Re: paleonet Origin of birds

[Dinogeorge@xxxxxxx]

In a message dated 4/13/2005 12:58:22 P.M. Pacific Standard Time,  
tijawi@yahoo.com writes:

>>A cladogram can indeed tell you the order in which individual  characters 
arose.  For example, a cladogram of the Dinosauria tells us that  theropods 
inherited obligate bipedalism, and then went on to evolve (in the  following 
order): furcula ("wishbone"); feathers; semilunate carpal  ("swivel-wrist' - 
essential for execution of the flight stroke); elongated  forelimbs; asymmetric 
vanes; and reversed hallux.  This sequence of  character acquisition contradicts 
George's own hypothesis, so he has a vested  interest in distrusting what the 
cladogram is telling him.<<
 
 
No, it cannot. This is an assumption built into the cladogram by choice of  
outgroup. You choose a bipedal form as the outgroup, and sure, your  cladogram 
will "prove" that the ancestor of the clade is a biped(!). The problem  with 
most dinosaur cladograms is that they have many character polarities  backward 
ab initio.
 
Semilunate carpal evolved at least twice in Maniraptora (segnosaurs and  
deinonychosaurs independently: Alxasaurus had no semilunate carpal, eg).  Reversed 
hallux evolved very early in theropods and occurs in all theropods at  or 
above the ceratosaur level--look at theropod foot anatomy, fer  chrissake, or at 
theropod footprints from the Triassic. It is not "essential"  for the 
execution of the flight stroke, it is an adaptation to make the flight  stroke more 
efficient. The flight stroke comes first, then the improvements, not  vice versa.
 
Feathers? We know nothing about the evolution of feathers from any  
cladogram. But do you think they appeared fully formed by magic in  Archaeopteryx?
 
Bipedality. I claim that many dinosaurs were bipedal because the forelimbs  
of their volant ancestors had become too winglike to be used for walking by  
their ground-dwelling descedants. Current models of dinosaur evolution provide  
NO reason for the appearance of bipedality in dinosaurs except the 
tautological  one: they somehow made dinosaurs "better."
 
And so on.