Complex multicusped postcanine teeth from the Lower Triassic of South Africa

ABSTRACT

Two incisors and five postcanine teeth of complex crown morphology were found in the lower levels of the Burgersdorp Formation of the Beaufort Group, corresponding to the basal Subzone A of the Cynognathus Assemblage Zone (late Olenekian). All the teeth bear a single root and the postcanines show two rows of mesiodistally aligned cusps and a central basin or groove. Among the postcanines, two general patterns of crown morphology are recognized on the basis of relative length of the cusp rows, number of cusps per row, and width of the central area. Phylogenetic affinities of the described specimens remain unclear, and thus they are regarded as Eucynodontia incertae sedis. However, comparisons with non-mammalian cynodonts with labiolingually expanded postcanines show that they are most similar to those of Aleodon, Candelariodon, and some haramiyids. Many cynodont taxa such as Aleodon, Candelariodon, Cromptodon, haramiyids, and tritylodontids, which are probably not closely related to each other, have labiolingually expanded postcanines with cusps arranged mesiodistally in rows and a central basin; thus pointing to the homoplastic nature of dental morphologies in the cynodont lineage. The teeth presented here are the oldest record of therapsid teeth with crowns having parallel rows of cusps, representing a temporal extension of approximately 10 million years for this crown pattern.

ACKNOWLEDGMENTS

This research was conducted with financial support from the National Research Foundation of South Africa. We are grateful to S. Chapman for grating access to the collections at the Natural History Museum, London, and to M. Raath and B. Zipfel who allowed the study of the specimens from the Bernard Price Institute for Palaeontological Research, University of the Witwatersrand. We thank P. Butler, W. Clemens, Z. Kielan-Jaworowska, and D. Sigogneau-Russell who provided information on haramiyids and comments on the material studied. William Clemens, G. Rougier, and C. Cataldo are thanked for reading and commenting on different versions of the manuscript. The editor and reviewers (Dr. Butler, Dr. Kammerer, and Dr. Modesto) are thanked for their valuable comments and help. Scanning electron microscopy units from the University of Witwatersrand and the University of Johannesburg provided access to an SEM. We acknowledge the support of the Bi-national Cooperation project between South Africa (DST to Bruce Rubidge) and Argentina (MYNCIT to Claudia Marsicano) for travel funds. This is L.C.G.'s R-57 contribution to the IDEAN. F.A.'s research was funded by the National Research Foundation of South Africa.

Handling editor: Sean Modesto