[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: I knew it!
Greg Paul (GSP1954@aol.com) wrote:
<The hadrosaur radius and ulna can only articulate crossed, which is why
the palms face strongly backwards in trackways. So the notion that all
dinosaurs had permanently uncrossed lower arms is incorrect. Am very
suspicious of arguments that this was true of any dinosaur, except perhaps
those with such reduced arms that it does not matter.>
I do not think anyone has published or professionaly supported any
implication that ALL dinosaurs could not supinate or pronate the forearm
and back again. Sereno, at least, has proposed this for basal theropods
and various upper-level theropods, including tyrannosaurs and
allosauroids, which articulated specimens show the radius has a limited
cross-over capability and would have not permited the palms to face
caudally. The hadrosaur forearm cannot, based on its articulation,
supinate, if the radius/ulna articulations are to tell anything.
Ceratopsian and sauropodan manus have to have articulated facing caudally,
yet at least in the later, no articulation of the forearm permits this
posture, suggesting the solution is at the shoulder. Other analysis
implies that the absence of a distal ulnar--radial contact in
*Sinosauropteryx* would have permitted a good deal of inter-ulnar/radial
movement; similarly, the distal forearm appears to have easily rotated in
basal ornithischians and likely most non-hadrosauroid ornithopods, in
which the ulna and radius do not appear so closely appressed. The relevant
figure in Kobayashi and Lü (not Lu) (2003, fig. 16A) appears to indicate
the radius is not articulated to the distal medial humerus, as it is in
*Gallimimus* (unless the radial condyle has migrated cranial to the ulnar,
as occurs in basal mammals and non-suarian reptiles); this condition
appears to have resulted in the so-called "crossed" forearm.
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
Do you Yahoo!?
SBC Yahoo! DSL - Now only $29.95 per month!