The petrosal bone of extinct Suoidea (Mammalia, Artiodactyla)

Abstract

The morphology of the petrosal is often employed in mammalian systematics, yet this bone has not been described in detail for a comparative sample of extinct members of Suoidea (the clade encompassing pigs, peccaries and their extinct relatives), a total clade that represents one of the major divisions within Artiodactyla. Here, the petrosal osteology of fossil Suoidea ranging from their early representatives (Late Eocene) up to Late Miocene is described. A sample of petrosal specimens documenting eight genera from the four suoid families (Suidae, Tayassuidae, Sanitheriidae and Palaeochoeridae) has been collected from in situ mechanical preparation, CT-based reconstruction or identification of isolated petrosals. The diagnostic significance of petrosal characters for suoid systematics is assessed by the inclusion of the new petrosals data in a phylogenetic analysis. As in other mammal groups, petrosal characters are shown to be of primary phylogenetic interest. The monophyly of the included families and subfamilies shown by craniodental and postcranial characters is supported by petrosal characters, and the problematic New World suoid Perchoerus is interpreted as the first offshoot of the Suoidea clade. This work allows definition of Suoidea on the basis of petrosal morphological characters and reveals the shaping over time of the peculiar petrosal morphology observed in extant suoids, notably the drastic reduction of the mastoid of this ‘amastoidean’ group, convergently present in hippos.

Keywords:

• middle ear
• cranial morphology
• CT-scan
• phylogeny
• Suidae
• Tayassuidae

Acknowledgements

I am particularly grateful to Maureen O’Leary for fruitful discussions on petrosal morphology and contributions to an early version of the manuscript; and to A.-L. Charruault for the preparation of the material from Maragheh and her substantial help on the isolated petrosals from the UM2 collections. I thank R. Lebrun, R. Rudorf and J. Thostenson for their help and access to the CT-scan facility in Montpellier and at the AMNH (high resolution CT-scanner facility of the AMNH funded by NSF grant MR1-R2 0959384), respectively, as well as P.-O. Antoine and M. Steiper for constructive comments on an early version of the manuscript. I am grateful to C. Argot, C. Sagne and Y. Laurent for access to the collections in their charge at the MNHN, Paris, and the MHNT, Toulouse. Many thanks to M. Pickford for kindly providing access to the material from Namibia. This work was conducted with the support of the ANR [ERC programme Palasiafrica (ANR-08-JCJC-0017-01)] and is ISE-M publication 2011-189.