Body size estimation and evolution in metriorhynchid crocodylomorphs: implications for species diversification and niche partitioning

Authors

  • MARK T. YOUNG,

    Corresponding author
    1. Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ, UK
    2. Department of Palaeontology, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
      Current address: School of Geosciences, Crew Building, The King's Buildings, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK. E-mail: zoologika@gmail.com
    Search for more papers by this author
  • MARK A. BELL,

    1. Department of Geographical and Earth Sciences, Gregory Building, Lilybank Gardens, University of Glasgow, Glasgow, G12 8QQ, UK
    Search for more papers by this author
  • MARCO B. DE ANDRADE,

    1. Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ, UK
    Search for more papers by this author
  • STEPHEN L. BRUSATTE

    1. Division of Paleontology, American Museum of Natural History, Central Park West at 79thStreet, New York, NY 10024, USA
    2. Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA
    Search for more papers by this author

Current address: School of Geosciences, Crew Building, The King's Buildings, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK. E-mail: zoologika@gmail.com

Abstract

Metriorhynchids were a peculiar group of fully marine Mesozoic crocodylomorphs, some of which reached large body size and were probably apex predators. The estimation of their total body length in the past has proven problematic. Rigorous size estimation was provided using five complete metriorhynchid specimens, by means of regression equations derived from basicranial and femoral length against total body length. The use of the Alligator femoral regression equation as a proxy to estimate metriorhynchid total body length led to a slight underestimation, whereas cranial regression equations of extant genera resulted in an overestimation of body length. Therefore, the scaling of crania and femora to total body length of metriorhynchids is noticeably different from that of extant crocodylians, indicating that extant crocodylians are not ideal proxies for size reconstruction of extinct taxa that deviate from their semi-aquatic morphotype. The lack of a correlation between maximum, minimum, or the range of generic body lengths with species richness demonstrates that species diversification is driven by factors other than just variation in body size. Maximum likelihood modelling also found no evidence for directionality in body size evolution. However, niche partitioning in Metriorhynchidae is mediated not only by craniodental differentiation, as shown by previous studies, but also by body size variation.

© 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, 1199–1216.

Ancillary