A new crocodile displaying extreme constriction of the mandible, from the late Oligocene of Riversleigh, Australia

ABSTRACT

A new fossil crocodile, Ultrastenos willisi, is described from a cranium and postcranial materials collected from the Riversleigh World Heritage Area, northwestern Queensland, Australia. The mandible displays pronounced anterior constriction, approaching that seen in the extant gharial, Gavialis gangeticus, and false gharial, Tomistoma schlegelii. As such, U. willisi potentially filled the ecomorphological niche associated with longirostry that has been previously unaccounted for in Riversleigh's Oligo–Miocene crocodile fauna. The pronounced constriction and features of the posterior cranium further distinguish U. willisi from all other known crocodiles, including the only reported Australian Oligo–Miocene longirostral crocodile, Harpacochampsa camfieldensis, from Bullock Creek in the Northern Territory. Ultrastenos willisi is recognized as a new genus and species assigned to subfamily Mekosuchinae on the basis of phylogenetic analysis.http://zoobank.org/urn:lsid:zoobank.org:pub:7C6DC891-BD9C-4F84-AF7D-409A4A8C720D

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Citation for this article: Stein, M., S. J. Hand, and M. Archer. 2016. A new crocodile displaying extreme constriction of the mandible, from the late Oligocene of Riversleigh, Australia. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1179041.

ACKNOWLEDGMENTS

This research has been funded by ARC research grants (LP100200486 and DP130100197) to M. Archer and S. J. Hand. We thank R. Sadlier from the Australian Museum, Sydney, and S. Hocknull of the Queensland Museum, Brisbane, for access to holotype materials for comparison, as well as B. Yates and P. Lund of Queensland X-Ray for the use of CT scanning services that have contributed to this paper. We also thank A. Gillespie for expertise and efforts in preparation of the specimens described here, and S. Salisbury, J. D. Scanlon, and P. M. A. Willis for valuable comments on refining the diagnosis, and acknowledge the efforts of the editor and anonymous reviewers for improving the manuscript.