Re: [dinosaur] Archaeopteryx had active flapping flight ability based on wing bone geometry (free pdf)

[Tim Williams <tijawi@gmail.com>]

Mike Habib <biologyinmotion@gmail.com> wrote:

> Indeed - with the one caveat that bats donât actually fall to launch from 
> ceilings. There are no confirmed gravity launching flyers, interestingly 
> enough. The reason for this has to do with the details of wing vorticity - 
> which
> depends on additional factors beyond velocity.


The lack of gravity-assisted launching by bats is one reason (though
not the only reason) why I'm not convinced that bats are descended
from passive gliders.  Instead, they may have evolved from arboreal
hawkers or gleaners that used their patagia for aerial leaping (so a
'flapping-start' origin of chiropteran flight).  Alas, while this is
theoretically possible, I don't have any analogs to back up this
hypothesis.  There are diverse and abundant patagial gliders among
modern mammals, but no known 'patagial leapers' to serve as potential
analogs for hypothetical leaping 'proto-bats'.  Nor are there any
inferred patagial leapers among fossil mammals AFAIK (though we'll see
what happens with _Volaticotherium_, which apparently has a patagium
but plots outside patagial gliders; it's also inferred to be
insectivorous/faunivorous, which sets it apart from typical gliders).



Ruben Safir <ruben@mrbrklyn.com> wrote:

> It is impossible to image that the birds would develop the leaping launch 
> that is so prevalent without the strong upward flight stroke and the two can 
> not be separated.


Not impossible at all.  This argument of yours was refuted by Earls,
who further proposed that the hindlimb-driven launch impulse evolved
separately from the wing-driven climb-out phase that came later.
Earls proposed a model for flight evolution under which the initial
launch evolved prior to sustained, flapping flight.  She even provided
a hypothetical rationale for incipient flight.  As she puts it: "Any
downward movement of a feathered forelimb after the initiation of a
leap could potentially add height or distance to the ballistic path,
regardless of the reason for jumping."