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Re: Perching, climbing, roosting was Re: 11th specimen of Archaeopteryx



On 11/9/2011 12:11 AM, Tim Williams wrote:

I agree wholeheartedly, as far as roosting is concerned.  The hallux
of archaeopterygids and deinonychosaurs remained stubbornly
un-reversed, and fairly elevated.  The argument that these critters
sought out tree crotches or large boughs or the crowns of cycads for
roosting strikes me as special pleading.

From an evolutionary perspective, the idea that merely roosting in a tree would counteract a terrestrial ground-foraging lifestyle and alter foot-design in a clawed animal that can already climb is the special pleading.

Ditto the claim that re-arranging foot design to satisfy somewhat anthropomorphic assumptions about roosting stresses is a trivial matter, design-wise...

Is the flamingo's foot shaped while it sleeps, or while it is foraging?

The foot is already optimized to standing around.

"There is no direct evidence of roosting in (...)" is a correct statement. Claiming that simple roosting would necessarily be evident in the bones once the physical capacity to do so is established, is NOT supportable.

I do not think you can explicate a scenario by which selection will measurably alter the central limit of design variance in the foot, incrementally expanding upon a small fortuitous change -- when all the heck it is doing is standing/crouching/huddling/squatting/whatever while sleeping.

At least, not one which overwhelms the selection occurring during terrestrial foraging, fleeing and mating.

But I am listening.

Another thing is that the hands of paravians like _Archaeopteryx_ and
_Microraptor_ were not adapted for grasping small objects; they could
only grasp large objects with both hands.  Either these objects were
large prey (as posited for velociraptorines)... or something else.

Hmmm -- how about a tree-trunk?

The next part of David's stream of consciousness concerned how we
should not extrapolate the range of motion that mammalian (especially
therian) skeletons are capable of to dinosaurs.  No arguments there -
I've been banging on about this, but David expressed this sentiment
far more succinctly and articulately than I did.

Yet it had nothing to do with the actual mechanics of climbing...

Why? Are your feet evolutionarily adapted to sleeping in a bed?

While sleeping, my feet aren't securing my body to the substratum.

Where is the selection occurring?

The occasional windstorm does not outweigh the thousands of steps taken daily while foraging in a presumably predator-rich environment -- especially when the windstorm most likely results in only a minor inconvenience.

Has the discussion relapsed into "Well, they topple over when they go to sleep, which kills them, ya know..."?

They were small animals and had clawed feet, not little roller bearings. Considering also their clawed hands and wings, the claim that they needed "securing to the substrate" appears to be special pleading as well.

-- So far, I don't see a reason to assume any climbing or roosting in
any dinosaur that wasn't able to fly into a tree.

Ah! So you are strictly a "ground-upper", then? Tell me how you manage that,
in the face of a limited wing-stroke?

You raise an interesting point.

Actually, that has been a central point all along. Thank you for acknowledging it.

I agree that a limited upstroke tends
to rule out a "ground-up" origin of flight, because scenarios such as
WAIR emphasize the role of a full wingstroke in the incipient stages.
However, there are other reasons aside from roosting that might put
small paravian theropods at elevation.

Foraging is out, because their feet are not adapted to foraging in trees. Daily foraging in trees will indeed quickly change the extremities, being a locomotor activity -- keyword = "activity"...

I do not see any likely alternatives, given limited wingstroke -- again, that is my point.

You have alluded to "other reasons" twice now, iirc. I am listening.