[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)
Don Ohmes wrote:
> It is not too surprising that there are no gliders currently making the
> transition to powered flight,
> considering the fact that they would have to invade niches occupied by birds
> and/or bats as they did so.
> Seems a lot to ask...
It sure is. However, I'm setting the bar much lower. I'm not asking that
gliders have to make the transition to powered flight. All I'm pointing out is
that no glider that I know of (not amphibian, reptile, mammal) shows the
slightest interest in flapping their arms. If flapping confers advantages to a
glider, why is this the case?
Also, the inception of flapping should not be assumed to be equivalent to
"moving in the direction of powered flight". In order to be selected, this
behavior (gliding+flapping) should be beneficial in its own right, rather than
just be a stepping stone to flapping flight.
There is a swathe of empty morphospace available to gliders who want to engage
in occasional flapping. This ecomorphology would put them outside the vast
morphospace currently occupied by flying vertebrates (birds and bats). So
competitive exclusion shouldn't hold for flapping gliders, given that it's only
one step up from passive gliding, but a long way from powered flight.
BTW, I'm not arguing that bats didn't evolve from patagial gliders. I'm just
saying that the transition by which this might have occurred is not as simple
as it sounds. It'd be interesting to know what circumstances led to the
gliding-fluttering flight inferred for _Onychonycteris_ (the most basal known
bat), given that lack of echolocation would make aerial hawking behavior highly
unlikely. _Onychonycteris_ seems to be have been very well-adapted to life in
the trees (especially scansorial and suspensory behaviors), so there's little
doubt that the evolution of flight in bats had an 'arboreal' component.
> Competitive exclusion logically explains the paucity of gliding predators,
I don't see things quite the same way. The paucity of gliding predators may
have more to do with the paucity of specialized arboreal predators, and/or the
demands imposed by predation and using the forelimbs for prey capture (damage
to the patagium by struggling prey; reduced mobility when chasing prey when the
fore- and hindlimbs are joined by a patagium; etc).
> And that in turn explains
> why most extant gliders are 'just moving from tree-to-tree'.
Most extant gliders are 'just moving from tree-to-tree' because that's what
gliding is for in these taxa: for commuting.
> BTW, are there ANY cursorial vertebrates currently "moving in the direction
> of powered flight"?
None that I can see. So that's zero cursorial vertebrates currently "moving in
the direction of powered flight"? Thats' the same number (zero) as arboreal
gliders currently "moving in the direction of powered flight"? So it's a level
Stay up to date on your PC, the Web, and your mobile phone with Windows Live.