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Re Kiwi and NZ Separation etc.
Just some information to add to Derek Tearne's message
New Zealand separated from the rest of Gondwana some time between 84 and
90 million years ago. Recent work on the rocks of the West Coast of the South
Island of NZ showed considerable strain build-up for a good 10+mys before the
strain was released at about 90my ago. This is the date we snapped off
Gondwanaland. New seafloor between NZ and the Australian part of Gondwana
has been dated at 84myo (So far).
There is no reason why some of our flightless birds ancestors were not already
present when NZ separated from Gondwana. This would be a much simpler
explaination for the distribution of the large ratites over the present
fragments (NZ, Australia, Africa, South America etc.) Many of the ancestors of
modern bird families are considered to have been around in the Cretaceous
anyhow. This would make it easier for a large ancestor for the Kiwi evolving
a smaller species, but retaining the larger egg.
Just because we don't have the fossil record doesn't mean they were not here!!
Take the case of the Moas here in NZ, the oldest fossil we have so far is just
over 2 million years old, there is a lot we don't know!!! The fossil record we
for the kiwi is almost nonexistant!!! There have been the odd bits of evidence
from DNA studies on Moa and Kiwi material from dried specimens etc. that
indicate a relatively "recent" arrival to NZ, but all DNA work must be
for the species/family you are looking at and to do this we need the fossil
record. With Moas & the Kiwi - well we don't have that!!
Yes - we do have Aussie immigrants the most recent are the swallow and the
spur-wing plover which have arrived in the 1960's and 1970's
Regarding the NZ Bats, well we do need a fossil record for them. One of our
bats is closely related to a South American family - which would have been a
very much longer flight than a flight from Australia no matter how far back in
(Unless the ancestors came via Antarctica during warmer times).
Given the work done so far in searching for terrestrial mammals from NZ, there
is only one serious attempt going on and that is looking for Cretaceous
mammals which we should have had, given that we had dinosaurs here in NZ
and considering mammals have been found elsewhere in the world where they
have found dinosaurs. (Watch this space & vrtpaleo).