[muawiyah]

The "explosion" as they called it had to do with the fact that all at once you had all these multicelled animals full of bones and shells and teeth and such.

At the time they'd not been able to research what went on at the microscopic level. More recently some of the researchers report that the hard stuff began much earlier. Doesn't make it a "fizzle", just that it happened at a different scale, and much earlier. I've not been terribly impressed with the macro-critters ever since I read a piece where the guy took some of the wierdest stuff and flipped it over showing that it was quite recognizable. BTW, I have an interesting selection of shells from the New Cut on the Ohio (at Madison) as well as fossil sponges made out of silicon. Always wondered what happened to those sponges.

A long term, continual stream of viral bodies could have provided the genetic input necessary to turn all that bacterial slime into critters.

[furball4paws]

"...all at once ..."

This is the "fizzle" as compared to an "explosion".

[furball4paws]

Since you have great library facilities available, get this book "Invertebrate Paleontology and Evolution" by E.N.K. Clarkson, 4th edition. It is highly readable. It will help you understand about those sponges (BTW, many still have Si spicules).

[furball4paws]

How did the "bacteial slime" get here?

[Virginia-American]

...all at once you had all these multicelled animals full of bones and shells and teeth and such....

Are you sure about bones? There are apparent chordates in the Burgess shale, but no vertebrates. I believe the earliest bony (as opposed to cartilaginous) fishes are Devonian.