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



Erik Boehm wrote:

<I think the perching adaptation that birds have is only of use once a minimum 
proficiency in precision flight is attained, and for the first examples of 
therepod flight, the absence of a reversed toe for perching probably is 
irrelevant in the arboreal vs cursorial debate.>

The problem here is that *Archaeopteryx* doesn't appear to even be that 
important of a player on the direction toward birdiness. The problem lies in 
several elements, including the apparent "half of a wing". What use is such a 
structure on the evolution towards flight? There is no actual direction just as 
there is not actual destination, so what features we peg as "towards flight" 
have to operate under a paradigm while the animal was alive. WAIR can help 
explain this, but it doesn't answer everything.

Your argument is still flawed in what you are using to analogize your climbing 
*Archaeopteryx*:

<However, humans still regularly climb trees(some more than others depending on 
where one is), despite an evolutionary trend away from adaptations to do so. It 
does coincide with a dramatically decreased need or reason to climb trees 
however.>

Humans possess pronating and supinating wrists, a highly mobile shoulder joint 
that can rotate the arm about its axis with a nearly 160 degree range of 
movement in three dimensions, and they can, to some degree, supinate the ankle. 
They also, like Scott mentioned with squirrels, climb close to the substrate 
and now out and away from it on less flexible levers that are the legs and arms.

*Archaeopteryx*' legs and hips were so incapable of this modus that it is 
unlikely they were in any aspect arboreal. This doesn't mean they couldn't 
climb, but they certainly weren't arboreal or even scansorial in this 
perspective. The ankle and leg suggest, rather, a more terrestrial modus for 
the legs, with a combination of digital proportions and claw curvature that 
implies some ability to grip a substrate, which Yalden and Feduccia both have 
linked to some scansorial possibilities, although the latter makes more of this 
than the former. This can be used also as an argument for climbing _prey_, 
although not much bigger than crocodylians appear in the Solnhofen beds.

<IF birds evolved from the trees down - as flight got better, I would expect to 
see tree climbing abilities getting worse, as flight would become the prefered 
method of getting up (can any bird "climb" a tree now? the most I see is 
gripping on the side of a trunck one and moving a few inches inbetween flight) 
Was archie even close to being a good enough flyer that it could sacrafice any 
(hypothetical) ancestral climbing abilities? (probably not)>

This seems odd, because many living bird groups, significant among them but not 
limited to them being Pici (aka, the woodpeckers) are exceptional as being 
arboreal, and can even walk up vertical surfaces. Others, including parrots and 
colies, take agility while on a branch to extremes rivaling much of the rest of 
the avian tree; and all are prodigious and capable fliers. It's when a modus 
becomes enforced that adaptation to other modi becomes reduced: Living on the 
sea or under it does not require the ability to fly through the air, so several 
lineages have lost flight as a consequence of adapting to this, including 
cormorants, auks, and penguins. Note that they didn't lose flight TO adapt; 
these birds still use their flight apparatus underwater, but can no longer fly 
in the air (with the exception of some auk relatives and clumsily for some 
cormorants).

  Cheers,

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

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