Trionyx triunguis, the African Softshell Turtle, is a member of Trionychidae within Cryptodira. Trionyx triunguis is considered to be the only extant species of its genus (Ernst and Barbour, 1989; Bonin et al., 2006), although relationships among members and taxonomy within the clade are still poorly understood (e.g., Meylan, 1987; Engstrom et al., 2004). Trionychidae has an extensive fossil record dating from the Cretaceous (Meylan, 1987). Long thought to be the sister-group to Kinosternidae (e.g., Gaffney, 1975; Gaffney and Meylan, 1988), the relationship of this taxon to other turtles has recently been called into question on the basis of both molecular and morphological features (e.g., Shafffer et al., 1997; Joyce, 2007).

The most striking feature of Trionyx triunguis, along with other soft-shelled turtles, is the flattened, skin-covered carapace lacking horny scutes. The skull of these turtles is also very distinctive, however, in being relatively very elongate and narrow (Ernst and Barbour, 1989; Bonin et al., 2006). Trionyx triunguis exhibits a typical skull for the group. Members of Trionychidae, including T. triunguis, exhibit a highly derived cranial arterial circulation that has implications for turtle phylogeny (e.g., Albrecht, 1967; Jamniczky and Russell, 2007). The species is also interesting in having only a single neural, and an unreduced eighth pair of costals that meet in the midline (Ernst and Barbour, 1989). Trionyx triunguis is quite large, reaching up to 112 cm in length and weighing up to 60 kg. It is dark brown to olive colored, and covered with white or yellows spots (Ernst and Barbour, 1989; Bonin et al., 2006).

Trionyx triunguis is found in most of Africa except in southern- and northwestern-most areas. It also occurs in coastal areas of Israel, Lebanon, Syria, and Turkey (Ernst and Barbour, 1989; Bonin et al., 2006). It inhabits slow-moving bodies of fresh water, but is occasionally found in brackish environments in coastal parts of its range. It is an omnivorous ambush hunter, and preys on a variety of fish, amphibians, crustaceans, mollusks, and insects, as well as some fruits and nuts. Females lay 25-100 eggs in one clutch each year (Ernst and Barbour, 1989; Bonin et al., 2006).

This specimen was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Heather Jamniczky of the University of Calgary. Funding was provided by Dr. Jamniczky and by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe. of the Department of Geological Sciences, The University of Texas at Austin.

The specimen was scanned by Matthew Colbert on 2 August 2004 along the coronal axis for a total of 780 slices. Each 1024x1024 pixel slice is 0.145 mm thick, with an interslice spacing of 0.145 mm and a field of reconstruction of 67 mm.

Literature

Albrecht, P.W. 1967. The cranial arteries and cranial arterial foramina of the turtle genera Chrysemys, Sternotherus, and Trionyx: a comparative study with analysis of possible evolutionary implications. Tulane Studies in Zoology 14:81-99.

Bickham, J.W., and J.L. Carr. 1983. Taxonomy and phylogeny of the higher categories of cryptodiran turtles based on a cladistic analysis of chromosomal data. Copeia 1983:918-932.

Bonin, F., Devaux, B., and A. Dupré. 2006. Turtles of the World. Translated by P.C.H. Pritchard. Johns Hopkins University Press, Baltimore MD.

Engstrom, T.N., Shaffer, H.B. and W.P. McCord. 2004. Multiple data sets, high homoplasy, and the phylogeny of softshell turtles (Testudines: Trionychidae). Systematic Biology 53:693-710.

Ernst, C.H., and R.W. Barbour. 1989. Turtles of the World. Smithsonian Institution Press, Washington DC.

Ferri, V. 2002. Turtles and Tortoises. Firefly Books, Willowdale, ON.

Gaffney, E.S. 1972. An illustrated glossary of turtle skull nomenclature. American Museum Novitates 2486:1-33.

Gaffney, E.S. 1975. A phylogeny and classification of higher categories of turtles. Bulletin of the American Museum of Natural History 155:387-436.

Gaffney, E.S. 1979. Comparative cranial morphology of recent and fossil turtles. Bulletin of the American Museum of Natural History 164:1-376.

Gaffney, E.S., and P.A. Meylan. 1988. A phylogeny of turtles. In: Benton, M.J., editor. The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds. Clarendon Press, Oxford, pp. 157-219.

Jamniczky, H.A., and A.P. Russell. 2007. Re-appraisal of patterns of non-marine Cryptodiran turtle carotid circulation: evidence from osteological correlates and soft tissues. Journal of Morphology 268:571-587.

Joyce, W.G. 2007. A phylogeny of Mesozoic turtles. Bulletin of the Peabody Museum of Natural History 48:30-102.

Luiselli, L., Akani, G.C., and E. Politano. 2006. Effects of habitat alteration caused by petrochemical activities and oil spills on the habitat use and interspecific relationships among four species of Afrotropical freshwater turtles. Biodiversity and Conservation 15:3751-3767.

Meylan, P.A. 1987. The phylogenetic relationships of the soft-shelled turtles (family Trionychidae). Bulletin of the American Museum of Natural History 186:1-101.

Meylan, P.A., and E.S. Gaffney. 1989. The skeletal morphology of the Cretaceous cryptodiran turtle, Adocus, and the relationships of the Trionychoidea. American Museum Novitates 2941:1-60.

Orenstein, R. 2001. Turtles, Tortoises, and Terrapins: Survivors in Armor. Firefly Books, Buffalo, NY.

Pritchard, P.C.H. 1979. Encyclopedia of Turtles. TFH Publishing, Neptune FL.

Shaffer, H.B., Meylan, P., and M.L. McKnight. 1997. Tests of turtle phylogeny: molecular, morphological, and paleontological approaches. Systematic Biology 46:235-268.

Links

Trionyx triunguis page from the Mediterranean Association to Save the Sea Turtles (MEDASSET)

Front page image.