Re: Thou Shalt Not Climb!

["Jaime A. Headden" <qilongia@yahoo.com>]

David Marjanovic (david.marjanovic@gmx.at) wrote:

<It isn't. It's just that in the absence of such adaptations we have no 
evidence that it ever _was_ in the trees.>

  Not just that, but the implied agreement that there were no Solnhofen trees,
thus it couldn't climb them. Been through this. Climbing does not require
trees. 

<But they clearly didn't evolve _for_ climbing. They are ordinary theropod 
finger claws, a _retention_, not an adaptation that evolved in *Archaeopteryx*.
Archie simply lacked selective pressure that would have led to the _loss_ of
the curvature.>

  Actually, they could have evolved for climbing and the selective pressure
lost for Archie, but it retained the curved "talons" in a tree-less
environment, scampering up rock faces and the like as an extension of this
ancient behavior adapted to environment.

  There IS a selective pressure in keeping such unguals; Archie could have
developed them in its own time from more terrestrial ancestors, simply by
choosing a choice of prey that required more dextrous grasping or rock-climbing
skills to aquire. There is an implication in the works of some, as I see it,
that tends to mark Archie as a throwback based on the whole of avian evolution
or the dinosaur to bird shift in biology, but this looks at Archie in too small
of a focus to address the particulars. There are, as it were, multiple
three-dimensional puzzles to which Archie's a part of which would not
ordinarily come together were it not for it.

<So do *Gigantoraptor* and *Allosaurus*.>

  Curvaceousness of the claws compared to size? No. *Allosaurus* is a grasping
animal, and the fact that it's manual unguals are more highly curved than those
of *Gigantoraptor* tell you something, in which that the latter is not so
active in aquiring living prey or dealing with grasping objects with its manus.
Not so, it seems, *Archaeopteryx*, retaining high degrees of curvature and size
of unguals to limbs in both sets, far more than closely-sized dromaeosaurs like
*Microraptor*. One must also note that Archie possesses highly recurved unguals
not just in the manus but in the pes, as well, which is absent in even the
small "arboreal" dromaeosaurs, but which its features indicating it was
grasping _something_ with its feet.

  Yalden has concluded that the pes of Archie is not suited for perching, but
this is a nobrainer, given that few perchers lack a reversed hallux, and those
that don't have one don't sleep perching (say, swifts -- which I understand
have a reversible one, but not fixed). However, Archie retains a degree of
curvature far and above its "ancestral" form in dromaeosaurs, and this is
hardly evidence of a retentive feature, but evidence for a derived morphology.
The putative ancestor to Archie that derived from dromie stock as given in
Paul's hypothesis has yet to be found, though hypothetical, but to keep Archie
as a remnant of a morphology, it would need to be MORE avian than either Archie
OR dromies. At least in the foot.

<Sure. But the increased range of motion is still pathetic by comparison to 
extant climbing animals.>

  Pershaps, but increased motion is increased motion, and this level of
flexibility is curious. Not all climbing animals are so adapted for it than
"true climbing animals" are.

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


       
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