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Re: sickle-claws



Greg Paul (GSP1954@aol.com) wrote:

<This suggests that velociraptorines did not emphasize the head as a killing
device. Certainly the long, big clawed hands were important predatory devices,
but the arms and slender fingers appear to lack the power needed to deliver
killing blows. That's probably true of all theropods.>

  Actually, they are probably correct in applying limb-based strategies in
engaging prey or carcasses. It has been stressed elsewhere that the power of
the arms in engaging a target are not neccessarily in the hands, which were not
just gracile but acted with the second and third digits in a single unit (see
Gishlick's work), but also that the wrist was restricted in mobility as was the
elbow (Gishlick again, but also see Paul's own work). The data, however, does
not invalidate arm useage as prey-grappling devices, since the humerus (tending
to be robust) and the sternae (large elements which in one specimen of
*Velociraptor* produces a keel-like medial morphology) act to anchor large
muscles that help strengthen the arm. In addition, the so-called predatory
power-stroke doesn't require moble or robust hands to work, but can allow the
arm to move primarily at the shoulder. The extremely long neck and head of
*Velociraptor* also likely permitted using head and arms in tandem, not just
one or the other. As Paul and Therrein et al. state *Dromaeosaurus* has a
robust skull that would suggest, if we had a more sufficient postcranium to
test this against, might have less robust limbs than *Velociraptor*.

<As others have noted, the target used by the researchers in the BBC project do
not appear particularly realistic - the failure to first test their machine by
replicating the wounding action of cassowary saber claws is a major failing 
(albeit common to paleontological studies) - and a crude mechanical model may
not be able to deliver a wounding stroke with the sophisticated application of
force that maximizes the damage that can be achieved by a well experienced
living organism.>

  The machine, the "crude mechanical model" of note, was designed to do only
one thing, KICK. Other more "advanced models" like those Paul works with are
designed to walk, and thus the difference in function is deliberate. The model
used in the study was probably sufficient for the task, I would argue. 

  However, on the subject of cassowaries, why would they NEED to test cassowary
kick-strikes? In these animals, it is usually just the tip of thye claw used to
gouge anything; in dromaeosaurids, the ungual is MUCH narrower, taller than
wide, with an elliptical rather than triangular section unlike the other toes,
and more strongly curved. I beleive they also have a narrower venter than
dorsum. In cassowaries, we would be testing with the keratin sheath intact, but
we haven't this option in dromaeosaurids, where the ventral or cross-sectional
structure of the keratin sheath is unknown. Thus, cassowaries lack "sabre"
claws, and a slashing strike is essentially dragging the narrower tip through
the flesh. Cassowaries are hardly trying to maintain physical contact with the
victim, as is certain dromaeosaurids were trying to do. Using cassowaries and
testing their strikes is a good comparison test, indeed, of why dromaeosaurid
claws are not shaped the same way.

  Furthermore, the authors were testing the ungual shape and its effectiveness,
no more. This does not invalidate the test, but allows further tests to
strengthen or weaken the hypothesis. As stated by the lead author in public,
the test started to measure the effect of kicking and slashing, and the model
was designed to kick and slash with the claw, NOT to figure out whether a
kick-strike, slash-strike, crampon foot-spike, morse-code machine or tap-dancer
was the more effective. Thus the test was very narrowly based and a better
apparatus would be required for a more extensive test. Since this paper arose
out of a tv show testing the effect of a kick into a side of meat, it was
fairly well done!

<If velociraptorines used the head to kill then the Velociraptor should have
been biting the Protoceratopds, instead its head is pulled well away from - but
is looking at - the herbivore. The predator is using its cranium to see what
it's doing, not to attack the supposed victim. It is the sickle claws that are
attempting to dispatch the Protoceratops, apparently by slashing at the veins
or trachea.>

  The animals may also be reacting to the sandslide that killed them, which
will alter the forensics of their deathpose a tad, such as Vel pulling his head
back from a dangerous position, Proto lifting his head up (Vel's hand in
mouth), a forefoot raised, a reaction of the one Vel left closer to the body,
and consequently closer to the Proto throat. All possibly related to the slide,
not really to the "combat".

<It is hard to see how or why velociraptorines would use the big, sharp,
powerful sickle claws merely to hold onto prey while they used their slender
jaws to try to kill it. That wouldn't be smart.>

  I certainly agree with this wholeheartedly. What may even be better is to use
all four limbs and jaws to grapple a smaller prey animal. This doesn't solve
the "who is the aggressor" however.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


        
                
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