[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Cladistics and extinction

------------Jeff Martz wrote:
>Cladistics may be a nice taxonomic system, but its naming
>system should be left out of a lot of discussions on evolution and

        As a matter of fact, phylogenetic taxonomy was *created* to aid in
the discussion of evolution.  Please see my previous posts on this thread.
The idea is that paraphyletic groups do not act as discreet units of
evolution, but monophyletic groups do.  See below for example.

>or at least cladists should not let the purely inclusive
>nature of cladistics cloud thier reasoning as to WHAT and WHY things
>happened in evolution.

        In the case you were discussing, your tendancy to think
non-phylogenetically has you emphasizing the wrong point.  You want to know
why the non-avain dinosaurs went extinct.  You seem to think it is
unreasonable that these animals, which obviously had some flaw that led to
their extinction, should not be their own seperate group.
        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.

>Stepping around the extinction of dinosaurs by
>saying that  "dinosaurs did not become extinct because birds are still around"
>clouds and misleads the issue.

        It redirects the debate to a more meaningful evolutionary context.
You must then concentrate on why certain members of a monophyletic group did
survive, while their kin did not.

| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |