The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, scientific understanding of the Cambrian biology surpasses that of some later periods.[7]
The Cambrian marked a profound change in life on Earth: prior to the Cambrian, the majority of living organisms on the whole were small, unicellular, and simple (Ediacaran fauna and earlier TonianHuainan biota being notable exceptions). Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized – hence readily fossilized – organisms became common.[8]
The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of most modern animal phyla. Phylogenetic analysis has supported the view that before the Cambrian radiation, in the Cryogenian[9][10][11] or Tonian,[12]animals (metazoans) evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates.[13]
Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren – with nothing more complex than a microbial soil crust[14] and a few mollusks and arthropods (albeit not terrestrial) that emerged to graze on the microbial biofilm.[15]
^Orr, P. J.; Benton, M. J.; Briggs, D. E. G. (2003). "Post-Cambrian closure of the deep-water slope-basin taphonomic window". Geology. 31 (9): 769–772. Bibcode:2003Geo....31..769O. doi:10.1130/G19193.1.
^Maloof, Adam C.; Rose, Catherine V.; Beach, Robert; Samuels, Bradley M.; Calmet, Claire C.; Erwin, Douglas H.; Poirier, Gerald R.; Yao, Nan; Simons, Frederik J. (17 August 2010). "Possible animal-body fossils in pre-Marinoan limestones from South Australia". Nature Geoscience. 3 (9): 653–659. Bibcode:2010NatGe...3..653M. doi:10.1038/ngeo934.