Biostratigraphic biozones are classified into standard types based on the range and overlap patterns of fossil taxa: a taxon-range biozone represents the total stratigraphic range of a single taxon, a concurrent-range biozone represents the overlapping ranges of two or more taxa, an interval biozone is defined by the interval between two biostratigraphic events (e.g., first/last appearances), and an assemblage biozone is defined by a characteristic natural association/cluster of taxa.