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Evolving between land and water: key questions on the emergence and history of the Hippopotamidae (Hippopotamoidea, Cetancodonta, Cetartiodactyla)

Authors

  • Jean-Renaud Boisserie,

    Corresponding author
    1. CNRS, USR 3137 CFEE, P.O. BOX 5554, Addis Ababa, Ethiopia
    2. CNRS & Université de Poitiers, UMR 6046 IPHEP, 40 Avenue du Recteur Pineau, 86022 Poitiers cedex, France
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  • Rebecca E. Fisher,

    1. Department of Basic Medical Sciences, University of Arizona, College of Medicine-Phoenix, Phoenix, AZ 85004, USA
    2. School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
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  • Fabrice Lihoreau,

    1. Université Montpellier II & CNRS, UMR 5554 ISEM, Place Eugène Bataillon, CC64, 34095 Montpellier cedex, France
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  • Eleanor M. Weston

    Corresponding author
    1. Palaeontology Department, Natural History Museum, London, SW7 5BD, UK
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Errata

This article is corrected by:

  1. Errata: Erratum Volume 86, Issue 4, 975, Article first published online: 12 October 2011

J.-R.B. at address 1 (E-mail: jean.renaud.boisserie@univ-poitiers.fr); E.M.W. (Tel: +44 (0) 2079426653; E-mail: eweston29@googlemail.com).

Abstract

The fossil record of the Hippopotamidae can shed light on three major issues in mammalian evolution. First, as the Hippopotamidae are the extant sister group of Cetacea, gaining a better understanding of the origin of the Hippopotamidae and of their Paleogene ancestors will be instrumental in clarifying phylogenetic relationships within Cetartiodactyla. Unfortunately, the data relevant to hippopotamid origins have generally been ignored in phylogenetic analyses of cetartiodactyls. In order to obtain better resolution, future analyses should consider hypotheses of hippopotamid Paleogene relationships. Notably, an emergence of the Hippopotamidae from within anthracotheriids has received growing support, leading to reconciliation between genetic and morphological evidence for the clade Cetancodonta (Hippopotamidae + Cetacea). Secondly, full account needs to be taken of the Hippopotamidae when studying the impact of environmental change on faunal evolution. This group of semi-aquatic large herbivores has a clear and distinct ecological role and a diverse and abundant fossil record, particularly in the African Neogene. We examine three major phases of hippopotamid evolution, namely the sudden appearance of hippopotamines in the late Miocene (the “Hippopotamine Event”), the subsequent rampant endemism in African basins, and the Pleistocene expansion of Hippopotamus. Each may have been influenced by multiple factors, including: late Miocene grass expansion, African hydrographical network disruption, and a unique set of adaptations that allowed Hippopotamus to respond efficiently to early Pleistocene environmental change. Thirdly, the fossil record of the Hippopotamidae documents the independent emergence of adaptive character complexes in relation to semiaquatic habits and in response to insular isolation. The semiaquatic specializations of fossil hippopotamids are particularly useful in interpreting the functional morphology and ecology of other, extinct groups of large semiaquatic herbivores. Hippopotamids can also serve as models to elucidate the evolutionary dynamics of island mammals.

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