Biostratigraphic units or Biozones are intervals of geological strata that are defined on the basis of their characteristic fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...


A biostratigraphic unit may be defined on the basis of a single taxon or combinations of taxa, on relative abundances of taxa, or variations in features related to the distribution of fossils. The same strata may be zoned differently depending on the diagnostic criteria or fossil group chosen, so there may be several, sometimes overlapping, biostratigraphic units in the same interval.

The length of time represented by a biostratigraphic zone is called a biochron
A Biochron is the length of time represented by a biostratigraphic zone. Biochrons are named after characteristic fossil organisms or taxa that characterise that interval in time.-References:...

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