The Cambrian period is of particular interest to evolutionary biologists as it represents a problematic boundary line in the emergence of animal life on Earth. At the time Darwin was writing “On the Origin of Species” this boundary was stark – below the Cambrian strata there were no signs of animal life but from the Cambrian strata onwards there were not only signs of animal life but life in such abundance and complexity that it gave rise to the term “Cambrian Explosion”. Suddenly creatures with remarkably good vision and mobility were moving throughout the oceans of the planet. Predator and prey had clearly emerged with the associated developments of armoured limbs and protective shells. Darwin understood this to be a problem for his own theory of evolution which necessarily pointed to a long line of antecedents from which the Cambrian organisms could arise. Where were these ancestors?
