Perissodactyla (Rhinocerotidae and Equidae) from Kanapoi

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Abstract

The Kanapoi collection of Rhinocerotidae, first studied by Hooijer and Patterson (1972), now consists of 25 specimens and substantial reinterpretation of their affinities is made here. Kanapoi post-dates the extinction of Brachypotherium and the whole collection belongs to the Dicerotini. It is important because it includes the type-specimen of Diceros praecox, a species that remains poorly known, but looks slightly larger and more primitive than the modern ‘black’ rhino, Diceros bicornis. A second species is probably ancestral to the modern ‘white’ rhino, Ceratotherium simum; it looks identical to the Pleistocene North African Ceratotherium mauritanicum, of which Ceratotherium efficax is probably a synonym. The evolution of the Dicerotini in Africa can be regarded as an increasing divergence in diet and related morphofunctional adaptations in the two lineages. The co-occurrence at Kanapoi of both Diceros and Ceratotherium, with distinct dietary preferences, suggests some habitat heterogeneity, although the low sample size prevents robust paleoecological conclusions.

The Equidae are also rare and consist mostly of isolated teeth. I take the most parsimonious option of tentatively including all of them in a single species, whose identification is left open. Dental features of eastern African Pliocene to Pleistocene hipparions may reflect increasing adaptation to grazing.

Introduction

The Perissodactyla do not make up a high proportion of the Kanapoi large mammals, and no previous publication specifically deals with them, although Hooijer and Patterson (1972) and Hooijer (1975), respectively, studied the Rhinocerotidae and Equidae known at that time, together with fossils from other sites. Since then, renewed research at Kanapoi has significantly increased the faunal sample. The following revision is based upon the study of the material in the National Museums of Kenya (KNM) during several visits between 2002 and 2016, and takes into account all the material of Perissodactyla known to date. It includes no remains of the Chalicotheriidae, although this family was present in Africa from the Early Miocene until the Early Pleistocene with a sparse fossil record (Coombs and Cote, 2010.

Section snippets

Materials and methods

The comparisons of the Equidae are mostly based upon published literature, but the Rhinocerotidae have been extensively compared with the rich collections from other Pliocene and Pleistocene Kenyan sites in the KNM, as well as with the Hadar and Omo material in the National Museum of Ethiopia, Addis Ababa (NME). Late Miocene rhinos were principally examined in the Muséum National d'Histoire Naturelle, Paris (MNHN); Faculté des Sciences, Lyon (FSL); Naturhistorisches Museum, Basel (NHMB);

Systematic paleontology

  • Family Rhinocerotidae Gray, 1821.

  • Description: Hooijer and Patterson (1972) assigned all the Rhinocerotidae material known from Kanapoi at this time to a new species that they called Ceratotherium praecox, assuming that it was ancestral to the modern ‘white’ rhinoceros, Ceratotherium simum. No other study devoted to the Kanapoi rhinos has been published since then, although Harris et al., 2003, Geraads, 2005, Geraads, 2010, Giaourtsakis et al., 2009, and Hernesniemi et al. (2011) discussed them

Paleoecological interpretations

Paleoecological interpretations are hard to draw because of the small size of the collection. For instance, it would not be meaningful to calculate the relative abundance of the browser Diceros vs. the grazer Ceratotherium, but the presence of both genera and the sharp difference in their isotopic values attest to the presence of grassy plains but also of significant arboreal vegetation.

The Equidae are also rare, and the lack of metapodials or phalanges prevents the ecomorphological analyses

Conclusions

In spite of its small size, the Kanapoi rhino sample is important because it corresponds to a poorly documented time period in the evolution of the lineages leading to the modern forms. Still, only the discovery of well preserved, undistorted skulls could settle the disagreements regarding the evolution of the Rhinocerotidae in Africa, because their rather uniform cranial morphology and the scarcity of complete remains too often leads researchers to over emphasize dental features whose

Acknowledgments

I am grateful to C. Ward, F.K. Manthi, and M. Plavcan for having invited me to participate in this special issue about Kanapoi; to all people who allowed me to access modern and fossil collections in their care during the last decades: C. Argot and J. Lesur (MNHN), M. Bertling (GPMM), P. Brewer and A. Currant (NHMUK), G. Daxner-Höck (NHW), B. Engesser (NHMB), G. Senichaw (NME), B. Garevska (NHMMS), E. Heizmann (SMNS), W. Munk (SMNK), M. Muungu (KNM), A. Prieur (FSL); and to V. Eisenmann, L.

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