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Re: Help with Cladistics



>From: Thomas_R_HOLTZ@umail.umd.edu (th81)
 >
 > Although the chance of finding fossils of the population directly ancestral
 > to later species is very small, a cladist can recognize a potential ancestor
 > as one which: a) shares derived features with the hypothesized descendant;
 > b) lacks derived features unique to itself; 

I consider this criterion to be too strong.  Reversals are quite
common, as shown by almost all real cladograms.  And, at the individual
species level I consider reversals to be even more prevalent than most
cladograms would indicate.

A good example of where I think this criterion has caused problems
is in the hominid specimen KNM-WT 15000 (if I remember the id right),
which is in most respects about what one would expect in the common
ancestor of the robust australopithecines (aka Paranthropus). But,
since it is somewhat more robust than one of the later species,
many workers have ruled it out as a possible ancestor.  But robust-
ness is about as the most easily reversed type of character there is
(right there along with overall size).

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.