University of Bristol


The Precambrian-Cambrian fossil record has been the basis for palaeontologist's ideas about metazoan origins for a long time, before genetics, molecular clocks and cladistic methods added to the picture. Indeed it was the lack of fossil evidence from the Precambrian which Darwin saw as the biggest stumbling block to his theory of gradualistic evolution through natural selection. He envisaged a Precambrian swarming with life as yet undiscovered. The 'explosion' scenario of course has no prerequisite for such a well stocked Precambrian, and in fact reads the origin of metazoan life directly from the fossil record as it stands.

There are several important groups of fossils contributing to the Cambrian story, three of them are described here.

Lines of evidence other than the fossil record have more recently been used to change the timing of the metazoan radiation, and question the existence of the explosion at all (see timing of metazoan origins). A clade divergence time of up to 1000 million years ago has been suggested despite the lack of fossil evidence (see references Wray et al.1997).

timing triggers fossils controversies

This report was written by Abby Lane and was last updated on 20th January 1999