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Re: woops! Sorry everybody (: Aaah! The EYE is back!þ C
Quoting Sim Koning <firstname.lastname@example.org>:
> > Date: Mon, 22 Sep 2008 13:01:30 +1000
> > From: email@example.com
> > Subject: RE: Campbell's even crazier than a MANIAC? (archeopteryx
> > To: firstname.lastname@example.org
> > 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.
> 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
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
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:
Compare it with the swivel-claw of Velociraptor:
> 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
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).
GIS / Archaeologist http://geo_cities.com/dannsdinosaurs
Melbourne, Australia http://heretichides.soffiles.com