Chelydridae is a family of turtles which has seven extinct and two extant genera. The extant genera are Chelydra, the snapping turtles, and Macrochelys, of which its larger relative the alligator snapping turtle (Macrochelys temminckii) is the only species. Both are endemic to the Western Hemisphere. The extinct genera are Acherontemys, Chelydrops, Chelydropsis, Emarginachelys, Macrocephalochelys, Planiplastron, and Protochelydra.
FOSSIL HISTORY The Chelydridae have a long fossil history, with extinct species reported from North America, all over Asia and Europe, far outside its present range. The earliest described chelydrid is Emarginachelys cretacea, known from well preserved fossils from the Maastrichtian stage of the Late Cretaceous of Montana. Another well preserved fossil chelydrid is the Late Paleocene Protochelydra zangerli from North Dakota. The carapace of Protochelydra is higher domed than that of the recent Chelydra, a trait conjectured to be associated with the coexistence of large, chelonivorous (i.e., turtle-eating) crocodilians. Another genus, Chelydropsis, contains several well known Eurasian chelydrid species that existed from the Oligocene to the Pliocene.