Author's note: these pages were written some years ago. I am not planning to update them. For a more current coverage, see the link to palaeos com Palaeos website (to which many links on these pages point to anyway. More info here


Family Eothyrididae



Eothyris parkeyi
Eothyris parkeyi, skull length about 6 cm

This family of very primitive Pelycosaurs includes only two small pelycosaurs, known only from several skulls anf limb bones from the early Permian of North America. In terms of cranial morphology the eothyridids are the most primitive of any pelycosaur. For this reason they are, in modern cladistic classifications, considered a sort of ancestral group (or rather, the sister group to all other Pelycosaurs). However they appear quite late in the fossil record (they are one of the last groups of Pelycosaurs to appear), which means either they existed for a long time but in upland areas or isolated geographic regions away from any chance of fossilisation, or alternatively they are actually only secondarily primitive. Either hypothesis is valid, and the answer, if it is ever known, must await further fossil discoveries.

The Eothyririds share a few unique characteristics (synapomorphies) with the caseids, indicating they may be ancestral to the latter. The two groups are united in the clade (suborder?) Caseasauria


Palaeos link to palaeos com Technical Diagnosis of this family


List of Genera and species


Eothyris pakeyi Romer
Oedaleops campi Langston



Eothyris, from the Early Permian of Texas (Belle Plains formation, link to palaeos com Artinskian age), is known from a single skull (left), 62mm in length, The teeth are simple conical structures, and there are distinct caniniform teeth.

Oedaleops, from the Early Permian of New Mexico (Abo Cutler Formation, link to palaeos com Sakmarian , is known from three partial skulls and some limb elements.


some printed references some Links and References Web links

web pagesmall photographsBiology 356 - Major Features of Vertebrate Evolution - Permo-Carboniferous Synapsids - by Dr. Robert Reisz, University of Toronto

Palaeos link to palaeos com Eothyrididae - Palaeos - incorporating Toby White's Vertebrate Notes and material from these pages

cladogramSynapsida (cladogram)

monograph Romer, A.S. and Price, L.I. Review of the Pelycosauria, Geological Society of America Special Papers,. no.28,

monographRobert R. Reisz, Pelycosauria, Encylopedia of Paleoherpetology, Part 17A, 1986, Gustav Fischer Verlag, Stuttgart and New York



Pelycosauria index page

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page uploaded 20 July 2000, links updated 16 January 2010

text content by M.Alan Kazlev