†family Protostegidae Cope 1873 (sea turtle)
Parent taxon: Chelonioidea according to B. P. Kear 2006
Sister taxa: Dermochelyoidae, Desmatochelyidae, Nichollsemys, Oxemys, Pancheloniidae, Pandermochelys, Plesiochelyidae, Thalassemyidae
Subtaxa: Bouliachelys, Chelospharginae, Cratochelone, Pneumatoarthrus, Protostega, Protosteginae, Terlinguachelys
Ecology: aquatic omnivore