Centre of origin digression

[Robert Mesibov]

"I cannot agree with Robert that we systematists exclude geographical
information.  We need it, and we use it.  In fact, some of us use it in
keys.
Robin Leech"

Do you _define_ your taxa with the help of geography? Or do you define them
with inherent characters alone? Does the geographical information in your
keys tell people anything more than where your character-based taxa can be
found? There are very, very few papers in the taxonomic literature in which
names are given to what one brave specialist has explicitly called
"pheno-geographic units".

Check the TAXACOM archives in mid-2002 for an illuminating discussion on how
systematists use or don't use geographical information. The hard-nosed
position was very ably put by Tom diBenedetto in a series of posts,
finishing with:

"I actually do not think that there is phylogenetic evidence in spatial
distributions. There is geopgraphic evidence - there is biogeographic data,
but I don't think it rises to the level of phylogenetic evidence. To be
evidence, particular data must have a well-understood set of implications
relative to phylogenetic conclusions (as in character evidence - matching
states indicate common descent). The problem with spatial data is not
extracting the evidence, it is meeting the basic requirements of evidence."

I don't argue against the objections to putting geographical information
into the character mix when doing phylogenetic analysis. I'm just sad (all
right, grumpy) that so many systematists do so little biogeography in
parallel with character-based analysis. For those systematists "centre of
origin" means nothing. They've got their tree and they're happy. The tree
shows character-based ancestor-descendant relationships, based exclusively
on living forms in the many groups where fossils or their use is
problematic. The tree doesn't show times and it doesn't show places, so it's
certainly _not_ an evolutionary history.

Getting those times and places requires accepting and working with
non-character-based evidence. The results are often messy and inconclusive,
as indicated by the ongoing discussion here about "centre of origin" of
archaeopterygids.

I'm way out of my depth here, but do I understand that these bird-like
fossils come from what's NE China today? And wasn't that area one of the
terranes that docked with the Eurasian core fairly late, like mid-Jurassic
or early Cretaceous? Suggesting the beasts originated somewhere else and got
rafted to "Asia"?
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Dr Robert Mesibov
Honorary Research Associate, Queen Victoria Museum and Art Gallery
and School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 6437 1195

Tasmanian Multipedes
http://www.qvmag.tas.gov.au/zoology/multipedes/mulintro.html
Spatial data basics for Tasmania
http://www.geog.utas.edu.au/censis/locations/index.html
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