Re: Gliders to Fliers? (Was Re: Ruben Strikes Back)

[Dinogeorge@aol.com]

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.