Gavialis gangeticus, the Indian gharial, is perhaps the most distinctive of living crocodylians. Its long, tubular snout is usually viewed as an adaptation for catching the fish that make up the bulk of its diet. It is also one of the largest living crocodylians, with exceptionally large males thought to exceed five meters in total length. It occurs today only in certain drainages of the Indian subcontinent, and despite intensive efforts at captive breeding, the species remains in danger of extinction.

The extremely long snout seen in Gavialis reflects a condition called "longirostry" that is thought to have arisen multiple times independently among crocodylians and their closest relatives. The Australian freshwater crocodile (Crocodylus johnstoni) is one of three species of Crocodylus with relatively slender snouts, and numerous fossil groups have similarly-shaped skulls. Some of the largest of all crocodyliforms, such as Sarcosuchus and Rhamphosuchus, had snouts like this.

The lineage including Gavialis (Gavialoidea) had a wide geographical distribution for most of the Cenozoic, and the earliest forms appear to have lived in coastal or estuarine settings. The current restriction of Gavialis to freshwater environments may be a fairly recent phenomenon, as the group is thought to have crossed major marine barriers several times, including a crossing of the Atlantic from the Old World to South America sometime during the Tertiary.

Gavialis is at the center of an evolutionary puzzle. Based on its anatomy and the fossil record, Gavialis is distantly related to other living crocodylians and is part of a lineage that diverged in the Late Cretaceous. Some of the features thought to indicate its basal position relative to other crocodylians can be seen in this data set; for example, the postorbital bar (the bony rod behind the eye socket) is robust and bears a prominent tubercle. But molecular data generally suggest a close relationship between Gavialis and Tomistoma schlegelii, the Indonesian false gharial, and a comparatively more recent divergence between them. This data set was obtained as part of an ongoing effort to revisit all of the relevant data, both morphological and molecular, to resolve this problem.

This specimen was collected from Sulmansky Head, Punjab, Indus System, India by J. A. W. Anderson in May, 1966. It was acquired in 1967 by Dr. Wann Langston and donated to the Vertebrate Paleontology Laboratory of the Texas Memorial Museum of Science and History.

The specimen was made available to Scientific Measurement Systems, Inc. for scanning by Dr. Chris Brochu of the University of Iowa and Drs. Langston and Timothy Rowe of the Department of Geological Sciences, The University of Texas at Austin. Funding for scanning was provided by a 1995 NSF Dissertation Improvement Grant to Dr. Brochu. The specimen was scanned along the coronal axis for a total of 971 slices, each slice 0.228 mm thick, with an interslice spacing of 0.228 mm. See the inspeCTor for unreduced CT data.

Literature

Brochu, C. A. 1997. Morphology, fossils, divergence timing, and the phylogenetic relationships of Gavialis. Systematic Biology 46:479-522.

Brochu, C. A. 2001. Congruence between physiology, phylogenetics, and the fossil record on crocodylian historical biogeography, pp. 9-28. In G. Grigg, F. Seebacher, and C. E. Franklin (eds.), Crocodilian Biology and Evolution. Surrey Beatty and Sons, Sydney.

Brochu, C. A. 2003. Phylogenetic approaches toward crocodylian history. Annual Review of Earth and Planetary Sciences 31:357-397.

Brochu, C. A., and L. D. Densmore. 2001. Crocodile phylogenetics: A review of current progress, pp. 3-8. In G. Grigg, F. Seebacher, and C. E. Franklin (eds.), Crocodilian Biology and Evolution. Surrey Beatty and Sons, Sydney.

Buffetaut, E. 1982. Systematique, origine et évolution des Gavialidae Sud-Américains. Geobios, Memoire Special 6:127-40.

Kälin, J. A. 1931. Ueber die Stellung der Gavialiden im System der Crocodilia. Revue Suisse de Zoologie 38:379-88.

Langston, W., and Z. Gasparini. 1997. Crocodilians, Gryposuchus, and the South American gavials, pp. 113-154. In R. F. Kay, R.H. Madden, R. L. Cifelli, and J. J. Flynn (eds.), Vertebrate Paleontology in the Neotropics: The Miocene Fauna of La Venta, Colombia. Smithsonian Institution, Washington, D. C.

Ross, C. A. (ed.) 1989. Crocodiles and Alligators. Facts on File, New York. 240 pp.

Ross, J. P. 1998. Crocodiles - Status Survey and Conservation Action Plan. International Union for the Conservation of Nature, Gland, Switzerland. 96 pp.

White, P. S., and L. D. Densmore. 2001. DNA sequence alignments and data analysis methods: Their effect on the recovery of crocodylian relationships, pp. 29-37. In G. Grigg, F. Seebacher, and C. E. Franklin (eds.), Crocodilian Biology and Evolution. Surrey Beatty and Sons, Sydney.

Links

Gavialis gangeticus on Crocodilians: Natural History & Conservation

Gavialis gangeticus on The Animal Diversity Web (The University of Michigan Museum of Zoology)

None available.