On Thu, 7 Dec 95 11:36:48 MST you wrote:
>On Thu, 07 Dec 95 06:33:01 EST, sjones@iinet.net.au (Stephen Jones) said:
>
JT>Did anyone else get a chance to review the most recent issue of
>_Time_ magazine: "Evolution's Big Bang"? It's cover story is on the
>most recent discoveries related to the Cambrian explosion. ......
SJ>Thanks for posting this. On the Australian fidonet Creation v
>Evolution echo I have been taunted about the Ediacaran forms as a
>"failed experiment". It now looks more like a single comples event.
JF>The Ediacaran fauna is Precambrian (i.e. before the Burgess
>fauna), and quite different from the Burgess Shale stuff, so the
>"failed experiment" explanation is still viable.
Even before this latest discovery, Gould seems to have been
backpedalling away from this "failed experiement" line:
"The first fauna, called Ediacaran to honor the Australian locality of
its initial discovery but now known from rocks on all continents,
consists of highly flattened fronds, sheets and circlets composed of
numerous slender segments quilted together. The nature of the
Ediacaran fauna is now a subject of intense discussion. These
creatures do not seem to be simple precursors of later forms. They
may constitute a separate and failed experiment in animal life, or
they may represent a full range of diploblastic (two-layered)
organization, of which the modern phylum Cnidaria (corals, jellyfishes
and their allies) remains as a small and much altered remnant."
(Gould S.J., "The Evolution of Life on the Earth", Scientific
American, October 1994, p67).
But in any event, the Time article is confusing. It does not mention
Ediacaran fauna by name but it seems to imply it. For example, it
speaks of fossil evidence from Namibia:
"AN HOUR LATER AND HE MIGHT NOT have noticed the rock, much less
stooped to pick it up. But the early morning sunlight slanting across
the Namibian desert in southwestern Africa happened to illuminate
momentarily some strange squiggles on a chunk of sandstone. At first
Douglas Erwin, a paleobiologist at the Smithsonian Institution in
Washington, wondered if the meandering markings might be dried-up
curls of prehistoric sea mud. But no, he decided after studying the
patterns for a while, these were burrows carved by a small, wormlike
creature that arose in long-vanished subtropical seas- an archaic
organism that, as Erwin later confirmed, lived about 550 million years
ago, just before the geological period known as the Cambrian." (Nash
J.M., "When Life Exploded", TIME, December 4,1995, p71)
which is also mentioned in the Gould article as a source of Ediacaran
fossils:
"SLAB CONTAINING SPECIMENS of Pteridinium from Namibia shows a
prominent organism from the earth's first multicellular fauna, called
Ediacaran, which appeared some 600 million years ago. The Ediacaran
animals died out before the Cambrian explosion of modern life."
(Gould, p63).
Also, the dates given in both articles seem to be closing the
gap between the Ediacaran and the Cambrian.
600 590 580 570 560 550 540
|---------|---------|---------|---------|---------|---------|
----------------------------->? -------------------->
Ediacaran Vendian Cambrian
"By 1990, for example, new dates obtained from early Cambrian sites
around the world were telescoping the start of biology's Big Bang from
600 million years ago to less than 560 million years ago. (Nash, p74)
Finally the articles above both talk of their respective fauna dying
out before the Cambrian:
"The first fauna, called Ediacaran to honor the Australian locality of
its initial discovery but now known from rocks on all continents,
consists of highly flattened fronds, sheets and circlets composed of
numerous slender segments quilted together....they apparently died out
well before the Cambrian biota evolved." (Gould, p67).
and
"The key to the Cambrian Explosion researchers are now convinced, lies
in the Vendian, the geological period that immediately preceded it.
But because of the frustrating gap in the fossil record, efforts to
explore this critical time interval have been hampered. For this
reason, no one knows quite what to make of the singular frond-shape
organisms that appeared tens of millions of years before the beginning
of the Cambrian, then seemingly died out." (Nash, p74-75).
Are we talking about *two* pre-Cambrian faunas dying-outs in the one
area? I doubt it, so I conclude that it is the Ediacaran that is
being now re-dated and re-named to be continuous with the Cambrian:
"We now know," says Grotzinger, "that evolution did not proceed in two
unrelated pulses but in two pulses that beat together as one." (Nash,
p76).
Regards.
Stephen
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