Re: No island fossils

Paul Crowley wrote:
"Tim Tyler" <seemysig@xxxxxxxxxxxxxx> wrote in message news:fqas6f$29ls$1@xxxxxxxxxxxxxxxxxxxxxx

[Re: http://alife.co.uk/essays/no_island_fossils/]

However islands leave relatively few fossils.

Many islands are volcanic - and fossils tend to prefer to take up
residence in sedimentary rocks.

Many other islands are eventually eroded and crumble into the sea.
This must be an extremely common fate of small islands. Such an island
will leave no fossils.

You have ignored the fact that sea-levels
constantly rise and fall. This has two
enormous consequences. Firstly, islands
are (over evolutionary time) frequently
created and destroyed. But, broadly,
they last long enough to allow for new
speciations.

No, no. The idea is that island fossils
tend not to survive - not that speciation
on islands does not have time to happen.

Such islands can be very large, and we
have numerous examples created by the
last rise (of about 100 metres) in sea-levels
about 12 kya . One is Borneo. On such
islands, large predators quickly go into
extinction. On smaller ones, even small
predators will suffer the same fate.
Predator populations are too small to
avoid the fatal effects of inbreeding.
Their disappearance allows other species
to evolve in wholly different ways from
their ancestral populations on the
mainland.

Indeed. Another of my essays deals with
such effects:

http://alife.co.uk/essays/new_species/

However, it is true that very large islands
(such as Borneo) are too large for many of
the island effects I describe to apply - though
they can still be geographically isolated.
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