Osteohistology of the non-mammaliaform traversodontids Protuberum cabralense and Exaeretodon riograndensis from southern Brazil

Abstract

The current study presents a detailed analysis of the osteohistology of the Triassic non-mammaliaform traversodontid cynodonts Protuberum cabralense and Exaeretodon riograndesis. The data provided here adds new information on the growth patterns of South American traversodontids. A single subadult individual of P. cabralense revealed bone tissues comprising uninterrupted fibrolamellar bone. Patches of slower growing lamellar bone at the periphery of one of the elements suggests a transition to overall slower growth in later ontogeny. The bone tissues of E. riograndensis also exhibit uninterrupted fibrolamellar bone during early ontogeny, but growth became cyclical from mid-ontogeny. The early rapid, sustained growth observed in these taxa is similar to that seen in other traversodontids, and may be related to the achievement of large body size in the derived members of the clade.

Keywords:

• Cynodontia
• Traversodontidae
• growth patterns
• body size

Acknowledgments

We thank L.A. Hartmann from the Universidade Federal do Rio Grande do Sul (UFRGS) for providing constructive suggestions for improving earlier versions of the manuscript. We also thank reviewers Ignacio Cerda and an anonymous reviewer for their suggestions and comments.