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Re: Cladistics and extinction



Jonathan R. Wagner writes;

>        Look at the problem in terms of monophyletic groups.  The birds
>survived.  Mass extinction is a broad sweeping phenomenon, but survival
>appears to be restricted to certain clades.  Since there seems to be a
>common cause (or causes) for the extinction, we must look not at what "flaw"
>in any group caused their extinction (symplesiomorphy), but what
>charactersitics of the derived clade allowed them to survive (synapomorphy).
>If one looks for "fatal flaws" in each extinct group, one will never get as
>far as fast as if one looks at derived characters in the clades that survived.

If I may jump into the feeding frenzy, I question how useful
cladistics would be BY ITSELF in terms of evolutionary/diversity
studies.  One of my objections to cladistics is that it totally
ignores the geologic timescale.  In most cladigrams I've seen, genera
are placed on the same "horizontal line."  In this way, wouldn't we
miss episodes of adaptive radiations, or extreme speciation?  Also,
wouldn't it be more useful for one to *automatically* superimpose the
timescale on a cladigram?

In my calculus class, we find that very complex functions tend to have
deceptively simple graphs.  However, when we change the scale and
"stretch" the graph, hidden subtleties and small "wavelets" begin to
emerge.  In the same way, isn't a cladigram over-simplifying the
history of the lineage, ironing out the complexities?  This could be
useful if one is simply looking for "who is related to who," but it
would be lacking for those who wish to learn the dynamics of
evolution.

Rob Meyerson
Orphan Vertebrate Paleontologist

***
"the Wolf and I are now on a first name basis."
        -S.I.