Eohyosaurus

Eohyosaurus is an extinct genus of basal rhynchosaur known from the early Middle Triassic (early Anisian stage) Burgersdorp Formation of Free State, South Africa. It contains a single species, Eohyosaurus wolvaardti.
Discovery.
"Eohyosaurus" is known solely from the holotype SAM-PK-K10159, a partial skull missing the front end, with associated incomplete lower jaws currently housed at the Iziko South African Museum, Cape Town. The specimen was discovered by Frederik Petrus Wolvaardt in December 2000, loose on boulder-strewn slopes at the base of a cliff, at Farm Lemoenfontein 44, Rouxville District of the Free State Province. It was collected from the middle deposits of the Burgersdorp Formation of Beaufort Group. This horizon belongs to Subzone B of the "Cynognathus" Assemblage Zone, dating to the early Anisian stage of the early Middle Triassic period, about 246 million years ago. Farm Lemoenfontein 44 also yielded remains of the archosauriform "Erythrosuchus africanus", the bauriid "Microgomphodon oligocynus", the cynodont "Trirachodon", the kannemeyeriid "Kannemeyeria" as well as unidentified procolophonid remains. All known basal rhynchosaurs came from similar deposits in the Beaufort Group, and while "Howesia browni" and "Mesosuchus browni" are also known from Subzone B of Burgersdorp Formation (from different localities), "Noteosuchus colletti" is known from the earliest Triassic Katberg Formation ("Lystrosaurus" Assemblage Zone).
Etymology.
"Eohyosaurus" was first described and named by Richard J. Butler, Martín D. Ezcurra, Felipe C. Montefeltro, Adun Samathi and Gabriela Sobral in 2015 and the type species is "Eohyosaurus wolvaardti". The generic name is derived from Greek ', meaning "early"/"dawn", ', meaning "pig"/"hog", and "" meaning "lizard", in reference to "Eohyosaurus" being one of the earliest stratigraphically occurring rhynchosaurs, a group commonly described as "pig-like reptiles". The specific name honors Frederik Petrus Wolvaardt who discovered the type specimen SAM-PK-K10159.
Description.
Due to the limited material known of "Eohyosaurus", the holotype partial skull was scanned in the Museum für Naturkunde, Berlin, focusing on its tooth rows and endocranium due to being too large to be scanned completely. The computed tomography data was provided to the Iziko South African Museum, to be archived along with the holotype. "Eohyosaurus" possesses one autapomorphy, a unique trait among Rhynchosauria, a jugal bone with elongate dorsal portion that forms the entire front margin of the infratemporal fenestra and that articulates from the front with the entire back margin of the elongated bottom portion of the postorbital bone. Other traits that together comprise a unique combination of characters include some traits that are shared with "Howesia" and Rhynchosauridae, but not with "Mesosuchus". Such traits include the presence of a sagittal crest on parietal bone, maxillae and dentaries that are expanded from the middle to the sides, and with teeth present on both the occlusal and lingual surfaces. However, unlike rhynchosaurids, but like both "Howesia" and "Mesosuchus", "Eohyosaurus" lacks a longitudinal occlusal groove and an occlusal blade on its maxillae and dentaries, respectively. Like in Rhynchosauridae and possibly "Howesia" (but not "Mesosuchus"), the occlusal margin of its maxilla is offset to the bottom from the lower margin of the main body of the jugal bone. Unlike rhynchosaurids that possess a short anguli oris crest on the jugal, in "Eohyosaurus" it is present on the side surface of the maxilla, while "Mesosuchus" lacks it entirely and it is unknown in "Howesia". As in "Howesia" but not "Mesosuchus" and most rhynchosaurids (where it contacts the quadratojugal), the back portion of its jugal is short and ends at approximately 50% of the front-to-back length of the infratemporal fenestra. Unlike in both "Howesia" and "Mesosuchus", but similarly to the rhynchosaurids, the elongated back portion of the postorbital ends above the front margin of the bottom portion of the squamosal. Finally, as in "Mesosuchus" and Rhynchosauridae (but not "Howesia"), the elongated bottom portion of the squamosal extends for more than 50% of the back margin of the infratemporal fenestra.
Phylogeny.
The following cladogram is simplified after the phylogenetic analysis of Butler "et al." (2015) and shows the placement of "Eohyosaurus" within Rhynchosauria. Butler "et al." (2015) used an updated version of Montefeltro "et al." (2013), expanded specifically to better resolved basal rhynchosaurs.