Enamel microstructure defines a major Paleogene hippopotamoid clade: the Merycopotamini (Cetartiodactyla, Hippopotamoidea)

Abstract

We present new material of the selenodont anthracothere Hemimeryx blanfordi from the Oligocene deposits of the Bugti Hills (Balochistan, Pakistan), collected between 1999 and 2002. This is the first undisputed Oligocene occurrence of the species, previously known from the early Miocene of Pakistan. Investigation of the molar enamel microstructure reveals a surprising mono-zonal Schmelzmuster, already detected in some middle to Late miocene selenedont anthracotheres. We include this observation combined with a morphological revision of H. blanfordi and a cladistic assessment of the dental evidence, to propose a new phylogenetic hypothesis regarding Hemimeryx and its close relatives. We confirm the clade including advanced bothriodontines, which we erect to a tribe rank and name Merycopotamini. The South Asian origin of Merycopotamini is consistent with hypothesized subsequent dispersal events of Merycopotamini from Asia to Africa.

Keywords:

• Anthracotheriidae
• Bugti Hills
• Pakistan
• Oligocene
• phylogeny
• cladistic analysis

Acknowledgements

The authors are grateful to H. E. I. Akhund and K. Majidullah (Karachi) and to G. Roohi (Pakistan Museum of Natural History, Islamabad) for their support and to participants to the MPFB 1999 field campaign in Balochistan. We would like to thank the people who gave us access to their collection in Harvard University (J. Barry), in Natural History Museum of London (P. Brewer), in Museum d’Histoire Naturelle (C. Sagne), and in National Museums of Kenya (F.K. Manthi). We are grateful to C. Cazevieille, in charge of COMET (plateau de microscopie électronique), MRI facilities, INM Montpellier. We also acknowledge S. Jiquel (University of Montpellier) and A.-L. Charruault (CNRS) for technical support. This is contribution #ISEM 2016-266 of the Institut des Sciences de l’Évolution de Montpellier (UMR5554-CNRS).