Smallest turtle family

Three different taxonomic families of turtle each contain only a single living species. These families are: Carettochelyidae, containing only the pig-nosed or Fly River turtle Carettochelys insculpta, native to rivers in Australia and New Guinea; Dermatemydidae, containing only the hickatee or Central American river turtle Dermatemys mawii, native to rivers in southern Mexico, Belize and Guatemala; and Dermochelyidae, containing only the leathery or leatherback sea turtle Dermochelys coriacea, native to the Atlantic, Pacific and Indian Oceans, plus a subpopulation confined to the South China Sea.

Although only a single species exists today, several fossil carettochelyid species have been formally described and named. Moreover, at least 19 fossil genera of dermatemydid have been described, collectively spanning the Jurassic to the Cretaceous, and including Compsemys, Trachyaspis and Tsaotanemys. So both of these sole surviving species have been deemed by some researchers to be living fossils.