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Re: questions about the Odontochelys study
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.