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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.



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Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
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