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Re: Again: origin of bird flight
At 04:50 PM 18/03/01 +0100, David Marjanovic wrote:
OK, er... still I think *Archaeopteryx* doesn't look anywhere near a
climber, so close relatives probably didn't climb much either.
Well, chickens don't look much like climbers either, but their relatives
the guans run about in trees as a matter of course. Note that this does
not make them climbers, merely arboreal - but then they don't have
functional arms to give them an assist. There is a difference between what
it takes to get up into a tree and what you do when you are up there,
especially if the tree is large and has good-sized horizontal limbs (mind
you, the kind of angiosperm trees I am thinking of weren't around in the
Jurassic, but gingkgos (which were) or something equivalent to the living
Podocarpus might have done just as well).
Nesting in trees, BTW, which has often been cited as an advantage of
arboreality, seems to be a rather recent innovation among Neornithes;
*Gobipteryx* nests are AFAIK also known to lie on the ground.
Many tree-living birds today nest on the ground, too. However, I would be
very careful about making conclusions about what an entire fauna did based
on what we know from the fossils of one or two forms. I would be extremely
surprised if Jurassic faunas were not ecologically diverse. The fact that
a Cretaceous bird is known to be a ground nester may tell us little more
about what other Cretaceous birds were doing than the fact that, say,
mallards nest on the ground today tells us about the nesting habits of
other ducks (some of which, of course, nest in holes in
trees). Furthermore, I would expect that a nest on the ground is much more
likely to show up as a fossil than a nest in a tree, so the fossil evidence
may be even less useful in predicting the range of diversity that must have
existed at the time than a single piece of information chosen at random
from living species would be.
My basic point, which often seems to be overlooked, is that you cannot draw
ecological or behavioral conclusions about species whose fossils you do not
have, and that before you make statements of what is or is not possible for
a given body form, you have to have a pretty good idea of the range of
diversity that exists today. Even then, you may overlook a unique
adaptation that no longer exists.
There must be a reason why 1 *Compsognathus* specimen is known from the
Solnhofen/Eichstätt area, while 8* specimens of *Archaeopteryx* plus the
isolated feather are known from there... Ebel suggests the later were more
likely to die in/above the place where they fossilized.
The reason, as far as I can see, is that Archaeopteryx could probably fly
out over the water, fall in, and drown now and then, while Compsognathus
could not. Flying Foxes in Australia, which roost over the water,
occasionally fall in and drown; that does not make them underwater
swimmers. Further, there are great many waterbirds that cannot swim
underwater, so there is no reason to conclude that even if Archaeopteryx
was the equivalent of some sort of shorebird (which I doubt) that is
actually represented the World's Worst Attempt to Design a Penguin.
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:email@example.com