[5] It consists of clay lenses within depressions in the upper part of the Patuxent Formation that may represent oxbow swamp facies.

[4] 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.

[3] Dinosaurs present include the large theropod Acrocanthosaurus,[6][7][8] the giant sauropod Astrodon, the possible ornithischian Magulodon,[6] the poorly known theropods "Allosaurus" medius, "Creosaurus" potens, and "Coelurus" gracilis, the ornithomimosaurian "Dryosaurus" grandis,[9] as well as another indeterminate ornithomimosaurian (though it most likely is Nedcolbertia),[10] the nodosaurid Priconodon,[11] a possible basal ceratopsian,[12] and potentially the ornithopod Tenontosaurus.

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.

[28] Pteraichnus[28] [28] William Bullock Clark (1897) described lignitized trunks of trees often found in upright positions with their roots still intact.