Ophiacodontidae is an extinct family of early synapsids from the Carboniferous and Permian. Archaeothyris, and Clepsydrops were among the earliest ophiacodontids, appearing in the Late Carboniferous. Ophiacodontids are among the most basal synapsids, an offshoot of the lineage which includes therapsids and their descendants, the mammals. The group became extinct by the Middle Permian, replaced by anomodonts, theriodonts, and the diapsid reptiles.