Familia Chelydridae

Gray, 1831b
Snapping turtles

This semi-aquatic New World family ranges from southern Canada to Ecuador. There are only two living genera, Chelydra and Macroclemys. Several fossil species are recognized, although only four species are extant. Extinct genera include Hoplochelys (Paleocene to Eocene, North America), Gafsachelys (Eocene, Europe), Chelydropsis (Oligocene to Miocene, Europe, Asia, and possibly Africa), Acherontemys (Miocene, North America), and Chelydrops (Miocene, North America). Of the living genera, Macroclemys dates from the Miocene, and Chelydra from the Pleistocene of North America.
The temporal region of the large skull is slightly emarginate, and the frontals do not enter the orbit. There is no parietal-squamosal contact. The maxilla is not connected to the quadratojugal, and only rarely is its crushing surface ridged. The quadrate encloses the stapes. There is no secondary palate, and the tip of the upper jaw is hooked. The well-developed, rough carapace is keeled, strongly serrated posteriorly, has 11 peripherals on each side, and does not become fully ossified until late in life. Seven or eight neural bones and one or two suprapygals are present. The carapace is connected to the reduced, cross-shaped, hingeless plastron by a narrow bridge. Inframarginal scutes are present, and a series of supramarginals also occurs in Macroclemys. The abdominal scutes are reduced to the bridge, and do not usually meet at the midline. A T-shaped entoplastron and a median plastral fontanelle are present. The 10th dorsal vertebra lacks ribs, and there is only one biconvex vertebra in the neck. Limbs are well-developed, webbed, and heavily clawed. The saw-toothed tail is as long or longer than the carapace. There are only two living genera; Macroclemys with a single species, and Chelydra with three species.