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: | |
 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
| Notes Uncertain or tentative taxa are in small text; |
| Dinosaurs reported from the Arundel Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Acrocanthosaurus[5][12] | A. cf. atokensis[12] |
| "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] |  | |
| "A." medius[13] |
| "Tooth."[14] | An indeterminate theropod tooth. |    | |
A. johnstoni[15] | "Tooth."[17] | |||||
"C." potens |
| "Vertebra."[14] | A neotheropod possibly synonymous with Acrocanthosaurus.[19] | |||
| "C." gracilis | "Manual ungual and teeth."[14] | A dromaeosaurid synonymous with Deinonychus.[19] | |||
| "C." potens[13] | Reclassified as "Capitalsaurus" potens | ||||
cf. Deinonychus[13] | Indeterminate[13] |
| A dromaeosaurid | |||
| "D." grandis |
| "Limb elements."[20] | An indeterminate member of Ornithomimosauria. | ||
M. muirkirkensis[21] |
| "Tooth"[21] | Likely an ornithischian, this genus is a nomen nudum that has not been formally published. | |||
| Neoceratopsia indet.[10] | Indeterminate[10] |
| "Teeth"[10] | An indeterminate member of Neoceratopsia. Initially believed to have belonged to an indeterminate member of Dryosauridae or the genus Tenontosaurus. | ||
| "O." affinis | Junior synonym of "Dryosaurus" grandis | ||||
P. altus[13] |
| "Tibia [and] fibula."[22] | Possibly synonymous with Astrodon. | |||
P. nanus[13] |
| Possibly synonymous with Astrodon. | ||||
P. crassus[13] |
| "Teeth, tibia."[23] | A large nodosaurid. | |||
Indeterminate[24] |
| |||||
Pterosaurs
Unassigned pteradactyloid tracks.[25]
Color key
| Notes Uncertain or tentative taxa are in small text; |
| Pterosaurs of the Arundel Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
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
Footnotes
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
