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Re: Claws of Baryonyx and Sinosauropteryx
Fam Jansma wrote-
> If in higher mairaptorans the pedal claws are important in some groups
> (Dromeosaurs e.g.), why is it shrinking than in later genera like
> Achillobator and Adasaurus? It's like reversing evolution when you have
> this great tool to slice those poor Hypsies to shred and than to
> into something that makes a scap on it's toe or whatever.
You're assuming that Adasaurus and Achillobator had large clawed ancestors.
The only analysis I know of containing them is Norell et al.'s (2001), which
has them in a polytomy with dromaeosaurids, Utahraptor and Unenlagia. My
analysis has never been very precise in the eumaniraptoran area, but
Achillobator being further from birds than dromaeosaurids is certainly a
possibility. Also, I'm not convinced the supposed second pedal ungual of
Achillobator isn't from the hand.
> Here's one "just-so" scenario to explain the "shrinking" sickle-claw:
> "Mid-sized" dromaesoaurids _Deinonychus_ and _Velociraptor_ needed a
> particular large sickle-claw because they targeted prey of comparable (or
> even larger) size than themselves. The preferred prey of larger
> dromaeosaurids (like _Utahraptor_ and _Achillobator_), by contrast, was
> relatively smaller than themselves: the importance of the sickle-claw
> declined, since the predator could rely more on physical strength to
> prey. The sickle-claw of _Microraptor_ was rather undersized too,
> to _Deinonychus_ and _Velociraptor_.
> (As for _Adasaurus_, I didn't think it was very big.)
As Utahraptor has comparatively large pedal unguals, I don't think the size
differences can explain it. Adasaurus wasn't very big- only about 2.5
meters long for the old holotype.