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

Re: Flightless Birds (was Re: BCF ANDPDW)



[George, I assume that the DD14 means this will end up in one of your list
digests, as has been the case in the past. I am therefore forwarding the
reply to the list]
        At 12:06 PM 8/5/98 -0400, Dinogeorge wrote:
>Say what? Will somebody please explain this sentence to me, including among
>other things the meaning of the word "better" in this context? Then show me
>where I may have said anything like this to be "taken to task" for.

        I wrote:
>        T) As some have observed, birds tend to become flightless in
>environments which have been depleted of other fauna (e.g. islands). How was
>it that successive groups of flighted theropods were more successful within
>niches than dinosaurs which had had millions of years to adapt to those same
>niches in the past? Was the Mesozoic just so different from today that
>terrestrial niches lay open for the taking?
        I am under the impression, from your Omni article and inumerable
postings to this dinosaur list, that your "BCF" theory suggests that the
natural history of non-avian dinosaurs consists of a successive radiations
of a lineage of progressively more birdlike flighted arboreal archosaurs.
You use this concept to explain the sequence of progressively more birdlike
morpholgies you note in non-avian dinosaurs. Is this impression incorrect?
        In order to evaluate the likelihood of such a scenario, I chose to
use our experience with flightlessness under more conventional theories. My
point that birds seem to become flightless in depleted faunas may be not be
true in every instance, but seems to hold in some. It also seems to be a
commonly made generalization that flightless birds do not often last in
competition with established terrestrial fauna ("the age-old battle between
flightless bird and mammalian carnivore" [Romer?] comes to mind). Again,
this may not always be so. However, if I were to make a third generalization
out of the first two, I'd say that, in order to become flightless, a taxon
would have to have both the motive (open niches) and the opportunity (an
environment where a bird could start doing the terrestrial thing again
without worrying constantly about being eaten by its ground-bound cousins).
        However, we may suppose that the dinosaurs who radiated in the first
wave from your hypothetical arboreal lineage spent a good amount of time on
the ground, learning to be good terrestrial dinosaurs. So why did the next
wave succeed? Did being more birdlike make them "better" terrestrial
carnivores (with "better" meaning able to "out-compete" the natives)? You
have repeatedly said that this doesn't make sense! Did the first wave just
give up and say "look, you guys are closer to being birds, so we give up". I
could maybe buy this, if couched in less facetious terms, once. Your theory
implies that it happened repeatedly.
        If you're going to say that groups of terrestrial theropods
repeatedly radiated from their flying cousins, you're going to have to
account for why they kept surviving in a world where the members of the last
radiation had millions of years longer to adapt to terrestriality, to being
better "running-and-jumping-and-killing" guys in the case of theropods.

        Wagner

        "To fly, long a dream of man and flightless bird alike"
                                                -- Gen. "Hap" Happablap
----------------------------------------------------------------------------
    Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
                    "...To fight legends." - Kosh Naranek