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Biol Lett. 2010 Dec 23;6(6):830-3. doi: 10.1098/rsbl.2010.0371. Epub 2010 Jun 9.

Transitional fossils and the origin of turtles.

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  • 1Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA. 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.

PMID:
20534602
PMCID:
PMC3001370
DOI:
10.1098/rsbl.2010.0371
[PubMed - indexed for MEDLINE]
Free PMC Article
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