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RE: Palms in



I have to agree with Matt (and Serano, well I'm at it) that many, if not most theropods couldn't pronate the palmar side of their manus ventrally. This is taken to an extreme in allosaurs, which seem to have modified the distal end of the ulna and radius in order to reduce mobility around the long axis of the forearm. Why did they do this? In a paper I presented at the Tate '96 Paleoenvironments of the Jurassic conference (sadly, these annual get-togethers ended recently due to political infighting involving a certain famous paleontologist that is mentioned on the list from time to time...) I suggested that one benefit would be that long duration use of the forlimbs in the remaining planes of mobility would require less effort, since the energy required of the muscles that would normally have to stabilize the forelimb in the prontation/suppination plane of rotation would be diminished, if not absent all together. In other words, if a large allosaur picked up Matt in one hand, and me in the other, and decided to carry us for a mile or so, it would have a much easier time than a similarly sized theropod who could still pronate its forelimbs.
Of course, there is yet another "why" here, specifically: Why would an allosaur want to do this? At the time, I was working with Bob Bakker on Nail Quarry out at Como Bluff. The taphonomy of the quarry suggested that juvenile allosaurs were regularily feeding on large animals (mostly sub-adult sauropods) to the exclusion of crocodillians and non-allosaur theropods. So he speculated that the quarry may represent a "lair," or some place were juvenile allosaurs were waiting for an adult to bring home the Apatosaurus bacon. Naturally this dovetailed nicely with my work. I balk, however, at commiting myself to this kind of (what, 17th level inference?) behavioral hypothesis without better support.


Scott
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