Re: questions about the Odontochelys study

[David Marjanovic <david.marjanovic@gmx.at>]

To continue my monologue:

> I'll check out *Palaeochersis* and *Australochelys* tomorrow, but unless 
> filling in the thyroid fenestra was fashionable in the Triassic, it looks 
> like a safe bet that turtles ancestrally lack the thyroid fenestra.

*Australochelys* is only known from a skull. *Palaeochersis* lacks a 
full-size thyroid fenestra according to the 2007 monograph on it; it may 
just have an obturator foramen like *Proganochelys* or some kind of 
intermediate condition.

So, it is one step more parsimonious to assume that turtles ancestrally lack 
the thyroid fenestra, no matter what their sister-group is.

Incidentally, sauropterygians ancestrally have both an obturator foramen and 
a thyroid fenestra: the obturator nerve does not have to pass through the 
thyroid fenestra just because it's there.

However, *Placodus* hasn't got a thyroid fenestra either, just a little 
notch: 
http://images.google.com/hosted/life/f?q=Placodus+skeleton&imgurl=8dce0f7b976103f9 - 
- at least *Proganochelys* and *Odontochelys* lack even this notch, though.