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Re: questions about the Odontochelys study



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.