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RE: origin of bats/reply 2 to TMK
At 12:21 AM -0500 6/25/08, Tim Williams wrote:
>Yep; and my apologies if my response came across as a criticism (it wasn't
>intended as such). You also mentioned nesting, and opening new niches for
>predation. I'd certainly like to hear more about the latter. Are you
>thinking along the lines of small maniraptorans (especially microraptorines)
>launching ambush attacks from trees against ground-dwelling prey?
>In general, pre-avian cursorial maniraptorans had so few arboreal/scansorial
>adaptations that I doubt that predator evasion or nesting behaviors would have
>been sufficient to lure such maniraptorans into the trees - unless they could
>fly (thereby avoiding a vertical ascent) and perch (which allowed these bipeds
>to roost). For example, when a large predator is in sight, why is heading up
>a tree preferrable to simply running away? The morphology of pre-avian
>maniraptorans tells us they were decent runners (some more than others), but
>atrocious climbers. And so far (although this could change) there is no
>evidence of flight or perching adaptations in pre-avian maniraptorans.
I suspect there was a lot going on when maniraptors evolved gliding and/or
flight, and whatever actually happened was far from obvious.
Small maniraptors probably were both predators and prey, like housecats are
predators on mice and lunch for coyotes (to borrow a convenient example from a
seriously human-altered environment). A proto-flyer that dashed up a tree to
escape a bigger and faster (but non-climbing) predator would have a big
advantage in getting down if it had feathers to help it 'fall' in a more
controlled manner. That could have evolved into swooping down on prey as well
as simply getting down after escaping a predator. That's important because it's
easier for many animals that don't habitually climb to get up a tree than to
get back down.
Animals can evolve some pretty odd behavior that works in their environment.
Early in the 2nd episode of Attenborough's Birds (the one on flight), he shows
shearwaters climbing a slanting tree, pumping their wings a bit like in
Wing-assisted incline climbing, then flying off. According to Attenborough,
they need to climb the tree to launch themselves into the air so they can fly,
and they pick one tree that's easiest to climb. Could something like that have
launched avian flight?
Jeff Hecht, science & technology writer
525 Auburn St., Auburndale, MA 02466 USA