Re: Again: origin of bird flight

["David Marjanovic" <david.marjanovic@gmx.at>]

Old answers forthcoming:

----- Original Message -----
From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: <david.marjanovic@gmx.at>; <dinosaur@usc.edu>
Sent: Monday, March 19, 2001 1:13 AM
Subject: Re: Again: origin of bird flight


> 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.
>
> Again: An animal's behavioral repertoire may extend beyond simply what its
> functional anatomy suggests it is *best* at.

true

> Hey, I can climb trees (not very well), and my unguals aren't even sharp
and
> tapered.  Give me sharp claws to dig into bark and explain to me how
> advantageous sitting in a tree might be if I feed on small, fast-moving
prey
> that might be hard to spot at ground-level.  For a small-ish predator (say
> _Sinornithosaurus_-size) it may be even harder to peak over vegetation to
> spot a lizard in the distance.  But, with smaller body size, it becomes
> easier to climb up a tree (against the force of gravity) and stand on a
> branch (which, hopefully, won't snap under your weight).

BUT you have several arboreal adaptations that no known dinosaur has: Your
shoulder joints are terribly mobile; in combination with your elbows and
wrists you can turn your hands around by nearly 360°, and you can reach
every spot on your body with your hands. You can sprawl your legs. A few
bird species that live in reed can do this, but no other dinosaur, including
the most arboreal birds, AFAIK. Your argument about size is true, and I can
imagine that a dromaeosaur could lurk clinging to a tree trunk in the
position Chatterjee has suggested (though climbing in this position must
have been very difficult, and the poor dromaeosaur would have had to jump
off backwards at its prey, respectively to turn around in the air); but I
can't see this poor climbing ability connected to flight. And even if the
ancestors of birds were better climbers, parachuting can arise in arboreal
animals (and apparently only there), the same holds for gliding, but not
flight.

The "pouncing on prey" hypothesis by Garner, Taylor & Thomas has one logical
problem for me -- it seems to require quite large animals that pounced down
from _high_ ambushes on rather large prey that couldn't escape while the
predator was jumping down. I can't imagine *Caudipteryx* or smaller ones
hunting insects that way! (Though Taylor, in the following article which is
all what I have on this hypothesis, makes a reasonably good case IMHO for
*Caudipteryx* being an insect-eater, like the aardwolf, which also has
gastroliths.) Taylor writes that *Caudipteryx* has remiges exclusively on
its hands, which is impossible to say from the not fully prepared specimen
that he shows in a figure. (I have now copied the Vertebrata PalAsiatica
description of *C. dongi*, which has good figures, and will say a few things
about it next week.)

Graham Taylor: Winging it, New Scientist 28 August 1998, p. 28 -- 32

But you're right, I should wait to get the *Carnopteryx* papers before
saying more... B-D

I really wait for troodontids, alvarezsaurs and yandangornithids from
Liáoníng...