"Kimberella" and "Wiwaxia " of the Precambrian and Cambrian may be related to ancestral polyplacophora. "Matthevia" is a late Cambrian polyplacophoran preserved as individual pointed valves, and sometimes considered to be a chiton. The polyplacophorans may have formed when an aberrant monoplacophoran was born with multiple centres of calcification, rather than the usual one. Selection acted on the resultant conical shells to form them to overlap into protective armour. Their original cones are homologous with the tips of the plates of modern chitons.