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RE: Campbell's even crazier than a MANIAC? (archeopteryx







> Date: Wed, 24 Sep 2008 09:39:10 +1000
> From: dannj@alphalink.com.au
> Subject: Re: woops! Sorry everybody (: Aaah! The EYE is back!þ C
> To: dinosaur@usc.edu
>
> Quoting Sim Koning :
>
>>> Date: Mon, 22 Sep 2008 13:01:30 +1000
>>> From: dannj@alphalink.com.au
>>> Subject:>>> To: dinosaur@usc.edu
>>>
>>> Quoting Tim Williams :
>>>
>>>>> Sim Koning 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.
-------------------------------------

True, but many specially adapted climbing animals do not have sharply curved 
grasping hooks for claws. Iguanas are a great example of this 

http://alumnus.caltech.edu/~keith/photos/claws.jpg

and bears 

http://www.evolutionnyc.com/ImgUpload/P_886505_950485.jpg. 

Notice that in both cases the claw is very long and less curved than a cats.

 Just to be clear, I'm not trying to say dromaeosaurid claws were adapted 
primarily for climbing. I'm simply trying to say that it is a little 
unrealistic to say these creatures weren't fully capable of climbing up trees. 
We humans don't even have claws on our feet, yet we have no problem using them 
to climb trees. I also think it's pretty obvious that basal avians such as 
archaeopterx must have evolved from highly arboreal acestors, simply becasue 
they could fly. The intermediary stage proceeding flight has to be gliding and 
I don't know of any gliding animals (execpt flying fish) that are not highly 
arboreal.  


> 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).

This doesn't mean much, my legs are much stronger than my arms and I have no 
problem climbing up a tree.

> 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.

Not really, it could have had just as much weight, if not more, on its other 
toes.

> 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 the killing claws of a dromaeosaur would have been subjected to far 
more twisting force while being plunged into a strugling, thick skinned and 
scaly dinosaur than they would be while simply hanging on to the rough surface 
of tree bark. If their claws couldn't simply support their weight while 
climbing a tree, I seriously doubt they could use them to kill a dinosaur.

> 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.

Bears do it. My parents have a tree with huge claw marks that were created when 
a black bear shapened its claws, just like a big cat.


> 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).

The point is I doubt tree climbing would have had much of a dulling effect on 
their claws. If it did, they could simply keep their use for this purpose to 
minimum by using their other toes just as you said.

Once again I am not trying to say that the killing claw of a dromaeosaur was 
designed primarly for climbing, just that it could have use it to climb if the 
situation called for it.

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