Abyssomedon

Abyssomedon (meaning "Guardian of the Abyss") is an extinct genus of a nyctiphruretid parareptile known from the late Early Permian (Kungurian age) Garber Formation of Comanche County, Oklahoma, south-central United States. It contains a single species, Abyssomedon williamsi, which represents the third known nyctiphruretid species, the oldest species of the family and the first to be discovered in North America.

Abyssomedon is known solely from the holotype BMRP 2008 33a, a partial skeleton housed at the Burpee Museum of Natural History at Rockford, Illinois, and contains a semi-articulated partial skull and disarticulated but associated postcranial remains. BMRP 2008 33a was discovered in 2008 at the claystone and conglomerate Oklahoma Museum of Natural History (OMNH) Locality V51, at Dolese Brothers limestone quarry of Richards Spur, Fissure Fills, just west of U.S. Highways 62 & 281, 10.5 miles south of Apache and 6 miles north of Fort Sill, of Comanche County, Oklahoma. It was collected from the Garber Formation (also known as the Willington Formation) of Summer Group, Arbuckle limestone, which is probably equivalent to the Arroyo Formation of Texas, dating to the middle Leonardian stage, of the upper Rotliegend epoch, Early Permian, about 275 million years ago. The Richards Spur locality presents a very rich Early Permian vertebrate paleofauna, including species of Lepospondyli, seymouriamorphs, basal synapsids, basal eureptiles and seven species of parareptiles apart from Abyssomedon, including the basal Microleter mckinzieorum, the bolosaurid Bolosaurus grandis, and the lanthanosuchoids Colobomycter pholeter, Delorhynchus priscus, Delorhynchus cifellii, Feeserpeton oklahomensis, and an unnamed new species of Acleistorhinidae.