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

Family Eothyrididae

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

Technical Diagnosis of this family

List of Genera and species

some Links and References

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

Eothyrididae - Palaeos - incorporating Toby White's Vertebrate Notes and material from these pages

Synapsida (cladogram)

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

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