Again :-] : Re: Again: origin of bird flight

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

----- Original Message -----
From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: <david.marjanovic@gmx.at>; <dinosaur@usc.edu>
Sent: Sunday, April 01, 2001 9:22 PM
Subject: Re: Again: origin of bird flight


> David Marjanovic wrote:
>
> >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

Also, I think it will have jumped into this position in most cases rather
than having climbed up the trunk.

> No, it only climbed trunks to get into the branches - once there, the
little
> predator had a wonderful vantage point.

This still requires it was able to climb up the trunk.

> Or, as Naish (2001) has suggested,
> certain small theropods could clamber up trees using branches as hand-
(and
> foot-) holds.

This requires low branches, which were surely not available on a large part
of the trees.
Which paper do you mean?

> >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.
>
> Why?

Short-lasting jumps (from low heights) wouldn't offer any opportunity for
selective pressures to, er, press: The direction of a jump from 1 m can be
controlled enough by just jumping off in a direction, and if this fails the
predator (I imagine blackbird to crow size here) is still very close to the
prey, so it can easily run there.
If, OTOH, the predator jumps off from 2 m, the jump lasts so long that the
prey will escape in too many cases.

> >I can't imagine *Caudipteryx* or smaller ones
> >hunting insects that way!
>
> What about frogs, urodeles, lizards, small mammals, eggs, baby
dinosaurs...

Hunting frogs is difficult. Considerably larger size, and maybe arboreality
or an ability to swim, will help. Same except for arboreality for urodeles.
Compsognathid size is a good idea for a lizard and mammal hunter, while
average Mesozoic mammal size is not one for nest raiders.

> >I really wait for troodontids, alvarezsaurs and yandangornithids from
> >Liáoníng...
>
> Or a tyrannosaurid (either a small species or a juvenile - either would
> probably be feathered.)

I forgot that there is already evidence for EK Asian tyrannosauroids... :-]