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Re: dino extinction



Nick Longrich wrote:

>        Now, I can understand severe environmental shifts, but the
>disappearance of ALL large land herbivores and ALL large land carnivores
>implies to me something more on the order of environmental holocaust.
>        I sit and wonder how on earth the dinosaurs could have gone
>extinct, after all that success. And then when I'm done with that, I
>wonder how on earth mammals could have gone extinct. They did in one place
>in the world, New Zealand. New Zealand broke apart from the remains of
>Gondwana ~80 mya ago bearing a full cargo, and the only things that
>survived to modern times were ratites, geckos, the tuatara, frogs, etc.
>Now, what the HELL happened to all the mammals? They were in Australia and
>Antarctica and South America, they must have been in New Zealand, and the
>survival of large flightless birds and various vertebrates seems to imply
>they could have done well, certainly if you look at how rats- even
>flightless bats!- have coped. I don't think that they were there in the
>past 65 million years and went extinct. And I don't buy that they weren't
>there initially. Which makes me think that it's likely that whatever did
>in the dinosaurs did in New Zealand mammals as well.

You could be confusing two different phenomena here. New Caledonia, similar
to New Zealand, has a long history of isolation and also lacks native
mammals (other than recently arrived rats and bats). It seems that there is
some kind of landmass-size dependancy on the survival of mammals: if a
landmass is below a certain size, mammals cannot survive longterm). This
has been put forward by various people and linked by some to the phenomenon
of island dwarfism in mammals. But, while such a correlation seems to
exist, there is no explanation as to why it occurs nor why birds seem to be
uneffected.

Although the suspicion must be that mammals were in New Zealand prior to
separation, remember that no fossils have been found to prove this. There
also seems to have been faunal filters between Australia and South America
in the early Tertiary even though they were part of a contiguous land mass.
It is possible that such faunal filters could have presented faunal
barriers to the entry of mammals into New Zealand.

Anyway, there is no reason to link the survival of mammals across the K/T
boundary with the lack of mammals in New Zealand (excluding bats of course
and the recently introduced rats).

Cheers, Paul


Dr Paul M.A. Willis
Consulting Vertebrate Palaeontologist
Quinkana Pty Ltd
pwillis@ozemail.com.au