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



I think it is difficult to say how many times flight evolved from
trees-down or from ground-up. All cases, bats, birds, insects, pteros
may be questionable. Bats and pterosaurs resemble many gliders in
possessing extensive patagia, but that do not necessarily imply
gliding ancestry, as the most apparent outgroups of both taxa are
apparently not gliders (unless David Peters is right with
Sharovipteryx).

To phylogenetically support to the hypothesis that flight comes from
gliding we should find that each clade in which flying appears there
should be at least three sucessive outgroups of gliders. Of course,
incompleteness of the fossil record will tend to impede this, but
until then there will not be sufficient parsimonious support.

But I sometimes read that the trends towards gliding are opposite to
these towards flapping flight; can somebody tell me why? Most flyers
seem to be good when gliding (although small bats and birds generally
glide less). Among the basalmost living birds, I have been told by
biologists that tinamous commonly glide after a phase of flapping
during their short-range flights. Many other birds glide
intermittently with flapping.

So, I think, if a bird flyer can achive a velocity comparable to that
of the tinamou once it stops flapping, by jumping forwards from an
elevated point, for example, I do not see problematic that it just
glided, flapping again once it lost some velocity because of
deceleration due to air resistance .

Thus, I think that flyers can come from gliders in as much as there is
apparently nothing that can impede them to glide as a toy plane. This
does not mean I think a flying squirrel can flap. But accepting in an
hypothetical glider a change so that the forelimb (and digits) is
sufficiently hypertrophied (as to later permit it to manage the
paragium with its movements), should we have to hypothesize it
severely lost its gliding potential?. If not, very fast morphological
evolution would be required to at the same time enlarge the size of
the forelim and the flying musculature (althoug both can be
hypothesized to increase in size together, as the flying musculature
is part fo the forelimb).

In any case, there exists a case against the "tendences", urged by
Gould. So that, perhaps most gliders do not necessarily would evolve
to become better gliders, but can conceivably change to non-gliding,
better flapping, etc. So, if what is better to glide opposses to what
is better to fly, it does not follow that a mediocre glider will be
"routed" only in way to become a more perfect glider (if such
evolutive tendences were ever invocated for this case).

Cheers.

Augusto Haro.