RE: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

[Tim Williams <twilliams_alpha@hotmail.com>]

Augusto Haro wrote:


> It is true that primates can grasp, but what I said is that they do not
> have such a retroverted pollex as in birds, yet they can grasp the same. If
> the digits are sufficiently splayed out, they can grasp more firmly, even if
> not having a completely retroverted pollex.
>
> I do not think that the lack of perching foot is to be strange in a glider.
> as far as I know, there are no retroverted digits in either colugos, *Draco*,
> or gliding squirrels. Indeed, grasping foots are most developed in slow
> climbers, such as chameleons, or lorisids. Arboricole iguanas do not present
> perching feet yet they are faster moving than chameleons.


Yes... but all these critters have (by and large) a quadrupedal gait, flexible 
wrist and ankle joints, and a supple spine.  In short, they're fairly well 
adapted to life in the trees (or at least climbing).  Gliding squirrels, for 
example, use gliding to commute from tree to tree and so bypass the ground.  
So, the comparison between any of these animals and _Archaeopteryx_ breaks down 
very quickly.  _Archaeopteryx_ was a biped with a fairly rigid backbone, and 
wrist and ankle joints with proscribed ranges of motion.


Perching is a way of reconciling obligate bipedalism with arboreality.  
Theropods (as dinosaurs) are primitively bipedal.  So if birds had descended 
from arboreal animals (like a 'tetrapteryx'), or had become arboreal early in 
their history, one might expect to see specialized perching adaptations in the 
most primitive birds, like _Archaeopteryx_.  Yet we don't.  


> Yikes, that paper you pointed to seems to get the arboreal-claw-argument to
> trash (will try to download). Serious blow to the arboricole theory (and I
> think perhaps its better support), but thank you.


You're welcome.  The "tree-dwelling _Archaeopteryx_" idea has never had much 
support from anatomical evidence.  Sure, _Archaeopteryx_ might have ventured up 
trees; but it certainly wasn't very well adapted to this kind of behavior.  
Glen and Bennett's study reinforces the hypothesis that _Archaeopteryx_ divided 
its time between the ground and the trees.  There's other studies that support 
this idea (e.g., Hopson's paper in the Ostrom symposium volume.) 



> You can climb without using the forearms, for example, using WAIR. 


But can WAIR get you all the way up a vertical trunk?


>From another thread...


Eric Boehm wrote:

> So my related question is: Is there a fundamental superiority to Mammalian 
> quadruped predators that 
> resulted in them outcompeting the Biped "terror birds" (really the closest 
> thing after the KT to a classical
>  dinosaur), or was it an accident of geographhy?


Maybe the success of predatory mammals vs predatory birds has more to do with 
teeth, rather than bipedality vs quadrupedality.


Cheers

Tim
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