[Taxacom] Two primitive mammals in one week

John Grehan jgrehan at sciencebuff.org
Sat Dec 16 09:16:51 CST 2006


Those are all pertinent points, which in my mind shows that their
approach is just standard Darwinan centers of origin and dispersal
theory dressed up in molecular clocks and tacked onto their beliefs
about geohistorical narratives. From my own panbiogeographic perspective
there is nothing much riding on the mammal finds at all. They show
nothing other than there were mammals present at a certain date and this
has not bearing on anything other than that fact. It may confound
dispersal theories, but then dispersalism in practice is very resilient
as one sees from the way that it jumped ship so easily from static
landmasses to mobile tectonics - after it became popular.

By citing Cowie etc the way they did they have made oceanic islands
relevant, and if mobile island arcs are relevant to oceanic islands then
just designating islands as "oceanic' is of itself not very informative.
They make the point that oceanic islands require chance dispersal in a
way that is different from continents. The Galapagos and Fiji examples
show that this is not necessarily the case. Admittedly the Fiji example
by Heads is too recent for their citation, but Galapagos is certainly
not (and it was ignored by Cowie etc).

The possibility of Oligocene impacts is not something that lies purely
with the molecular approach. Trewick etc conveniently ignore Heads'
(1990) micro-dipping model that allows for both extensive submersion and
extensive retention of diversity.

John Grehan 

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Geoff Read
Sent: Saturday, December 16, 2006 1:07 AM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Two primitive mammals in one week

John Grehan wrote:
 > They [Trewick SA, Paterson AM, Campbell HJ 2007. Hello New Zealand]
> ignore that fact that that there are biogeographic and geological 
> models whereby so-called "oceanic islands" such as the Galapagos and 
> Fiji may have inherited older biota through mobile island arcs etc.

They don't. Mobile island arcs as such aren't relevant, but they allow
that ephemeral islands might have existed during 'total immersion' of
Zealandia, and that some Gondwanan lineages might have survived,
although the geological evidence permits the idea of total drowning. 
Their point is that the submergence or near submergence greatly, greatly
reduced the biota.

But back to the hard fossil evidence. If it holds up to scrutiny the
apparent survival of a tiny primitive mammal on NZ to post-Oligocene is
a major development in NZ biogeography is it not? It casts doubt on
Trewick et al's more favoured total immersion option. There's a lot
riding on a couple of tiny bits of jaw bone, and a femur head.

   Geoff Read <g.read at niwa.co.nz>

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