Re: New alvarezsaurid

[Dinogeorge <Dinogeorge@aol.com>]

In a message dated 98-03-29 17:42:12 EST, m_troutman@hotmail.com writes:

<< The development of volant adaptations is essential for flight. If an 
 ancestral bird did not have modified pectoral musclature, a posteriorly 
 directed coracoid, or assymetric flight feathers, flight would be 
 impossible. So flight adaptations must have evolved for reasons other 
 than flapping flight. >>

None of the listed features is >essential< for flight; they are, however,
improvements that might be expected in already volant animals, to make the
animals better fliers by giving them more control over their aerial
trajectories. I have a broader idea of what constitutes "flight" than just
"flapping flight." Anything that allows an animal to control its motion while
airborne, no matter how slightly, becomes a flight characteristic or feature.
Flapping flight is a specialized form of flight that evidently appeared late
in the evolution of birds well after numerous flight features had already
evolved--indeed, it's not yet clear whether _Archaeopteryx_ itself was a
flapping flier. I would certainly agree that many flight adaptations evolved
for reasons other than flapping flight; but I would tend to disagree that they
evolved for reasons other than flight (for the most part), as I have described
it.

Speaking of the furcula, I would agree with Haubold and Buffetaut that it
appeared in archosaurs such as _Longisquama_ to brace the pectoral girdle
during arboreal leaps and flights. So--is it a flight adaptation? Well, if
_L._ weren't this kind of flier, perhaps it wouldn't have needed the furcula.
So in that sense, the furcula >is< a flight adaptation. Might have to split
lots of hairs, so to speak, to get at the reasons why certain features first
appeared.