| Eohyosaurus | |
|---|---|
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Rhynchosauria |
| Genus: | †Eohyosaurus Butleret al.,2015 |
| Type species | |
| †Eohyosaurus wolvaardti Butleret al.,2015 | |
Eohyosaurus is anextinctgenus ofbasalrhynchosaur known from the earlyMiddle Triassic (earlyAnisian stage)Burgersdorp Formation ofFree State,South Africa. It contains asingle species,Eohyosaurus wolvaardti.[1]
Eohyosaurus is known solely from theholotype SAM-PK-K10159, a partialskull missing the front end, with associated incompletelower jaws currently housed at theIziko 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 theFree State Province. It was collected from the middle deposits of theBurgersdorp Formation ofBeaufort Group. This horizon belongs to Subzone B of theCynognathus Assemblage Zone, dating to the earlyAnisian stage of the earlyMiddle Triassicperiod, about 246million years ago. Farm Lemoenfontein 44 also yielded remains of thearchosauriformErythrosuchus africanus, thebauriidMicrogomphodon oligocynus, thecynodontTrirachodon, thekannemeyeriidKannemeyeria as well as unidentifiedprocolophonid remains. All knownbasal rhynchosaurs came from similar deposits in the Beaufort Group, and whileHowesia browni andMesosuchus browni are also known from Subzone B of Burgersdorp Formation (from different localities),Noteosuchus colletti is known from theearliest TriassicKatberg Formation (Lystrosaurus Assemblage Zone).[1]
Eohyosaurus was first described and named byRichard J. Butler,Martín D. Ezcurra,Felipe C. Montefeltro, Adun Samathi and Gabriela Sobral in2015 and thetype species isEohyosaurus wolvaardti. Thegeneric name is derived fromGreekeos, meaning "early"/"dawn",hyos, meaning "pig"/"hog", andsauros meaning "lizard", in reference toEohyosaurus being one of the earlieststratigraphically occurring rhynchosaurs, a group commonly described as "pig-like reptiles". Thespecific name honors Frederik Petrus Wolvaardt who discovered the type specimen SAM-PK-K10159.[1]
Due to the limited material known ofEohyosaurus, the holotype partial skull was scanned in theMuseum für Naturkunde, Berlin, focusing on its tooth rows andendocranium due to being too large to be scanned completely. Thecomputed tomography data was provided to the Iziko South African Museum, to be archived along with the holotype.Eohyosaurus possesses oneautapomorphy, a unique trait amongRhynchosauria, ajugal 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 thepostorbital bone. Other traits that together comprise a unique combination of characters include some traits that are shared withHowesia andRhynchosauridae, but not withMesosuchus. Such traits include the presence of a sagittal crest onparietal bone,maxillae anddentaries 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 bothHowesia andMesosuchus,Eohyosaurus lacks a longitudinal occlusal groove and an occlusal blade on its maxillae and dentaries, respectively. Like in Rhynchosauridae and possiblyHowesia (but notMesosuchus), 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, inEohyosaurus it is present on the side surface of the maxilla, whileMesosuchus lacks it entirely and it is unknown inHowesia. As inHowesia but notMesosuchus 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 bothHowesia andMesosuchus, but similarly to the rhynchosaurids, the elongated back portion of the postorbital ends above the front margin of the bottom portion of thesquamosal. Finally, as inMesosuchus and Rhynchosauridae (but notHowesia), the elongated bottom portion of the squamosal extends for more than 50% of the back margin of the infratemporal fenestra.[1]
The followingcladogram is simplified after thephylogenetic analysis of Butleret al. (2015) and shows the placement ofEohyosaurus withinRhynchosauria. Butleret al. (2015) used an updated version of Montefeltroet al. (2013), expanded specifically to better resolved basal rhynchosaurs.[1]
| |||||||||||||||||
| |||||||||||||||||
