[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: bird origins / pouncing scenario



At 06:38 PM 9/28/96 -0500, Wayne wrote:

>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,

        In my scenario, he uses his arms to slow himself and control his
fall, in a flapping motion (which will, if done correctly, produce more drag
and possibly control than just holding them out).  This motion is then used
to make the angle of attack shallower, until the animal is flying short
distances to intercept his prey.

>Interestingly, James and Jonathan continue in their commentaries
>along somewhat different lines.

        Dr. Norton does have a fundamentally different theory in some respects.

>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 I am not mistaken, Dr. Norton postulates that they carried
smaller prey with their feet.  The problem with this is how did they push
off for the jump...

> Again, my point exactly.  With such powerful development in the leg and hip,
>why not become a cheetah?

        Perhaps some of them did.  Just because an animal *can* do it
doesn't mean it did.  Perhaps there were already "cheetahs" around (although
there's never a mongoose around when you need one...).

>Further, such powerful leg development does not exist in extant
>flying predators

        Sorry, but you are right, they just don't need it, and they lost it.
Sure, no modern flyin predators have it, none of them jump to the trees
after they make their kill.

>Why not just develop from gliding, or ... 

        Perhaps a stiff-legged bipedal animal that glides does not develop a
patagium, but I am still not convinced that gliders don't just stay gliders.
Someone was saying recently (Nick L.?) that history is replete with gliders,
but has few fliers.
        Now, before you say what you're about to say, listen to this:  If
you try to argue that these gliders were not becoming fliers because those
niches were taken, remember that the latter two of the three vertebrate
flier radiations took place _*WHILE THERE WAS ALREADY A FLAPPING FLIER*_,
and you are not going to tell me that there weren't arboreal animals
cruising around before the pterosaurs which (according to conservative
theories which regard all of archosaurs as ectotherms, and/or say that
flapping can come easily from gliding, gliding easily from arborality (I
will not argue this one), and arborality from Bill Gates.  Oops, wrong
theocracy...) could not just as easily have become active fliers.  Clearly,
this is a complex situation, but we cannot easily say that it is easier to
"just develop from gliding".

>dare I say it?  Start out flying in the first place...

        We're trying to explain how that came about, doesn't help to take it
as a given...
        The possibility that flapping developed as a braking motion for
interbranch leaping (perhaps after it developed for grasping the trunk of
the next tree) is not beyond reason.  I cannot tell which is more
parsimonious.  The vertical attack theory incorporates the sicle claw more
fully, and does not necessarily require its use as a climbing peton, the
latter either says it is a peton, or doesn't explain it.  I dunno.  I can be
sold on other theories, should a better argment come along...

>have been thus. But then, as my wife says, I need more imagination ;))...

        Everyone I know says I have too much.  :)
        (Yeah, I left myself open.  We're all friends here...)
        Wagner
+-------------******ONCE AGAIN, NOTE NEW E-MAIL ADRESS******---------------+
| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |
+--------------------------------------------------------------------------+