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By Keith Pecor
These turtles release a malodorous musk when disturbed, hence the common name.
The family Kinosternidae contains 22-23 species within either three or four genera, depending on the source. They are solely New World turtles, inhabiting both North and South America. Kinosternids inhabit slow-moving bodies of water, often with soft bottoms and abundant vegetation.
Members of this family are variable in size, with some species of Kinosternon growing to carapace lengths of less than 15cm and those of Staurotypus growing to nearly 38cm. The shell is oval in shape, and ranges from dusky yellow to black in color. The carapace may or may not possess keels. The plastron is often reduced and cruciform in shape and may be hinged. Musk glands are found on the bridge of the shell. Skeletal features diagnostic of this group include the following: (1) There are ten pairs of peripheral bones. (2) The acetabulum possesses an ilio-ischial notch. (3) The frontal bone does not contact the orbit.
All members of the family are carnivores, feeding on crustaceans, aquatic insects, mollusks, annelids, amphibians, and small fish. Predation occurs most often on eggs and juveniles by vertebrates of all classes. Adults are more seldom predated, although some mammals (e.g., raccoons) and alligators are known predators.
Depending on regional climates, Kinosternids may be active all year or seasonally active. Both aestivation and hibernation are found among the members of the family. Females lay one to several clutches of < 11 eggs per season, with an average clutch size of five eggs. Sex determination is dependant on incubation temperature in all but Staurotypus, which has an XX-XY sex chromosome system.
Kinosternids are most closely related to the Dermatemydidae based on skeletal characters. Within the family, two subfamilies- Staurotypinae (Staurotypus and Claudius) and Kinosterninae (Kinosternon and Sternothorus)- are recognized. Based on chromosomal evidence, the Staurotypinae has been elevated to family status (Staurotypidae) by some workers, although this classification is not widely accepted. Within the Kinosterniniae, there is some controversy about the validity of the genus Sternothorus. Some researchers consider Sternothorus synonymous with Kinosternon and suggest that recognition of Sternothorus as a separate genus renders Kinosternon paraphyletic, while others disagree.
Based on fossil evidence, it is clear that the Kinosternidae evolved in the New World. The oldest fossil is Xenochelys formosa, which dates from the Oligocene of South Dakota. This species shares features with both Staurotypus and the Dermatemydidae. The oldest modern genus is Kinosternon, which dates to the Pliocene.
Ernst, C.H., and Barbour, R.W. 1989. Turtles of the World. Smithsonian Inst. Press, Washington, D.C.
Ernst, C.H., Lovich, J.E., and Barbour, R.W. 1994. Turtles of the United States and Canada. Smithsonian Inst. Press, Washington, D.C.
Pough, F.H., Andrews, R.M., Cadle, J.E., Crump, M.L., Savitzky, A.H., and Wells, K.D. 2000. Herpetology, 2nd ed. Prentice Hall, Upper Saddle River, NJ.
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Keith Pecor 
(author).
