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Re: Gliders to Fliers? (Was Re: Ruben Strikes Back)
In a message dated 9/26/99 5:42:50 PM EST, mbonnan@hotmail.com writes:
<< Are not the boney articulations constraints? You can only put the bones
together so many ways, and of those, only certain angles and articulations
make sense. I don't think I've said anything here about the bones
themselves where one could say "perhaps" or "maybe." You put the bones
together, they only fit certain ways, you constrain what's going on. In
many of these dinosaurs, the only way to get the freedom of movement you see
in the arms and legs of mammalian tree-dwellers (or descendants thereof) is
to break or dislocate the bones. >>
Over the years, I've done my share of rearticulating fore- and hindlimb bones
in museum collections, and let me tell you there's a >lot< of play in
dinosaur limb and hand bones versus mammal limb and hand bones (which are
themselves pretty loose). This play must be taken up by cartilage, muscles,
ligaments, and tendons whose exact conformation is almost entirely
unavailable in the fossil record. Even in so basic an animal as _Triceratops_
we still argue over just what its stance was, how it habitually held its
forelimbs, and how much excursion there was to the various limb elements. For
example, there is >at least< 90 degrees of play in the articulation of the
first theropod metatarsal versus the second, which is more than enough to
change an aligned digit I to a retroverted digit I. So the question, "Was
digit I retroverted in nonavian theropods or not?" becomes meaningless: Check
the footprints if you can, perhaps, not the foot-bone articulations. I have
little faith in arguments based on rearticulating limbs and in limb elements
preserved "the way they were held in life," though of course I'm always
interested in hearing them.