They were the earliest known herbivorous amniotes and, along with the Diadectidae, the earliest known herbivorous tetrapods. The head is small in relation to the bulky body, and there is a tall sail along the back, which may have functioned as a thermoregulatory device.
^David M. Mazierski and Robert R. Reisz (2010). "Description of a new specimen of Ianthasaurus hardestiorum (Eupelycosauria: Edaphosauridae) and a re-evaluation of edaphosaurid phylogeny". Journal of Vertebrate Paleontology. 47 (6): 901–912. Bibcode:2010CaJES..47..901M. doi:10.1139/E10-017.