A new specimen of Orthosuchus stormbergi (Nash 1968) and a review of the distribution of Southern African Lower Jurassic crocodylomorphs

Abstract

Orthosuchus stormbergi (Nash 1968) is a rare member of the Lower Jurassic crocodylomorph fauna of Southern Africa. Here we report on a new specimen, consisting of a nearly complete dentary bone, and a previously collected specimen that can confidently be referred to this taxon. The dentary presents several features of utility for generic-level identification of Southern African crocodylomorphs, and furthermore the anatomy of this specimen allows for a modest revision of the generic diagnosis. Furthermore, it provides an opportunity to reassess differences in dentary morphology between basal South African crocodylomorphs with the intention of refining taxonomic identification. Finally, we review the stratigraphic provenance of all of Southern Africa’s known crocodylomorph taxa, and show that most are confined to the uppermost Elliot Formation. Protosuchus, Litargosuchus, Notochampsa, and Orthosuchus have first appearance data in uppermost Elliot Formation. Only Notochampsa has a confirmed last appearance datum in the Lower Clarens Formation. These findings have implications with regards to the true position of the Triassic-Jurassic Boundary, and paleoenvironmental pressures acting on the Crocodylomorpha over the boundary of the Upper Elliot and Lower Clarens Formations.

Keywords:

• Stormberg
• Elliot Formation
• dentary
• Triassic-Jurassic boundary

Acknowledgments

We would like to thank the owners of Mosamane Guest Farm for allowing access to their premises and assistance in the collection of this specimen. We would like to thank Adam Yates for collecting the specimen. Furthermore, we would like to thank the Wits Micro-CT Facility, Stellenbosch CT Facility, Kudakwashe Jakata and Anton du Plessis for CT scanning the specimens. This research was funded by grants from the DST-NRF Centre of Excellence in Palaeosciences, the Palaeontological Scientific Trust, and a Royal Society Grant to J. N. Choiniere and P. M. Barrett.