> We are talking over geological time here - what sort of time span Peter?
> 2-500,000 years?
The general scheme that I was describing is somewhat like as follows, The
barrier between Oz and NG was resurrected around 7000 years ago. There
was a series of 6-10 repeated events over the last 1-2 million years in
regard to climate and sea level change. Strong aridity seemed to have
begun in the western portion of Australia's deserts perhaps around 5
million years ago, as mentioned lungfish were last recorded around Lake
Eyre 1 million years ago. I think that some of what we see today is as a
result of the last two million years in terms of species distributions.
I think the development of the distribution of some species and genera
goes back much further, perhaps 10 million years. The origin of some
Australian freshwater families is known from fossils around 40 million
years, no doubt they were there for some time before that. Australia
split from Antartica around 95 million years ago, some fishes no doubt
predate that.
> The sympatry/allopatry thing is interesting. Remember when we went to the
> Walker River
> Barry? We were surprised at the lack of variety compared to the
> surrounding regions - only one species of Rainbowfish, one species of
> Hardyhead, two species of Ambassis, very few gudgeons and no Blue-eyes. Why
> should there be this island of "monotony" in a region of diversity?
This may be due to local conditions such as an unusually dry spell or a
cyclone or something else. It is not a terribly large river basin either
which makes it more prone to change.
Tootles
Peter Unmack