Boring baselines (biogeography)

John R. Grehan jrg13 at PSU.EDU
Tue Nov 6 10:52:24 CST 2001

At the risk of boring too many people (in which case hit the delete now) I
draw attention
to a nice example of phylogeny and baseline represented by Fig. 5. for the
freshwater mollusk family Melanatriidae in Glaubrecht (1999/200) Zoology
(Jena) 102: 127-147.
The figure shows the family distributed in central and northeastern S.
America, west and central
Africa, Madagascar, S East Asia and NG. In the phylogeny SEA-NG are sister
groups, and Africa-
Madagascar are sister groups, and each of these has a sister group
relationship, and finally the S America
group as the basal lineage. Glaubrecht states the distribution and
relationships match a general pattern of
continental fragmentation and so this distribution could be explained by
large scale vicariance.

Galubrecht's approach provides a traditional match of a phylogenetic
pattern with a geological narrative,
so the  distribution itself is uninformative, and the phylogeny is
informative only in that it matches
a historical theory. Since the theory (sequence of fragmentation) may be
wrong, the match is only
meaningful in acceptance of its current validity. In this sense the
biogeography is based on narrative.

In panbiogeographic methodology one would draw a track connecting the
localities over the Indian and Atlantic
oceans. Since there is concordance between biological relationship and
geographic distance this map
is unproblematic (i.e. a track link first for SEA-NGuinea, another for
Africa-Madagascar then the two linked together, and
then another link between the nearest neighbors across the Atlantic Ocean.
By phylogenetic relationship and main massings the track would have an
Atlantic and Indian Ocean baseline. Since this assignment agrees with a
model it would be possible to agree with Glaubrecht's classification on the
basis of spatial homology.

John Grehan
Frost Entomological Museum
Pennsylvania State University
Department of Entomology
501 ASI Building
University Park, PA 16802. USA.

Phone: (814) 863-2865
Fax: (814) 865-3048

Frost Museum

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