>Where are you getting your date for 5 million? The Cambrian lasted about 70
>million years. There are (I think 3) phyla that are thought to pre-exist
>the Cambrian and at least one that arose afterward. This is from the
>Encyclopedia Britanica:
>"At least 11
>extant animal phyla (Annelida, Arthropoda, Brachiopoda, Chordata,
>Ctenophora, Echinodermata, Hemichordata, Mollusca, Onychophora, Porifera,
>and Priapulida), including most of those with a fossil record, first appear
>in Cambrian rocks. Most of these rapidly diversified as they seemingly
>adapted to numerous unfilled ecological niches. Another five phyla
>(Nemertea, Phoronida, Platyhelminthes, Pogonophora, and Sipuncula) are
>questionably known from Cambrian fossils. The only extant animal phylum with
>a good fossil record that is not known from Cambrian rocks is the Bryozoa,
>which first appears in rocks of Early Ordovician age."
You seem very confident that there were no Cambrian bryozoa. Well, what
if there weren't? The triviality of the counter-example is telling. Sorry, I
don't have a reference for the >5-million year period of creativity.
Hopefully someone will post one. I offer this from Gould in Scientific
American:
In any case, they apparently died out well before
the
Cambrian biota evolved. The Cambrian then began
with an assemblage of bits and pieces, frustratingly
difficult to interpret, called the "small shelly
fauna."
The subsequent main pulse, starting about 530
million
years ago, constitutes the famous Cambrian
explosion,
during which all but one modern phylum of animal
]ife
made a first appearance in the fossil record. (
Geologists had previously allowed up to 40 million
years for this event, but an elegant study,
published
in 1993, clearly restricts this period of phyletic
flowering to a mere five million years.) The
Bryozoa,
a group of sessile and colonial marine organisms, do
not arise until the beginning of the subsequent,
Ordovician period, but this apparent delay may be an
artifact of failure to discover Cambrian
representatives.
>I disagree with "qualitatively." Certainly more rapid than usual.
You figure these wonderfully complex organisms with their inter-related
systems formed through incremental additive evolution? Within
5 million years?
>a tree does not put out new branches from its trunk?
Why just the one tree? Why a bunch of big branches ascending
from ground level and no more big branches? Darwinian theory
does not predict or explain this pattern, it is at odds with it.
>There are not huge wide-open nitches?
Niches are more biotic than geographic. Fewer species, fewer
niches. The niche approach doesn't seem satisfying. Maybe if we
think of the whole planet as a niche and the biota since the Cambrian
as the occupant, an occupant who somehow prevents whole new
types of organisms from getting a foothold.
Oxygen use will never be new again?
Oxygen could help explain the timing of the Cambrian explosion,
but it doesn't explain how it happened, or why such evolution hasn't
happened since.
>It has been demonstrated repeatedly that evolution can proceed very rapidly
>at times.
Are you talking about evolution through loss, or simple changes in
gene-frequencies? This does not explain how the Cambrian explosion
occurred.
>There is still a great deal to learn about the Cambrian, but it
>is not a total mystery. For example that is also the time when the
>atmosphere became oxygenated. That *might* have something to do with it.
>That's an event that will only happen once (we hope!) and therefore perhaps
>the life that developed then will only develop that way once. Even so, 70
>million years is a good long time for evolution to take place. The Cambrian
>"explosion" is only comparatively rapid.
"will only develop that way once"--okay, what is "that way"? That's what we
need to know. 70 million is a way wrong figure. Give it up.
It doesn't worry me that early Cambrian evolution was very rapid, because
creationists don't worry me. I'm looking at things objectively, and I see an
interesting conflict between fact and theory.
>The short timespan that Darwin had to work with was only about 5-10 million
>years. *Way* too short for even a Cambrian-style explosion.
How do you know 10 million years was too short a time? How do you know
the experts are wrong about the 5 million figure?
>Also Darwin
>wasn't just concerned with the origin of the phyla, but of all the species
>we see today. Even given a starting point in the Cambrian for most phyla
>that's still 540 million years for the rest of life to develop.
The 'starting point' idea implies that the phyla did not appear fully
formed and anatomically complex. This is not true. Subsequent evolution
is just variation on the themes.
>>I don't see what fun there is in indignantly arguing for old evolutionary
>>dogma, and ignoring the anomalies that make the subject interesting.
>The Cambrian is an anomoly, yet it's not. There have been other
>"explosions" and die-offs since that time.
Great radiations after great extinctions, but no new phyla.
>The Cambrian certainly is
>interesting, but I'm not sure what you are getting at. It's obviously not
>the creation event, there were animals alive before it. Also a great many
>new phyla that evolved at that time which have since died out. Our
>phylum--cordata--includes mammals, birds, fish, and reptiles. What's
>remarkable about the original emergence of cordata?
If that isn't remarkable, nothing is.
>And I still don't know what you are getting at. Say what you are saying.
Extraordinary mechanisms were at work 530 million years ago. Scientists
will puzzle them out, defenders of conventional approaches will not.
--Cliff Lundberg ~ San Francisco ~ cliff@noe.com