Edaphosaurus is an extinct genus of herbivorous synapsid reptile that lived during the Late Carboniferous and Early Permian periods, around 307 to 280 million years ago. Synapsids were a group of reptiles that eventually gave rise to mammals.

Edaphosaurus was a relatively large animal, growing up to 3 meters in length. It had a distinctive sail on its back, which was made up of elongated vertebral spines. The sail likely served a variety of purposes, including thermoregulation, display, or even as a form of protection.

Edaphosaurus was herbivorous, and its teeth were adapted for grinding tough plant material. It likely lived in swampy or forested environments, feeding on a variety of plants and possibly using its sail as a means of camouflage.

Fossils of Edaphosaurus have been found in various locations around the world, including North America and Europe. Its discovery and study have helped researchers better understand the diversity of reptiles that lived during the Paleozoic era and the evolution of synapsids towards mammals.