Caseidae is an extinct family of synapsids from the Carboniferous and Permian period. It was a widespread group of very primitive herbivorous, possibly aquatic synapsids, which appeared during the late Carboniferous and persisted over 30 million years until the late middle Permian. Estemmenosuchids replaced the caseids as the dominant megaherbivores of the Wordian age (middle of the Middle Permian).