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




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'm sorry, but "claws" are not really an important adaptation for climbing (primates, many squamates, and all amphibians that are arborreal do so without using claws), while limbs that can splay and mobile ankles and wrists are. Humans, while having secondarily lost many primate climbing adatations, are still far better suited for climbing than theropods. That's not to say that theropods couldn't climb under any circumstances, but they simple do not have any specializations for it, hence it's special pleading to put them in trees just to be in line with how you want them to learn to fly.


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. <<<


And this is exactly why we need to refrain from putting the theoretical cart before the morphological horse. There is no requirement that an arboreal gliding stage prece
d flight, nor is it a priori reasonable to assume that Archaeopteryx could in fact fly. It may be that Archaeopteryx represents a terrestrial stage that preceeded flight, or it could be that it has secondarily lost some features do to its habbitat, or it could be that Archaeopteryx is just not on the part of the basal maniraptoran bush the included many winged (and almost entirely terrestrial) linneages and isn't really that closely related to birds. Or all of these hypotheses could be wrong and some other explanation could occur. For example, the appearance of feathers on the distal part of the limbs prior to the proximal part is in fact more similar to the morphology in flying fish than it is to any arborreal glider. Is that important? Perhaps, but it has to be tested and not just assumed.


It's not being wrong that's the problem, the problem is "knowing" something is true when it isn't.


Scott Hartman Science Director Wyoming Dinosaur Center 110 Carter Ranch Rd. Thermopolis, WY 82443 (800) 455-3466 ext. 230 Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message----- From: Sim Koning <simkoning@msn.com> To: dinosaur@usc.edu Sent: Tue, 23 Sep 2008 10:01 pm Subject: 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!Ã 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/claw
s.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
bearin
g 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
___________________________________________________________________