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Interdental plates



I've gone through a little of the thecodontian literature and I find that
interdental plates occurred in many pre-dinosaurian archosaurs, particularly
in large predators such as _Postosuchus_, _Teratosaurus_, and so forth. On
the other hand, they seem to be absent or fused to the jawbones in other
forms, such as _Proterochampsa_. I haven't done an exhaustive study by any
means, but there is now little question in my mind that interdental plates
are primitive for Dinosauria. They certainly have no business being used as
one of the synapomorphies uniting Segnosauria and Theropoda. Unfortunately,
they therefore also can't be used as a synapomorphy uniting Segnosauria with
Phytodinosauria, though their presence in certain prosauropods as well as
segnosaurs does not contradict assignment of Segnosauria to Phytodinosauria.

G.O.