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Re: Giant flightless birds



OK,...here`s something else.There seems to be a trend in the number of
digits possessed by theropods. That trend seems to be a loss of such digits.
A good reason for lose of digits might be that they simply were not needed
as birds evolved more sophisticated wing structures. Archaeopteryx had three
free digits (even pterosaurs had three free digits), but they don`t seem to
be opposable. Still, they were functional for "hooking" onto branches and
clambering about in the treetops. Hoatzin chicks have two, which function in
similar manner. Now, T_Rex also has two. Again, I can see this as a holdover
from a previous "hoatzin-like" state.
What I can`t readily see is why T_Rex (if it was always terrestrial) had
lost the opposable quality of it`s digits . Again, it seems to make more
sense that a terrestrial animal would always be in need of good grasping
ability of its forelimbs for ther procurement of prey. The only reason for
loss of such ability, (that I can visualize) would be that the condition was
inherited from an Avian ancestor that itself had lost the third digit.