Eothyrididae is an extinct family of very primitive, insectivorous synapsids. Only three genera are known, Eothyris, Vaughnictis and Oedaleops, all from the early Permian of North America. Their main distinguishing feature is the large caniniform tooth in front of the maxilla. Eothyridids share with the Caseidae a number of specialised features associated with the morphology of the snout and external naris and it is likely that their common ancestor was close in build to Eothyris. The two together form the clade Caseasauria.