clashing codes; mammals & morganucodonts
kinman at HOTMAIL.COM
Sun Jan 13 09:48:47 CST 2002
Curtis and Tom,
Just in case my "paraphyly is real and inevitable" post did not
persuade you, I guess I'd better answer some of your other comments. I was
a little amused by the question: if morganucodonts were still living, would
we place them *in* Mammalia (or move monotremes out)?
Amusing because most mammalogists *do* classify morganucodonts as
mammals. Perhaps Curtis is going by McKenna's mammal classification which I
believe excludes morganucodonts, docodonts, and sinoconodonts. Of course
that is because McKenna is a strict cladist, and as such, he seems to think
a "crown group" Mammalia is such a fine idea.
But I have mentioned in the past the instability that results when
anchoring a major taxon on something like monotremes (instead of a lineage
with a good fossil record), merely to make it a crown group. This is more
like bureaucratic straight-jacketing than science. Mammalia should be a
textbook case of when you should not cladistically anchor a taxon as a crown
The point is that those who are not strict cladists prefer a
character-based Mammalia. Morganucodonts have the mammalian jaw and ear
ossicles that have long been used to separate mammals from therapsids. The
transition in these structures from therapsid to mammal was relatively rapid
(in geological and evolutionary terms), and replacing a very stable
character-based Mammalia with an unstable crown group makes no sense
Ask most mammalogists what is and what isn't a mammal, and there is
little problem. But ask a strict cladist, and the answer depends on whose
cladogram he happens to be using that day. With some topologies, even
multituberculates wouldn't make the cut. Why take something that works and
replace it with something that doesn't? Anyway, it was no surprise that it
was a strict cladist who asked about moving morganucodonts *into* Mammalia.
Strict cladism does cause instability, and blaming it all on the
molecular biologists (as Tom seemed to do) is a bit like passing the buck.
Dinosaur science is about as morphological as you can get, and changing
cladograms are causing a nomenclatural mess, with different cladists seeming
to want to get their definitions and names priority before PhyloCode kicks
in. The debate "de jour" this weekend on the dinosaur member list is
Segnosauria vs. Therizinosauria (priority and definitions very messy and
contentious), and not only do cladists disagree among themselves, but it
seems that PhyloCode and the ICZN could clash "head on" in such cases.
So much for peaceful coexistence of these codes. And all this because
some people insist that paraphyletic groups aren't real, and splintered
cladifications are superior. Peter Dodson's term "tortured" immediately
comes to mind. It's not easy to live a normal life if you live nextdoor to
a "circus". The codes will clash, and it will eventually affect us all.
Ironically it is the phylocode proposal which has gotten this controversy
really stirred up again in the last few years. Perhaps that is one reason
a lot of strict cladists actually oppose phylocode.
------ Ken Kinman
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