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

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

My thoughts in random order. I hope I haven't forgotten half of them.

-- 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.
-- 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.
-- Conversely, grasping feet -- including feet shaped by compromises 
between grasping and walking/running -- may not have grasped any plant 
matter, but prey. Today, the most extreme phalangeal ratios, claw sizes 
and claw curvatures are found in predatory birds. The hands of theropods 
are plesiomorphically in that range; this includes *Archaeopteryx*. 
Perhaps this also explains why carnosaurs had less extreme phalangeal 
ratios than extant cursorial birds.
-- 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.
-- 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. *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.
-- Why climb into a tree for safety rather than hide under a shrub? 
There are mammals and squamates in both places. Complete safety is for 
oceanic islands, if that.
-- Yes, the ability to perch is plesiomorphic for Neornithes. That 
doesn't mean it evolved much earlier. Crown-group turtles are amphibious 
plesiomorphically, and the extant terrestrial representatives are 
secondarily terrestrial, but among Testudinata as a whole, the marine 
*Odontochelys* is an outlier; the rest of the stem group was 
unambiguously terrestrial.
-- As someone mentioned, goats are fairly highly specialized rock 
climbers. Seeing them in a tree isn't any more surprising than seeing 
300-lb rednecks in a tree. And apparently the tree kangaroos are the 
sister-group of the rock wallabies (*Petrogale*).
-- *Zhongornis*? Underrated? Isn't it rather an overrated juvenile 
*Confuciusornis*?