''Eothyris'' is a

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 extinct

synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...

in the family

Eothyrididae Eothyrididae is an extinct family of very primitive, insectivorous synapsids. Only three genera are known, '' Eothyris'', '' Vaughnictis'' and '' Oedaleops'', all from the early Permian of North America. Their main distinguishing feature is the l ...

from the early

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

. It was a carnivorous

insectivorous A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant which eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores we ...

animal, closely related to ''

Oedaleops ''Oedaleops'' is an extinct genus of caseasaur synapsids from the Early Permian of the Southwestern United States. Fossils have been found in the Cutler Formation in New Mexico, which dates back to the Wolfcampian stage of the Early Permian. All ...

''. Only the skull of ''Eothyris'', first described in 1937, is known. It had a skull, and its total estimated length was . Eothyris is one of the most primitive synapsids known and is probably very similar to the common ancestor of all synapsids in many respects. The only known specimen of ''Eothyris'' was collected from the

Artinskian In the geologic timescale, the Artinskian is an age (geology), age or stage (stratigraphy), stage of the Permian. It is a subdivision of the Cisuralian Epoch (geology), Epoch or series (stratigraphy), Series. The Artinskian likely lasted between ...

-lower.

Discovery and naming

''Eothyris parkeyi'' was one of many new species of "

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile was used, and Pelycosauria was considered an order, but this is now thoug ...

s" discovered by

Alfred Sherwood Romer Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution. Biography Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...

as part of a series of paleontological expeditions for the

Museum of Comparative Zoology The Museum of Comparative Zoology (formally the Agassiz Museum of Comparative Zoology and often abbreviated to MCZ) is a zoology museum located on the grounds of Harvard University in Cambridge, Massachusetts. It is one of three natural-history r ...

(MCZ). The genoholotype (

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

of a genus) and only known specimen of ''Eothyris'' is a complete skull and associated jaws, with the collection number MCZ 1161. This skull was collected about one mile west of the former Woodrum ranch-house, in Early

sediments of the

-lower

Kungurian In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Arti ...

Belle Plains Formation The Belle Plains Formation is a Formation (geology), geologic formation in Texas. It preserves fossils dating back to the Permian Period (geology), period. See also * List of fossiliferous stratigraphic units in Texas * Paleontology in Texas R ...

Wichita Group The Wichita Group is a geologic group in the Permian Red Beds. It preserves fossils dating back to the Permian period. See also * List of fossiliferous stratigraphic units in Texas * Paleontology in Texas Paleontology in Texas refers to pa ...

, south of

Dundee, Texas Dundee is an unincorporated community located in Archer County, Texas, United States. According to the Handbook of Texas, the community had a population of 12 in 2010. Dundee is located within the Wichita Falls Metropolitan Statistical Area. ...

, USA. in rocks which are about 275 million years old. The generic name is

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 ...

for "dawn opening", likely in reference for its status as one of the most primitive known

s. 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 ...

refers to J.R. Parkey, of

Mankins, Texas Mankins is an unincorporated community located in Archer County, Texas, United States. According to the Handbook of Texas, the community had a population of 10 in 2000. Mankins is located within the Wichita Falls Metropolitan Statistical Area ...

, a local landowner who assisted the MCZ field crew in collecting fossils on his property. ''Eothyris'' was briefly described by Romer in 1937, and given a more comprehensive description by Romer and

Llewellyn Ivor Price Llewellyn Ivor Price (October 9, 1905 – June 9, 1980) was one of the first Brazilian paleontologists. His work contributed not only to the development of Brazilian but also to global paleontology. He collected ''Staurikosaurus'' in 1936, th ...

in 1940.

Description

''Eothyris'' is known only from its complete

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 ...

, however, the postcranial skeleton is unknown. Its skull is short and broad with a total skull length of , Benson ''et al.'' estimated the body to be long. The major distinguishing features of the skull are that it possessed a pair of long, large,

fang A fang is a long, pointed tooth. In mammals, a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes, it is a specialized tooth that is associated with a venom gland (see snake venom). Spiders also have external fangs, ...

-like

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

on each side of the

upper jaw 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 ...

. The main differences between ''Eothyris'' and ''

'' are related to the degree of specialization in the dentition of the geologically younger ''Eothyris''. Skull The superficial dermal elements are preserved, and the

occiput The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lobes of the ...

is visible. The skull is clearly low, very broad, and short. With normal length of postorbital and orbital regions. The face is much shorter than any other

except edaphosaurs. Lacrimal expanded laterally upper the canines.

Maxilla 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 maxil ...

contributes to the edge of the orbit as there is no lacrimal

jugal 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. Anatomy ...

contact in the orbit. 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 ...

and postorbital are extensively in contact because the temporal opening is small and of oval shape. Also, because the cheek slants outward to very higher degree than is usual in

s, the temporal opening is exposed in dorsal view. The

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

e and nasals are short and the frontals are of moderate length. The

supratemporal The supratemporal bone is a paired Skull, cranial bone present in many Tetrapod, tetrapods and Tetrapodomorpha, tetrapodomorph fish. It is part of the temporal region (the portion of the skull roof behind the eyes), usually lying medial (inwards) re ...

in ''Eothyris parkeyi'' is much more extremely developed than in any other pelycosaur. In ''Eothyris parkeyi'', the postorbital bone is probably the largest for any

, with large lateral and dorsal portions to the skull roof. The slope from skull table to quadrate is gentle, due to shortness of skull. The

quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

is very long and jaw articulation is in line with the tooth row. Typical pterygoid flanges and slender are present back in the skull, below the anterior part of the temporal opening. The quadrate is on the right side and is exposed dorsally. The interparietal and tabulars occupy the dorsal rim of the occipital surface. Teeth As ''Eothyris parkeyi'' has a short face, the lower

jaw The jaws are a pair of opposable articulated structures at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth ...

does not have a slender build. Dentary, angular, and

surangular The surangular or suprangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular bone, angular, splenial and articular. It is o ...

are visible on the outer surface, and also, the lower edge of the splenial is visible in the ventral view. The medial surface of the jaw is not visible. The teeth are pointed with slightly recurved. ''Eothyris parkeyi'' had about 14 or 15 teeth, depending on the disposition of the precanine. The premaxilla carried three not enlarged teeth. In ''Eothyris parkeyi'' due to shortness of the face, there are no precanine maxillary teeth. this feature is more specialized than any known

sphenacodont Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes '' Haptodus baylei'', '' Haptodus garnettensis'' and '' Sphenacodon ferox'', but not '' Edaphosaurus pogonia ...

. Very enlarged pair of canines, giving the snout distinctly a swollen appearance immediately posterior to the external

naris A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates, ...

. The most significant feature of ''Eothyris parkeyi'' is probably the morphology of the maxilla, because of its unique dental pattern. The maxilla in ''Eothyris parkeyi'' is a thin, elongate element with an abrupt dorsal expansion in the area of the primary canine pair.

Classification

''Eothyris'' is classified in the

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

family

. It is one of two genera in the family, the other being ''

''. The family is grouped in

Caseasauria Caseasauria is one of the two main clades of early synapsids, the other being the Eupelycosauria. Caseasaurs are currently known only from the Late Carboniferous and the Permian, and include two superficially different families, the small insect ...

, and only cranial remains are known from it. The family is greatly supported, with nine dental and cranial features. Below is the cladogram of the analysis of Reisz ''et al.'' (2009).

Paleobiology

The short face and dental structures represent an extreme type of development of predaceous habits far off from those in a

ancestor and entirely distinct from the milder dental differentiations of

ophiacodontids Ophiacodontidae is an extinct family of early synapsids from the Carboniferous and Permian. ''Archaeothyris'', and ''Clepsydrops'' were among the earliest ophiacodontids, appearing in the Late Carboniferous. Ophiacodontids are among the most bas ...

. The skull measure of ''Eothyris parkeyi'' is extremely small for a

. ''Eothyris parkeyi'' is represented by a complete skull, but the

postcrania The postcranium ("behind the cranium"; plural: postcrania) or postcranial skeleton in zoology and vertebrate paleontology is the skeleton apart from the skull. The postcranium encompasses the axial skeleton, which includes the entirety of the verte ...

l skeleton is unknown. Therefore, there is the little foundation to diagnose the extended family. Also, the skull of ''Eothyris parkeyi'' is described according to that form. Whether many of the striking primitive features were repeated in other genera is unknown. The order of the portion of bones in the skull roof of ''

'' and ''Eothyris parkeyi'' conforms to a basic pattern in primitive reptiles and is shared with various groups such as millerosaurs and captorhinomorphs, and ophiacodonts. The major distinguishing features of the skull are that it possessed a pair of long, large, fang-like teeth on each side of the upper jaw. The use for these teeth is not known, but ''Eothyris parkeyi'' might have used them to eat small prey. All teeth in its mouth were sharp, with all but the enlarged four fangs being small and short. The skull is short and broad, two features which suggest that ''Eothyris parkeyi'' had a snapping, rapid bite. Dental specializations are related to predaceous habits. The Eothyrids tended to be dominant types and it is interesting that except for little ''Eothyris parkeyi'', which may be considered as a small late survivor. Its teeth suggest that it was a carnivore, but because ''Eothyris parkeyi'' is known only from a skull, it is difficult to say much else about its way of life.

References

External links

www.kheper.net
{{Taxonbar, from=Q136636 Eothyrididae Prehistoric synapsid genera Cisuralian synapsids of North America Artinskian genus first appearances Artinskian genus extinctions Taxa named by Alfred Romer Fossil taxa described in 1937