Arundel Formation

The Arundel Formation, also known as the Arundel Clay, is a clay-rich sedimentary rock formation, within the Potomac Group, found in Maryland^[2] of the United States of America. It is of Aptian age (Lower Cretaceous). This rock unit had been economically important as a source of iron ore, but is now more notable for its dinosaur fossils. It consists of clay lenses within depressions in the upper part of the Patuxent Formation that may represent oxbow swamp facies.^[3] It is named for Anne Arundel County, Maryland.^[4]

Arundel Formation
Stratigraphic range: Aptian 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)[1]
Lithology
Primary	Clay
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[1]

Vertebrate paleofauna

Dinosaurs

Dinosaurs present include cf. Acrocanthosaurus,^[5][6] the possible ornithischian Magulodon,^[5] the poorly known theropods "Allosaurus" medius, "Creosaurus" potens, and "Coelurus" gracilis, the ornithomimosaurian "Dryosaurus" grandis,^[7] as well as another indeterminate ornithomimosaurian (though it most likely is Nedcolbertia),^[8] the sauropod Astrodon, the nodosaurid Priconodon,^[9] a possible basal ceratopsian,^[10] and potentially the ornithopod Tenontosaurus.^[3] Other vertebrates are not as well known from the formation, but include a freshwater shark, a lungfish,^[11] at least three genera of turtles, and at least one crocodilian.^[3]

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.

Dinosaurs reported from the Arundel Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Acrocanthosaurus[5][12]	A. cf. atokensis[12]	Maryland[2]		"Teeth",[5] "incomplete skeleton"[12]	A large carcharodontosaurid theropod. Presence long suspected but uncertain, but confirmed in 2024 following the discovery of more complete remains.[12]	Acrocanthosaurus
Allosaurus[13]	"A." medius[13]	Maryland[13]		"Tooth."[14]	An indeterminate theropod tooth.	Astrodon Deinonychus Tenontosaurus
Astrodon[15]	A. johnstoni[15]	Maryland[13] Washington D.C.[16]		"Tooth."[17]
"Capitalsaurus"[18]	"C." potens	Washington D.C.[13]		"Vertebra."[14]	A neotheropod possibly synonymous with Acrocanthosaurus.[19]
Coelurus[13]	"C." gracilis			"Manual ungual and teeth."[14]	A dromaeosaurid synonymous with Deinonychus.[19]
Creosaurus[13]	"C." potens[13]				Reclassified as "Capitalsaurus" potens
cf. Deinonychus[13]	Indeterminate[13]	Maryland[13]			A dromaeosaurid
Dryosaurus	"D." grandis	Maryland[13]		"Limb elements."[20]	An indeterminate member of Ornithomimosauria.
Magulodon[21]	M. muirkirkensis[21]	Maryland[21]		"Tooth"[21]	Likely an ornithischian, this genus is a nomen nudum that has not been formally published.
Neoceratopsia indet.[10]	Indeterminate[10]	Maryland[13]		"Teeth"[10]	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[13]	P. altus[13]	Maryland[13]		"Tibia [and] fibula."[22]	Possibly synonymous with Astrodon.
	P. nanus[13]	Maryland[13]			Possibly synonymous with Astrodon.
Priconodon[13]	P. crassus[13]	Maryland[13]		"Teeth, tibia."[23]	A large nodosaurid.
cf. Tenontosaurus[24]	Indeterminate[24]	Maryland[13]

Pterosaurs

Unassigned pteradactyloid tracks.^[25]

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.

Pterosaurs of the Arundel Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Pteraichnus[25]				[25]

Other fossils

William Bullock Clark (1897) described lignitized trunks of trees often found in upright positions with their roots still intact.^[1]

G. J. Brenner (1963) described spores and pollen within the formation.^[26]

See also

• Earth sciences portal
• Paleontology portal
• Dinosaurs portal

• List of dinosaur-bearing rock formations

Footnotes

1. Clark, W.B., 1897, Outline of present knowledge of the physical features of Maryland: Maryland Geological Survey Volume Series, v. 1, pt. 3, p. 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. 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.
4. "Geologic Unit: Arundel". National Geologic Map Database. USGS.
5. 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.
6. 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.
7. Brownstein, Chase D. "Redescription of Arundel formation Ornithomimosaur material and a reinterpretation of Nedcolbertia justinhofmanni as an "Ostrich Dinosaur": Biogeographic implications". PeerJ Preprints. e2308v1.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. "3.25 Maryland, United States; 1. Arundel Clay," in Weishampel, et al. (2004). Page 556.
14. "Table 4.1," in Weishampel, et al. (2004). Page 78.
15. "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.
16. "3.34 Washington D. C., United States; 1. Arundel Clay," in Weishampel, et al. (2004). Page 556.
17. "Table 13.1," in Weishampel, et al. (2004). Page 270.
18. 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.
19. Brownstein, Chase D. (2018). "The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia". Palaeontologia Electronica: 1–56. doi:10.26879/801.
20. "Table 6.1," in Weishampel, et al. (2004). Page 139.
21. Kranz, P. (1996). Notes on the sedimentary iron ores of Maryland and their dinosaurian faunas. Maryland Geological Survey Special Publications 3:87–115.
22. "Table 13.1," in Weishampel, et al. (2004). Page 266.
23. "Table 17.1," in Weishampel, et al. (2004). Page 368.
24. Listed as "?Tenontosaurus sp." in "3.25 Maryland, United States; 1. Arundel Clay," in Weishampel, et al. (2004). Page 556.
25. 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.
26. 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