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Re: New finds



----- Original Message -----
From: <Dinogeorge@aol.com>
Sent: Thursday, July 11, 2002 8:52 AM

> The so-called "linear model" is and always has been nothing more than an
> artifact of arranging taxa in a cladogram.

Let me disagree... anthropologists hardly ever use cladistics. The
*Sahelanthropus* paper doesn't either. (I think that's a reason why so
little is known about human phylogeny.)

> To convert any cladogram into a
> "linear model," or Hennigian comb as it's sometimes called,

A Hennigian comb is anything but linear. Like every cladogram, it puts all
emphasis on dichotomy. This here is a Hennigian comb:

--+--+-----------A
  |  `--+--+-----B
  |     |  `--+--C
  |     |     `--D
  |     `--------E
  `--------------F

> simply single out
> one lineage to be the spine of the comb

C or D in this example

> [...] Singling out the lineage that leads
> to man, for example, produced the notorious "scala naturae" that dominated
> phylogeny for circa 200 years.

Much longer than cladistics :-)

> So the model is not breaking down; we're
> simply finding lots more side branches.

In contrast, anthropologists assert all the time that it has broken down
quite some time ago

> As for mosaicism, if you get enough
> of it, it makes practically all cladistic analyses suspect. Too much
> convergence turns the cladograms into mush.

I think it's the other way around, when enough taxa are included. Make a
data matrix with yourself as the outgroup and *Geochelone*, *Oviraptor*,
*Archaeopteryx*, *Rahonavis*, *Confuciusornis* and *Gallus* as the ingroup.
You'll likely find a strange cladogram coming out of PAUP*. But if you add
*Sinornis* that tells you *Confuciusornis* lost its teeth independently of
Neornithes, *Sapeornis* that tells you that the long 3rd finger of
*Confuciusornis* is a reversal from the saurischian condition that the 2nd
is the longest, and so on, you'll soon find something more like current
hypotheses.
        As many taxa as possible are crucial because they add the data
necessary to tell reversals from real plesiomorphies. Suppose we find
something like Messel or Jehol of EJ or MJ age and a little flying
tyrannosaur and a little flying ornithomimosaur in them, complete with big
sterna and coracoids, horizontal scapulae, big semilunate carpals and so on.
Suddenly parsimony will consistently find that *Tyrannosaurus* and
*Ornithomimus* are secondarily flightless, and probably, depending on
features that I've been too lazy to think up right now, closer to living
birds than (to) *Archaeopteryx*. Parsimony just can't tell the whole story
when the data don't say enough. :-)