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Re: Vancleavea campi - what is it? - not an archosauriform.
David [P.], I am not sure what you mean about thalattosaurians, but
thalattosaurus (from *Askeptosaurus* to *Dakosaurus*) possess both
supratemporal fenestrae as well as antorbital fossa and fenestrae.
Hang on a second, Jaime. You're confusing Thalattos_aur_ia, a clade of
Triassic marine diapsids of rather uncertain affinities (though they're
probably somewhere close to the ichthyosaurs, somewhere around the base
of the diapsid crown-group), and Thalattos_uch_ia, a clade of Jurassic
marine crocodyliforms. *Askeptosaurus* belongs to the former (as do
*Thalattosaurus*, *Clarazia*, *Hescheleria*, *Xinpusaurus*,
*Miodentosaurus*), *Dakosaurus* to the latter (like *Steneosaurus*,
*Teleosaurus*, *Machimosaurus*, *Metriorhynchus*, *Geosaurus*).
The supratemporal fenestra is always small in thalattos_aur_s when it's
present; in some, the upper temporal bar (formed by postorbital and
squamosal) approaches the parietal so closely as to reduce the fenestra
to a slit, and in some it even touches the parietal, eliminating the
Thalattos_uch_ians retain the antorbital fenestra of their archosaurian
ancestors. Thalattos_aur_s retain the _lack_ of an antorbital fenestra
from their non-archosaurian ancestors. (I'm not aware of any antorbital
fenestrae outside of Archosauriformes and the non-amniote Chroniosuchia,
unless you count the naris extension of the trematopid temnospondyls or
the orbit extension of the baphetids.)
In lacking both the antorbital fenestra and the supratemporal fenestra,
*Vancleavea* does indeed resemble the thalattos_aur_s. In particular,
where the supratemporal fenestra would be, we find a straight
rostrocaudal contact between the parietal and a very narrow upper
temporal bar, just like in those thalattos_aur_s that have completely
lost the fenestra.
Now, I still haven't read the *Vancleavea* paper, so I don't know if
there's more than these two characters, though of course I suspect there
are when the paper has 51 pages!
If, as previously argued, you think the diapsid condition
cannot reverse to the anapsid condition,
That would not be defensible -- the loss of the supratemporal fenestra
happens gradually _within_ Thalattos_aur_ia (or perhaps rather
Thalattosauriformes... the nomenclature is a bit strange in that part of