New remains of Chambius kasserinensis from the Eocene of Tunisia and evaluation of proposed affinities for Macroscelidea (Mammalia, Afrotheria)

Abstract

Chambius kasserinensis from the late Early or early Middle Eocene Chambi locality, central Tunisia, is undoubtedly the oldest known macroscelidid and possibly the basalmost representative of the order Macroscelidea. Hence, since its discovery in 1986, Chambius has played a key role in analyses focusing on afrotherian and eutherian phylogeny; for instance, as early as 1995, Butler’s review of fossil macroscelideans highlighted the central position of Chambius in the origin of the order. Despite this, Chambius remained poorly known until recently. Here based on new mandibular fragments, well-preserved upper molars and CT scan analysis of the holotype maxilla, Chambius is revised. Its dentition is first described in detail, providing a precise characterization of the genus. Chambius is notably defined by a submolariform P₄ with a three-cusped talonid, a reduced talonid on M₂, and a prominent metaconule on M¹⁻². Interestingly, the two transverse lophs of the upper molars are basically formed by preconulecristae, evoking the recently defined peculiar bilophodonty of paenungulates. Comparisons with other Paleogene and modern macroscelidids, European Louisinidae, and North American Apheliscidae are also made, allowing the various hypotheses about the origin and early evolution of macroscelidids to be reviewed.

Keywords:

• Macroscelidea
• Herodotiinae
• Paleogene
• Africa
• Chambius

Acknowledgments

I wish to thank Gregg Gunnell (Duke University Lemur Center, Durham), David Polly (Indiana University, Bloomington) and Jerry Hooker (Natural History Museum, London) who invited me to contribute to this volume. I am very grateful to my colleagues Laurent Marivaux and Monique Vianey-Liaud (Université de Montpellier), El Mabrouk Essid, Wissem Marzougui and Hayet Khayati Ammar (Office National des Mines, Tunis) for their help during fieldtrips in 2008, 2009, and 2012. I thank David Carrasco and Marc Gindt (Université de Montpellier) for their preliminary studies, Anne-Lise Charruault (Université de Montpellier) for her efficient technical assistance (acid etching of the fossiliferous limestone), and Didier Cot (IEM, Montpellier) for SEM images. I thank R. Lebrun (Université de Montpellier) for his help and advice during micro-CT scan acquisitions and treatments; many thanks to the Montpellier RIO Imaging (MRI) and the LabEx CeMEB for the access to the μCT-scanning station Skyscan 1076 (ISEM, Montpellier). Special thanks are also due to Thierry Smith (Royal Belgian Institute of Natural Sciences, Brussels) and Philip Gingerich (University of Michigan, Ann Arbor) for giving access to comparative material. I thank Robert Asher (University Museum of Zoology, Cambridge), Julien Benoit (University of the Witwatersrand, Johannesburg), Nick Crumpton (University College London), Jacques Cuisin (Museum National d’Histoire Naturelle, Paris), Emmanuel Gilissen and Wim Wendelen (Royal Museum for Central Africa, Tervuren), and Frieder Mayer (Museum für Naturkunde, Berlin) for granting access to collections or CT scan of living macroscelids. I finally thank Erik Seiffert (University of Southern California) and Jerry Hooker (Natural History Museum, London) for their valuable comments and suggestions to improve the quality of this paper.