Re: Bird flight once more (was Re: What is a Dinosaur? and semilunate carpal)

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

David Marjanovic (david.marjanovic@gmx.at) wrote:

<<< Wait a minute. There have _never_ been any _bipedal_ predators other than 
theropods, most or
all of which have (had) very stable hands.>>>

George Olshevsky (Dinogeorge@aol.com) wrote:

<<How about >people<?>>

David replies:

<People have become predators more or less yesterday, and have always used 
>weapons<. A totally
unfair comparison. BTW, as I said it isn't necessary to have stiff wrists, it 
just helps.>

  Actually, the comparison here should have nothing to do with the hands. Like 
basal dinosaurs and
basal theropods in general, as well as pre-Iguanodontian ornithopods (i.e., 
"hypsilophodontians")
the wrist is relatively flexible, not so much as one sees in mammals, but it is 
rather mobile in
supinatory actions, as well as the biplanar movement afforded by a lack of a 
large distal carpal
block with a trochleate surface [I think Luc Bailley wrote on a list of animals 
that had or had
not this block, and of that list, only tetanurans have it, including 
*Allosaurus* and
*Gallimimus*, and *Tyrannosaurus*; it is lacking in non-tetanurines, and I an 
unsure that the
fossils indicate whether *Afrovenator* or *Suchomimus/Baryonyx* have it, 
either].

  A mobile wrist in primitive dinosaurs and mammals is a _manipulatory_ 
function, it allows
short-range control over _small_ objects. This includes human weapon control, 
and raccoon feeding.
It is likely that aside from medium-sized prey that *Coelophysis* may have 
taken, small prey as in
lizards and the like were preferred prey, and the animal would even have 
possibly benefited in
various other "twist-wrist" activities: just look at small carnivoran mammal 
hand functions, or
rodentians. The stiffening wrists of theropods occur after coelophysids and 
kin, not before. This
appears to correlate with larger hands and more robust claws and arms, 
indicating a greater
predatory capability in the arms.

  Humans are flexible wristed bipedal predators because of the mentality, not 
because of the
wrist. If you disagree, look at how societies changes. We can _be_ predators, 
coelophysids don't
have as much as a choice. As Leakey might say, "human evolution is written in 
the teeth."


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

__________________________________________________
Do You Yahoo!?
Get email alerts & NEW webcam video instant messaging with Yahoo! Messenger
http://im.yahoo.com