RE: Claws on deinonychosaurs

["Jaime A. Headden" <qilongia@yahoo.com>]

Ken Carpenter (Ken.Carpenter@dmns.org) wrote:

<Argh! Somebody please explain to me (not done in the original description by
Maxwell and Ostrom) how multiple predators/scavengers on a carcass suddenly
fall over dead! (and please don't say volcanic ash because they aren't buried
in ash, nor is there evidence for poison gas, blah, blah). The specimens in
question (Deinonychus and Tenontosaurus) are mostly disarticulated so their
association may be incidental). Some facts, please, rather than unsubstantiated
speculation (this is NOT a criticism directed at Mickey, but my colleagues who
make such statements).>

  I am of all things curious aboute more than the Maxwell and Ostrom
association of a *Tenontosaurus* with the remains of at least three different
*Deinonychus* corpses, given the preserved tails of other fragments. Such an
assemblage indicates they were deposited together, but does not give us data on
how they died. We infer they died together because of the amount of shed teeth
associated with *Tenontosaurus* skeletons in the Cloverly, which Ostrom (1969)
mentioned. Such teeth were also associated with the holotype of *Microvenator*,
AMNH 3041, but the number is so high I cannot imagine a single animal loosing
over 20 teeth on an prey item 1/24th it's own size. It has also not been
addressed that the corpses of *Tenontosaurus* were dead prior to *Deinonychus*
scavenging, at least in print, largely due to the effects of romantic, wolfish
hunters taking on a large prey animal, lion vs wildebeats and bobcats vs moose!

and in a later email:

<The question I asked has far greater ramifications than just the
Deinonychus-Tenontosaurus assemblage (I thought someone would pick that up). It
applies to all mixed multiple theropod-prey assemblages (e.g.,
Daspletosaurus-hadrosaur bone bed, etc.).>

  In truth, unless there was incontrovertible evidence that predation on a
corpse occurs, the null hypothesis is that both skeletons were deposited at the
same time, without any allusion to what they may or may not have been doing to
one another (queue cheesy 70s porn music).

  But getting back to sickle claw useage, Ken wrote in Carpenter (1998)
[Carpenter, K. 1998. Evidence of predatory behavior by carnivorous dinosaurs.
_GAIA_ 15:135-144.] that "[t]he fighting pair provides the best evidence for
the function of the sickle claw in dromaeosaurid theropods. This function is
not the same as that suggested by OSTROM, (1969) for another dromaeosaurid,
*Deinonychus*. Ostrom proposed that Deinonychus "caught and held its prey in
its fore hands and disemboweled it with the large pedal talon" (OSTROM 1969:
143). However, in the *Velociraptor*, the sickle claw is extended in the
vicinity of the throat (Fig. 1A). This evidence suggests that the claw was not
used to disembowel the prey, but that it may have been used to pierce the
jugular vein, carotid artery, or trachea. These are areas that many extant
mammalian carnivores attack in prey." (pg. 138)

  Unfortunately, the evidence for the position of the foot, while valid,
requires that the association of the skeletons in question, in the Fighting
Dinosaurs pair, to be natural and unaffected by death postures or deposition
conditions (the accumulation of the sandslide, for example). Indeed, the
positions of both feet in the GIN 100/25 *Velociraptor*, are tucked up into the
same position, with the lower of the two in the same position as the one
positioned at the *Protoceratops*' throat. The body is curled up, the tail and
head pulled back, the arms up and forward. My cat makes the same position as a
defensive posture, and I do not recall ever seeing a predator engage prey from
below, not that I am sure it's not possible, but that the likelihood seems a
bit far to reach when the sides and rear seem more viable attack positions.
When cats turn into a defensive posture, they protect the vulnerable back,
sides, and neck; they also while exposing the ventral side, bring into play ALL
of their claws and teeth, and while using the forelimbs to grip and pull, can
use the rear to "catscratch" and if neccessary inflict defensive bites on what
they are holding, hoping (as my cat does) that it can be as annoying as
possible to force the attacker to retreat. On top of this, you have an animal
the size of a *Protoceratops* [which it so coincidentally appears to be], which
likely weighed 2-3 times as much as *Velociraptor*, nearly sitting on TOP of
the *Velociraptor*.

  It seems at least as likely to me that the *Protoceratops* forced the
*Velociraptor* into a defensive posture, resulting in the reflexive retraction
of the head, the "curled" body with the hindlimbs drawn up and onto the
aggressor's body while the arms tried to grip the head as well. In the process,
the *Protoceratops* has grabbed hold of the *Velociraptor*'s forelimb, and has
broken the radius where the upper jaw has connected with the arm. Does this
position not beg the question of why an aggressive predator has taken the risk
of sliding beneath a *Protoceratops* to go after just the throat? Perhaps it
may seem more viable to attack the back and sides. Despite it's rarity, when
lions do go after porcupine, they learn that the only viable attack direction
is to find a way to get the animal exposed onto it's back, whereas otherwise
the animal is protected from nearly all directions. Similarly, the proto head
shield protects the neck from attack from above and to the sides, but this does
not mean the underside, when the proto needs but to sit on the predator, to
effectively disable it. A horse landing on a man has a similar effect in making
much of an attack horrendously pyrrhic.

  Cheers,

Jaime A. Headden

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


        
                
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