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Re: Polytomy question

On 10/26/05, Manuel Parrado <meparrado@yahoo.com> wrote:

> What I find interesting is that every evolutionary
> change is always modeled as a split.  How about
> species that simply change over time without spliting
> into two different lineages?  This is rarely captured
> in any phylogenetic tree.  Is it because of lack of
> evidence?  Would we know them if we see them (not me
> of course but you get the point).

The most important thing to remember here is: CLADOGRAMS ARE NOT
PHYLOGENIES.  They're two different things.  O'Keefe & Sander (1999)
describe the situation as such: "A cladogram is defined as 'a
branching diagram depicting the pattern of shared similarities thought
to be evolutionary novelties among a series of (previously defined)
taxa.'  A phylogeny is 'a diagram (not necessarily branching!)
depicting the actual pattern of ancestry and descent among a series of
taxa,' or a cladogram plus a time component and hypotheses of
ancestor-descendant relationship."

Unfortunately, many people seem to miss this point and treat the two
as the same.  This is a problem that is of special interest to me
lately, as some of my buddies and myself are looking into what we
think might be an anagenetic series of mosasaurs in the WIS.  In any
case, check this out for more:

O'Keefe, F. R., and P. M. Sander.  1999.  Paleontological paradigms
and inferences of phylogenetic pattern: a case study.  Paleobiology
25: 518-533.

Jordan Mallon

BScH, Carleton University
Vertebrate Palaeontology & Palaeoecology

Paleoart website: http://www.geocities.com/paleoportfolio/
MSN Messenger: j_mallon@hotmail.com