Order Testudines
Suborder Pleurodira

Family Podocnemididae

Madagascan Big-headed Turtles and American Sideneck River Turtles

Podocnemis unifilis © Wayne Van Devender

Appearance: Podocnemidids have broad domed, streamlined shells adapted to swimming.

The jaw closure mechanism articulates on a pterygoid trochlear surface that lacks a synovial capsule but contains a fluid-filled saclike duct from the buccal cavity. Both epipterygoid and parietal-squamosal contacts are missing in the skull; the internal carotid canal lies in the prootic, and the postorbital has strong contact to the squamosal. The facial nerve has a hyomandibular branch. The plastron has a mesoplastron and well-developed plastral buttresses that articulate with the costals on each side of the carapace; the carapace has 11 pairs of sutured peripherals around its margin and a nuchal without costiform processes. The neck withdraws horizontally, and this mechanism is reflected in an anteriorly oriented articular surface of the first thoracic vertebra; other vertebral traits are the inclusion of the 10th thoracic vertebra in the sacral complex and procoelous caudal vertebrae. The pelvic girdle is firmly fused to the plastron, and the ilium lacks a thelial process. The karyotype is 2N = 28 (after Zug et al. 2001).

Size: 20 cm (Podocnemis erythrocephala) to 80 cm (Podocnemis expansa) carapace length (adults).

Distribution: Madagascar, Northern South America.

Habitat: Rivers and other moderate currents.

Food: Mostly plants but occasionally small, slow-moving animal prey and carrion is also eaten.

Reproduction: Nesting takes place on sandy river banks. P. expansa nests in larger groups and each female lays s60 to 120 eggs (smaller species produce smaller clutches). Incubation periods in P. expansa eggs is 42 to 47 days, whereas those of P. vogli require 127 to 149 days.

Relationships: The Podocnemididae have been considered as subfamily (Podocnemidinae) of the family Pelomedusidae, and some recent authors maintain this classification (such as Georges et al. 1998).

• Erymnochelys
• Peltocephalus
• Podocnemis

Click on genus to get a list of species. Use the Search form for more sophisticated searches (HELP on Search).

Phylogeny

Phylogenetic relationships of the pelomedusoid genera. A consensus of nodes in the pleurodiran phylogeny to receive 70% or greater bootstrap support in one or more of the maximum parsimony (weighted and unweighted) or maximum likelihood sub-analyses. Numbers shown in parentheses give the analyses that provide the support: 2, all taxa using 12S rRNA and 16S rRNA only; 3, Australasian chelids using 12S rRNA, 16S rRNA and CO1. Numbers bearing an asterisk indicate that bootstrap support was equal to or greater than 70% only in some of the three sub-analyses (after Georges et al. 1998).

References:

Ernst,C.H. & Barbour,R.W. (1989)
Turtles of the World
Smithsonian Institution Press, Washington D.C. - London

Gaffney, E. S.;Meylan, P. A.;Wyss, A. R. (1991)
A computer assisted analysis of the relationships of the higher categories of turtles.
Cladistics 7: 313-335

GEORGES A, BIRRELL J, SAINT K. M., McCORD W & S. C. DONNELLAN (1998)
A phylogeny for side-necked turtles (Chelonia: Pleurodira) based on mitochondrial and nuclear gene sequence variation
Biological Journal of the Linnean Society 67: 213&endash;246.

Shaffer, H.B.; Meylan, P. & McKnight, M.L. (1997)
Tests of turtle phylogeny: molecular, morphological, and paleontological approaches.
Syst. Biol. 46: 235-268

Wermuth,H. & Mertens,R. (1977)
Liste der rezenten Amphibien und Reptilien:
Testudines, Crocodylia, Rhynchocephalia
Das Tierreich, Lfg. 100, XXVII + 174 pp.
Walter de Gruyter, Berlin-New York

Williams, E.E. (1954)
A key and description of the living species of the genus Podocnemis (sensu Boulenger) (Testudines, Pelomedusidae).
Bulletin of the Museum of Comparative Zoology, Cambridge 111(8): 279-295.

Zug,G.R.; Vitt, L.J. & Caldwell, J.P. (2001)
Herpetology, 2nd ed.
Academic Press San Diego, London, [...]XIV + 630 pp.

BACK to the THE REPTILE DATABASE Top Page