The Potomac Group is a geologic group in Delaware, Maryland, New Jersey, and Virginia. It preserves fossils dating back to the Cretaceous period. An indeterminate tyrannosauroid and Priconodon crassus, a nodosaurid, are known from indeterminate sediments belonging to the Potomac Group.[1] The Potomac Group was initially believed to have been Late Jurassic in age by Othniel Charles Marsh[2] but later studies, such as Clark (1897), have found that the Potomac Group is in fact Early-Late Cretaceous (Aptian-Turonian) in age.[3] The most famous member of the group is the Arundel Formation, which preserves a high diversity of terrestrial vertebrate fauna and provides the most comprehensive look at the dinosaurian fauna of eastern North America during the Early Cretaceous.[4]
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