In cases when fossils of mammals are abundant, stratigraphers and paleontologists can use these biozones as a more practical regional alternative to the stages of the official ICS geologic timescale.
European Land Mammal Mega Zones are often also confusingly referred to as ages, stages, or intervals.
[1] Mammal zones were, like all biozones, established using geographic place names where fossil materials were obtained.
If two taxa are found in the same fossil quarry or at the same stratigraphic horizon, then their age-range zones overlap.
The geologic timescale of the ICS is therefore based on marine fossils, that don't occur in terrestrial sediments.
A fine stratigraphic division of the terrestrial record can in most places only be made using fossils of land species.
[4] The scheme does not define boundaries but instead is accompanied by a range chart, where the entry and exit dates for the taxa are indicated.