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RE: Theropod shoulder movement



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Martin Baeker
>
> This may be a rather stupid question, but after the brillant explanation
> of semi-lunate carpals in maniraptorans I wondered how the did move their
> shoulders.
>
> AFAIK, in most mammals, movement in the shoulder is rather restricted to
> the humerus moving in a plane which is more or less parallel to the median
> plane of the animal (I hope I use all these to me rather unfamilar terms
> correctly), i.e. forward and backwards, but not up and down sideways. Only
> in some primates (like humans) is this different. Is this
> true?

It is true that many terrestrial mammals have limited degrees of motion in
their forelimbs; part and parcel of being a large striding quadruped...

> And if so,  I wonder: Was this the same for theropods. Could they move
> their arms to the sides? And if not, could someone explain to me how birds
> move their wings in the shoulders? Because I cannot imagine how this could
> be done if the arms can only move forward and backwards (and not
> up and down)?

The same is not true for theropods, and least true for maniraptorans.  Even
theropods with relatively limited possible motion in the arms (like T. rex)
could still move them "outwards" as well as within the plane of the body:
see Carpenter & Smith's chapter in Mesozoic Vertebrate Life for a
description of the motion in the Big Guy.

In maniraptorans, the glenoid (shoulder joint) faces more laterally than in
dinosaurs primitively, giving them much more motion out and away from the
body.

                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): 301-405-0796