[Taxacom] Pacific biogeography

Richard Zander Richard.Zander at mobot.org
Mon Dec 17 09:34:34 CST 2012

What an interesting note, Michael. If there were lots of islands in the
Pacific long ago, their existence would likely explain certain

Facts about sea floor subsidence may lead to good, pursuable scientific
theories, which, though having to do with historical science, are
nevertheless in the broad range of scientific ratiocination. 

The problem is with panbiogeographic analysis, the method of which is
questioned. New facts about the possibility of lots of stepping stone
islands in the Pacific may not make panbiogeographic "tracks" more
revealing of historical processes. Submerged islands make poor
repositories of evidence.

Richard H. Zander
Missouri Botanical Garden, PO Box 299, St. Louis, MO 63166-0299 USA  
Web sites: http://www.mobot.org/plantscience/resbot/ and
Modern Evolutionary Systematics Web site:
UPS and FedExpr -  MBG, 4344 Shaw Blvd, St. Louis 63110 USA

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Michael Heads
Sent: Monday, December 17, 2012 2:08 AM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Pacific biogeography

Dear Taxacomers,

A few months ago we were debating Hawaiian biogeography. In a discussion
of this topic in the book cited below, I mapped the 2000, 4000 and 5000
m isobaths of the central Pacific. O'Grady et al. (Taxon 61: 702. 2012)
have now suggested that this was 'disingenuous', because sea-level has
not dropped by more than 100 m or so. But the authors overlooked the
*1000s* of meters of subsidence that the Pacific seafloor itself has
undergone. This is well-known to geologists and I discussed it in the

As the seafloor has drifted away from the East Pacific Rise - the
spreading ridge that produced it - it has cooled (increasing its
density) over tens of millions of years and has subsided by these large
amounts. This has led to the submergence of most of the islands that
were perched on it.
The current high islands are new ones. Evidence for the subsidence is
seen in the numerous atolls of the region, formed by coral reefs which
have grown as the seafloor subsided. The many flat-topped seamounts
(guyots) located north, south, east and west of Hawaii are former high
islands that were eroded to sea-level before being submerged with the
tectonic subsidence.

Michael Heads
Wellington, New Zealand.

My new book: *Molecular panbiogeography of the tropics. * University of
California Press, Berkeley.

More information about the Taxacom mailing list