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Sickle-claws (was RE: a little background)



Jaime Headden wrote:

> I'd like to think that the large, recurved claw on the toe of the
> cassowary would serve very well as an analogy, in the case of the use in
> attacking an opponent, attacker, etc., though not in any manner of
> predation. I see no reason why the large toe claws of deinonychosaurs
> must be equipped to take on such larger prey as to validate any 
> *Deinonychus* + *Tenontosaurus* association. In this manner, the 
> morphology of the toe claw is important. 

True.  But me mindful that just because a device or organ is ideally suited
to one function, does not preclude the device or organ from being employed
for other (perhaps secondary) functions.  The latter is the foundation for
novel specializations (exaptations).  I think it was Mayr who said that
adaptation often involves compromise.

> In the largest taxon, *Utahraptor*, the ventral edge is developed into > a
sharp crest; in smaller taxa, this is more rounded, and suggests that 
> the claw (which is also more hooked) may have functioned more as a 
> piton, or grappling hook. 

I don't know who came up with the "grappling hook" idea for the dromie
sickle-claw (has it been published?), and it has been discussed on the list.
I like the idea.  The beauty of the sickle-claw is that it may have had more
than one function in dromies - "grappling" large prey (to enhance the
predator's hold); evisceration (after said grip was achieved);
immobilization of small prey; defense against other predators; and
intraspecific combat (though I wouldn't want to be the loser!).  It's also
possible that smaller dromies used the sickle-claw as a tree-climbing aid,
an idea suggested by Chatterjee (though he may not have been the first).

> Lack of animals to grapple for *Velociraptor* suggests it may have 
> locked predator to prey much as claws of felids do during grapping 
> attacks. This does not require the prey to be so much larger than the 
> predator and does not then serve any objective evidence for dromies 
> feeding on larger prey.

As you mentioned in a previous post, adult _Protoceratops_ is nearly double
the size (mass) of _Velociraptor_.  This isn't even close to the disparity
between _Deinonychus_ and _Tenontosaurus_, but it is impressive nonetheless.


Tim


------------------------------------------------------------ 

Timothy J. Williams 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 3163