RE: Claws of Baryonyx and Sinosauropteryx

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Fam Jansma wrote:

>They did suggest Compsognathus was a specialized fish-eater actually.
>There is this old book, can't remember the titel anymore, but it had the
>French specimen restored with flippers on it's frontlimbs. 

Yeah, the alleged flipper-handed _C. corallestris_ (now referred to _C.
longipes_).  That particular restoration has been refuted beyond all doubt.


>Based on shitty evidence

*blush*

>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 re->evolve
into something that makes a scap on it's toe or whatever.

Well, for the (in)famous dromaeosaur sickle-claw it's not just the size but
what was done with it that counts.  An enlarged sickle-claw was no doubt
extremely useful in eviscerating prey.  However, it was a pretty heavy thing
to carry about with you if it isn't absolutely necessary.  Judging from its
presence in dromaeosaurids, troodontids and at least one basal avian
(_Rahonavis_), the sickle-claw may well be primitive for the clade embracing
these three taxa (Paraves).  At least a few analyses have determined that
this is the most parsimonious explanation for the sickle-claws observed
distribution.  Therefore, it seems likely that the sickle-claw was actually
*lost* several times in maniraptoran evolution: in _Archaeopteryx_,
Pygostylia, and by certain troodontids.

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 subdue
prey.  The sickle-claw of _Microraptor_ was rather undersized too, compared
to _Deinonychus_ and _Velociraptor_.

(As for _Adasaurus_, I didn't think it was very big.)

By the way, Darren was right: cariamas do use their enlarged inner toe-claws
for tree-climbing, as well as for predation.



Tim