Ophiacodontidae

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. Some ophiacodonts were semi-aquatic, and few were fully aquatic, but some were fully terrestrial like Archaeothyris. Several ophiacodontids resembled small lizards, while others were larger with elongated skulls and massive shoulder girdles, probably to provide muscle attachment to support the weight of the large head. 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.