[Taxacom] NZ biogeographers Annual Exam Q4

John Grehan calabar.john at gmail.com
Mon Feb 6 09:45:36 CST 2017


NZ biogeographers Annual Exam Q4

How are valid biogeographic questions avoided when biological evidence is
excluded and how does this avoidance affect understanding of endemic
origins?

"Mortimer and Campbell (2014: 205) wrote that “The biological evidence for
permanent land appears to be no more convincing than the geological
evidence, but on close inspection, it too is wanting in detail. The fossil
record is just too weak.” But the biological evidence includes much more
than the fossil record; the extant biota has contributed a wealth of data
on the submersion debate.

The total submersion theory predicts that terrestrial life in New Zealand
was destroyed during the flooding, and was then replaced, when land
reemerged, but dispersal from other continents (Campbell, 2013; Mortimer
and Campbell, 2014: 229). Nevertheless, Campbell also considered problems
that their theory has in accounting for biogeography:

 ‘If life were so easily moved about, though, why is it that the world is
not more mixed up? Why are there not more Australian animals…in New
Zealand? Conversely, why does New Zealand have such strong endemism? There
are fair questions, and they are common criticisms of the drowning
hypothesis. Again, as a geologist I am not the one to answer it…perhaps
there is no need to answer it: *perhaps it really is just a matter of
chance, of luck*… ‘(Campbell, 2013: 52; italics added).

Rather than avoiding valid biogeographic questions in this way, other
authors have considered data from biogeography together with
paleontological and geological information. These studies have found that
the facts are incompatible with total submergence and the subsequent
arrival of the entire terrestrial biota (e.g. Craw et al., 1999; Lee et al.
2001; Gibbs, 2006; Knapp et al., 2007; Edgecombe and Giribet, 2008; Bunce
et al., 2009; Cree, 2014: 507). As Wallace and Trewick (2009: 3) wrote,
‘Total inundation is hard for biologists to reconcile with some apparently
archaic elements of the fauna.’

For example, the New Zealand tuatara (*Sphenodon*) is a member of the order
Rhynchocephalia, which is known elsewhere only from Mesozoic fossils. Cree
(2014: 71) argued against a post-Oligocene dispersal to New Zealand as (1)
no source population is known, despite extensive vertebrate fossils in
Australia; (2) further dispersal, for example, to the Chatham Islands, has
been unsuccessful (Sphenodon does not enter seawater voluntarily, and has a
high water loss through the skin); (3) dispersal of many terrestrial
reptiles, such as agamid lizards and snakes, from Australia to New Zealand
has not been recorded; (4) fossils show that *Sphenodon* was already
present in New Zealand in the Early Miocene (19-16 Ma), soon after the
flooding; and (5) *Sphenodon* can survive in very large numbers on very
small islands. Cree (2014: 507) concluded: ‘From a biological perspective
the evidence is strong that [through the Cenozoic] New Zealand remained an
emergent archipelago…’


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