[2][4][5] Eothyris parkeyi was one of many new species of "pelycosaurs" discovered by Alfred Sherwood Romer as part of a series of paleontological expeditions for the Museum of Comparative Zoology (MCZ).

This skull was collected about one mile west of the former Woodrum ranch-house, in Early Permian sediments of the Artinskian-lower Kungurian Belle Plains Formation, Wichita Group, south of Dundee, Texas, USA.

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.

[6] 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.

Also, because the cheek slants outward to very higher degree than is usual in pelycosaurs, the temporal opening is exposed in dorsal view.

In Eothyris parkeyi, the postorbital bone is probably the largest for any synapsid, with large lateral and dorsal portions to the skull roof.

Typical pterygoid flanges and slender are present back in the skull, below the anterior part of the temporal opening.

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

The maxilla in Eothyris parkeyi is a thin, elongate element with an abrupt dorsal expansion in the area of the primary canine pair.

[9] Diadectomorpha Reptilia Casea broili Casea rutena Cotylorhynchus Eothyris Oedaleops Archaeothyris Ophiacodon Mesenosaurus Mycterosaurus Varanops Archaeovenator The short face and dental structures represent an extreme type of development of predaceous habits far off from those in a pelycosaur ancestor and entirely distinct from the milder dental differentiations of ophiacodontids.

[2][3] 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.

[7] 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 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.