Kambara implexidens, from the early Eocene of Queensland, was a mekosuchine, an ancient group of primitive Gondwanan crocodiles. Species of Kambara are the most well 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.
Mekosuchines are distinguished by a large size differential between the alveoli of the largest to smallest teeth, development of a wedge of the supraoccipital bone on the top of the skull, and reduction or loss of the anterior process of the palatines (from Willis 2006).
Species of Kambara were broad-snouted (platyrostral) mekosuchines with this disparity in size between teeth. Kambara also had 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 an unusual, interlocking dentition (its species name comes from the Latin implexus, meaning 'interlocking or entwined'; and dens, meaning 'tooth'). Kambara implexidens differs from the similar Kambara murgonensis mainly in the way the teeth occlude: interlocking in Kambara implexidens and non-interlocking (an 'overbite') in Kambara murgonensis.
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.
Kambara implexidens in known only from Murgon, southeastern Queensland. A second species of Kambara, Kambara murgonensis, was also found at Murgon although these two species 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 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.
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.
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, and there were many unusual types. 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.
Kambara murgonensis and Kambara implexidens have both been found in what appears to be the same stratigraphic horizon. This suggests that they co-existed together (i.e., were sympatric). This would be unusual in crocodiles, since they are normally quite territorial. However, it is also possible that these species might be from different time periods and that the Murgon clays are not well sorted stratigraphically. The depositional environment suggests that the waterbody might have been ephemeral at times, and these two crocodile species may have been forced together as the pond or billabong dried up.
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