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Re: Stratigraphy, biogeography & cladograms



--Original Message-- From: Thomas R. Holtz, Jr. <th81@umail.umd.edu>:
Monday, January 18, 1999 04:58 PM



>Howdy,


[snip]
>
>Oh, and John Jackson:

Hi there... (by the way, like all your (indeed anyone's) reports, the SICB
one was appreciated).

>can you demonstrate from a published analysis on
>either modern insects or Cenozoic birds (both of which have produced many
>flightless groups) that cladistics biases towards grouping flightless forms
>together?  Otherwise your claim is extraordinarily weak, and it just sounds
>like your upset because no current analysis of theropods favors your
>particular phylogeny.  If on the other hand you could find such a bias
>outside of the theropod taxa in question (or in the case birds, so far deep
>inside that they aren't part of the Mesozoic analysis...) you might have a
case.
>

Modern insects and birds are not a good analogy for this reason:  early
flightless dino/birds went from one form to another and then back to the
earlier one:
    flightless -> flying -> flightless

modern flightless birds and insects effectively just do this:
    flying -> flightless

The confusion in early birds/dinos is between the first and the second
flightless stages, and since the time difference might be
10mys..5mys...0.1mys, little divergence need have arisen.  In modern
birds/insects, the comparisons would have to be between flightless forms all
to the right of the arrow.  We seldom confuse such groups since, in the case
of birds at least, they split say 60-80 mys ago.

However, if we did - how would we know?  (Especially if we are placing most
of our trust in one method.)  When a cladistics result is obviously wrong,
people usually aren't keen to publish it - especially if the problem can be
solved
by adjusting the input data.  And when it's actually wrong but there is no
way of telling for sure - well, that can't be used as an example of a
mistake either.


>  Otherwise your claim is extraordinarily weak, and it just sounds
>like your upset because no current analysis of theropods favors your
>particular phylogeny.

No analysis based solely on current cladistic methods, maybe.  But why
concentrate on that and throw everything else out the window?  Stratigraphy
of course doesn't offer fine resolution, but it tells a story with a
different drift, as does much of the circumstantial evidence.

Moral issues upset me; mistakes don't.  Being apparently one of only two
people in the world with the correct idea about an entirely academic issue
may be a little exasperating but on the whole it's a positive feeling.  It's
embarrassing and a little sad to have to make people change their minds when
they don't want to.  This is particularly the case when those concerned
allow the issues and evidence to be appraised fairly.


>Sorry to have to ask that of you, but you know what they say about burden
of
>proof and all that.

Proof with regard to theories...  Though I tend to qualify and supplement
it, I don't dispute the usefulness of the "testing/refutation" approach.

However, neither BAMM nor 2F has yet been disproved.  With regard to levels
of "proof" for circumstantially supported theories, the evidence need only
differ by the estimation of a hair in a person's mind for them to support
one side or the other.

"...burden of proof..."  "...lies with the accuser".  Doesn't apply - unless
I'm accusing Padian, Chiappe & Norell of not mentioning 2F.  Well, the case
is proven for everything I've ever seen or heard of theirs, though there may
exist something somewhere that someone keener than me might have found.  But
I'm being asked to prove a negative here.  And if they had made some highly
obscure mention of it, it wouldn't support the notion that they'd been
contributing much to a fair discussion.


>To add fuel to the fire, or better yet to put things in perspective, some
>weaknesses inherent in stratigraphic and biogeographic data that are absent
>in morphological or molecular data.

It's true, all techniques have their weaknesses.  Data from one source may
simply be inferior to another.  Just means you place less weight on it.
Well established principle used everyday by guidance systems.  No need to
throw it out though - better to reduce them to probabilities and merge them
somehow.