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Re: Theropod limbs - how mobile?



----- Original Message -----
From: "Fam Jansma" <fam.jansma@worldonline.nl>
Sent: Friday, May 17, 2002 11:44 AM

> Let's say he didn't, the following makes perfect in a neoflightless sort
of
> way...: take Deinonychus, big bad Dromie. The immobility in it's hands
make
> it difficult for capturing prey, our poor Dromie sees all those delicious
> Hypsies just walking right by him and he is getting hungry. In a while, he
> solves it: he evolves an alternate tool to slice his prey up.

And in the meantime he starves, doesn't he!?! -- As has been discussed very
often onlist, that immobility is a great thing for such a predator, as this
makes it much more difficult for prey to escape, relatively much easier --
no muscular effort is required -- for the predator to hold it. And while
it's holding its prey, it finishes it off by means of the sickle claw. Looks
like *Tyrannosaurus* likewise used its arms to hold prey in place -- not up,
not down, just in place -- and used its jaws to finish the job. The paper in
Mesozoic Vertebrate Life explains this. *T. rex* arms are incredibly strong
and not vestigial in any way. They are so short because this -- like in the
mononykines -- brings maximal force at the expense of unnecessary velocity;
dromaeosaur arms are built for maximal velocity instead, and human arms are
a compromise for climbing. Take-home message -- unfortunately, one must read
the most expensive books available. :-)

> This in the
> shape of of an enlarged pedal ungual II who practicly takes over the
> function the hands had in predation. With this tool in place the hands
have
> time to re-evolve their mobility. If the hands had re-evolved that
function,

Did they?

> there is no use in the specially adapted killer claw and therefore is
> getting smaller. This is something that is known in several late
Cretaceous
> forms (Adasaurus (although possibly paravian), Velociraptor)

The claw of *Velociraptor* isn't small at all.

> >It is interesting to note that, based on _Eotyrannus_, the craniodental
> >specializations seen in tyrannosaurids preceded truncation of the
> forelimbs.
> >
> Nasal rugosities don't count :)

The diagnostic teeth do.

> >That's ONE purpose - and I never said the arms were used to bring chunks
of
> >flesh to the mouth.  Of course, they were too short.  However, another
> >purpose is that the little arms were used sort of like grappling hooks to
> >help secure prey held by the head.
> >
> Or they could not have had a function after all.

Then they'd look more vestigial. While the 3rd finger is indeed gone,
indicating that precision grasping was not an issue, everything else is
still there and very strongly built.

> When something get's progressively shorter,

Were they getting _progressively_ shorter? Aren't all known tyrannosaurid
arms of pretty similar sizes?

> Take your own appendix for example, it is very reduced and serves no
> function at all,

Looks like it does serve a function in the immune system, I've heard.