Mollusc outgroups (was 'cladistics' of sequences)
jgrehan at SCIENCEBUFF.ORG
Mon Jun 7 10:02:31 CDT 2004
From: Taxacom Discussion List [mailto:TAXACOM at LISTSERV.NHM.KU.EDU] On
Behalf Of Ken Kinman
Sent: Sunday, June 06, 2004 11:00 PM
To: TAXACOM at LISTSERV.NHM.KU.EDU
Subject: [TAXACOM] Mollusc outgroups (was 'cladistics' of sequences)
John Grehan wrote:
No, but if one cannot polarize the characters and determine which
are potential synapomorphies before the analysis then the implication is
that such individuals do not know their group very well.
Not necessarily. In the case of Mollusca, I believe that many
hundreds (maybe thousands) of malacologists know the details of that
group better than I do. However, I still think that they probably have
severely misrooted molluscan phylogenies due to a mistaken notion of
what (1) an "Urmollusc" was really like. The same goes for (2) the
"Urarthropod" with multiple identical repeated segments, (3) various
hypotheses of the Urbilateria, and (4) Woese's concept of a
hyperthermophilic cenancestor of all life (remember his 3 Urkingdoms?).
This potential situation does not conflict with my characterization.
If such mispolarization of characters do occur at thedse highest
taxonomic levels by scientists who know their taxa fairly intimately,
the same thing can also repeatedly occur at various lower taxonomic
levels as well.
It all depends on the 'if'.
The double whammy of homoplasy and misrooting is something of which we
should always be wary. Even Thomas Cavalier-Smith (for whom I have the
greatest respect) was mistaken about the nature of the earliest
eukaryotes, but he admitted the error and has moved on. I can only hope
there will be similar admissions of error by others and a timely "moving
on" to other rootings of the appropriate taxa. Whether or not great
apes have been misrooted still remains to be seen. Personally, I am
still hoping for the relatively neglected phylogeny: Pongo (Homo (Pan,
Well that's interesting in that on one hand you have said (if I recall
correctly) that you place your faith in DNA sequences but chose an
arrangement that is contradicted by those molecular systematists who now
way that the human-chimp relationship is proven. How can you question
the veracity of the human-orang relationship on the basis of its
conflict with DNA sequencing and yet accept the Pan, Gorilla
relationship which is also in conflict (although it makes plenty of
sense in terms of morphology).
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