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Science Forum Index » Bio Evolution Forum » No island fossils
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| Tim Tyler |
 Posted: Fri Feb 29, 2008 8:13 pm |
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Most of my recent, brief essay on why islands leave relatively
few fossils is presented below:
Islands are important as crucibles for new species, and it seems
reasonable to expect that much of the world's gradual evolution has
taken place on them.
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.
Next, fossils tend to form in sediments in lakes. Islands are less
likely to have lakes in the first place. Many lakes are high in the
mountains - where the ground is rocky. Islands tend to form from more
coastal land. Islands have large perimeters, and it is easy for the
perimeter to intersect what was once a lake - and thus drain it. Even
for lakes inland, the small scale of an island may reduce its drainage
basin - and fewer animals will leave bones in smaller lakes.
These facts may help explain the relatively low frequency of
transitional forms in the fossil record.
http://alife.co.uk/essays/no_island_fossils/
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|im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply. |
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| Lorentz |
| Posted: Fri Mar 07, 2008 8:36 am |
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On Mar 1, 1:13 am, Tim Tyler <seemy...@cyberspace.org> wrote:
Quote: Most of my recent, brief essay on why islands leave relatively
few fossils is presented below:
Islands are important as crucibles for new species, and it seems
reasonable to expect that much of the world's gradual evolution has
taken place on them.
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.
There is a spot in New Mexico where the fossils are supposed to
be from an ancient lagoon in the Pennsylvanian era. The Kinney Brick
Quarry, Late Pennsylvanian, in Central central New Mexico provides a
range of fossils of both animals and vegetation which I was told seem
characteristic of lagoon life.
I went there and all I collected was a teleost fish scale, with
the rest of the fish missing. Therefore, I can't really tell why
anyone would think these different from any other marine fossil. I
suspect the vegetation found there may provide a clue.
In any case, this would be a sort of island fossil. Lagoons are
"ring islands." I don't know how isolated such life would be.
I think terrestrial mountain ranges of any type would provide as
much isolation as islands, which are just underwater mountains anyway.
The reason is the climate changes radically going up the mountain. The
flora and fauna change radically going up the mountain. Unless they
evolve to adapt to other climates quickly, in the face of fierce
competition, they are stuck. They can evolve all sorts of ways
different ways. The climate can change allowing them to leave their
zone and mix with different subspecies on different mountains,
allowing more radical changes. We may see some of this happen as
global warming commences, regardless of what is causing it.
Also deep trenches in oceans. They can isolate species for a long
time.
I recently saw a Discovery channel special where scientists
climbed a steep plateau near the Amazon river. All sorts of radically
altered creatures lived on top of the plateau. Alas, no dinosaurs
which one was looking for. But these really odd spiders. Granite
chomping bacteria were found in a cave, forming silica stalactites.
That is pretty weird. I think the weird variations on this plateau was
far greater than anything Darwin found in the Galapagos islands.
I don't think "islands in the sea" are actually the most
productive means of isolation for stimulating evolution. The sea
surface provides a rather convenient road for certain forms of life.
Komodo dragons, for instance, swim from island to island. Coconuts
float from island to island. The sea surface tends to homogenize
climate. |
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| Tim Tyler |
| Posted: Sat Mar 08, 2008 3:12 pm |
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Lorentz wrote:
Quote: I don't think "islands in the sea" are actually the most
productive means of isolation for stimulating evolution.
Caves and mountains represent other types of isolation, though
often do not represent terribly hospitable environments.
Freshwater lakes can be isolation - for fishies.
E.g. the Cichlid fishes of the great lakes.
These would seem to offer relatively good fossil potential.
Glaciation and deserts could also produce isolation.
It is normally the interior - not the exterior of the desert that
is isolated - and again this is not a terribly hospitable environment,
and might not leave too many fossils.
--
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| Aidan Karley |
| Posted: Sun Mar 09, 2008 12:33 pm |
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In article <fqs1vb$2gnl$1@darwin.ediacara.org>, Lorentz wrote:
Quote: I recently saw a Discovery channel special where scientists
climbed a steep plateau near the Amazon river.
I suspect that you're thinking of the tepuis, which form part of
the watershed between the Amazon and Orinoco basins.
Quote: All sorts of radically
altered creatures lived on top of the plateau. Alas, no dinosaurs
which one was looking for. But these really odd spiders. Granite
chomping bacteria were found in a cave, forming silica stalactites.
Lots of unusual and endemic species for sure. I've not heard of
"granite chomping bacteria" though, nor "silica stalactites". There are
a modicum of reports of bacteria living in rocks, and caving literature
has reports of some pretty unusual bactrerially-mediated stalactites
(e.g. "snottites" found in places from Cheshire to Mexico). The
chemistry of silica in water isn't amenable to the formation of
stalactite-like forms, at least not by any process reasonably
comparable to the formation of "flowstone" in caves. Can you cite a
reference for this?
--
Aidan Karley,
Aberdeen, Scotland
Written at Sun, 09 Mar 2008 00:03 GMT, but posted later.
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0 |
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| Paul Crowley |
| Posted: Tue Mar 18, 2008 7:28 pm |
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"Tim Tyler" <seemysig@cyberspace.org> wrote in message news:fqas6f$29ls$1@darwin.ediacara.org...
Quote: Most of my recent, brief essay on why islands leave relatively
few fossils is presented below:
Islands are important as crucibles for new species, and it seems
reasonable to expect that much of the world's gradual evolution has
taken place on them.
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.
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.
The second major effect of constantly
changing sea-levels is the progression
of coasts backwards and forwards over
the landscape. Coasts can be seen as
giant grinding machines, working day
and night, year after year, reducing all
material to sand and dust. As a result,
species that inhabit low-land coastal
areas will leave very few fossils.
My own pet theory is that humans
(and their hominid ancestors) are
exactly that -- nearly always living
close to the sea, primarily for the
benefit of its warmth at night. Parties
would have travelled inland on
occasion, but would have been
predominantly young adult and male.
Those are, in effect, the only hominid
fossils that can survive.
Paul. |
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| Tim Tyler |
| Posted: Wed Mar 19, 2008 7:18 am |
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Paul Crowley wrote:
Quote: "Tim Tyler" <seemysig@cyberspace.org> wrote in message news:fqas6f$29ls$1@darwin.ediacara.org...
[Re: http://alife.co.uk/essays/no_island_fossils/]
Quote: 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.
Quote: 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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|im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply. |
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| Lorentz |
| Posted: Thu Mar 20, 2008 7:19 am |
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On Mar 8, 9:12 pm, Tim Tyler <seemy...@cyberspace.org> wrote:
Quote: Lorentz wrote:
I don't think "islands in the sea" are actually the most
productive means of isolation for stimulating evolution.
Caves and mountains represent other types of isolation,
Freshwater lakes can be isolation - for fishies.
Glaciation and deserts could also produce isolation.
It is normally the interior -
I think my point is that all these environments can form pockets
of isolation. Furthermore, these pockets don't have to last millions
of years, just maybe a few thousand. The pocket has to be isolated
just long enough to form a hybridization barrier. Once the subspecies
has formed a hybridization barrier, even a partial hybridization
barrier, it has the potential of becoming a new species and eventually
a new class of animals.
The hybridization barrier in effect becomes a portable island. The
animal is embedded in its pocket of isolation. The pocket will grow
deeper with time. Maybe a hole in the pocket will form, generating a
taxon much higher than species. Even a difference in mating behavior
can start the evolution ball rolling.
Suppose the environmental pocket stops being isolated. If the
hybridization barrier is partial, then a new species can form by
hybridization or by selection. Animals with the partial hybridization
barriers are selected to avoid the other animals. If the
hybridization barrier is complete, essentially a reproduction barrier,
natural selection will proceed to make this new species far different
from the other one.
Look at the Amazon. Every meander of the river contains different
"species" of salamander. But these are only new "species" in the sense
of hybridization barrier, for the differences are slight. Surely,
these breaks in river last only a few thousand years. However, once
there is a hybridization barrier one has a portable form of isolation.
When the river system starts shrinking, these different "species" will
compete among themselves. Then larger differences will be seen. |
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