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Re: Dinosaur Genera List corrections #67



At 03:26 PM 1/30/97 -0500, you wrote:
>In a message dated 97-01-30 13:49:12 EST, znc14@ttacs1.ttu.edu (Jonathan R.
>Wagner) writes:
>
><<  Thus, any other tree should include a
> *greater* number of homoplasies.  So what you're saying is nonsense. >>
>
>A reversal is not a homoplasy. I'm not talking about homoplasies here. Again,
>please read what I wrote: "...Unfortunately, his character matrix contains so
>many
>>reversals and unknowns as to make the analysis dubious...."
>

(Ummm, let me take this one, guys...)

Homoplasy: Character incongruence with the most parsimonious hierarchy.
Homoplasies are thus shared similarity which can be explained by convergence
(the independant acquisition of the same character state in two or more
lineages) or reversals (the change of the immediately ancestral character
state to the state found in a more distant ancestral condition).

Also, to counter an earlier comment of the "infallability" of cladograms, I
can offer no better words than Olivier Rieppel (Proc. R. Soc. Lond. B (1996)
263:1395-1398):

"It is understood that the addition of taxa, or of characters, to a
phylogenetic analysis may alter tree topology, and characters formerly
believed to be homologous may come to be considered homoplasies, whereas
characters formerly believed to be homoplastic may have to be considered
homologies.  As with every empirical science, cladistics does not provide
truth or proven theories, but only hypothetical knowledge subject to test
and corroboration." (p. 1395)

Hardly a statement of infallability!

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877