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



Do recall in the TV spot that the experimentalists using ONLY the
bony cores of *Deinonychus* pdII-3s were unable to acheive a cutting action in soft
material, which is why the "crampon" idea has received more attention recently.<<<


Sure, but try to cut through flesh with the bony core of a felid claw...yet tigers regularly dissembowel ungulates, and even my cat can give a nasty gash to a careless stranger. As the "crampon" spike gross morphology does not match with that of Archaeopteryx or deinonychosaur #2 pedal claws, it's a poor functional analog.

Who says they had a cutting edge? Not all dromaeosaurid claws have
a tomial
ridge on the ventral edge. In fact, only that of *Utahraptor* has this feature,
and that holotypic claw is crushed mediolaterally, exaggerating the degree to
which the claw seems narrowed. The sharpened ventral margin is an inferrence
that's been applied to them _because_ they were assumed to be cutting devices.<<<


Well wait here, "tomial" is the cutting edge itself (e.g. the cutting edge of raptorial bird beaks) and itself depends on the morphology of the keratinous sheath. If you were to strip the ramphotheca from a falcon skull I doubt very much that it would tear through meat with the same prowess as the living animal does (with ramphotheca intact). The #2 pedal claw morphology in Deinonychus and Velociraptor certainly constrict ventrally, leaving an inverted teardrop shape that is very derived compared to the primitive condition (and indeed the condition of the other pedal claws) which are sub-triangular in crossection with the widest portion at the base. Also, in the Thermopolis Specimen and in Chinese dromaeosaurs that preseve impressions of the keratinous sheath or the second there is more keratin on the ventral surface, so unless the sheath cross-sectional morphology differed radically from the bony core it the already narrowing claw would have to pinch out to an edge.


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: Jaime A. Headden <qilongia@yahoo.com>
To: david.marjanovic@gmx.at
Cc: dinosaur@usc.edu
Sent: Sun, 7 Sep 2008 2:16 pm
Subject: Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)




David Marjanovic wrote:

<Don't crampons work side-to-side? Sickle claws worked top-down and probably had
a cutting edge. They were not round in cross-section.>


Who says they had a cutting edge? Not all dromaeosaurid claws have a tomial
ridge on the ventral edge. In fact, only that of *Utahraptor* has this feature,
and that holotypic claw is crushed mediolaterally, exaggerating the degree to
which the claw seems narrowed. The sharpened ventral margin is an inferrence
that's been applied to them _because_ they were assumed to be cutting devices.


Do recall in the TV spot that the experimentalists using ONLY the bony cores
of *Deinonychus* pdII-3s were unable to acheive a cutting action in soft
material, which is why the "crampon" idea has received more attention recently.


 Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

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