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Re: Velociraptor footprints
> Extant ratites, that have been known to kill even humans with their inner
> digit's claw, do fine without carrying their second digit off the ground.
The cassowary digit is not, as far as I know, exactly comparable.
For one, it doesn't look as if it had the ability to hyperextend as in
dromaeosaurs (I can check up on this one). Dromaeosaurs could hyperextend
their second pedal digits and logically must have done so frequently.
Also, the cassowary's large claw is not the thin, bladelike structure of
a dromaeosaur, and cassowaries don't have a shortened second metatarsal
and more-or-less equal metatarsals III and IV. So the comparison may only
go so far.
> Wouldn't the constant hyperextension of the second digit cause a decrease in
> the performance of the rest of the locomotory musculature of the hind limbs?
Not if the fourth metatarsal is elongate to allow a didactyl gait.
> This is all good speculation, but until even ONE shred of physical evidence
> exists, I will remain unconvinced. Of the tens of thousands (hundreds of
> thousands?) of small theropod tracks that have been documented, NOT EVEN ONE
> unambiguously shows a retracted second digit. Period. Occam's Razor tells us
> that small theropods simply didn't carry their second digits off the ground.
The absence of these prints is really puzzling, but until the past
few years, if you asked someone where all the pterosaur footprints were
they would have been forced to shrug their shoulders. Since then, some
new discoveries and some reinterpretation of old prints have answered our
questions. Even so, I'm still not aware that anyone has found
rhamphorhynch prints (with a big uropatagium-supporting fifth toe) but I'd
love to have someone correct me on this. (also I was looking at the
Dimorphodon paper by Padian the other night and it seems to me that the
supposedly short forelimbs don't really present a problem to quadrupedal
motion, at least, once you put the animal on its heels).
Despite their enormous success and diversity a
group like the pterosaurs is not incredibly common in the record of fossil
prints. So the absence of these didactyl prints should not necessarily be
taken as a huge problem. In fact, we could just as easily take the
argument the other way and say, "well, if the toes were on the ground,
where are the prints with enormous imprints of bladelike second toe
claws?" Either way, we're still lacking dromaeosaur prints, it seems, they
should be pretty distinctive regardless of whether they held the claw up
and ran on the other two digits (as the skeleton certainly appears capable
of doing) or held it down. And even if we do find an imprint of digit II I
don't think that would totally solve the problem- you could argue
something along the lines of "well, it's in soft muck and not worried
about damaging the claw and it needs a little better stability in the
stuff, so it's using its claw but wouldn't normally" etc.