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



Augusto Haro wrote:


> Tim, I'm not saying that *Archaeopteryx* runs in branches, but that using
> the wings for balancing purposes when climbing has not necessarily to be
> related to fast locomotion, and can be used also when going to fall even if
> not running.


OK, I understand now.  Still, using only the hindlimbs for any kind of arboreal 
locomotion has to take into account the poor grasping abilities of both the 
hands and the feet.  Climbing and perhaps 'perching' would have required both 
fore- and hindlimbs to be used.


> I forgot to mention in the phrase of the perching foot that its relatively
> early appearence is suggestive of arboreal habits in early birds, altough it
> is apparently not present in the earliest avialae (so that it might be a
> further refinement to a formerly invaded arboreal habitat).


Quite possibly.  But the incipient grasping pes shows that arboreality could 
not have long preceded _Archaeopteryx_.  BTW, I'm not against the idea of 
_Archaeopteryx_ (or _Microraptor_, or _Epidendrosaurus_, or even 
_Protarchaeopteryx_) occasionally venturing up into trees.  However, the 
question to ask is: why were their climbing/perching abilities so darn awful?  
Did something hold them back; or were all these guys very close to the origin 
of arboreal habits in theropods? 


> That the foot of *Archaeopteryx* is not perching does not seem to be
> sufficient evidence against arboreal habits, or to invalidate what the
> curvature of unguals indicate. Indeed, many animals that climb do not have a
> perching foot. 


True.  But the absence of a specialized perching foot is strange for animal 
that supposedly spent most of its time in trees and/or evolved from a 
'tetrapteryx'-style glider.  


Overall, I think discussions on the arboreal versus cursorial habits of 
_Archaeopteryx_ should not be presented as black and white, but in shades of 
grey.  On the claw curvature issue, I'd highly recommend reading Glen and 
Bennett (2007; 'Foraging modes of Mesozoic birds and non-avian theropods', 
Current Biology 17: R911-R912).


> Among mammals, not even the Primates present such a opposable
> pollex (the pollex never forms a 180° angle with other toes), yet there are
> many good climbers among mammals, which use curved claws. 


Primates happen to have a superbly prehensile manus.  


> Yes, the horizontal femur is much probably useful for maintaning the center
> of gravity upon the feet, but it seemingly restricts cursoriality
> by removing a segment from the stride lenght. However, as many birds retract
> the femur extensively while running, perhaps no segment was lost after all
> when needed.


Cursorial birds can run quite fast, although not elegantly.  Apparently in 
ratites the femur is mobilized during running.  In any case, the effective 
'removal' (decoupling) of the femur from most forms of locomotion is 
compensated by changes to the length of the more distal hindlimb segments.



Cheers

Tim
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