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

[Tim Williams <twilliams_alpha@hotmail.com>]

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