Cambrian Explosion: The Evolutionary Life System

Introduction

Approximately 530 million years ago, there was a rapid diversification of animal species. In this relatively short evolutionary event, most major phyla appeared. The term Cambrian Explosion describes the geologically sudden appearance of multi-cellular animals in the fossil record. Pre-Cambrian organisms consisted of prokaryotes, eukaryotes, bacteria and ediacaran life forms. In less than 5 million years, most of the basic body plans that we observe in modern groups appeared; cnidarians, molluscs, arthropods, echinoderms and the chordates all came on to the scene. This explosion directly conflicts Darwin’s theory of natural selection acting on random variation, the Cambrian fossil record contradicts the empirical expectations of

The Cambrian fossils where found in 1909 (Shale Geo Foundation, 2011) by Charles Doolittle Walcott. The fossils found are an early snapshot of the complexity of evolving life systems. Continual studies on this area have resulted in a collection of over 60,000 specimens from the Cambrian period (Ridley, 1997). During these studies it was established that the ancestors of almost every animal in the planet were represented in the fossil record, along with other species that didn’t fit into any distinguishable categories. The fossils found were extremely well preserved for soft bodied organisms. The reason for the extraordinary quality of preservation in the burgess shales are not clear. The soft tissues and calcareous hard parts are now composed of silicates, this may be due to a rapid burial from turbid clouds of sediments (Butterfield,

Darwin acknowledged this gap, and was unable to explain it himself and described this evolutionary event as an incomplete fossil record. He quoted “to the question why we do not find rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, I can give no satisfactory answer” (origin of species Darwin). Since the recognition of the geological boundaries, stratigraphic sections have been located throughout the world where pre-Cambrian sediments grade continually into the Cambrian, possibly voiding Darwin’s incomplete fossil record theory (Allen and Briggs, 1991). Other theories claim that the ancestors of the Cambrian organisms were small and soft-bodied, hence hard to fossilise in marine depositional environments (Fortey, 1981). Animal evolution that preceded the Cambrian explosion has been highly researched and some studies indicate by molecular diversification, comparative developmental statistics, evolution of oxygen transport proteins, phylogenic analyses of Cambrian fossils and biogeography suggest that the major specie clades diverged tens of millions of years prior to their first presence in the fossil record (Zhang et al, 2014b). The exact motivation has yet not been established, although there have been many hypotheses to what invoked the explosion in the fossil