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Re: woops! Sorry everybody (: Aaah! The EYE is back!þ C



Quoting Sim Koning <simkoning@msn.com>:

> > Date: Mon, 22 Sep 2008 13:01:30 +1000
> > From: dannj@alphalink.com.au
> > Subject: RE: Campbell's even crazier than a MANIAC? (archeopteryx
> climbing)
> > To: dinosaur@usc.edu
> > 
> > Quoting Tim Williams :
> > 
> >>> Sim Kining wrote:
> > 
> >>> An eagle's talons are highly specialized for predation, so are the claws
> of large cats, 
> >>> neither seem to have a problem climbing around or perching in trees. 
> > 
> >> Neither of these has claws *as* specialized as the sickle claw (and its
> >> supporting digit) of dromaeosaurids. Not even seriemas (cariamas).
> > 
> > Indeed. Eagle and cat claws tend to have circular or ovoid cross sections
> (as do the claws of just 
> > about any climbing, perching or grasping creatures). The narrow blade-like
> sickle claws of the 
> > larger dromaeosaurs would seem to be ill-suited to standing up to twisting
> or sideways forces.
> 
> http://www.evolutionnyc.com/ImgUpload/P_886549_950527.jpg
>  
> Cat claws are just as blade like, if not more so, than dromaeosaur claws.

The swivel-claw of Velociraptor is longer, narrower, and much less curved than 
that of a cat. Its 
shape matches that of a piercing weapon, more than a grasping hook.

Also, cats have a total of 18 claws to support their weight, spread over four 
limbs that are roughly 
of equal strength (in climbing species like leopards the forelimbs can be even 
stronger than the 
hindlimbs). Dromaeosaurs were primarily bipeds, so their hind limbs would have 
been better 
adapted to supporting their weight than their forelimbs (at least in larger 
species). If the swivel-
claws were specifically climbing adaptations then that would mean that a 
Velociraptor would be 
bearing most of it's weight on just two long, narrow, slightly recurved claws 
while climbing. Their 
length and narrowness would have made them vulnerable to twisting forces, which 
the shorter, 
thicker, more recurved and more numerous claws of a cat are better at resisting.

I think it's more likely that when larger dromaeosaur species climbed (and most 
animals can climb 
if pressed hard enough), that they did so more like a bear - digging in with 
the forelimbs but using 
the smaller toe claws on the hind feet for traction (since we know these can 
easily support the 
animal's weight). I would think that a climbing Velociraptor would try to avoid 
bringing the swivel-
claws into play against a tree trunk.

This of course doesn't necessarily apply to the smaller bodied dromaeosaurs 
with their shorter and 
thicker swivel-claws. Here's a picture of the swivel-claw of Dromaeosaurus:
http://www.schoolersinc.com/images/Dromaeosaurus_claw_1000.jpg

Compare it with the swivel-claw of Velociraptor:
http://www.geocities.com/dannsdinosaurs/vmongclw.gif


> Cats sharpen their claws by digging them into trees. Dromaeosaurs (and other
> theropods) may have done the same.

I don't know of any other animals that sharped their claws in this manner. If 
there are non-cat 
species that do this, then it may be behaviour only seen in mammals. Cat claws 
grow from the 
inside out, with new layers of keratin layed down on the inside of the claw 
sheath. As cats dig their 
claws into a substrate like wood and deliberately pull then straight out again, 
the older outer layer 
of keratin is stripped off to leave younger, sharper layers behind. I have 
quite a collection of outer 
claw sheaths from my own cat - they're a bit like discarded spider skins in 
that they retain the 
original shape, but are essentially fragile husks.

I don't recall ever seeing birds or reptiles sharpening claws in this manner. 
That's not to say it 
doesn't happen of course, although a quick Google search of "claw sharpening 
behaviour" mostly 
seems to return cat-related pages. The search "claw sharpening behaviour -cat" 
doesn't seem to 
return anything useful, except for references to civets (which seem to be 
kissing-cousins to cats).

-- 
___________________________________________________________________

Dann Pigdon
GIS / Archaeologist              http://geo_cities.com/dannsdinosaurs
Melbourne, Australia             http://heretichides.soffiles.com
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