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

Re: The "ideal" Eumaniraptoran arm motion



>-----Original Message-----
>From: Pharris Nicholas J <pharrinj@plu.edu>
>To: Larry Febo <larryf@capital.net>
>Cc: James R. Cunningham <jrccea@bellsouth.net>; Jeffrey Martz
<jeffmartz@earthlink.net>; >dinosaur@usc.edu <dinosaur@usc.edu>
>Date: Wednesday, March 03, 1999 9:30 PM
>Subject: Re: The "ideal" Eumaniraptoran arm motion




>On Wed, 3 Mar 1999, Larry Febo wrote:


>> Why such a limited motion in one plane?? Can that be
>> called optimal? You`d think it had time to evolve more freedom of
movement
>> in the shoulder girdle.
>> And the thought that this "optimal" restricted motion "just happened" to
be
>> the ideal for avian flight.........it`s just too hard for me to buy it.

>I'm not sure in what way you consider eumaniraptoran arm motion to be
>"limited."  Eumaniraptoran shoulders, like those of other tetrapods, were
>ball-and-socket joints, and hence the arms could lunge in any forward
>direction.  It's just that the wrist was constructed to operate in the
>same plane as the elbow.

>Nick Pharris
>Pacific Lutheran University
>Tacoma, WA 98447
>(253)535-7045



I used to assume that theropods had unlimited motion of the forearms (as in
primates), then was surprised to learn that motion was restricted to a plane
similar to motion of a birds wings. There`s a mention of this in an article
from "Patterns and Processes of Vertebrate Evolution" (Carroll
pg314)..."Ostrum (1974) argued that dromaeosaurs used movements very similar
to those of avian flight in the capture of prey. He suggested that they may
have used their forlimbs, with evolving feathers, like nets to capture
insect prey. This specific hypothesis is difficult to test, but whatever
they fed upon, the major muscles to move the forelimbs must have been
located ventrally, medially, and anteriorly if the hands were used together
in the capture of prey. Hence, the movement of the forelimbs in any bipedal
dinosaur in which they were used to capture prey would have approximated the
flight stroke of birds."

This is not exactly the reference I was looking for,...I believe I read
something about the restricted arm movements in (I think) Oviraptors.  I
think the arguement had to do with the limitations of the theropod shoulder
joint.