Get access

Fins to limbs: what the fossils say1

Authors

  • Michael I. Coates,

    Corresponding author
    1. Department of Organismal Biology and Anatomy, University of Chicago, 1027 E57th Street, Chicago, IL 60637, USA
      *Author for correspondence (email: mcoates@uchicago.edu)
    Search for more papers by this author
  • Jonathan E. Jeffery,

    1. Institute of Evolutionary and Ecological Sciences, Leiden University, Kaiserstraat 63, Postbus 9516, 2300 RA Leiden,
      The Netherlands
    Search for more papers by this author
  • Marcello Ruta

    1. Department of Organismal Biology and Anatomy, University of Chicago, 1027 E57th Street, Chicago, IL 60637, USA
    Search for more papers by this author

  • 1

    From the symposium on Starting from Fins: Parallelism in the Evolution of Limbs and Genitalia.

*Author for correspondence (email: mcoates@uchicago.edu)

Abstract

SUMMARY A broad phylogenetic review of fins, limbs, and girdles throughout the stem and base of the crown group is needed to get a comprehensive idea of transformations unique to the assembly of the tetrapod limb ground plan. In the lower part of the tetrapod stem, character state changes at the pectoral level dominate; comparable pelvic level data are limited. In more crownward taxa, pelvic level changes dominate and repeatedly precede similar changes at pectoral level. Concerted change at both levels appears to be the exception rather than the rule. These patterns of change are explored by using alternative treatments of data in phylogenetic analyses. Results highlight a large data gap in the stem group preceding the first appearance of limbs with digits. It is also noted that the record of morphological diversity among stem tetrapods is somewhat worse than that of basal crown group tetrapods. The pre-limbed evolution of stem tetrapod paired fins is marked by a gradual reduction in axial segment numbers (mesomeres); pectoral fins of the sister group to limbed tetrapods include only three. This reduction in segment number is accompanied by increased regional specialization, and these changes are discussed with reference to the phylogenetic distribution of characteristics of the stylopod, zeugopod, and autopod.

Get access to the full text of this article

Ancillary