The Cambrian Fossil Record and the Origin of the Phyla1

SYNOPSIS. Whilst the ‘‘Cambrian Explosion’ ’ continues to attract much attention from a wide range of earth and life scientists, the detailed patterns exhibited by the terminal Proterozoic–Early Cambrian biotas remain unclear, for reasons of systematics, biostratigraphy and biogeography. In particular, recent changes in absolute dating of the Cambrian have refined the period of time that the fossil record might be of most help in revealing the dynamics of the undoubted radiation taking place at this time. The famous exceptionally preserved faunas seem to be rather close temporally, and as yet reveal little about the earliest and critical period of evolution, deep in the Cambrian. Nevertheless, the most parsimonious interpretation of the Cam-brian fossil record is that it represents a broadly accurate temporal picture of the origins of the bilaterian phyla