Emydidae

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Emydidae is the largest and most diverse turtle family.

The family Emydidae includes approximately 95 species in 33 genera. Members are distributed throughout North America, northern South America, Europe, northwestern Africa, and Asia. Emydids are primarily freshwater species, though some species inhabit brackish waters (Malaclemmys terrapin) or are terrestrial (Terrapene, except T. coahuila).

Sizes are variable and range from only 11 cm (Clemmys) to nearly 60 cm (Kachuga) in carapace length. Coloration is also quite variable. The family doesn't have a distinguishing suite of superficial characters. In some species, the carapace is domed, while most have a low-arching carapace. The plastron is hinged and movable in some, while fixed in others. Unanimous skeletal features are few, but include a lack of contact between the squamosal and parietal bones in the skull and the presence of the frontal bone in forming the orbit.

Food habits range from strict carnivory to strict herbivory. The carnivores feed on annelids, crustaceans, and fish. In several species, there is a shift from carnivory in juveniles to herbivory in adults. Small mammals, especially raccoons, are responsible for the destruction of many Emydid nests. Members of all vertebrate classes predate eggs and hatchlings. The wide range of sizes in mature animals leads to an assortment of predators. While snapping turtles are responsible for predation in some smaller species (e.g., Glyptemys muhlenbergii), they cannot eat larger species. Alligators pose a risk to adults of several species, but humans are chiefly responsible for the deaths of adults either through collection for food or the senseless shooting of basking animals.

Knowledge of reproductive behavior ranges from some of the most detailed, long-term study of any taxa (Chrysemys picta in Michigan) to a total lack of information. In many species, dimorphisms include elongated foreclaws or a concave plastron in the male. The longer claws are used in a courtship routine in which the male faces the female and fans her face. The concave plastron allows the male to mount females in species with more domed carapaces (e.g., Terrapene). Reproduction is on an annual cycle, and multiple clutches may be produced in a single season. Clutch size is quite variable, ranging from as few as two to more than 30 eggs.

Emydids are the principle turtles sold through the pet trade. The pond slider (Trachemys scripta) has expanded its range through the careless release of pets into the wild. Many Asian species are threatened by over-collection of animals for sale in markets and into the pet trade. The North America species Glyptemys muhlenbergii is listed as an Appendix II species by CITES and is considered threatened or endangered in many states. This status is the result of habitat degradation and over-collection.

The Emydidae are most closely related to the tortoises (Testudinidae) and are included along with that family in the Testudinoidea. Shared features include a lack of inframarginal scutes, the shape and muscle attachment of the ilium, and the shape of the eighth cervical vertebra (biconvex). Within the Emydidae, two subfamilies are recognized along biogeographic lines. The Emydinae contains New World species (except Emys), while the Batagurinae contains Old World species (except Rhinoclemmys). Osteological characters, such as the construction of the mandible and articulations of the cervical vertebrae also distinguish the two subfamilies. Some authors have felt these differences worthy of family status for the two groups (Emydidae and Bataguridae). In this configuration, the Batagurids are placed in closer association with the Testudinidae in a group called the Testudinoidae, which excludes the Emydidae.

Emydids are well-represented in the fossil record. Gyremys sectabilis and Clemmys backmani are both extinct, North American species that date from the Upper Cretaceous and Paleocene, respectively. These are the two oldest fossil species. Many other extinct species are known from the Eocene of Asia, Europe, and North America.

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.

Contributors

Keith Pecor (author).

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

motile

having the capacity to move from one place to another.