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Turtles (was Re: Vote on the Definition of "Aves")



Roberto Takata wrote:

Crocodylia+Testudines clade (some genetic study place Testudines as an archosaur taxon - syster to Crocodylia).

Yes, molecular phylogenetic analyses do ally Testudines with archosaurs (e.g., Zardoya and Meyer, 1998; Hedges and Poling, 1999), with the latter even recovering strong support for a Crocodylia-Testudines clade. I find this last relationship highly suspect. Nevertheless, both molecule- and morphology-based analyses usually (but not invariably) place turtles inside the crown group diapsids, implying that the anapsid condition in turtles is secondary.


Morphology-based phylogenies (with lots of fossil taxa) tend to put Testudines within the Lepidosauromorpha (e.g., Rieppel, 1994; Caldwell, 1996; Rieppel and deBraga, 1996; deBraga and Rieppel, 1997). Including sauropterygians and ichthyosaurs in these morphological analyses apparently has a huge effect on where turtles end up in the cladogram. Taxon sampling might be the critical factor, so if somebody would be good enough to pop over to Loch Ness and collect some plesiosaur DNA, it might prove extremely useful for molecular analyses.

Cheers

Tim