Delorhynchus Skull

''Delorhynchus'' is an extinct genus of lanthanosuchoid parareptile known from the late Early Permian (Artinskian age) Garber Formation of Comanche County, Oklahoma. It contains three species: the type species ''D. priscus'' is based on a series of maxillae. The second species to be described, ''D. cifellii'', is known from a larger number of well-preserved skulls and skeletal material. The third species, ''D. multidentatus'', is based on a fragmentary skull with several rows of teeth on its jaw.

Discovery

The type species, ''D. priscus,'' was first described and named by Richard C. Fox in 1962. The generic name "''Delorhynchus''" is derived from Greek ''rhynchos''/''ρυγχος'', meaning "beak" (a common suffix for extinct reptile genera names). The specific name of the type species ''D. priscus'' is derived from Greek ''πρίσκος'', meaning "ancient" or "venerable" in reference to the fragmentary nature of the known remains. ''D. priscus'' is known from the holotype KU 11117, a fragmentary left maxilla bearing 4 teeth, and from the fragmentary referred specimens KU 11118 and KU 11119, a right and a left maxillae respectively, each bearing 4 teeth. All known specimens of ''D. priscus'' are housed at the University of Kansas Natural History Museum in Lawrence, Kansas.

''D. cifellii'' was first described and named by Robert R. Reisz, Mark J. Macdougall and Sean P. Modesto in 2014. Its specific name honors Dr. Richard L. Cifelli, a paleontologist at the Sam Noble Oklahoma Museum of Natural History (OMNH), for his contributions to the paleontology of Oklahoma and support in studying ''D. cifellii''. Unlike the type species, ''D. cifellii'' is known from a well-preserved partial subadult skeleton, an isolated adult skull, and other disarticulated elements, all housed at the OMNH. The subadult individual preserves both the partial skull and the postcranial remains in articulation, and thus was chosen as the holotype, represented by OMNH 73515. OMNH 73362 represents the complete skull of the large, adult, individual. Other remains referred to ''D. cifellii'' include OMNH 73363, a complete right mandibular ramus of an individual equal in size to OMNH 73362, as well as the right maxilla OMNH 73524.

''D. multidentatus'' was described by Dylan C.T. Rowe, Diane M. Scott, Joseph J. Bevitt, and Robert Reisz in 2021. It is based on ROMVP 87042, a fragmentary skull housed in the Royal Ontario Museum of Toronto. It was named in reference to the multiple rows of teeth on the lower jaw of the skull, a unique feature which distinguished it from other ''Delorhynchus'' species.

''Delorhynchus'' is only found in the fissure fill claystone and conglomerate of OMNH Locality V51. This locality, also known as Richards Spur, is found at the Dolese Brothers limestone quarry near Fort Sill in Comanche County, Oklahoma. The fissure fill deposits of Richards Spur are probably equivalent to the Garber Formation of Oklahoma and the Arroyo Formation. Uranium-Lead dating of speleotherms in the cave deposits suggest that the fossils of Richards Spur were deposited in the Artinskian stage of the Cisuralian (Early Permian).

Classification

Until recently, the phylogenetic position of ''Delorhynchus'' within Procolophonomorpha was uncertain, due to the fragmentary nature of the remains of ''D. priscus''. However, with the description of ''D. cifellii'' by Reisz ''et al.'' (2014), ''Delorhynchus'' could be added for the first time into a phylogenetic analysis to resolve its position. Reisz ''et al.'' (2014) recovered ''Delorhynchus'' in a sister taxon position to the clade formed by ''Acleistorhinus'' and ''Lanthanosuchus''. Thus ''Delorhynchus'' was either considered to be the sister taxon of Lanthanosuchoidea, or a basal lanthanosuchoid, depending on the definition of Lanthanosuchoidea used. The following cladogram is simplified after the phylogenetic analysis of MacDougall and Reisz (2014), an updated version of Reisz ''et al.'' (2014), and shows the placement of ''D. cifellii'' within Parareptilia. Relationships within bolded clades are not shown.

Paleoecology

The Richards Spur locality presents a very rich Early Permian vertebrate paleofauna, including species of chondrichthyes, lepospondyls, seymouriamorphs, basal synapsids, and basal eureptiles. At least six species of parareptiles have been described apart from the three ''Delorhynchus'' species. They include the basal parareptile '' Microleter mckinzieorum'', the bolosaurid ''Bolosaurus grandis'', the nyctiphruretid '' Abyssomedon williamsi'', and three other lanthanosuchoids: ''Colobomycter pholeter'', ''Colobomycter vaughni'', and ''Feeserpeton oklahomensis''.

References

{{Taxonbar, from=Q252747

Acleistorhinidae
Cisuralian reptiles of North America
Fossil taxa described in 1962
Fossil taxa described in 2014
Extinct animals of the United States
Paleontology in Oklahoma
Prehistoric reptile genera