Which animal and protistan phyla appear simultaneously (within the resolution of chronostratigraphy)?
I think the review of Briggs & Fortey (2005) on this topic is not yet far from the current state of knowledge. During the last 50 or so million years of the Ediacarian the diversification of bilaterians begins and for various reasons (biomineralization events, body size increase, Burgess-shale-type lagerstätten conditions) the fossil record of animals becomes a lot better during the Early Cambrian. In the Chengjiang biota (520 Ma) and other contemporaneous assemblages almost all phyla are recorded. Arguably some acceleration of diversification took place during the Cambrian but estimates of diversity changes and divergence times may be much affected by taphonomy/lagerstätten effects.
Derek E. G. Briggs and Richard A. Fortey (2005) Wonderful strife: systematics, stem groups, and the phylogenetic signal of the Cambrian radiation. Paleobiology: June 2005, Vol. 31, No. sp5, pp. 94-112.
http://www.psjournals.org/doi/abs/10.1666/0094-8373%282005%29031%5B0094%3AWSSSGA%5D2.0.CO%3B2
Both Gould's Wonderful Life and Conway Morris's Cambrian Explosion offer very readable descriptions for the interested reader = perhaps a little light for serious research though. There are so many new finds being made in China, and increasing recognition of the role of soft body fauna and the small shelly taxa so the start is being pushed back constantly. As for the end - well it sort of morphed into the Ordovician Radiation - Thomas Servais recently suggested it was a Canbrian Radiation and an Ordovician Explosion
I agree that the Ordovician has much the character of a continuation of the Cambrian event, but the other end of the Cambrian is a different story. Fully formed fish (Myllokunmingia), echinoderms (Helicoplacus), ?cephalopods (Nectocaris), brachiopods (articulate and inarticulate), and anomalocarids and many others all appear in the Early Cambrian. Many stem groups also appear at this moment, for example we see the mickwitziids tripping over the bivalved brachiopods in the same sedimentary rocks. The phylogenetic telescoping makes all this appear rather sudden.
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