The existing Upper Cambrian stages for North America are obsolete. Three new stratotype-defined stages are equivalent to, and replace, three successive biomeres: Marjuman Stage (replaces Marjumiid Biomere, lower boundary at base Ptychagnostus atavis Zone), Steptoean Stage (replaces Pterocephaliid Biomere, lower boundary at base Aphelaspis Zone), Sunwaptan Stage (replaces Ptychaspid Biomere, lower boundary at base Irvingella major Subzone). The base of the overlying Ibexian Series is placed at the base of the Eurekia apopsis Subzone.

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