The systematics, palaeobiology and palaeoecology of Kambara taraina sp. nov. from the Eocene Rundle Formation, Queensland

2017-01-19T02:32:55Z (GMT) by Buchanan, Lucas Allen
A recently excavated bonebed in the Kerosene Creek Member of the Eocene Rundle Formation has yielded an abundance of crocodilian material. Fossils representing nearly all osteological elements, both cranial and postcranial, have been recovered and described. The described cranial remains are clearly indicative of a new species, Kambara taraina. This new species belongs to the earliest known genus of an endemic Australasian group, the Mekosuchinae, a group which radiated in Australasia during the mid to late Cenozoic and utilized various morphologies to exploit a range of ecologic niches. The early Cenozoic remains poorly known with respect to vertebrates and so this discovery of a new Eocene form is significant, showcasing a large sample of well-preserved material. Cranial material reveals functional divergence among the species of early mekosuchines, reflecting subtle partitioning of feeding strategies. The enlarged insertion area in the caudoventral part of the surangular suggests an increase in adductor mass resulting in a greater bite force. Bite marks in a large chelid plastron, attributable to K. taraina, support this inference. K. taraina is further distinguished from other Kambara species by the possession of a fully interlocking dentition and a decreased number of alveoli. Analysis of the postcranial anatomy suggests an overall generalist crocodilian body plan. However, aspects of the tarsal elements suggest that K. taraina may have been more adept at either terrestrial or shallow water ‘bottom-walking’ locomotion than other generalist aquatic crocodilians. Due to the completeness and size of the sample, description of the Kerosene Creek Member postcranial elements provides a standard reference text for mekosuchine postcranial anatomy, setting a precedent for consideration of postcranial anatomy in a field where little previous work has been done. Functional morphologic analyses of both the cranium and postcranium of K. taraina along with its palaeoenvironmental context suggest that this crocodile fed foraged along the shallow lake margins, operating as an opportunistic ambush predator. Macroscopic and radiographic analyses have revealed pathologic deformities in some elements demonstrating the presence of infection, neoplasm, and fractures that likely resulted from intraspecific fighting in K. taraina. A severely deformed left humerus has been shown to have suffered chronic osteomyelitis, a condition that, although well-documented in the fossil record, has not been previously reported for Australasian fossil crocodiles. A left fibula possesses evidence of neoplastic growth, tentatively attributed to a vascular tumour. The legion is expansile, exhibiting cortical thinning and formed coarse trabeculae in the medullary cavity. This is the first report of neoplasm in a fossil crocodilian from the southern hemisphere, and the first report of a bony vascular tumour in a crocodile. Thorough description of nearly all osteological elements has allowed a comprehensive scoring of K. taraina for cladistic analysis. Preliminary analyses supported the allocation of Mekosuchinae to within Crocodylidae. However, resolution was insufficient to determine taxon relationships within Mekosuchinae and requires a far more thorough analysis. This preliminary analysis demonstrates the inadequacy of current mekosuchine phylogenetics and the necessity for greater attention to be given to the lack of transparency in published cladistic analyses.