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Re: Adaptive advantage (was Re: ABSRD BAND on Sinornithosaurus feathers)

Tom Hopp wrote:

I'm having difficulty with the scansorial ancestor. I'll bet Xu is already
sorry he said the pedal unguals of Microraptor looked like they might climb

How much do you want to bet?

The operative word in my previous post(s) was "facultative". I even said that these semi-arboreal theropods were comfortable in both trees and on the ground. This idea isn't new; Bock and Buhler proposed it some years back (I'll try and dig up the reference).

Another issue: once the draggy leap-from-a-tree hunter was on the ground,
what would it do if it saw prey THEN.

Chase it!!! Once on the ground, it would chase the prey. This is the major reasons why the proavian did not dispense with its cursorial adaptations. Jumping could bring it close to the prey, but not necessarily on top of it. Then the proavian's legs did the work.

Go look for a tree to climb? How does
drag help now?

It doesn't. Now it's in the terrestrial realm. Drag is only useful in getting there, where the real predation begins. See above.

   And another issue: cats hunt from the ground right? Even leopards, who
like to take prey into trees, do most of their catching from the ground. So
what is the modern example of a jump-from-a-tree predator?

Does there have to be a modern example of a "jump-from-a-tree predator" in order to validate the theory? How many bipedal predators OF ANY KIND do you see today? (Apart from _Homo sapiens_.)

All that said, I find it hard to ignore the fact that ALL the avian-like
theropods have very long legs. Why not some with shorter legs?

Long legs = cursoriality. This is not an inconvenience to the theory - it is integral. The proavians were essentially like any other small maniraptoran: fast, vicious and predatory. The tree-climbing ability is an added bonusa. Heading up to a tree branch is highly advantageous: camouflage; escape from larger predators; great vantage point to spy prey below; surprise in ambush predation; nesting perhaps? Once on the ground they could chase down prey with the best of them.

If they were
busy climbing trees all the time, why retain very long legs?

See above. And see my previous posts.

They ALL look
like terrestrial cursors to me.

Because a lot of the time they were running on land. Again, they were only FACULTATIVELY arboreal.

Thus, secondary flightlessness in maniraptors
or oviraptors asks for too much convergence for my liking,

I DID NOT claim that _Caudipteryx_ or velociraptorines were secondarily flightless. I suggested (like Xu et al. did in the _Microraptor_ paper) that they may be *less* scansorial and arboreal than their smaller ancestors - the same ancestors that gave rise to birds.

with everybody
somehow needing to be adapted to running, but a mysterious missing link
adapted to scansorial climbing in between.

Huh? The proavians were adapted for both running AND climbing.

I still think Ostrom had it exactly right from the first. He never thought
protobirds were runners who taxied for a take off. In his original papers, he
described them as leaping off the ground. Drag gets in the way of this.

Yes, drag does get in the way. But in tree-to-ground jumps, it can be very useful.



Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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