[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Perching, climbing, roosting was Re: 11th specimen of Archaeopteryx
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
-- 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
-- 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