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

Re: Syntarsus [longish]



In a message dated 96-09-10 10:45:21 EDT, znc14@ttacs1.ttu.edu (Jonathan R.
Wagner) writes:

> Pardon my tone, but who are are any of us to say how nature may
> work?  We may say that this structure is so complex (can't say that
> I agree on that, but anyway...) that it is unlikely to have evolved
> twice, but this must be wieghed with other characters, to determine
> the most parsimonious evolutionary hypothesis.  It is statements
> like the one made above which guided, and still guide, may very
> intelligent people (from Romer to Olshevsky) to premature
> conclusions about the phylogeny of a group because they (the person,
> not the group) were unwilling to accept that a certain structure
> *might* be homoplastic (homoplaisic?)(ie. a reversal, or a result of
> parallel or convergent evolution).

The three major problems of cladistic analysis are these: (1) the assumption
that the most parsimonious distribution of characters gives the correct
phylogeny is not testable; (2) the way morphological characters are defined
is inherently subjective; and (3) no reliable method exists to weigh
morphological characters against one another (for example, how many skull
characters is a postcranial character worth? one? one-half? ten?). There is
simply no way around these problems, so most cladists ignore them--and
happily continue to consume mass quantities of grant money producing endless
streams of cladograms with their computers.

If at most one cladogram for any group is the correct one, virtually all the
cladograms so generated >must< be wrong. How does one pick the right needle
from this huge haystack? What statistical manipulation of 66 cladograms, at
least 65 of which are wrong, will miraculously produce the right one?

> By me old Bio 202 training, not lost on me even as I plow through
> the pleasures of Structural Geology, there's a little joy called
> preaption (now, I hear, replaced with the concept of exapation,
> which now has me royally confused).  Basically, the idea is that an
> organism can have the potential to develop a character without
> actually expressing it, which said potential can be passed to
> daughter species, which then may or may not express that character(
> BOY does it sound hokey when it's written out like that).

This is a tautology. How will you know when the potential to express a
character is present, except if the character is expressed?? You DARE to
criticize paleontologists at the same time that you try to pass THIS off as
science?

> In the example we are using here, the ur-coelophysoid may have had
> everything it needed to develop crests (in fact, probably did),...

Yeah--like a SNOUT!

> ...but may not have actually developed them (in the same way that it
> had arms and perhaps feathers, and had lots of what it needed to be
> a bird, but it didn't express those features, even though a
> decendant of one of it's ancestor *did* express them).  However,
> it's decendants, dilophosaurs and some coelophysids, then expressed
> the trait (more appropriately, they both followed the same
> evolutionary path from similar genetic makeups, and reached the same
> conclusion).  This is a gross oversimplification, but you can see
> the danger in picking one trait to define your phylogeny on.

Sorry, but I have no idea what you're talking about.

I have wings, but the trouble is they are >unexpressed< and look and function
like arms.

> I still say that if you're gonna base your phylogeny on a "by hand"
>  analysis of characters, try not to bas it on characters that have a
>  *direct* effect on reproduction, feeding strategy, movement, or
>  gross longbone ratios (in that order).  You might ask, what does
>  that leave?  Hey, that's why I > don't do it that way!  :)

But--if you do your phylogeny by computer, you can, of course, include all
these kinds of characters and many more besides into the mix.

Since cladistic analysis of dinosaurs is a hopeless, inbred mess, with
everyone using everyone else's character matrices and so forth, you might
just be better off doing Tarot readings or something.

> Anyway, the only way you're going to convince me of this is to set
> up a data matrix (you can cop some characters off of Rowe in various
> places, including _The Dinosauria_), add the feature "paired
> naso-lacrimal crests...

Why would this be any more convincing than any other reasonably organized
methodology?

> ...Do a little research, add some other characters (I think there
> may be some in Holtz 1994), then run it.  If you use at least 40
> characters and get Dilophosaurus and S. kaentakae as a clade, I
> beleive that both myself and Tim Rowe will probably have a tasty
> bite of hat.  But you will have achieved a laudable scientific goal:
> testing a theory.
>         :)
>         Wagner >>

So your particular convincement-cutoff is 40 characters. Why? Why not 39 or
26?