Re: Again: origin of bird flight

[Ronald Orenstein <ornstn@home.com>]

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:ornstn@home.com