Why is taxonomy placeless? (My overview)
kinman at HOTMAIL.COM
Sun Feb 3 11:09:32 CST 2002
An excellent question. Actually, "place" is already entering the
taxonomy of eutherian mammals: Afrotheria, Boreoeutheria, and so on. I
personally think that these should be informal names, rather than formal
taxa, but I won't belabor that point here except to say: too many "formal
names" spoil the broth.
It seems to me that biogeography on a large scale becomes extremely
important in studying evolutionary radiations (especially on land) which
follow huge mass extinctions, in particular the end-Cretaceous (K-T)
extinction. I believe that the northern hemisphere was almost wiped clean
of mammals and birds, and if there were any survivors, they were killed off
by extremely acidic rain, starvation, or later driven to extinction by
invaders from the south.
The southern hemisphere was also devastated, but it was in southern
Gondwanaland that a number of mammal and bird clades managed to survive,
repopulated Gondwana in the earliest Paleocene, and then quickly spread
north (radiating explosively as it went). The afrotherian mammals would do
quite well back in Africa until its connection with Eurasia, and the
boreoeutherian invaders would then largely outcompete the afrotherians
(which are today very species poor--- elephants, the aardvark, hyraxes,
sirenians, and a few insectivores).
Note that only the "marine" afrotherians (sirenians and the extinct
desmostylians) seem to have successfully spread to the New World. But
without a known phylogeny, who would have guessed that the desmostylians of
western North America and Eastern Asia were actually afrotherians?
Phylogeny trumps biogeography, and the latter will almost always play second
On dry land, elephants' invasion of Eurasia was fairly successful
(being large helped alot), but smaller afrotherians just didn't compete very
well at home or in Eurasia. The radiation of birds from south to north
(after K-T) seems to follow a broad pattern similar to that of the mammals.
The paleognaths (ratites and tinamous) have held on in the south, but
neognaths took over the empty northern hemisphere and then invaded the
But even after mass extinctions, phylogeny (whether eclectic or purely
cladistic) has precedence over biogeography. This is generally even more
true of marine organisms. Of course that is no excuse for ignoring
biogeographic patterns, because these are often of considerable value. John
Grehan certainly has his hands full trying to remedy the tendency to dismiss
biogeography as relatively unimportant. Using a balanced approach, they can
usually complement one another quite nicely. All approaches have their
limitations, so one should never put all of your eggs in one basket. That
is why I like being an eclecticist, which allows you to diversify your
"portfolio of ideas" to the greatest extent.
------- Cheers, Ken Kinman
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