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Mike Keesey wrote-
> ?!?! First I've heard of any Tetanurae having four manual digits!
> That would certainly make the case for a carcharodontosaur-abelisaur
> relationship seem better ... I think....
Perhaps I should have clarified. My statement was correct with respect to
the number of metacarpals, but the amount of phalanges on metacarpal IV
varies. Dilophosaurus has two phalanges on its fourth digit. Ceratosaurus
had at least one, and possibly a much smaller second phalanx. Carnotaurus
has a huge modified fourth metacarpal without phalanges. The holotype of
Xuanhanosaurus lacks the distal end of metacarpal IV, but it looks
well-developed enough to have a phalanx. Sinraptor dongi has a short
metacarpal IV that did not support a phalanx. "Szechuanosaurus" zigongensis
appears to be similar. Allosaurus and most coelurosaurs lack metacarpal IV.
The sole exception is Coelurus, which had a tiny fourth metacarpal without
phalanges. How this applies to their life appearance varies- Dilophosaurus,
Ceratosaurus and Xuanhanosaurus probably appeared to have vestigial fourth
fingers, Carnotaurus a large spike-like projection and Sinraptor,
"Szechuanosaurus" zigongensis and Coelurus three fingers. Their fourth
metacarpals were probably embeded in the skin, like the third metacarpals of
tyrannosaurids. I suppose some carnosaurs and abelisaurids only retain
metacarpal IV, but I'm unsure of the condition in carcharodontosaurids.
Perhaps the new paper on "Fran" has some information.