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Re: Do not misunderestimate the king was Re: Evolution of tyrannosauroid

Thanks, David. There is much new data in Lipkin and Carpenter's paper in the
T rex book due out soon. The evidence includes various pathologies (stress
fractures, fractures, muscle avulsions of the humerus) that it it clear that
the forelimbs are placed under a great deal of stress. Remarkably, the
incidence (as %) of these pathologies of JUST the forelimb bones (including scapula,
coracoid, and furcula) is highest of any theropod...

...Thus, the new evidences from the entire forelimb system of
T rex show  the forelimb was used actively.

Very interesting stuff! One thought to toss out, though: given the extremely high incidence of pathologies, is it conceivable that the arms were 1) used actively but 2) not actually terribly important. That is, Lipkin and Carpenter obviously show that the forelimbs were subjected to substantial loads and thus were not kept out of harms way. At the same time, the safety factor was apparently quite low, as the forelimbs were regularly being pushed beyond their failure points. This suggests to me, at least, that the arms were not under strong selection for increased resistance to load. Safety factors do vary, of course, but they appear to be pretty consistent within clades, based on the work published so far. The fact that tyrannosaurs seemed to have a strangely low safety factor makes me wonder a bit.


--Mike H.

Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280 0181 habib@jhmi.edu