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chelydridae
The Chelydridae are a family of turtles which has seven extinct and two extant genera. The extant genera are ''Chelydra'', the snapping turtles, and ''Macrochelys''. 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 their 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.〔Danilov G. and J. F. Parham. (2008). A reassessment of some poorly known turtles from the Middle Jurassic of China, with comments on the antiquity of extant turtles. ''Journal of Vertebrate Paleontology'' 28(2):306-318〕 The carapace of ''P. zangerli'' 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.〔Böhme, M. (2008). Ectothermic vertebrates (Teleostei, Allocaudata, Urodela, Anura, Testudines, Choristodera, Crocodylia, Squamata) from the Upper Oligocene of Oberleichtersbach (Northern Bavaria, Germany). ''Courier Forschungsinstitut Senckenberg'' 260:161-183〕
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