Genus Chelydra

Schweigger, 1814
Snapping turtles

Turtles in the genus Chelydra have massive, rounded, strongly posteriorly serrated carapaces with three low keels composed of knobs located well behind the centers of the scutes, large heads, and long tails. With age these keels become less conspicuous and old individuals often have smooth shells. Vertebral scutes are broader than long, and the 5th is laterally expanded. The cervical scute is short and broad. Beneath the vertebrals is a series of eight quadrilateral or hexagonal neurals, and two suprapygals. Costals are laterally reduced, leaving fontanelles between them and the 11 peripheral bones on each side. Submarginal scutes are normally absent, but there are 24 marginals. The bridge is small and the plastron reduced, giving a cruciform appearance. The entoplastron is T-shaped, and a medial fontanelle is present. The abdominal scutes are confined to the bridge, do not usually meet at the midline, and are separated from the marginal scutes by two or three inframarginals. The plastral formula of all species is: an >< hum > pect > fem > gul > abd. The head is large with a blunt to acute, slightly to protruding snout, a slightly hooked upper jaw, and large dorsolateral orbits (the eyes can readily be seen from above). There is little emargination of the temporal region of the skull; the squamosal bone contacts the long postorbital but not the parietal. The maxilla does not touch the quadratojugal; the quadrate completely encloses the stapes. The prootic bone forms a portion of the roof of the internal carotid canal. No secondary palate is present, and there is a strongly developed medial ridge in the ventral surface of the vomer. There are no dermal projections on the side of the head, but there are chin barbels and dermal tubercles on the neck. Both temporal region and back of the head are covered with large, flat, overlapping scales. The powerful jaws are often pigmented with dark bars; no medial ridge occurs on the premaxilla or maxilla. The tongue lacks a wormlike process. Skin is brown, olive, gray or black with some yellow, white or pinkish flecks. Lateral rows of tail tubercles are much less conspicuous than the median row, so that there appears to be only one sawtoothed row; the lower surface of the tail is covered with flat scales. Toes are webbed, and each foot has strong claws.
Males grow larger and have longer preanal tail lengths commonly over 120% of length of posterior plastral lobe; that of females is usually under 110%. The male vent is usually posterior to the carapace rim.

Phillips et al. (1996) studied the mitochondrial DNA of Chelydra from throughout the range, and demonstrated that enough differences occur to recognize three species: C. serpentina (Linnaeus, 1758); C. rossignonii (Bocourt, 1868), and C. acutirostris Peters, 1862. Formerly, the latter two were considered subspecies of the C. serpentina (Medem, 1977; Gibbons et al., 1988; Ernst et al., 1994).

Species identification
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