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Re: dromaeosaurs and birds

At 02:43 PM 9/26/96 -0500, J. Norton wrote:

>Only a small creature would be able to leap up onto low-lying vegetation
>without crushing it or breaking the branches; perhaps the larger 'running
>predator' style dromaeosaur predecessors never exploited the
>off-the-ground niches.

        Not enough.  I was postulating that the sicle claw developed from an
arboreal adaption, which means that the ancestral dromaeosaurs (and possible
the ancestral coelurosaurs (?!?) were arboreal at some point (sounds
spookily like BCF, no?).

>Features of the "pouncing on ground-level prey from above" scenario
>that I like are; 1) a bipedal creature could do it;

        So could a quadraped.

>2) the forelimbs would be used initially for balance (as we do when we jump
>from a low height)

        I aggree that this seems more likely to happen with a biped, but can
this impression be justified?

>and later could be exapted for control during the fall; 3) the creatures
>would not be spending all of their time in the trees and would therefore
>tend not evolve  the "four grasping limbs" design of most arboreal

        If they are already bipeds, and they're in the trees, they don't
need to.  They become branch walkers rather than trunk clingers, perhaps
using the sicle claw as a "climbing peton" to overcome the disadvantages of
their stiffer pelvic structure.
        See my latest BCF posting...

>4) one could envision a gradual evolution of both control and
>lifting capabilities, with each intermediate stage adaptive and useful;

        I still don't see the need for many intermediate stages...  Flapping
pouncer, to flapping pounce-chaser, to flyer.

>5) birds do this sort of thing all the time (owls catching mice from above,
>eagles swooping down on rabbits) and we are not forced to invent a
>type of predation (leaping after flying insects) that does not exist today;

        Hey, I chase fireflies!  Cats chase moths... :)

>6) the hindlimbs could move gradually from a running foot to a foot
>designed to grasp both branches and prey, driven by the likelihood that

        Better, this explains why the running organs were exapted to a
killing function with an enlarged raptorial claw.

>and 7) small theropods seem to be the most likely to have had feathered

        But remember that all large theropods were small theropods once!

>The more I think about this, the better I like it.

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