''Eohyosaurus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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 epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

(early

Anisian In the geologic timescale, the Anisian is the lower stage (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...

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 fossili ...

of Free State,

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

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

Discovery

''Eohyosaurus'' is known solely from the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

SAM-PK-K10159, a partial

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

missing the front end, with associated incomplete

lower jaw In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

s currently housed at the

Iziko South African Museum The Iziko South African Museum, formerly the South African Museum (Afrikaans: Suid-Afrikaanse 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 ...

Cape Town Cape Town is the legislature, legislative capital city, capital of South Africa. It is the country's oldest city and the seat of the Parliament of South Africa. Cape Town is the country's List of municipalities in South Africa, 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 under ...

. 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 * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

, about 246

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

. Farm Lemoenfontein 44 also yielded remains of the

archosauriform Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles encompassing archosaurs and some of their close relatives. It was defined by Jacques Gauthier (1994) as the clade stemming from the last common anc ...

Erythrosuchus africanus ''Erythrosuchus'' (from , 'red' and , 'crocodile') is an extinct genus of archosauriform reptiles from the early Triassic of South Africa. Remains have been found from the Cynognathus Assemblage Zone of the Beaufort Group in the Karoo of South ...

'', the bauriid '' Microgomphodon oligocynus'', the

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

Trirachodon ''Trirachodon'' (Greek: "three ridge tooth") is an extinct genus of cynodonts. Fossils have been found in the ''Cynognathus'' Assemblage Zone of the Beaufort Group in South Africa and the Omingonde Formation of Namibia, dating back to the Earl ...

'', the kannemeyeriid ''

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 Daniel Rossouw Kannemeyer, the South African fossil collector w ...

'' 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'' and ''

Mesosuchus browni ''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 para ...

'' 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 Richard James Butler is a vertebrate palaeontologist at the University of Birmingham, where he holds the title of professor of palaeobiology. His research focuses on ornithischian dinosaur evolution, dinosaur origins, and fossil tetrapod macroe ...

, Martín D. Ezcurra, Felipe C. Montefeltro, Adun Samathi and Gabriela Sobral in

2015 2015 was designated by the United Nations as: * International Year of Light * International Year of Soil __TOC__ Events January * January 1 – Lithuania officially adopts the euro as its currency, replacing the litas, and becomes ...

and the

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

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

Greek Greek may refer to: 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 of all kno ...

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

pig The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...

"/"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: lithost ...

ally occurring rhynchosaurs, a group commonly described as "pig-like reptiles". The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

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 () 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 museums in Germany alongside Naturm ...

, Berlin, focusing on its tooth rows and

endocranium The endocranium in comparative anatomy is a part of the skull base in vertebrates and it represents the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater in human anatomy. Structure Structurally, t ...

due to being too large to be scanned completely. The

computed tomography A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

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 Synapomorphy, 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 (cladistics), outgroup taxa, not ...

, 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 bone, zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by spe ...

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

temporal fenestra Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit (eye socket). These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly (al ...

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 ...

. Other traits that together comprise a unique combination of characters include some traits that are shared with ''

Howesia ''Howesia'' is an extinct genus of Basal (phylogenetics), basal rhynchosaur from early Middle Triassic (early Anisian stage) deposits of Eastern Cape of Good Hope, Cape, South Africa. It is known from the holotype South African Museum, SAM 5884, ...

'' 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 para ...

''. 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 known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...

maxillae In vertebrates, the maxilla (: maxillae ) 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 two maxillar ...

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 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 ancestra ...

. 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 language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

is simplified after the

phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

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 Rhynchosauria Middle Triassic reptiles of Africa Fossils of South Africa Anisian life Fossil taxa described in 2015 Prehistoric reptile genera