Re: _Odontochelys semitestacea_ comes out of its shell

[Tim Williams <tijawi@yahoo.com>]

David Marjanovic wrote:

> (http://www.nature.com/news/2008/081126/full/news.2008.1260.html)
>
> Well, I'm glad that this was published early enough to
> be used in my PhD thesis on amniote phylogeny and the origin
> of turtles. I like living in interesting times. :-)


Cute little critter.  The picture of _Odontochelys_ looks like a turtle that's 
gone skinny-dipping.

Li &c's phylogenetic analysis finds the same topology as Rieppel & Reisz (1999 
- they use much the same matrix, with _Odontochelys_ added).  They recover a 
sister taxon relationship between turtles (Testudinata) and Sauropterygia 
within Lepidosauromorpha (i.e., the Testudinata+Sauropterygia clade is sister 
taxon to the Lepidosauria).  _Odontochelys_ comes up as the most basal 
testudinate.  

This is the same analysis that recovers placodonts as basal sauropterygians, 
which suggests that the morphological similarities shared by basal testudinates 
and placodonts might be primitive for the sauropterygian-turtle clade.  Based 
on this analysis, anyway.  If _Odontochelys_'s inferred marine habits are 
primitive for the turtles, then it's certainly consistent with sauropterygian 
affinities. 

Li &c also note that a cleithrum is absent from _Odontochelys_, and its 
presence is ambiguous in _Kayentachelys_.  Coding Testudines and Odontochelys 
for the presence of a cleithrum had no effect on the topology.
 

Cheers

Tim