[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
--- On Fri, 9/26/08, Mike Habib <email@example.com> wrote:
> It could just as easily be support for the hypothesis that
> gliding to
> powered transitions are very rare for mechanical reasons,
Not really. Competitive exclusion is a basic principle, while postulating that
mechanical hurdles prevent a passive-to-powered flight transition are not,
especially when it is consensus that bats and pterosaurs did it.
Heh. Although I gather there is a contingent that favors a terrestrial origin
for ptero's. Sorry, that was a cheap shot. Anything (almost) is possible.
> could be right on the money, but it just seems like such a
> blanket statement that it makes me slightly skeptical.
It was a comment made in rebuttal of the assertion that our current lack of
'gliders flapping feebly' supports the idea that powered flight evolved w/out a
preliminary gliding phase.
> >> but birds and bats certainly both appeared in the
> presence of pre-
> >> existing powered flyers.
> > I think it is a safe assumption that they were not
> faced w/ the
> > competitive barriers modern-day putative transitionals
> would have to
> > overcome, from the perspective of niche
> Why is that? There was certainly specialist ecologies
> among flyers in
> the Mesozoic, and it's not clear how much specialist
> ecologies impact
> competitive exclusion. One could make the argument that it
> actually "generalist" feeding modes, etc that
> would be more likely to
> produce exclusion.
I note that incipient birds did not have to compete w/ either modern birds, or
bats. Or (I assume) mice, shrews, weasels....
> > Of course, pure gliders are MUCH more numerous than
> > "ground-up" animals.
> Yes, this is true (at least in the modern time slice). So
> we have two
> different types of rarity - terrestrial origins for flight
> probably rare because heavy exaption is involved (i.e.
> rarity by
> ancestor constraints).
Heh. Oh, do you have an example of "terrestrial origins for flight"? :D
More seriously, "ancestor constraints" are what I call "pre-conditions", and
they require lots of evolution to fulfill. And seem to be rare in themselves.
> Arboreal origins of powered flight
> are rare
> most likely because transitions to powered flight from an
> gliding morphology are rare (i.e. rarity by mechanical
But "known" to have occurred; quote marks inserted because anything is possible.