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



On 11/8/2011 1:35 AM, David Marjanovic wrote:

-- The 2nd toe of dromaeosaurids was able to be flexed very far. It may
well have been used to hold branches against the metatarsus, all else
being equal -- but all else wasn't equal. There's a reason why the huge
claw is called "sickle claw": it's flattened from side to side, and its
very narrow palmar edge, while blunt on the ungual bone, may have
supported an outright cutting edge on the horny sheath in the living
animal. Cutting off the branch on which you sit brings the Darwin Award
to mind. Unfortunately, no keratinous claw of a dromaeosaurid is
preserved in 3D as far as I know.

I am agnostic on sickle-claws, at least as related to trees. Cutting of branches while sitting on them isn't gonna happen, though.

-- Any species that climbs trees and stands around in them for
evolutionary significant spans of time -- say, a few decades -- will
show adaptations to this.

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

-- Conversely, grasping feet -- including feet shaped by compromises
between grasping and walking/running -- may not have grasped any plant
matter, but prey.

Seems logical enough. Or both, or versa...

-- 300-lb rednecks are _better_ suited for climbing trees than
*Archaeopteryx* was. Sure, their weight is a massive disadvantage, I
presume they're wearing shoes, and they have laughably short toes; but
they've got amazingly flexible hands, insanely mobile shoulders,
forearms that can rotate through about 180° (and that's before we
consider rotation of the entire arm at the shoulder joint), hips almost
as mobile as a lizard's, rotatable lower legs, ankles that allow tilting
of the feet, a long, flexible vertebral column, and a dorsoventrally
flattened ribcage with the remarkably mobile shoulder blades on its
dorsal side. Do not project primate -- or even "just" general mammalian
or indeed general amniote! -- anatomy into dinosaurs. Do not take it for
granted; not everyone has it.

Steel climbing claws are commercially available -- should you actually try them, you will find your primate flexibility and mobility are actually undesirable, and that you spend all your time making short vertical motions w/ your arms more or less extended, hands in the thumbs-up position, and your feet in approximately the same orientation as when standing at the tree-base.

Left-hand up, right foot up, right hand up, left foot up, repeat...

Claw-ed trunk-climbers and hand-ed primates are apples and oranges.

-- 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?

I note yet again -- should the 'limited wing-stroke in pre-birds' contention be dis-proven, then the trunk-climbing capabilities of Archie-type animals are less relevant to those of us who wonder how birds became such wonderful fliers.

Expecting a vociferous debate on the validity of 'limited wing-stroke' to start, imminently... Silly me.

*Confuciusornis* may
be an exception, but it had moderately grasping feet, huge curved claws
on the 1st and 3rd fingers, an enormous deltopectoral crest on each
robust humerus, and IIRC shorter legs than Archie, especially shorter
lower legs; it was clearly better at trunk-climbing than Archie, even if
not much.

Interesting.

-- Why climb into a tree for safety rather than hide under a shrub?

Because it is safer...