Humeral morphology of the early Eocene mekosuchine crocodylian Kambara from the Tingamarra Local Fauna southeastern Queensland, Australia

Abstract

Stein, M., Salisbury, S.W., Hand, S.J., Archer, M. & Godthelp, H., December 2012. Humeral morphology of the early Eocene mekosuchine crocodylian Kambara from the Tingamarra Local Fauna southeastern Queensland, Australia. Alcheringa 36, 473–486. ISSN 0311-5518.

Mekosuchines (Crocodylia; Crocodyloidea) were a clade of crocodylians endemic to Australia and the South Pacific that underwent radiation during the Cenozoic. Numerous questions about mekosuchine palaeoecology remain unanswered. Tantalizing among these is the possibility that some mekosuchines were primarily terrestrial. To date, studies of mekosuchines have focused mainly on the cranium. However, the morphological signal for terrestriality is more likely to be found in the postcranial skeleton. Here, we present a comparative morphological study of fossil humeri referable to Kambara from the early Eocene Tingamara Local Fauna, Murgon, southeastern Queensland. The humeri of Kambara do not show the torsion between the proximal and distal extremity seen in extant crocodylians, illustrated here with Crocodylus porosus and Crocodylus johnstoni. They also differ in the structure of the medial and lateral condyles of the distal extremity. When the effects of these features on musculature and articulation are considered, it appears that the forelimb of Kambara could have facilitated a greater force at the glenohumeral joint and possibly swung the lower forelimb faster with a greater arc of motion than Australia's extant crocodylians. This is conducive to an improved capacity for both terrestrial locomotion and paraxial swimming. Although the former case suggests that Kambara may not have been as closely tied to water as extant crocodylians, it is unusual given the typically broad rostra of the cranium. Among crocodylians this is a common characteristic of semi-aquatic ambush predators. This study shows the utility of the postcranial skeleton in interpreting crocodylian palaeoecology.

Michael Stein [[email protected]] (corresponding author), Suzanne J. Hand [[email protected]], Michael Archer [[email protected]] and Henk Godthelp [[email protected]], School of Earth and Environmental Science, University of New South Wales, Sydney, NSW, 2052, Australia; and Steven W. Salisbury [[email protected]], School of Biological Sciences, University of Queensland, Brisbane, Qld, 4072, Australia. Received 13.1.2012, revised 24.2.2012, accepted 28.2.2012.

Key words:

• Mekosuchinae
• Kambara
• morphology
• postcranium
• humeral torsion
• palaeoecology
• terrestriality

Acknowledgements

This research has been funded by Australian Research Council research grants (LP0453664, LP0989969 and DP0453362) grants to M. Archer and S.J. Hand. We would like to thank R. Sadlier for collection and access to the materials at the Australian Museum. We also thank A. Gillespie for her technical advice relating to the materials kept at the University of New South Wales. Finally, we thank S. McLoughlin and two anonymous reviewers for their commentary and advice, which have greatly improved the article.