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

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 damage).
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.
------Ken Kinman
From: Dinogeorge@aol.com
Reply-To: Dinogeorge@aol.com
To: dinosaur@usc.edu
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, kinman@hotmail.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 (still
widely embraced) or birds came first (BCF). >>

One simply cannot tell from a cladogram what the common ancestral forms were
like for any group of theropod dinosaurs and birds. The common ancestor could
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 these
common ancestors were like the dinosaurs (terrestrial cursorial bipeds), but
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, gliders,
and fliers), particularly since this provides some pretty obvious reasons for
a whole lot of features seen in theropod dinosaurs that otherwise have no
rationale for their existence.
Get more from the Web.  FREE MSN Explorer download : http://explorer.msn.com