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RE: Gargantuavis a bird, not a pterosaur
> The ten sacral vertebrae do seem to be the character cited to diagnose
> Gargantuavis as a bird. Buffetaut and le Leouff cite Chiappe(1996), when
> they state that no non - avian dinosaur has that many sacral vertebrae.
> That leaves open three areas of doubt in my mind.
> 1) The authors were not certain of the vertebral number in Gargantuavis.
> To quote Buffetaut and le Loeuff, 1998:
> "...the exact number of vertebrae in the synsacrum is not easy to determine"
True, but you can make out at least nine transverse processes / sacral ribs in
> "...it appears that ten vertebrae are present...".
> 2) Have any non - avian maniraptorans been found since 1996 that have more
> than 8 sacral vertebrae?
Nope. Only ornithuromorphs and maybe Gobipteryx.
> 3) If this type of broad, highly fused, synsacrum with neurapophyses fused
> into a low median dorsal ridge is seen in therizinosaurs such as
> Nothronychus, can we rule out the possibility that gargantuavis is a
> previously unknown species of therizinosaur?
It can't be ruled out, though sacral neural spines are fused into a lamina in
quite a few theropods. Similarly, lots of theropods have completely fused
synsacra, often absent due to age. The breadth is similar, and has never been
used in an analysis to my knowledge.