Pelomedusidae

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A fossil Pelomedusid (Stupendemys geographica) is considered the largest freshwater turtle to have ever lived (carapace length = 230 cm).

The family Pelomedusidae contains approximately 26 species within five genera. They are native to South America, Africa, Madagascar, and the Seychelles. Preferred habitats are variable across members of the family and range from temporary ponds to large rivers to swamps.

Pelomedusidae is one of two families of sideneck turtles (the other is Chelidae). A wide range of adult sizes exists, from 12 cm (Pelusios nanus) to 107 cm (Podocnemis expansa) in carapace length. The carapace is usually oval with some shade of olive coloration. Skin coloration is variable. Pelomedusids are diagnosed by the lack of a cervical scute, nasal bone, and splenial bone, as well as the shapes of the cervical vertebrae.

Natural history is poorly known for many Pelomedusids. Many species appear to be carnivorous, feeding on mollusks, crustaceans, aquatic insects, fishes, and amphibians. Others are omnivorous, taking aquatic vegetation and fallen fruits as well. Description of courtship is so scarce as to prevent generalization. Females produce a clutch of as few as six to greater than 100 eggs per clutch and may produce multiple clutches in a single season.

The giant South American river turtle (Podocnemis expansa) has been over-collected for food and oil, and it is now considered endangered.

The Chelids and the Pelomedusids are united by their side-necked retraction of the head and are together known as the Pleurodira. Skeletal features associated with this feature include the articulation of the cervical vertebrae and the morphology of the jaw-closing musculature. Two subfamilies are recognized within the Pelomedusidae: Pelomedusinae (Pelomedusa and Pelusios) and Podocneminae (Podocnemis, Peltocephalus, and Erymnochelys). Differences between members of the subfamilies include the number of digits on the rear feet, the condition of the plastron (hinged or not), and the bones composing the occipital condyle. Some workers consider these differences great enough to warrant family status (Podocnemidae and Pelomedusidae), while others do not.

Fossil Pelomedusids have been found in Upper Cretaceous deposits in both North America and Europe, suggesting a broader distribution at that time and perhaps origin in the Northern Hemisphere. Bothremys is considered the oldest genus.

Ernst, C.H., and Barbour, R.W. 1989. Turtles of the World. 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.