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Re: Archaeopteryx (and bats)
>you look at one of the handful of gliding squirrels, you are
>seeing the ancestral bat, another species discovering flight.
I think this is stretching things a bit. You may be right, but bear in mind
that NONE of the gliding mammals today show any tendency towards elongation
of the fingers or other bat modifications. These include not just flying
squirrels but marsupial gliders (probably at least two independent lines),
anomalurid "squirrels" from Africa, and the colugo, which is a member of an
ancient group and seems no further along the road to flight than its fossil
I wonder if, in fact, bats did not take a rather different evolutionary
path. Gliding is fine if you want to escape a predator or take a short cut
through the trees (I have watched Draco lizards gliding in Borneo, and they
seem to use gliding as their normal way of getting around, not just as an
escape mechanism. I also saw a giant flying squirrel (Petaurista) do a
formidably long glide across a river with nothing obvious in pursuit).
However, gliding is useless for either catching prey in midair (as many
microchropteran bats do), hovering in front of flowers or clusters of fruit
(as other bats do) or soaring (as I have seen Pteropus bats do). It my also
be less than useful for highly colonial animals travelling a long way to
feeding grounds, or roosting in the upper levels of caves. None of the
gliders do these things; many bats do. It is possible, of course,that bats
adopted these behaviours after flight made them possible; but it may also be
that tendencies towards such behaviours caused bat evolution to proceed in
the direction of powered flight rather than gliding.
Remember that powerd flight is MUCH more energetically expensive than
gliding and will not be selected for unless it confers an advantage over
gliding. The flying squirrels may not be headed towards powered flight at all.
I'm going to forward this reply to BATLIST and see if anyone cares to comment.
>Archaeopteryx has too many characteristics of modern birds for
>anyone to seriously doubt it could fly.
So do many modern flightless birds. I suspect Archaeopteryx COULD fly,
poorly, but there are certainly arguments on the other side that are taken
I think it mostly glided, reserving its strength and
>flight muscles for bursts of powered flight to rise to a new
>glide path or to another thermal, or to fly into a tree to
I seriously doubt that Archaeopteryx could take advantage of thermals,
something restricted to specialized soaring birds like albatrosses and
condors. Its wings are simply the wrong shape. I see it more like a modern
cracid, a bird like a chachalaca or guan, capable of short bursts of flight
to get it into a tree.
>On the subject of speculative evolution, though, it would be
>nice to develop _some_ kind of cursorial flight hypothesis,
>even if we _can't_ shoehorn Archaeopteryx into it. It would
>also be fun to wonder if flying fish might not eventually
>evolve into true flying forms - but they will certainly need
>adaptions to airbreathing, which may not be easily attained
>in their bodyform.
Actually, freshwater hatchetfishes do something that is pretty close to
powered flight. On leaping from the water they flap their pectoral fins
rapidly, powered by the muscles in the deep keel that gives them their
Ronald I. Orenstein Phone: (905) 820-7886 (home)
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