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RE: The validity of cladograms (was Re: giant birds)




-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
chris brochu
Sent: Sunday, November 14, 1999 11:37 AM
To: dinosaur@usc.edu
Subject: Re: The validity of cladograms (was Re: giant birds)

Tracy Ford wrote:
>
> The answer is an overwhelming yes!!! In the majority of cases
> cladograms of extant organisms based on morphological characters are
> congruent with those based on morphologicl characters. I have mentioned
> this a couple of times to support my view that cladistics is the best
> method we have for reconstructing the phylogenies of extinct organisms.
> Your message implies that phylogenetic analysis of DNA is somehow
> "different" to that of morphological characters. Molecular characters
> (DNA) can be analysed using exactly he same methods as morphologicl
> characters (i.e. parsimony). Molecular characters can also be analysed
> using a modelling approach (i.e. maximum likelihood), and by a
> clustering approach (neighbour joining). The latter is not usually
> considered reliable enough on its own for evolutionary reconstructions.
>
> If yes, then why is it in paleontology, 90 % of the time, different
authors
> come up with different cladograms? Why isn't there more of a consensus?

Are they "different" 90 % of the time?  Tom "Captain Clade" Holtz
presented a good poster at SVP this year showing that, statistically,
the "different" theropod trees out there aren't so "different" after all
- certain select groups are bouncing around in different analyses, but
the general pattern is stable and uniform.



That -certain select groups etc, is what I'm talking about. Capain Clade
one, has a difference clade from Captain Clade two. Which one is right?
Which clade is right. Those minor differences are major in the schme of
things. They, for some of us, turn us off to clades.
Tracy