University of Bristol

First appearances

What makes the Cambrian radiation event so remarkable is the great range of metazoan body plans and life strategies which seem to make their appearance in such a short period of time. Although there are some soft bodied organisms known from the Precambrian, most metazoan phyla with skeletons, including the Arthropoda, Brachiopoda and Echinodermata, appear in rapid succession near the base of the Cambrian and exhibit remarkable taxonomic diversity and morphological disparity right from the outset. Whether this was truly a rapid diversification event, or simply the crossing of a taphonomic threshold by already disparate phyla aquiring hard skeletons, is the cause of much debate (see controversies). Either way it was an important event in the history of life.

Trace fossils, or fossilized animal behaviour structures, are known from the Precambrian and provide some of the most important lines of evidence for pre-Palaeozoic life. However the numbers and range of trace fossils increase dramatically at the base of the Cambrian, evidence perhaps of a morphological diversification amongst all animal phyla, not just those with skeletal structures which are readily preserved.

In addition to the apparent phyla 'explosion' the Cambrian also sees the advent of a modern type of community structure, with organisms being adapted for a large range of life strategies. These include mobile benthic, epifaunal and burrowing faunas all interacting with each other in complex communities. Predation as a means of aquiring food also makes an appearance at this time. What are even more unusual are the Cambrian organisms which display seemingly bizarre body plans and appendages, and which taxonomically are difficult to assign to any modern phyla (see Burgess Shale type faunas).anomalocaris

A reconstruction of the Cambrian Seas, with the predator Anomalocaris attacking a trilobite. Some of the Burgess 'weird wonders' can be seen on the sea floor. From The Crucible of Creation. Conway Morris S. 1998. Colour plate 3.

Back to: the Cambrian environment

timing triggers fossils controversies

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