Dinosaurs - Kambara implexidens

Introduction

Kambara implexidens, from the early Eocene of Queensland, was a mekosuchine, an ancient group of primitive Gondwanan crocodiles. Species of Kambara are the best known crocodiles from the Paleocene to Oligocene of Australia, as well as the oldest mekosuchines. Two closely related species of Kambara were found at Murgon in southeastern Queensland.

Identification

Mekosuchines are distinguished by the difference in size between the alveoli of the smallest and largest teeth, development of a wedge of the supraoccipital bone on the top of the skull, and reduced (or absent) anterior process on the palatines (from Willis 2006).

Species of Kambara were broad-snouted (platyrostral) mekosuchine with distinctive sculpturing (large sculptured pits between the eyes and the supratemporal fenestrae), and a deep excavation in the skull in front of the nostrils. Kambara implexidens had large eyes (orbits) and unusual, interlocking dentition (its species name comes from the Latin implexus, meaning 'interlocking or entwined'; and dens, meaning 'tooth'). Kambara implexidens differs from Kambara murgonensis mainly in the way the teeth occlude: interlocking in Kambara implexidens and non-interlocking in Kambara murgonensis.

Habitat

The Murgon fossil site during the early Eocene was a shallow swamp or lake. The vegetation and climate of the period have not yet been determined.

Distribution

Kambara implexidens in known only from Murgon, southeastern Queensland. A second species, Kambara murgonensis, was also found at the same site although it may not have lived at the same time. There may be a third species of Kambara, with a longer snout, from Rundle in eastern Queensland.

Feeding and diet

Kambara species were generalist feeders. Kambara implexidens, like other crocodiles, would have fed on small vertebrates such as mammals, turtles, snakes and fish (all of which are known from the Murgon fossil site).

Life history cycle

Crocodiles and alligators (living Crocodylia) are the largest living reptiles, the only truly large reptiles apart from the Komodo Dragon and sea turtles to have survived to the present. Most crocodiles and alligators are restricted to tropical or subtropical regions today. The Cretaceous and Eocene crocodiles of Australia, however, lived in areas that at the time were cooler and more temperate.

Living Crocodylia are all semi-aquatic predators that lay eggs and live close to water. Hatchlings and eggshell fragments of one or both species of Kambara have been found at Murgon, suggesting that Murgon might have been a crocodile nesting ground during the Eocene.

Fossils description

Kambara implexidens is represented by a nearly complete skull (missing the posterior part of the quadrate bones and part of the palate), a second partial skull, a dentary possibly belonging to the holotype skull, a second lower jaw (partial mandible), and other referred cranial/dentary fragments. Most of the material appears to have been of large adult individuals. All material is held by the Queensland Museum, Brisbane.

Evolutionary relationships

Crocodiles are an ancient group of archosaurs, first appearing in the fossil record in the Late Triassic over 200 million years ago. The oldest 'modern' crocodile (Eusuchia) may be Isisfordia duncani, from the middle Cretaceous of Queensland. Mekosuchines are an endemic radiation of primitive Gondwanan crocodiles. Mekosuchine fossils are known from Australia and the southwestern Pacific, with many unusual morphologies. The oldest mekosuchines are the Eocene Kambara species. Mekosuchines became extinct during the Pleistocene in Australia but survived much longer in New Caledonia and Vanuatu (almost to the present).

Relationships between mekosuchines and living crocodiles, all within the Crocodyloidea, are unclear. Mekosuchines may be members of Crocodylidae but alternatively may belong to their own family. 'Mekosuchinae' may in fact not be a natural group; it has been suggested that Harpacochampsa camfieldensis is instead closer to Crocodylidae (Salisbury and Willis 1996). The ancestors of mekosuchines might have reached Australia via South America, although fossil evidence for this is lacking.

References

• Molnar, R. E. 1991. Fossil reptiles in Australia. Pp. 605-701 in Vickers-Rich, P., Monaghan, J. M., Baird, R. F. and Rich, T. H. (eds) Vertebrate Palaeontology of Australasia. Pioneer Design Studio and Monash University Publications Committee, Melbourne.
• Nesbitt, S. The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. Bulletin of the American Museum of Natural History 302, 1-84.
• Salisbury, S. W. and Willis, P. M. A., 1996. A new crocodilian from the Early Eocene of southeastern Queensland and a preliminary investigation of the phylogenetic relationships of crocodyloids. Alcheringa 20, 179-226.
• Salisbury, S., Molnar, R. E., Frey, E. and Willis, P. M. A. 2006. The origin of modern crocodyliforms: new evidence from the Cretaceous of Australia. Proceedings of the Royal Society B: Biological Sciences 273, 2439-2448.
• Willis, P. M. A., Molnar, R. E. and Scanlon, J. D. 1993. An early Eocene crocodilian from Murgon, southeastern Queensland. Kaupia Darmstädter Beiträge zur Naturgeschichte 3, 25-32.
• Willis, P. 2006. Evolution and zoogeography of Australasian crocodilians. Pp. 331-348 in Merrick, J. R., Archer, M., Hickey, G. M. and Lee, M. S. Y. (eds) Evolution and Biogeography of Australasian Vertebrates. Australian Scientific Publishing, Oatlands.

Further reading

• Kelly, L. 2007. Crocodile: Evolution's Greatest Survivor. Allen and Unwin, Sydney.