New evidence concerning relationships within Artiodactyla, Mammalia: radicular morphology of the dp/4

Abstract

A synapomorphy of Artiodactyla is the three-lophed lower fourth deciduous molar (dp/4). Only a few non-artiodactyl mammals possess three lobes in the dp/4, among which are Macroscelididae and Deinotheriidae (both Afrotheria). Despite the general acceptance of this character for diagnosing the order Artiodactyla, there has been a curious lack of discussion about variability in root morphology of the tooth. This paper establishes the presence of three subgroups of Artiodactyla on the basis of root morphology of the dp/4. The first has a root under the protoconid (buccal side of the middle lophid) coalescent with the one under the paraconid (Cebochoeridae and some Choeropotamidae), the second group has a buccal root beneath the protoconid, well separated from the paraconid root (selenodont artiodactyls (ruminants and anthracotheres) and some Suiformes (suids, schizoporcids, sanitheres)), and the third group has no root associated with the protoconid (other Suiformes : Hippopotamidae, Doliochoeridae and Siderochoeridae, and non-suiform Camelidae and Diacodexidae (Diacodexis)). Further research is needed on the families Choeropotamidae and Anthracotheriidae, both of which appear to contain taxa with two kinds of root systems in the dp/4. The evidence of the radicular system of the dp/4 weakens the hypothesis that Anthracotheriidae represent the sister taxon of Hippopotamidae.

Keywords:

• Artiodactyla
• deciduous teeth
• Anthracotheriidae
• Hippopotamidae
• Doliochoeridae
• Siderochoeridae
• Choeropotamidae
• phylogeny

Acknowledgements

I appreciate the opportunity that the editors have provided for me to contribute to the Percy Butler Memorial Volume. During the late 1970’s and early 1980’s Percy studied the Early Miocene bats, macroscelidids and “insectivores” that I had collected in Western Kenya at Koru, Chamtwara, Legetet and other sites as part of the Western Kenya Project. It was always a pleasure to work with him, because it was clear that he got a lot of satisfaction from studying the fossils. He enjoyed contributing to the debate about dental nomenclature, function, taxonomy, systematics and phylogeny. I learned a great deal from him, especially how important it is to be part of a large and active community of scientists who not only debate ideas but also retain academic and intellectual independence within it. His approach and enthusiasm evidently kept his mind young and inquisitive, with the result that few scientists of the past century published over such a long time span as he did. I thank my colleagues at the Muséum National d’Histoire Naturelle and Sorbonne Universités for help and discussions, and the curators of fossil and extant collections in the various institutes where I was enabled to examine crucial material: Didier Berthet (Centre de Conservation et Etudes des Collections, Lyon), Medhat Said Abdel Ghany (Cairo Geological Museum), Emmanuel Robert (Faculty of Science, Lyon), Helke Mocke (Geological Survey of Namibia, Windhoek), Christine Argot (Muséum National d’Histoire Naturelle, Paris), Pip Brewer, Roula Pappa and Jerry Hooker (Natural History Museum, London), Michael Rummell (Nature Museum, Augsburg), Reinhard Ziegler (Staatliches Museum für Naturkunde, Stuttgart), Gertrud Rössner (BSPG München), Ursula Göhlich (Naturhistorisches Museum, Wien), and Sarah Musalizi (Uganda Museum, Kampala). Thanks are also proffered to Jessica Theodor, Jerry Hooker and an anonymous reviewer for suggestions that improved the paper. I am also anxious to thank Gareth Dyke for his interest in the project.