Animal Diversity Web

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).