Is Mantophasmatodea an order?

Bill Shear wshear at EMAIL.HSC.EDU
Mon Apr 22 11:57:05 CDT 2002


Riann is asking a very good question that deserves more of an answer than
the blow-off Pierre provided.

Of course there is currently a good deal of discussion of the role of
heirarchy in taxonomy, with at least one radical proposal having been
floated of a rankless system.

There are probably some good reasons, both practical and biological, for
ranked taxa.  Biologically, ranks can indicate either (or both) phylogenetic
or chronological distance from a common ancestor.  From the practical
standpoint, a series of nested categories makes the "filing system" easier
to construct and to use.

It has generally been accepted that above the rank of species, categories
cannot be objectively defined independent from specific examples.  "Order"
means different things in different groups of organisms.

Like our colleagues at the Max Planck Institute, I have described a new
Order (Devonobiomorpha).  A fossil centiped from the Devonian, also
described by myself and Pat Bonamo, had characters which seemed to us to
clearly set it apart from the already-described orders of centipeds.  The
differences were such that to place the new species in one of the existing
orders would have so radically altered the defining characters (as given by
the lower taxa included) as to be disruptive to the system.  So we set up a
new order, as well as new family and genus, to contain the species.

Some myriapodologists have been accepting of the new order, but at least one
centiped authority has argued strongly against it.  After some time, a
concensus should emerge on whether or not the new order will become a
permanent part of the system.

I have not yet seen the SCIENCE article, but from the press releases and
website, I would guess that the future of Mantophasmatodea is uncertain.
Much more evidence will have to be forthcoming for the new order to gain
acceptance.

So what is an Order?  I'll venture that it is a collection of closely
related families separated by a distinct phenotypical (and by implication,
phylogenetic) gap from other such collections.  How big the gap has to be
and what the specific characters involved are would depend entirely upon the
Class under which the Order is being described.

After the proposal (and remember, the description of any taxon is only a
proposal--a hypothesis, if you will) is made, it will be tested in various
ways by the community of specialists on that group.  If a concensus for
acceptance forms, the new taxon will be integrated into the system.

A separate issue is the description of high-level monophyletic taxa.  This
has been debated for a long time in the pages of SYSTEMATIC ZOOLOGY and
other methodological journals.  Fundamentally, one question is: do
monophyletic taxa increase or decrease the information content of the
system?  It seem that viewing the system qua system, they decrease
information.  Do they convey phylogenetic information?  I believe they do by
drawing attention to a significant phenological gap between the single
included taxon and others at the same level.  Does this justify setting them
up?  Again, only the evaluation of the arguments for doing so by the
community of specialists can provide the answer.

Thus, there appears to be no objective definition of higher taxa, only a
"feel for the organisms" that eventually results in acceptance or rejection.
Monophyletic high-level taxa may be justified in some cases and not in
others, or they may never be justifiable (on cladistic grounds).

Please, before getting out your napalm, recognize that I am merely
describing the situation as I see it, not advocating a particular approach!

Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
(434)223-6172
FAX (434)223-6374
email<wshear at email.hsc.edu>
Moderating e-lists:
Coleus at http://groups.yahoo.com/group/coleus
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MilliPEET website at
http://www.fmnh.org/research_collections/zoology/zoo_sites/millipeet/home.ht
ml
SHAPE OF LIFE website at
http://www.pbs.org/kcet/shapeoflife/episodes/conq_explo1.html

"It is only when we forget all our learning that we begin to know.  I do not
get nearer by a hair's breadth to any natural object so long as I presume
that I have an introduction to it from some learned man.  To concieve of it
with total apprehension I must for the thousandth time approach it as
something totally strange.  If you would make acquaintance with the ferns
you must forget your botany."
Henry David Thoreau, Journals, Oct. 4, 1859.




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