Transitional fossils and the origin of turtles
Tyler R. Lyson1,*, Gabe S. Bever1, Bhart-Anjan S. Bhullar2, Walter G. Joyce3 and Jacques A. Gauthier1
-Author Affiliations
1Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA
2Department of Organismic and Evolutionary Biology, Harvard University,Cambridge, MA 02138, USA
3Institut für Geowissenschaften, University of Tübingen, 72076 Tübingen, Germany
*Author for correspondence (tyler.lyson@yale.edu).
Abstract
The origin of turtles is one of the most contentious issues in systematics with three currently viable hypotheses: turtles as the extant sister to (i) the crocodile–bird clade, (ii) the lizard–tuatara clade, or (iii) Diapsida (a clade composed of (i) and (ii)). We reanalysed a recent dataset that allied turtles with the lizard–tuatara clade and found that the inclusion of the stem turtle Proganochelys quenstedti and the ‘parareptile’ Eunotosaurus africanus results in a single overriding morphological signal, with turtles outside Diapsida. This result reflects the importance of transitional fossils when long branches separate crown clades, and highlights unexplored issues such as the role of topological congruence when using fossils to calibrate molecular clocks.
turtle Diapsida molecular clock transitional fossil Eunotosaurus africanus Odontochelys semitestacea
Footnotes
Received April 18, 2010.
Accepted May 17, 2010.
© 2010 The Royal Society
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