University of Bristol


One thing which I hope this site makes clear is that even though the Cambrian is one of the most intensively researched periods of geological time, there are still many points of contention about the nature of the metazoan radiation event, with new discoveries and techniques adding to the picture all the time. Most researchers agree that a significant biotic event did occur around the base of the Cambrian. However opinion is divided upon whether this event was a true radiation of metazoan forms from a single Precambrian ancestor, or if it was simply a revolution in biomineralisation by already established phyla; an explosion of fossils rather than phyla.

The lists below summerise the main pieces of evidence for each of these viewpoints:

The Cambrian explosion was a true metazoan radiation:

The Cambrian event was the crossing of a biomineralization threshold by already established phyla:

These arguments are not clear cut however and many researchers take different viewpoints giving some pieces of evidence more weight than others. It is also clear that a morphological radiation of body forms and size does not have to be the same as a taxonomic radiation of phyla. A lot depends upon the individual's definition of the metazoan radiation event.

For elaboration of some of the arguments plus a summary of recently discovered fossils go to: