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bird origins / pouncing scenario
In my post regarding the pouncing biped, I clearly overstressed my concern
about our developing bipedal friend's behaviour immediately post-pounce.
Jonathan Wagner points out that he would do "...exactly the same thing a
dromaeosaur would do after jumping into the air to use it's sicle claw..."
and James Norton answers similarly that "...the creature would do the same
thing that strictly cursorial predators would do...".
Actually, this is exactly what I'd envisioned (after my first reaction, which
was an Eagle-to-be, swooping down, but before he had grown wings, and
snatching a bass.... then, remembering he can't fly, learning to swim... ;)
My real point was that I have a hard time seeing where this begins to select
for flight. As our agile little friend pounces on his prey, he is more
inclined to further utilize his forelimbs to subdue/kill/carry his prey, thus
making him more likely to evolve into a cheetah than an eagle. Perhaps this
is how quadrepeds evolved; but I digress...
All kidding aside, I like the general scenario, but it seems a stretch to
have a biped develop along these lines. Interestingly, James and Jonathan
continue in their commentaries along somewhat different lines. Jonathan, in
his "pure speculation", envisions a pair of dromaeosaurs slicing up a
juvenile protoceratops and running "...away carrying bolts of meat in their
hands..."; my point exactly; if they're carrying their dinner in their hands,
they're not learning to fly with their arms.
James has a more flight-oriented pre-flyer; in his scenario, our pouncing
theropod friend chooses smaller prey, which he can carry back up to his perch
with another leap. Here, though, our developing friend must evolve more
developed "...extensors of the leg and hip..." prior to developing flight.
Again, my point exactly. With such powerful development in the leg and hip,
why not become a cheetah? After all, upon the leap back, isn't he more
likely to use his arms to catch brances? Further, such powerful leg
development does not exist in extant flying predators; so we must now presume
that, once selected, it was un-selected after wings developed (a point I'm
willing to concede; but it seems the long way around). Why not just develop
from gliding, or ... dare I say it? Start out flying in the first place...
Again, I'm not saying 'it can't be thus'; I'm just not seeing why it should
have been thus. But then, as my wife says, I need more imagination ;))...