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Re: logic; BCF (going gets tough)
Philidor and Dinogeorge,
Cladograms aside, my gut instinct at the present time is that theropods
(non-avian) and birds probably had a common ancestor that was more birdlike
(as envisioned by George). But I am not inclined to believe that ALL
dinosaurs had such an ancestor.
As for how much data is needed, there is probably plenty of Cretaceous
data relevant to the question (although more couldn't hurt). But there are
too many missing pieces of the puzzle in the Triassic and Jurassic. That
might sound obvious, but I'm not sure it is widely appreciated just how
unstable such top-heavy cladograms can be. And if you translate a cladogram
directly into a "cladification" (to use Mayr's term) that transfers
instability into the formal nomenclature (where it can do a lot more
But to answer Philidor's question, I do not think just "enough"
Triassic and Jurassic data will suffice, and do worry that "mental inertia",
subjective decisions, and circular reasoning might cloud our thinking as new
data comes in (that is precisely the problem in bacteriology right now).
That's why I think such scientific wrangling is important, even at the risk
of giving people like cr******ists more anti-scientific ammunition. Comes
with the territory I guess.
But that aside, it is often difficult for scientists with different
viewpoints and philosophies to gauge just how subjective or objective they
are being when evaluating opposing views vis-a-vis their own. This causes
no major longterm problems at the level of cladistic analysis, but I think
it does translate into such problems when strictly cladistic classifications
are used to reflect rather "iffy" and fluid hypotheses. I think strict
cladists tend to be overly optimistic about how objective their methods
actually are, and that there is just as much subjectivity among strict
cladists as there is among other systematists.
If BCF is even just partially correct, it will have quite an impact on
strictly cladistic classifications of dinosaurs (earthquake equivalent of
perhaps 6.0). If all of the dinosaurs turn out to be descendants of
birdlike forms, such classifications will endure a major earthquake (like
maybe an 8.0). And BCF certainly isn't the only threat to dinosaur
cladifications, so my advice is to be prepared for a bumpy ride ahead.
Subject: Re: logic; BCF (going gets tough)
Date: Sat, 9 Dec 2000 14:21:54 EST
In a message dated 12/9/00 12:20:22 PM EST, email@example.com writes:
<< I think it is still up in the air whether or not current dinosaur
cladograms are flawed on the question of whether dinosaurs came first
widely embraced) or birds came first (BCF). >>
One simply cannot tell from a cladogram what the common ancestral forms
like for any group of theropod dinosaurs and birds. The common ancestor
have been more like dinosaurs, it could have been more like birds, it could
have been rather unlike either one, or it could have been like a mixture of
both (whatever that might mean). The orthodox position seems to be that
common ancestors were like the dinosaurs (terrestrial cursorial bipeds),
there's no basis other than mental inertia for thinking that this should be
the case. BCF asserts it makes better evolutionary sense to imagine the
common ancestral forms as being more like birds (arboreal climbers,
and fliers), particularly since this provides some pretty obvious reasons
a whole lot of features seen in theropod dinosaurs that otherwise have no
rationale for their existence.
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