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Re: R: Archaeopteryx chimaera

At 09:05 PM 2/22/99 EST, Jim "EctoDino" wrote:
>I know that the opisthopubic condition helps birds be arboreal, so I wonder if
>that same condition helped dromies be arboreal too?

Well, if you are arguing that opisthopuby helps perhaps in reorganizing the
hindlimb muscles or in changing the cross-sectional anatomy to allow better
passage through trees and these somehow help arboreality or scansoriality,
then okay.

However, Ruben et al. argue that the "arboreal" aspect of opisthopuby that
allows for life in the trees is the development of the hypopubic cup and the
"butt pump" (okay, not their phrase) for lung ventilation.  These same
authors do not consider dromaeosaurids to have the appropriate features, so
I doubt they would consider dromaeosaurids arboreal.

Incidentally, Ruben et al. (and many other authors, it must be admitted)
were still using outmoded skeletal restorations of _Deinonychus_ with a
vertical pubis (the idea c. 1976).  More recent discoveries of completely
articulated 3D dromaeosaurids show that they had fully opisthopubic pelves,
even more so than _Archaeopteryx_ (at least one potential synapomorphy for
an Archie + (Dromaeo. + more advanced birds) topology, but currently
outweighed by other features).

Jim "EctoDino" also wrote:
>> Ruben et al. do not consider Archie to have a "dinosaur pelvis": indeed,
>>  they restore it with a hyperopisthopuby not justified by any of the
>>  specimens.
>How about the Berlin Specimen?
Although the pubis points in an extreme opisthopubic condition in the Berlin
specimen, the evidence shows that it was displaced postmortem (see, among
others, Wellnhofer, P. 1985. Remarks on the digit and pubis problems of
_Archaeopteryx_. pp. 113-122 IN Hecht, M.K. et al. (eds.) The Beginnings of
Birds: Proceedings of the International _Archaeopteryx_ Conference Eichstatt
1984).  The particular details of the same type of displacement are better
preserved in the Solnhofen specimen (see Wellnhofer, P. 1992. A new specimen
of _Archaeopteryx_ from the Solnhofen Limestone. pp. 1-23 IN Campbell, K.E.,
Jr. (ed.) Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural
History Museum of Los Angeles County Science Series No. 36).

In the Solnhofen Aktien Verein specimen, in which the lateral suface of the
pelvis is not obscured by the hindlimb on the main slab, the natural
articulations can be clearly seen.  These show that the main shaft of the
pubis is at about a 110 degree angle from the horizontal: opisthopubic, but
not terribly far from vertical. (Wellnhofer, P. 1993. Das siebte Exemplar
von _Archaeopteryx_ aus den Solnhofener Schichten. ARCHAEOPTERYX 11:1-48).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661