Abyssomedon

Abyssomedon (meaning "Guardian of the Abyss") is an extinct genus of a nyctiphruretid parareptile known from Early Permian (Artinskian age) fissure fills at Richards Spur in Comanche County, Oklahoma, south-central United States. It contains a single species, Abyssomedon williamsi, which represents oldest known nyctiphrureptid species and the first to be discovered in North America.[1]

Abyssomedon Temporal range: Early Permian, 289 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Illustration of the holotype fossil
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	†Parareptilia
Order:	†Procolophonomorpha
Family:	†Nyctiphruretidae
Genus:	†Abyssomedon MacDougall & Reisz, 2014
Type species
†Abyssomedon williamsi MacDougall & Reisz, 2014

Discovery

Abyssomedon is known solely from the holotype BMRP 2008 33a, a partial skeleton housed at the Burpee Museum of Natural History at Rockford, Illinois. The specimen consists of a semi-articulated partial skull and disarticulated but associated postcranial remains. BMRP 2008 33a was discovered in 2008 in a claystone and conglomerate nodule found at Oklahoma Museum of Natural History (OMNH) Locality V51. This site, known as Richards Spur, is located 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. The fossils of Richards Spur are found in Early Permian fissure fills in Ordovician limestone.[1][2]

Abyssomedon was first described and named by Mark J. MacDougall and Robert R. Reisz in 2014 and the type species is Abyssomedon williamsi. The generic name is derived from Greek Abyssos, meaning "deep pit", and -medon, meaning "guardian", in reference to the cave system at Richards Spur. The specific name williamsi honor the collector of the holotype Mr. Scott Williams, a paleontologist at the Burpee Museum.[1]

Classification

The following cladogram is simplified after the phylogenetic analysis of MacDougall and Reisz (2014) and shows the placement of Abyssomedon within Parareptilia. Relationships within bolded clades are not shown.[1]

Parareptilia

Mesosaurus       Millerosauria   Procolophonomorpha   Australothyris smithi   Hallucicrania (=Ankyramorpha) Lanthanosuchoidea   Feeserpeton oklahomensis         Colobomycter pholeter     Delorhynchus cifellii         Acleistorhinus pteroticus     Lanthanosuchus watsoni             Microleter mckinzieorum     Bolosauridae   Belebey chengi     Eudibamus cursoris     Procolophonia Pareiasauromorpha   Nycteroleteridae     Pareiasauria       Nyctiphruretidae   Abyssomedon williamsi     Nyctiphruretus acudens     Procolophonoidea   Owenettidae     Procolophonidae

Paleoecology

The Richards Spur locality preserves a system of Early Permian sediments and fossils trapped in a cave eroded out of Ordovician Arbuckle Limestone. The Permian sediments of Richards Spur may be equivalent to the Garber Formation (also known as the Wellington Formation) elsewhere in Oklahoma, or the Arroyo Formation of Texas. Richards Spur presents a rich Early Permian vertebrate paleofauna, including species of Lepospondyli, seymouriamorphs, basal synapsids, basal eureptiles and many species of parareptiles apart from Abyssomedon, including the basal Microleter mckinzieorum, the bolosaurid Bolosaurus grandis, and the lanthanosuchoids such as Colobomycter pholeter, Delorhynchus priscus, Delorhynchus cifellii, and Feeserpeton oklahomensis. A speleotherm was used to Uranium-Lead date the deposits to 289 ± 0.86 million years ago, corresponding to the Artinskian stage.[1][3][2] However, the deposits were likely deposited over several million years, as evidenced by wider speleotherm sampling.[2]

References

1. Mark J. MacDougall and Robert R. Reisz (2014). "The first record of a nyctiphruretid parareptile from the Early Permian of North America, with a discussion of parareptilian temporal fenestration". Zoological Journal of the Linnean Society. 172 (3): 616–630. doi:10.1111/zoj.12180.
2. MacDougall, Mark J.; Tabor, Neil J.; Woodhead, Jon; Daoust, Andrew R.; Reisz, Robert R. (2017-06-01). "The unique preservational environment of the Early Permian (Cisuralian) fossiliferous cave deposits of the Richards Spur locality, Oklahoma". Palaeogeography, Palaeoclimatology, Palaeoecology. 475: 1–11. doi:10.1016/j.palaeo.2017.02.019. ISSN 0031-0182.
3. Woodhead, Jon; Reisz, Robert; Fox, David; Drysdale, Russell; Hellstrom, John; Maas, Roland; Cheng, Hai; Edwards, R. Lawrence (May 2010). "Speleothem climate records from deep time? Exploring the potential with an example from the Permian". Geology. 38 (5): 455–458. doi:10.1130/G30354.1. ISSN 0091-7613.