Lifting the Veil on the Rise of Animals during the Neoproterozoic and Cambrian Explosion of Life

In Darwin's day fossils indicating animal life in the Precambrian were not known. Since then there have been numerous reports on body and trace fossils indicating the existence of animals before the Cambrian. This has been accompanied by a healthy skepticism on the reality of many reports. In large part because of the presence of stem and extinct groups, fossils of animals are harder to recognize in the Precambrian. Nevertheless, in the twentieth century significant late Precambrian animal fossil faunas were documented, including the Ediacara fauna, cloudinids, and the earliest trace fossils.

The Ediacara fauna is found in strata as old as 575 Ma, but in the past decade molecular clock studies have indicated that animals evolved even earlier. This has focused much recent interest on the Doushantuo fauna of southwest China, which could be as much as 25 million years older than the Ediacara fauna. The microscopic Doushantuo fauna includes specimens interpreted as representing various types of animals. This implied complexity indicates that a significant period of metazoan evolution occurred before the Doushantuo, which warrants future searches for animal fossils from deeper in time.

By 542 million years ago numerous fossils with significant biomineralized skeletons had evolved, signaling the onset of the Phanerozoic fossil record. Much more on life during the Cambrian has been learned since Darwin's day, exemplified by intense study over the past several decades of the Burgess Shale and Chengjiang lagerstätte, with their remarkable soft-bodied faunas. Coupled with studies of body fossils have been those on the dramatically increasing bioturbation record, and the affect that increasing bioturbation had on the evolution of other benthic animals, termed the “Cambrian substrate revolution”.

Further fossil studies, combined with new approaches in molecular biology, particularly genomics, promise continued extraordinary advances in our understanding of the early evolution of animals.