Re: paleonet Origin of birds

[Dinogeorge@xxxxxxx]

In a message dated 4/13/2005 12:56:57 P.M. Pacific Standard Time,  
tijawi@yahoo.com writes:

>>Rather, the process of exaptation appears to have played a  crucial role in 
the evolution of the avian flight apparatus.  There are  cogent explanations 
for why many flight-related characters (in modern birds)  first appeared for 
reasons unassociated with flight (in non-avian theropods)...  but this is too 
much information for one email message.<<
 
Paleontologists have become so enamored of exaptation that they  have a 
tendency to see it everywhere. But birds have so many very  flight-specific 
adaptations and autoapomorphies that it is EXTREMELY unlikely  that they ALL arose as 
non-flight-related exaptations. We're not talking  one-in-a-million 
unlikelihood here, we're talking one-in-10^50 or so. Those  "cogent" explanations 
referred to above are nothing more than  hand-waving--which, incidentally, happens 
to be one "hypothesis" for  the origin of wings in birds. When we see a random 
assortment of birdlike  features in a ground-dwelling theropod--and different 
theropods exhibit  different assortments of these--it is because these 
features were retained  (those that were not lost or modified away) from a 
previously volant ancestor,  not because they somehow accumulated to "prepare" or 
"predispose" the  theropod's descendants for future flight, in an  aerial regime 
from which the theropod is entirely removed.
 
When secondary flightlessness occurs in modern birds, the wings of the  
ancestral form are too strongly modified for flight and are usually  simply 
vestigialized (or even lost entirely) in the flightless  descendant. Now suppose the 
ancestral form is an archaeopterygid-like Mesozoic  bird (or an even less 
birdlike ancestral form of such), with clawed wings that  retain much of their 
original grasping-hand function. In a flightless  descendant of such an ancestor, 
the forelimbs might reduce, but they could  certainly retain their grasping 
hands with claws (as an exaptation!) for a  predatory function. Voila, we have 
the archetypal theropod. All it has to do is  get big--like lots of modern 
flightless birds have.