Re: How did T. rexes hold their hands?

["Jaime A. Headden" <qilongia@yahoo.com>]

Brandon Pilcher (trex_kid@hotmail.com) wrote:

<I've heard it said that raptors could not pronate their wrists the way humans 
can; instead, their hands were stuck facing each other, as if holding an 
imaginary basketball. Was this restriction confined to the 
dromeosaurids/maniraptorans or was it general to theropods or coelurosaurs?>

  Presumably, any taxon with a distal ulna and radius with a tounge-in-groove 
arrangement will; not be able to rotate the distal end of the forelimb around 
the forelimb's long axis, with some give or take given how closely or rigidly 
the tongue fits into the groove. For most, if not all maniraptorans, this 
contact is a concave feature of the distal radius which locks around the distal 
ulna. In groups further from the avian origin, this feature may decrease, but 
it is pretty firmly locked in such taxa as *Tyrannosaurus rex* and *Gallimimus 
bullatus*, so this may tend to be nearly universal for coelurosaurs.

  If the distal end of these bones are more circular or voate, you will get 
more give on the rotation, but at this point, restriction of movement is 
dependant on the carpus. This is true for such taxa as spinosauroids or 
allosauroids, which possessed largeish carpals and a groove on the distal 
carpals which, as in coelurosaurs with this feature, focused the wrist's 
movement into an inboard flexure (towards external edge of the radius), as in a 
bird folding its forelimb.

  So take a look at the distal ends of the radius and ulna, since this is your 
primary evidence, and tends to preserve better than large carpals, as while 
they may be evidence of some restriction, they don't really tell you as much.

Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)