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Re: decoupling



George Olshevsky replies to a message from Ron Orenstein:

>> I still hold to the view that the considerably greater diversity
>> seen in birds than in bats (or pterosaurs) is primarily (though not
>> entirely) due to the fact that birds have decoupled their wing
>> mechanism from the hind limb, allowing a far greater range of
>> adaptations for walking, wading, swimming, climbing etc.
>
>I think "decoupled" is the wrong word to use here. There was never a time
>during which the wings of birds were coupled to the hind limbs in a single
>flight mechanism (a la bats and at least the earlier pterosaurs), as far as
>we know.

Actually, decoupled is correct, but referring to the decoupling of the tail
from the hindlimb that is apparent in more derived theropods, resulting in
three locomotor modules (tail, wings, and hindlimbs/pelvis) that later in
avian evolution (say, by the time the Sinornis or Iberomesornis grade
evolved) were recoupled as a "wings-tail" locomotor module and the
hindlimb/pelvis module. This novel functional and structural blueprint
_perhaps_ (please note that I did say _perhaps_) was a key factor in the
avian adaptive radiation. It did probably provide a basic novel
construction with potential for further specialization (e.g. different
locomotor specializations in penguins, rails, ostriches, passerines,
raptors, etc.).

Source: Gatesy, S.M. and Dial, K.P. 1996. Locomotor modules and the
evolution of avian flight. Evolution 50(1): 331-340. Highly, highly
recommended.

                        John R. Hutchinson
                  Evolving Evolutionary Biologist
                 Department of Integrative Biology
                  3060 Valley Life Sciences Bldg.
                University of California - Berkeley
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