South Carolina’s Williamsburg Formation is a Paleogene geologic unit of the coastal plain composed chiefly of sandy shale and clayey sand. Part of the Black Mingo Group and lying above the Rhems Formation, it is especially important for its Paleocene fossil record. Discoveries from the formation include coprolites and a diverse assemblage of vertebrates, including mammals, turtles, crocodilians, and snakes. Reported mammals include Ectoganus gliriformis, Ectoganus lobdelli, and Mingotherium holtae, while reptiles found there include Agomphus, Osteopygis, Trionyx, Bottosaurus, Hyposaurus, Thoracosaurus, and the snake Palaeophis.