Nice play on words. :-) You are correc that the Doushantou fossils are not
small, but they were found in a phosphatizing environment which is capable
of preserving small soft-bodied animals. The fact that they apparently had
no hard parts answers part of your question below.
They, like the
>Ediacara whatever-they-ares, are just below the usual Precambrian boundary.
> They still are not deciphered, and it looks like most of them are probably
>of plant origin...but even if they do represent animal morulae, where are
>the adults, and why do we only find morulae? These are of course questions
>everyone else, especially the discoverers are eagerly seeking answers
>to...again suggesting we not be too quick to blow the whistle on the
>Cambrian explosion.
The discoverers did not say they were plants, they said they were sponges.
"We propose that the Doushantuo sponges are monaxonid Demospongiae because
their skeleton consists exclusively of siliceous and monaxonal spicules.
However, it is generally interpreted that Hexactinellida evolved before
both Calcarea and Demospongiae, and the recently discovered Ediacarian
sponges from Mongolia are also referred to Hexactinellida. The Wengan
sponge remains of Doushantuo age (Early Vendian), therefore may require
revision of phylogenetic relations among the four major classes of phylum
Porifera. Sponges are a monophyletic metazoan group and comprise the
sister groups demosponges, hexactinellids, archaeocyaths, and calcareous
sponges. Our data imply that the ancestral form in sponges lies among the
demosponges." ~ Chia-Wei Li, Jun-Yuan Chen and Tzu-En Hua,"Precambrian
Sponges with Cellular Structures," Science 279(1998):879-882, p. 881
And for those who don't know, this is not the only example of a precambrian
sponge.
"Carbon and strontium isotopic data are used to show that the earliest
sponge spicule clusters and associated phosphatic sediments (with
Anabarites) from southwestern Mongolia are of Ediacarian age. Spicule
morphologies include bundles of oxeas arranged in three-dimensional
quadrules, linked together at junctions by tetracts, pentacts, hexacts, or
polyactines. All are referred to the Phylum Porifera, Class Hexactinellida.
These sponge spicules provide the oldest remains that can be assigned
without question to an extant phylum, and also the first firm evidence for
filter feeding and metazoan silica biomineralization in the fossil record.
It is suggested that siliceous and phosphatic members of the 'Cambrian
fauna' may have had their origins in eutrophic and outer shelf facies of
the Late Proterozoic." ~ Martin Brasier, Owen Green and Graham Shields,
"Ediacarian Sponge Spicule Clusters from Southwestern Mongolia and the
Origins of the Cambrian Fauna," Geology 25(1997):4:303-306, p. 303
And then there is the mollusc like animal from the precambrian also:
"The fossil Kimberella quadrata was originally described from late
Precambrian rocks of southern Australia. Reconstructed as a jellyfish, it
was later assigned to the cubozoans ('box jellies'), and has been cited as
a clear instance of an extant animal lineage present before the cambrian.
Until recently, Kimberella was known only from Australia, with the
exception of some questionable north Indian specimens. We now have over
thirty-five specimens of this fossil from the Winter Coast of the White Sea
in northern Russia. Our study of the new material does not support a
cnidarian affinity. We reconstruct Kimberella as a bilaterally
symmetrical, benthic animal with a non-mineralized, univalved shell,
resembling a mollusc in many respects. This is important evidence for the
existence of large triploblastic metazoans in the Precambrian and indicates
that the origin of the higher groups of protostomes lies well back in the
Precambrian." ~ Mikhail A. Fedonkin and Benjamin M. Waggoner, "The Late
Precambrian Fossil Kimberella is a Mollusc-like Bilaterian Organism,"
Nature, 388(1997):868-871, p. 868
>
>The following account describes an event that took place at a GSA meeting I
>attended a couple of years ago in New Orleans. I quote from one of my
>colleagues:
>
> "One of their [evolutionary scientists] biggest assumptions was that the
> molecular clock is reliable.... When Levinton gave his paper [at the 1996
> GSA meetings in New Orleans] he stated that the molecular clock can be
> best compared to a sun dial in the shade, which isnāt very encouraging
> for his method, but he and his colleagues still believed that it yielded
> data sufficient to test the theory of the rapid evolution of life at the
> base of the Cambrian....
>
> From their molecular clock data they concluded that the initial
> divergence of metazoan life forms occurred about 1.2 billion years ago
> (+/- 50 to 250 million years) . The base of the Cambrian is currently
> dated at about 543 million years ago , so their conclusions require a
half
> billion years of metazoan history before the Cambrian. They also
> concluded that the beginning of Metazoan phyla was not an explosion,
> but was somewhat spread out during that half billion years.
>
> A couple of days later these papers were discussed in a 'Hot topics
> discussion' during the noon hour. Four scientists gave brief
> presentations on the new ideas about the Cambrian explosion, followed
> by audience questions and comments. Many questions dealt with
> technicalities of their research method, but two questions stand out. A
> little background is necessary before dealing with these questions. The
> proposal that complex metazoan animals, ancestral to such things as
> molluscs, trilobites, vertebrates, sea urchins, corals, and many others,
> existed for a half billion years before the Cambrian implies that they
> lived all that time without leaving a fossil record. This pretty much
> requires that before the Cambrian they existed as soft worm- or
> larvae-like forms, with the general genetic make-up of the Cambrian
> groups but without their skeletonized morphology.
This may be the way it happened. what evidence is there that there were
skeletons prior to the Cambrian? Trick question? no.
>
> Now the questions. The first of the two questions was - why are trace
> fossils (fossil tracks, trails, and burrows) so rare before the base of
>the
> Cambrian, if these animals existed for that half billion years? An
> internationally recognized expert on trace fossils stood up, presumably
> to answer the question. However, he talked about other things and the
> very important question never was answered. At the end of the
> discussion another scientist stood up and commented on the implication
> that all the skeletonized phyla developed skeletons at about the same
> time in the Cambrian. He asked - why are all these types of animals
living
> for so long and then all making skeletons all at once? He then asked,
> with some vigor - 'Why are you avoiding the real question?' After a
> pause, one member of the original presenters answered 'because itās
> really hard (a hard question)'. He went on to say that they hoped
> answers would come from further study of developmental biology.
>
I can think of one possibility. If animals lived off of microbes in the
precambrian, and then began eating each other in the cambrian, it would
give rise to a selective pressure for protection i.e. shells. That would
make the animals of the Cambrian much more preservable.
glenn
Adam, Apes and Anthropology
Foundation, Fall and Flood
& lots of creation/evolution information
http://www.isource.net/~grmorton/dmd.htm