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RE: Palms in



Many dinosaurs have a forearm in which the radius and ulna do not cross one another, or only slightly cross one another. Therefore, it would have been difficult or impossible for most theropods to pronate (place their hands palm side down) their hands simply through rotation of the radius about the ulna. However, flexion at the elbow and rotation at the shoulder joint may have allowed them to fully pronate their hands to a palm side down orientation. At least, this is what I have observed through bone manipulation in Allosaurus, Herrerasaurus (a cast in this case), and the prosauropod Plateosaurus.

Sereno is probably correct in stating that most theropods held their hands palm-side in, as if you put your hands together to pray. This is an important functional observation, because many illustrations and some mounts of dinosaur skeletons show the radius crossing over the ulna like it does in primates -- the only way for the radius to cross over the ulna in most dinosaurs is to disarticulate it from the forearm and cross it over.

Matt Bonnan


From: "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>
Reply-To: tholtz@geol.umd.edu
To: <dbensen@gotnet.net>, <dinosaur@usc.edu>
Subject: RE: Palms in
Date: Fri, 7 Jul 2000 11:37:05 -0400

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> dbensen
>
> Apologies if this topic has already been hashed over on the DML,
> but I am asking
> which clades of dinosaurs held their hands birdwise, palms in?  I
> know that
> anything more birdlike then tyrannosaurs did, but what about the
> allosaurs, the
> staurikosaurs, or the prosauropods and ornithischians?  Where does the
> bird-wrist mutation happen?
>
Sereno has argued (at Dinofest 1998: no, I don't know when the volume is
coming out...) that all theropods held their hands palm-inward.  However, I
have seen handprints on probable coelophysoid tracks, which indicates they
could at least rotate their manus into such a position where the palm faced
downward.  Prosauropod tracks definitely show palms-downward when walking
quadrupedally.

Off hand, I'd think that tetanurines in general held palms-inward.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843


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