for	Anne Arundel County, Maryland
Named by	W. B. Clark, 1897

The Arundel Formation, also known as the Arundel Clay, is a clay-rich sedimentary rock formation, within the Potomac Group, found in Maryland of the United States of America. It dates to the Early Cretaceous, and is of late Aptian or (more likely) early Albian age. This rock unit had been economically important as a source of iron ore, but is now more notable for its dinosaur fossils. It is named for Anne Arundel County, Maryland.

It consists of clay lenses within depressions in the upper part of the Patuxent Formation that may represent oxbow swamp facies. The Arundel Formation contains a high number of terrestrial fauna, indicating that it was deposited in a freshwater fluvial environment, likely representing slow-moving river channels and oxbows. The Arundel Formation is the only major source for Early Cretaceous terrestrial vertebrates in eastern North America, and provides the best record of the dinosaurs that inhabited the region at the time.

Vertebrate paleofauna

Dinosaurs present include the large theropod Acrocanthosaurus, the giant sauropod Astrodon, the possible ornithischian Magulodon, the poorly known theropods "Allosaurus" medius, "Creosaurus" potens, and "Coelurus" gracilis, the ornithomimosaurian "Dryosaurus" grandis, as well as another indeterminate ornithomimosaurian (though it most likely is Nedcolbertia), the nodosaurid Priconodon, a possible basal ceratopsian, and potentially the ornithopod Tenontosaurus. Other vertebrates are not as well known from the formation, but include a freshwater shark, a lungfish, at least three genera of turtles, and several crocodilians.

The dinosaurian fauna of the Arundel Formation is very similar to that found in the concurrent, more comprehensive geological formations from further west (i.e. the Antlers, Cloverly, and Cedar Mountain Formations). This supports the idea of a largely homogenous dinosaur fauna stretching across North America during the Early Cretaceous, until the formation of the Western Interior Seaway divided the continent and led to major faunal changes on both halves. In contrast, among other vertebrate taxa, there are major differences between the Arundel and these western formations; in the Arundel, crocodylomorph and shark remains are far more common than those of bony fishes, whereas the opposite is true for the western formations. This may owe to differing environmental conditions on the Atlantic coast compared to the North American interior.

Cartilaginous fish

Cartilaginous fish reported from the Arundel Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Egertonodus	E. basanus	Maryland		Teeth, spine	A hybodont shark.
Planohybodus	P. ensis	Maryland		Teeth	A hybodont shark, formerly placed in Hybodus.

Ray-finned fish

Ray-finned fish reported from the Arundel Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
cf. Lepidotes		Maryland		Teeth, jaw	A semionotid.
cf. Vidalamiinae		Maryland		Teeth	An amiid.

Lobe-finned fish

Lobe-finned fish reported from the Arundel Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ceratodus	C. kranzi	Maryland		Tooth plate	A ceratodontid lungfish.

Reptiles

Dinosaurs

Dinosaurs reported from the Arundel Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Acrocanthosaurus	A. cf. atokensis	Maryland		"Teeth", "incomplete skeleton"	A large carcharodontosaurid theropod. Presence long suspected but uncertain, but confirmed in 2024 following the discovery of more complete remains.
Allosaurus	"A." medius	Maryland		"Tooth."	An indeterminate theropod tooth.
Astrodon	A. johnstoni	Maryland Washington D.C.		"Tooth."
"Capitalsaurus"	"C." potens	Washington D.C.		"Vertebra."	A neotheropod possibly synonymous with Acrocanthosaurus.
Coelurus	"C." gracilis			"Manual ungual and teeth."	A dromaeosaurid synonymous with Deinonychus.
Creosaurus	"C." potens				Reclassified as "Capitalsaurus" potens
cf. Deinonychus	Indeterminate	Maryland			A dromaeosaurid
Dryosaurus	"D." grandis	Maryland		"Limb elements."	An indeterminate member of Ornithomimosauria.
Magulodon	M. muirkirkensis	Maryland		"Tooth"	Likely an ornithischian, this genus is a nomen nudum that has not been formally published.
Neoceratopsia indet.	Indeterminate	Maryland		"Teeth"	An indeterminate member of Neoceratopsia. Initially believed to have belonged to an indeterminate member of Dryosauridae or the genus Tenontosaurus.
Ornithomimus	"O." affinis				Junior synonym of "Dryosaurus" grandis
Pleurocoelus	P. altus	Maryland		"Tibia fibula."	A sauropod synonymous with Astrodon.
	P. nanus	Maryland
Priconodon	P. crassus	Maryland		"Teeth, tibia."	A large nodosaurid.
cf. Richardoestesia	Indeterminate	Maryland		"Teeth"	A small theropod.
cf. Tenontosaurus	Indeterminate	Maryland

Pterosaurs

Unassigned pteradactyloid tracks.

Turtles

Turtles reported from the Arundel Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Arundelemys	A. dardeni	Maryland		"A single, incomplete skull lacking the lower jaws and cheek region"	A baenid.
Glyptops	G. caelatus	Maryland		"Carapace fragments probably pertaining to a single individual"	A pleurosternid.
Naomichelys	N. sp.	Maryland		"Shell fragments"	A helochelydrid.

Crocodylomorphs

Mammals

Other fossils

William Bullock Clark (1897) described lignitized trunks of trees often found in upright positions with their roots still intact.

G. J. Brenner (1963) described spores and pollen within the formation.

See also

• List of dinosaur-bearing rock formations

Footnotes

1. ^ Clark, W.B. (1897). Outline of present knowledge of the physical features of Maryland (Report). Volume Series. Vol. 1. Maryland Geological Survey. pp. 172–188.
2. ^ "Geologic Map Legends". Coastal Plain Rocks and Sediments. Maryland Geological Survey. Archived from the original on 26 May 2011. Retrieved 27 June 2011.
3. ^ Museum~Joseph.A.Frederickson-1@ou.edu, Joseph A. Frederickson~Sam Noble; Museum~thomas.r.lipka-1@ou.edu, Thomas R. Lipka~Sam Noble; Museum~rlc@ou.edu, Richard L. Cifelli~Sam Noble (2018-08-28). "Faunal composition and paleoenvironment of the Arundel Clay (Potomac Formation; Early Cretaceous), Maryland, USA". Palaeontologia Electronica. doi:10.26879/847. Retrieved 2024-10-28.{{cite web}}: CS1 maint: numeric names: authors list (link)
4. ^ Kranz, Peter M. (1998). "Mostly dinosaurs: a review of the vertebrates of the Potomac Group (Aptian Arundel Formation), USA". In Lucas, Spencer G.; Kirkland, James I.; Estep, J.W. (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin 14. pp. 235–238.
5. "Geologic Unit: Arundel". National Geologic Map Database. USGS.
6. ^ Harris, Jerald D. (1998). "Large, Early Cretaceous theropods in North America". In Lucas, Spencer G.; Kirkland, James I.; Estep, J.W. (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin 14. pp. 225–228.
7. Lipka, Thomas R. (1998). "The affinities of the enigmatic theropods of the Arundel Clay facies (Aptian), Potomac Formation, Atlantic Coastal Plain of Maryland". In Lucas, Spencer G.; Kirkland, James I.; Estep, J.W. (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin 14. pp. 229–234.
8. ^ Carrano, Matthew T. (2024-05-01). "First definitive record of Acrocanthosaurus (Theropoda: Carcharodontosauridae) in the Lower Cretaceous of eastern North America". Cretaceous Research. 157: 105814. doi:10.1016/j.cretres.2023.105814. ISSN 0195-6671.
9. Brownstein, Chase D. "Redescription of Arundel formation Ornithomimosaur material and a reinterpretation of Nedcolbertia justinhofmanni as an "Ostrich Dinosaur": Biogeographic implications". PeerJ Preprints. e2308v1.
10. Gilmore, Charles W. (24 October 1919). "An Ornithomimid Dinosaur in the Potomac of Maryland". Science. 50 (1295): 394–395. Bibcode:1919Sci....50..394G. doi:10.1126/science.50.1295.394. PMID 17830121.
11. Weishampel, David B.; Barrett, Paul M.; Coria, Rodolfo A.; Le Loueff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth M.P.; Noto, Christopher N. (2004). "Dinosaur distribution". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 517–606. ISBN 978-0-520-24209-8.
12. ^ Chinnery, Brenda J.; Lipka, Thomas R.; Kirkland, James I.; Parrish, Michael J.; Brett-Surman, Michael K. (1998). "Neoceratopsian teeth from the Lower to Middle Cretaceous of North America". terpconnect.umd.edu/. Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin No. 14. 297-302 pp. Retrieved March 13, 2019.
13. Frederickson, J. A., Lipka, T. R., & Cifelli, R. L. (2016). A new species of the lungfish Ceratodus (Dipnoi) from the Early Cretaceous of the eastern USA. Journal of Vertebrate Paleontology, e1136316.
14. Brownstein, Chase D. (2018-02-08). "The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia". Palaeontologia Electronica. 21 (1): 1–56. doi:10.26879/801. ISSN 1094-8074.
15. Frederickson, Joseph A.; Lipka, Thomas R.; Cifelli, Richard L. (2016-07-03). "A new species of the lungfish Ceratodus (Dipnoi) from the Early Cretaceous of the eastern U.S.A." Journal of Vertebrate Paleontology. 36 (4): e1136316. doi:10.1080/02724634.2016.1136316. ISSN 0272-4634.
16. ^ "3.25 Maryland, United States; 1. Arundel Clay," in Weishampel, et al. (2004). Page 556.
17. ^ "Table 4.1," in Weishampel, et al. (2004). Page 78.
18. ^ "3.25 Maryland, United States; 1. Arundel Clay" and "3.34 Washington D. C., United States; 1. Arundel Clay," in Weishampel, et al. (2004). Page 556.
19. "3.34 Washington D. C., United States; 1. Arundel Clay," in Weishampel, et al. (2004). Page 556.
20. "Table 13.1," in Weishampel, et al. (2004). Page 270.
21. Kranz, D. 1998. Mostly Dinosaurs: A Review of the Vertebrates of the Potomac Group (Aptian Arundel Formation), USA, in Lucas, Kirkland and Estep, eds., 1998: 235-238.
22. ^ Brownstein, Chase D. (2018). "The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia". Palaeontologia Electronica: 1–56. doi:10.26879/801.
23. "Table 6.1," in Weishampel, et al. (2004). Page 139.
24. ^ Kranz, P. (1996). Notes on the sedimentary iron ores of Maryland and their dinosaurian faunas. Maryland Geological Survey Special Publications 3:87–115.
25. "Table 13.1," in Weishampel, et al. (2004). Page 266.
26. "Table 17.1," in Weishampel, et al. (2004). Page 368.
27. ^ Listed as "?Tenontosaurus sp." in "3.25 Maryland, United States; 1. Arundel Clay," in Weishampel, et al. (2004). Page 556.
28. ^ Lockley, M.; Harris, J.D.; and Mitchell, L. 2008. "A global overview of pterosaur ichnology: tracksite distribution in space and time." Zitteliana. B28. p. 187-198. ISSN 1612-4138.
29. Brenner, Gilbert J., 1963, The spores and pollen of the Potomac Group of Maryland: Maryland Geological Survey Bulletin, no. 27, 215 p.

References

• Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.

External links

39°3′N 76°38′W / 39.050°N 76.633°W / 39.050; -76.633

• Lower Cretaceous Series of North America
• Cretaceous Maryland
• Natural history of Maryland
• Paleontology in Maryland
• Cretaceous Washington, D.C.
• Aptian Stage
• Albian Stage