Re: questions about the Odontochelys study

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

> The thyroid fenestra is present in Recent turtles, but Romer 1956 says
> the fenestra was too small in Proganochelys, so perhaps that count as
> that it was absent. Gaffney 1990 calls thyroid fenestra to something
> that incloses the obturator foramen, and is accepted as artificially
> enlarged, this sounds to me that there is just an obturator foramen
> and no thyroid fenestra.

I checked Gaffney 1990; that monograph says there's just an obturator 
foramen that is sometimes enlarged by breakage. Gaffney also says it's 
present in what he thinks is the crown-group; that leaves *Palaeochersis* 
and *Australochelys* to check.

*Odontochelys* has an obturator foramen of ordinary size that is connected 
to the cranial edge of the pubis by a slit. The text of the paper calls it 
"thyroid foramen" and the legend of fig. 3d calls it "thyroid fenestra", but 
that's misleading, judging from the good photo that is fig. 3d.

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.