[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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

Augusto Haro wrote:

<Now I read that what I expressed is far from new.


I was not specifically talking about throat-stabbing, but stabbing in general. 
But Carpenter's proposal fits better the available evidence. He also considers 
the Tenontosaurus-Deinonychus assemblages not necessarily indicating predation.>

  Carpenter's argument is that the animal is doing almost precisely what Ostrom 
proposed his animal was doing: Holding on to the animal, then using the feet to 
kick out and ruin the prey's life something fierce. The only distinctions here 
are in the relative size of the animals in question and in the postures. 
Apparently *Deinonychus* has to climb around *Tenontosaurus* or whatever, 
although it could easily trade this in for something smaller, while 
*Velociraptor* liked to lay on its side or back and play "puppy" with stomping, 
chomping *Protoceratops*, which, if you look at the size of that body and that 
huge beak up front, was a very dangerous thing. Unlike sabretooth cats, who 
would have grabbed their prey and then "climbed" to the neck and chomped down 
to strangle their prey by suffocation or simply (slower death) bled them out, 
precision jugular intercision is rather weak and highly dangerous.

  In this way, Carpenter proposes a model of behavior and functionality from a 
situation that was hardly (and actually) not favorable for the predator.

  Notice, however, that stabbing devices in predators are relatively straight, 
as are slashing devices. The curvature is used to grant inherent resistance to 
dorsal loading on the claw, and a triangular section inhibits torsional loading 
so that the claw does not shear off when engaged in whatever. Storks and 
anhingas spear with their beaks, hence they are straight and (when the two 
halves are together) roughly rhomboid and capable of resisting torsional loads 
in any direction. These are stabbing/slashing devices.

  Yet what we have is an ungual "core" which is transversely narrow, 
teardrop-shaped for some of its length, roughly ovoid for the rest, with the 
narrowest to depth region being limited close to the tip, about 15% of the claw 
length. (At least that's what Ostrom's work on *Deinonychus* and Bakker's work 
on *Utahraptor* claws seem to suggest. A similar study has not appeared to my 
knowledge on *Velociraptor*.) This has been extended to the keratinous sheath, 
which in this case creates a claw that is roughly a half-circle in aspect. 
Claws like this appear in some perching birds, and most importantly, birds of 
prey. Why so? My argument has been that this is an adaptation to grapsing. 
Unusually, only one of these claws per foot, while three of these claws per 
hand (and those could oppose one another in a sort of six-fingered "hand") 
imply that the legs and arms serve different functions when engaged with 
anything. In this way, like cat claws (which are also
 used for grasping and gripping [usually VERY deeply, grrr]) they are likely to 
have been used for penetrating and holding on to prey. That the tips of these 
claws can be used as a slashing device is consistent with (again) birds, cats, 
and so forth, and not as an argument against any other function. I should say, 
though, that climbing animals usually require proximal prehensibility in the 
limb, and climbing birds have slightly straighter claws than do grasping 
taloned birds, which is consistent with the "piton"/"crampon" angle, and 
inconsistent with *Deinonychus*. Note, however, that the argument for grasping 
still allows *Deinonychus* to use its feet to hold on to prey, but this seems 
to allow it freedom with the hands and jaws, rather than to climb up body walls.


Jaime A. Headden

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