Homology Among Divergent Paleozoic Tetrapod Clades

  1. Gregov K. Bock Organizer and
  2. Gail Cardew
  1. Robert L. Carroll

Published Online: 28 SEP 2007

DOI: 10.1002/9780470515655.ch4

Novartis Foundation Symposium 222 - Homology

Novartis Foundation Symposium 222 - Homology

How to Cite

Carroll, R. L. (2007) Homology Among Divergent Paleozoic Tetrapod Clades, in Novartis Foundation Symposium 222 - Homology (eds G. K. Bock and G. Cardew), John Wiley & Sons, Ltd., Chichester, UK. doi: 10.1002/9780470515655.ch4

Author Information

  1. Redpath Museum, McGill University, 859 Sherbrooke St. West, Montreal, Canada H3A 2K6

Publication History

  1. Published Online: 28 SEP 2007

ISBN Information

Print ISBN: 9780471984931

Online ISBN: 9780470515655

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Keywords:

  • homology;
  • paleozoic tetrapod clades;
  • phylogenetic origin;
  • paleozoic amphibians;
  • tetrapod miniaturization

Summary

A stringent definition of homology is necessary to establish phylogenetic relationships among Paleozoic amphibians. Many derived characters exhibited by divergent clades of Carboniferous lepospondyls resemble those achieved convergently among Cenozoic squamates that have elongate bodies and reduced limbs, and by lineages of modern amphibians that have undergone miniaturization. Incongruent character distribution, poorly resolved cladograms and functionally improbable character transformations determined by phylogenetic analysis suggest that convergence was also common among Paleozoic amphibians with a skull length under 3 cm, including lepospondyls, early amniotes and the putative ancestors of modern amphibians. For this reason, it is injudicious to equate apparent synapomorphy (perceived common presence of a particular derived character in two putative sister- taxa) with strict homology of phylogenetic origin. Identification of homology by the similarity of structure, anatomical position and pattern of development is insufficient to establish the synapomorphy of bone and limb loss or precocial ossification of vertebral centra, which are common among small Paleozoic amphibians. The only way in which synapomorphies can be established definitively is through the discovery and recognition of the trait in question in basal members of each of the clades under study, and in their immediate common ancestors.