''Eohyosaurus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of basal

rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

known from the early

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

(early

Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic ...

stage)

Burgersdorp Formation The ''Cynognathus'' Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossil ...

of Free State,

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

. It contains a single species, ''Eohyosaurus wolvaardti''.

Discovery

''Eohyosaurus'' is known solely from the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

SAM-PK-K10159, a partial

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

missing the front end, with associated incomplete

lower jaw In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

s currently housed at the

Iziko South African Museum The Iziko South African Museum is a South African national museum located in Cape Town. The museum was founded in 1825, the first in the country. It has been on its present site in the Company's Garden since 1897. The museum houses important ...

Cape Town Cape Town ( af, Kaapstad; , xh, iKapa) is one of South Africa's three capital cities, serving as the seat of the Parliament of South Africa. It is the legislative capital of the country, the oldest city in the country, and the second largest ...

. 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

Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underli ...

. This horizon belongs to Subzone B of the ''Cynognathus'' Assemblage Zone, dating to the early

stage of the early

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

, about 246

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...

. Farm Lemoenfontein 44 also yielded remains of the archosauriform ''

Erythrosuchus africanus ''Erythrosuchus'' (from el, ἐρυθρός , 'red' and el, σοῦχος , 'crocodile') is an extinct genus of archosauriform reptile from the Triassic of South Africa. Remains have been found from the Cynognathus Assemblage Zone of the Beauf ...

'', the bauriid '' Microgomphodon oligocynus'', the cynodont '' Trirachodon'', the

kannemeyeriid ''Kannemeyeria'' is a genus of dicynodont that lived during the Anisian age of Middle Triassic period in what is now Africa and South America. The generic name is given in honor of Dr. Daniel Rossouw Kannemeyer, the South African fossil collect ...

Kannemeyeria ''Kannemeyeria'' is a genus of dicynodont that lived during the Anisian age of Middle Triassic period in what is now Africa and South America. The generic name is given in honor of Dr. Daniel Rossouw Kannemeyer, the South African fossil collect ...

'' as well as unidentified

procolophonid Procolophonidae is an extinct family of small, lizard-like parareptiles known from the Late Permian to Late Triassic that were distributed across Pangaea, having been reported from Europe, North America, China, South Africa, South America, Antarc ...

remains. All known basal rhynchosaurs came from similar deposits in the Beaufort Group, and while ''

Howesia browni ''Howesia'' is an extinct genus of basal rhynchosaur from early Middle Triassic (early Anisian stage) deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5884, a partial skeleton with palate and partial lower jaws and from ...

'' 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 The Katberg Formation is a geological formation that is found in the Beaufort Group, a major geological group that forms part of the greater Karoo Supergroup in South Africa. The Katberg Formation is the lowermost geological formation of the Tar ...

( ''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 In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

is ''Eohyosaurus wolvaardti''. The generic name is derived from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

', meaning "early"/"dawn", ', meaning "

pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...

"/"hog", and ' meaning "lizard", in reference to ''Eohyosaurus'' being one of the earliest

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...

ally 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 The Natural History Museum (german: Museum für Naturkunde) is a natural history museum located in Berlin, Germany. It exhibits a vast range of specimens from various segments of natural history and in such domain it is one of three major muse ...

, 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 In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

, a unique trait among

Rhynchosauria Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

, a

jugal bone The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anato ...

with elongate dorsal portion that forms the entire front margin of the infra

temporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets ...

and that articulates from the front with the entire back margin of the elongated bottom portion of the

postorbital bone The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some v ...

. Other traits that together comprise a unique combination of characters include some traits that are shared with '' Howesia'' and Rhynchosauridae, but not with ''

Mesosuchus ''Mesosuchus'' ("middle crocodile") is an extinct genus of basal Rhynchosaur from early Middle Triassic (early Anisian stage) deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5882, a partial skeleton, and from the ...

''. Such traits include the presence of a sagittal crest on

parietal bone The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is nam ...

maxillae The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

and

dentaries In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

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 The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

. 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 A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

is simplified after the

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

of Butler ''et al.'' (2015) and shows the placement of ''Eohyosaurus'' within

. Butler ''et al.'' (2015) used an updated version of Montefeltro ''et al.'' (2013), expanded specifically to better resolved basal rhynchosaurs.

References

{{Taxonbar, from=Q22285148 Rhynchosaurs Middle Triassic reptiles of Africa Fossils of South Africa Anisian life Fossil taxa described in 2015 Prehistoric reptile genera