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Re: semilunate carpal
I once watched a mourning dove protect her nestlings by slamming a
California jay with her wings: She was using the flight stroke as a
weapon. Give her more primitive archaeopteryx-wings with claws instead of
wings she now has and a few million years of evolution, and she could
give rise to a lineage of velociraptor-like animals with predatory-stroke
The thing is, continued use of the wing as a defensive (or offensive) device
is not likely to be selected for in a volant bird. Using the wing to wack
an harrassing opponent might be used on occasion (like your dove vs jay
example), but it's going to wreak havoc on the integrity of the wing.
There's no way that a Velociraptor's arms would have been any good for
flying. How could you possibly think that they were a step >toward< flight
such an obviously non-volant animal (particularly since there were
contemporary flying birds)?
I'm not saying _Velociraptor_ is the ancestor of birds. (Yikes, did I
really need to point that out?) Velociraptorines and birds share a common
ancestor, and that ancestor used the predatory stroke (sensu Gauthier and
Padian) - the lunging, forward-and-downward motion of the forelimb and the
inward movement of the manus. Velociraptorines retain the primitive
raptorial function of this motion in theropods. The ancestors of birds used
this predatory stroke, and it was transformed into the flight stroke as the
feathers along the forelimb became incrementally more aerodynamic.
The trouble with evolution is that the characters
and features that we see in the fossil record don't come with little signs
attached to them saying things like, "I am evolving into a wing," or "I am
evolving from a wing."
I guess this is where phylogeny comes in to the picture. The sequence in
which different behaviors were evolved can be inferred from the acquisition
of characters associated with these behaviors.
It is extremely unlikely that the avian wing
evolved as a random collection of features that at some point in time all
miraculously came together into a unified structure perfectly adapted to
flight --like being dealt a royal flush as your first poker hand--without
already having some kind of flying function.
Poppycock! (And I mean that in the nicest possible way :-) )
Only *one* feature needed to refined in order to turn the ancestral
maniraptoran raptorial forelimb into a flapping wing - aerodynamic feathers.
This was the Ace which allowed theropods to fly - little maniraptorans
already had the rest of the cards in their hands.
The skeletal apparatus of dromaeosaurids required to work the predatory
stroke is *almost exactly* the same as _Archaeopteryx_ used to execute the
flight stroke. Apart from the sternal keel (which is actually not present
in most _Archaeopteryx_ specimens) name one substantive difference between
the skeletons of _Archaeopteryx_ and a samll dromaeosaurid (such as
_Microraptor_ or _Sinornithsoaurus_).
The Big Picture of dinosaur
evolution--the one that makes the most sense to me, anyway--is that birds
evolved by incremental improvements from small arboreal diapsids, and on
way scads of archosaur and dinosaur lineages and groups branched off this
evolutionary line, forever forsaking arboreality to become larger, heavier,
and more cursorial animals.
All that's missing in this intuitively attractive, well-thought-out,
explicit hypothesis is the fossil evidence to back it up.
Timothy J. Williams
Iowa State University
Ames IA 50014
Phone: 515 294 9233
Fax: 515 294 3163
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