Arachnids and phylogeny

[js314 at UMAILSRV0.UMD.EDU]

Hi,

Bill Shear  was right in his characterization of my proposal as
controversial (i.e. Scorpiones sister to Opiliones (Pseudoscorpiones,
Solifugae)) and also that it is explicitly supported by a
comparatively large number of characters.  This is in contrast to the supporters of
a eurypterid+scorpion clade in which there is only one clearcut
apomorphic similarity (the 5-segmented rather than 3-segmented metasoma or
"tail").  But the supporters of this hypothesis have the advantage of
a Gestalt similarity between eurypterids and scorpions and historical inertia
on their side, which seem to persist as an oddly significant barrier to the consideration of new
evidence.

As Bill also noted, one paleoarachnologist (both meanings) is accumulating evidence in an
apparent attempt to "prove" eurypterid+scorpion monophyly. The
characters "discovered" so far include an additional hypothetical
somite in the opisthosoma of both groups, similar "courtship" (yes, he
claims to know how fossil taxa courted ), big notches at the ends of
leg segments in eurypterids that to him are somehow homologous to slit
sensilla, book gills/lungs absent (or at least not found) on the genital
segment in both, etc. The same folks who accept this sort of stuff as
phylogenetic evidence also overlook the facts
that all arachnids have single genital opening, but eurypterids (of at
least one sex) have two like xiphosurans; all arachnids appear to have
epimorphic postembryonic development, but eurypterids have anamorphic
development like other primitive arthropods; etc., etc. etc. (see my
paper below if you care.)  If a person is willing to accept fossil courtship as phylogenetic evidence
and yet dismiss all similarities in muscles, joints (all
neontological morphology?) as convergences, I am afraid that there is
little point in arguing with them further.

It is odd that during a time when zoologists in general are
entertaining and testing the hypotheses that birds are dinosaurs and
that hippos and whales are sister groups, "most arachnologists"
(whoever they are) are satisfied with 19th century speculations based on virtually no evidence.


PS:  A couple of minor comments about Bill Shear's message. My name
is SHULTZ not "SCHULZ".  I only care about
this because some people might try to find the paper (Cladistics,
9:1-36) and may not be able to find it. (Those of us with
this Germanic family of names must get used to all kinds of spellings.)
Second, while Jerry Regier is a valued collaborator now, I didn't know
him in 1990 and he had nothing to do with the original paper on
arachnid phylogeny and its controversial placement of scorpions. (As
one might infer from my comments above, this correction is intended to protect
his interests and reputation rather than mine).

For what it's worth.

Jeff Shultz

Jeffrey W. Shultz
Associate Professor
Department of Entomology
University of Maryland
College Park, MD 20742

Voice: (301) 405-7519
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Email: js314 at umail.umd.edu