First 3D reconstruction and volumetric body mass estimate of the tapinocephalid dinocephalian Tapinocaninus pamelae (Synapsida: Therapsida)

ABSTRACT

Dinocephalians were the earliest large terrestrial tetrapods from Gondwana, making this group crucial in understanding body mass (BM) evolution in basal synapsids, but no detailed weight determinations are available for the clade. Here we present the first BM estimate for a dinocephalian on the basis of the remarkably well preserved and complete skeleton of the basal tapinocephalid Tapinocaninus pamelae from the lowermost Beaufort Group of South Africa. We reconstructed three 3D models of Tapinocaninus using mounted skeletons of the dinocephalians Moschops and Ulemosaurus to reconstruct the missing elements. Applying a density range between 0.9 and 1.15 Kg/1000 cm³ for living tissue to the model we reconstructed an average BM of 892.63 Kg for the taxon. Classic regression formulae, based on humerus and femur circumference, provide higher values of 1694.5 Kg and 2015.8 Kg, with an overestimation of 90% and 126% respectively. The study confirms that volumetric BM estimates are more precise, and are recommended if relatively complete skeletons are available. The ‘intermediate’ posture recognized for Tapinocaninus, more upright with respect to the sprawling condition characterizing sphenacodontid ‘pelycosaurs’, could represent a response to a large BM, which, for the first time in synapsids, reaches weights close to a tonne.

KEYWORDS:

• 3D restoration
• body mass estimate
• photogrammetry
• Guadalupian
• dinocephalian

Acknowledgments

The Editor in Chief Gareth Dyke and the reviewers Pia Viglietti and Mike Day are warmly acknowledged for helpful suggestions that have substantially improved the final manuscript. The authors are indebted to numerous people who assisted with this project: Preparation was undertaken by John Nyaphuli, Petrus Chalatsi, Joel Mohoi, Christian Nyaphuli, Stephen Mashubane, Caiphus Hlatswayo, David Dube, Jimmy Ndimande, Joseph, Sithole, Samuel, Tsabalala and Hemashen Naicker. Fabio Manucci is warmly thanked for assistance in 3D modeling end editing of the specimen. Mark Norell and the late Michael Ivakhnenko are thanked for kind hospitality and access to specimens in the care of the American Museum of Natural History in New York and Palaeontological Institute in Moscow respectively. Funding was provided by the DST/NRF Centre of Excellence for Palaeosciences (CoE in Palaeosciences), NRF African Origins Platform, Palaeontological Scientific Trust (PAST).

Disclosure statement

No potential conflict of interest was reported by the authors.