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Re: a little background



Graydon (graydon@dsl.ca) wrote:

<No perching birds have that kind of claw size disparity between claws on
the same foot, and so far as I am aware, no modern bird has a slashing
claw at all; the predatory birds all have _grasping_ claws, rather than
slashing ones.>

  I'm talking about relative claw size in the digit, not just claw:claw
ratios (which is really rather irrelevant to the discussion becuase the
third digit claw is not as excessively large as the first). In
passeriforms and falconiforms especially, the second digit claw is _very_
large, as long or longer than the length of the non-ungual digit itself,
and an interesting feature for birds that spend most of their life up on
branches.

<It's a weapon or a scansorial climbing adaptation, by shape and form --
sharply pointed, strongly curved, laterally compressed -- and the
carriage, which can be infered from the lack of tip wear on recovered
claws.>

  On the bone ... not the keratinous sheath, which is not known to any
degree to infer distal wear. All we have to go on is bone. Some claws in
*Velociraptor* vary in their curvature, as do they in *Deinonychus*, from
my own observation. At one point I considered claw geometry to be
different (and diagnostic) between the taxa but further examination has
proven this wrong. In fact, Yalden's work shows that scansors
(tree-climbers, to be exact) have claws that are not veryt strongly
recurved in the bone, but the sheath curved dramatically. Since this
cannot be guessed at all in the bone, conclusions to arboreal function are
limited. That they _may_ have served as pitons for tree trunks is
plausible, and I end my speculation there.

  I drew an example of how I conceived a small, Early Cretaceous
tree-climbing non-avian theropod would have managed the job, and it's
online, but the link is not functioning for me (grr...) but if anyone does
get this (my site infor says it's there, file size and everything) here it
is:

  http://qilong.gq.nu/Sinornithosaurus in a tree.jpg

<So it's either a specialized climbing adaptation or a predatory one, or
some third thing where sharpness is of benefit.  Since the climbing
scenario makes no sense for arid environments,>

  There are more things to climb than trees ... hills and cliffs are
equally susceptible to climbing. However, I never suggested *Velociraptor*
climbed with the claws, but that this is a plausible function of the claws
to begin with. All small eumaniraptorans have the claws, so this may have
evolved as a climbing feature, reduced or adapted in later forms (birds
lost it, then got it back, and developed other strategies to cope with
climbing; troodonts reduced, but retained it, and the claw pad can no
longer touch the ground; and dromaeosaurs adapted the claw to great size
... mayhap to climb with or as predatory equippage).

<If it _is_ a weapon, it's much much larger than the teeth of the animal
it belongs to, when there is no reason to believe that those teeth are
inadequate to preying on animals of approximately the same size or that
evolving larger teeth was difficult in theropod lineages. It's attached to
the strongest muscles, much more powerful than jaw muscles, the animal it
belongs to has.>

  I have this odd little hypothesis, running with it for a few years now:
dromaeosaurs may have adapted into two predatory strategies, co-adapted
with other theropods as Holtz has written, into a claws-first or a
head-first attacker. The teeth of velociraptorines and most basal dromies
are small and slender ... those of *Dromaeosaurus* rather large and
robust. It is therefore plausible to posit that dromaeosaurines were
head-first attackers, and may even have reduced ungual equippage as a
result. They were tyrannosaur-analogues, as it were. Velociraptorines, on
the other hand (manus), were claw-first, and use the snout to manipulate
prey ... but not take it down. I envision *Velociraptor* as a small-prey
hunter, a snatcher ... an hypothesis that runs in the face of the _one_
Tugrikin Shireh association (GI 100/25, 100/26) of the Fighting Dinos.
This adapts the theory of the association to something that both Barrett
and Tracy Ford have touched on previously (and which a friend and I were
looking at publishing but now find redundant): *Protoceratops* was the
aggressor, *Velociraptor* the jackal a defender. There's more, but that I
will be publishing on if I can get it written up properly.... But I'm sure
the intuitive on the list can read back and figure the rest out ... it has
been mentioned.

<Given that the jaws were adequate to comparable sized organisms, what's
the benefit of the sickle claw mechanism to a predator _other than_
becoming able to attack larger prey?>

  I disagree ... Ostrom's reconstructions aside, the snout of
*Velociraptor* is triangular in section and quite narrow and slender,
curving upwards. This is not a megapredatory feature. The snout of
*Deinonychus* is less curved, a little wider relative to length, and a
little deeper, more rectangular in section than triangular.
*Dromaeosaurus* had a very wide jaw, very little if any curvature, and
robust, wide teeth instead of narrow blades. Rostral teeth in the
Mongolian--Chinese taxa are elongated and longest in the jaw in
*Velociraptor*; in *Deinonychus* and *Dromaeosaurus* it is the opposite,
and these all suggest much different feeding (and by inference, hunting)
strategies. The abundance of small avian, mammalian, and reptilian game in
the Djadokhta suite of localities (see Gao and Norell, 2000, AMNH Bulletin
[they have the ref on the web, I have it not available to me at present],
for a discussion) suggests that *Velociraptor* was probably better at that
than *Protoceratops* and a beak that would have put the alligator snapper
(or an alligator!) to shame [and yes, I'm familiar with the wonderful jaws
of *Macroclemmys* quite well...].

  Back to *Deinonychus* ... it is all circumstantial to place
*Deinonychus* on the back of a struggling *Tenontosaurus*. We have no
struggling, fighting pair preserved, and though a group of big D may have
died while feeding on a carcass of a big T, and be preserved in a
high-energy water-flow bed, suggests something ain't right in this.
Putting this all together, I see no evidence that says that D climbed on
the back of T and procurred its food by acting as no other animal does
today (for good reason) in being so stupid -- even lions gang up only on a
weak water buffalo, and that's with extraordinary caution and the note
that T is so much larger than water buffalo, compared to D which are
smaller than lions (perhaps). The ratio is much different.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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