The Arundel Formation, also known as the Arundel Clay, is a

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay part ...

-rich

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

rock formation A rock formation is an isolated, scenic, or spectacular surface rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock formation'' can also refer to specific sedime ...

, within the Potomac Group, found in

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; ...

of the

United States of America The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territor ...

. It is of Aptian age ( Lower Cretaceous). This rock unit had been economically important as a source of

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the ...

, but is now more notable for its

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s. It consists of clay lenses within depressions in the upper part of the Patuxent Formation that may represent oxbow swamp facies. It is named for

Anne Arundel County, Maryland Anne Arundel County (; ), also notated as AA or A.A. County, is located in the U.S. state of Maryland. As of the 2020 United States census, its population was 588,261, an increase of just under 10% since 2010. Its county seat is Annapolis, w ...

Vertebrate paleofauna

Dinosaurs

Dinosaurs present include cf. ''

Acrocanthosaurus ''Acrocanthosaurus'' ( ; ) is a genus of carcharodontosaurid dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous, from 113 to 110 million years ago. Like most dinosaur genera ...

'', the possible ornithischian '' Magulodon'', the poorly known theropods ''"

Allosaurus ''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch ( Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alludi ...

" medius'', '' "Creosaurus" potens'', and ''" Coelurus" gracilis'', the ornithomimosaurian ''" Dryosaurus" grandis'', as well as another indeterminate ornithomimosaurian (though it most likely is '' Nedcolbertia''), the sauropod '' Astrodon'', the nodosaurid '' Priconodon'', a possible

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

ceratopsian, and potentially the ornithopod '' Tenontosaurus''. Other

vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...

s are not as well known from the formation, but include a freshwater

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

, a lungfish, at least three genera of

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked ...

s, and at least one

crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

Pterosaurs

Unassigned pteradactyloid tracks.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. .

Other fossils

William Bullock Clark William Bullock Clark (December 15, 1860 – July 27, 1917), was an American geologist. Early life William Bullock Clark was born on December 15, 1860, at Brattleboro, Vermont, to Helen (née Bullock) and Barna Atherton Clark. Clark had private ...

(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.Brenner, Gilbert J., 1963, The spores and pollen of the Potomac Group of Maryland: Maryland Geological Survey Bulletin, no. 27, 215 p

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Footnotes

References

* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. .

External links

{{Coord, 39, 3, N, 76, 38, W, region:US_scale:500000, display=title Lower Cretaceous Series of North America Cretaceous Maryland Natural history of Maryland Paleontology in Maryland Cretaceous Washington, D.C. Aptian Stage