Surplus time for Botanists

[Eric Zurcher]

In message Mon, 20 Mar 1995 14:30:33 EST,
  Una Smith <una at DOLIOLUM.BIOLOGY.YALE.EDU>  writes:

> PALEONET had a long discussion re nomenclature, ranks, and hierarchies
> a while ago, among mostly vertebrate and invertebrate palontologists (as
> far as I know), so it's not just botanists who worry about this stuff.
> It was my impression that a useful consensus was reached re the topic.
> With any luck, TAXACOM will similarly resolve this discussion quickly
> and amicably, and we'll all learn something in the process.

Is there a summary of the PALEONET discussion to be had anywhere. I'd be
interested in seeing it, particularly since paleontologists approach the
problem from a somewhat different view point. Indeed, recent data from the
paleontologists data may stimulate systematists to rethink their approach.
What I'm thinking of in particular is the increasing evidence that major
evolutionary radiations to not occur gradually, but instead occur in
remarkably rapid bursts. The classic example (as all readers of Stephen
Gould's essays in Natural History will be well aware ;-) ) is, of course,
the Cambrian "explosion". The fossil evidence indicates that virtually all
our present animal phyla came into existence within a period of no more than
a few million years, with no new phyla arising in the half billion years
since. This episode is perhaps the most impressive such event, but does not
seem to be unique. In a recent paper in Science, Alan Feduccia argues that
virtually all our current orders of birds arose within a very short time -
again no more than a few million years - immediately after the end of the
Cretaceous. A similar pattern seems to hold for mammals.

If this pattern is a general one -- that evolution occurs in "bursts" of
remarkable amounts of diversification with intervening periods of relative
statis -- what are the implications for systematics? Can the evolutionary
models of the cladists, with their tidy (though not necessarily biologically
realistic) dichotomous branches be stretched to fit a pattern where the
major branches actually arise in whorls? Might there be evolutionary
processes occurring during these bursts that we don't yet understand? Might
there be more introgression during these episodes than we currently think?
And might it be that SOME of the ranks within parts of the "Linnean"
hierarchy are NOT just the product of human desire to classify, but rather
reflect some biological/historical reality (e.g., might "phylum" be a real
category referring to an independent lineage arising in the Cambrian
explosion - a member of a specific whorl of branches, and not just a branch
that happens to arise somewhere near the trunk)?

P.S. - I'm not a systematist myself, and don't peruse the systematic
journals on a regular basis, so perhaps this matter has already been debated
in another forum, and I am unaware of it. If that is the case, please point
me in the direction of the relevant literature, then press your delete key.

Cheers,

Eric Zurcher
CSIRO Division of Entomology
Canberra, Australia
E-mail: ericz at ento.csiro.au
Phone: +61 6 246 4218