''Eothyris'' is a

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 extinct

synapsid Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...

in the family Eothyrididae 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 251.9 Mya. It is the last ...

. It was a carnivorous insectivorous animal, closely related to '' Oedaleops''. 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 or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of th ...

-lower.

Discovery and Historical Information

''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'' had been used, and pelycosaur was considered an order, but this is ...

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 A museum ( ; plural museums or, rarely, musea) is a building or institution that cares for and displays a collection of artifacts and other objects of artistic, cultural, historical, or scientific importance. Many public museums make thes ...

(MCZ). The genoholotype (

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

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 Ar ...

Belle Plains Formation, Wichita Group, south of Dundee, Texas, USA. in rocks which are about 275 million years old. The generic name is

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 ...

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

s. The specific name refers to J.R. Parkey, of Mankins, Texas, 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'', the first ...

in 1940.

Description

''Eothyris'' is known only from its complete

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 ...

, 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-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, t ...

on each side of the

upper jaw 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 ...

. The main differences between ''Eothyris'' and '' Oedaleops'' 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 overlies the occipital lobes of the cereb ...

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 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. T ...

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 ancestral co ...

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 mammal has ...

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

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

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 jaw is any opposable articulated structure 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 and serv ...

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

surangular The suprangular or surangular 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, splenial and articular. It is often a mu ...

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

naris A nostril (or naris , plural ''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 turbi ...

. 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 family Eothyrididae. It is one of two genera in the family, the other being '' Oedaleops''. The family is grouped in Caseasauria, 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. The skull measure of ''Eothyris parkeyi'' is extremely small for a

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

postcrania Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated sk ...

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 '' Oedaleops'' 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 Caseasaurs 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