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Aptian

The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), approximately. The Aptian succeeds the Barremian and precedes the Albian, all part of the Lower/Early Cretaceous.

The Aptian partly overlaps the upper part of the regionally used (in Western Europe) stage Urgonian.

Wiktionary

aptian

n. (context geology paleontology English) A subdivision of the Early (Lower) Cretaceous epoch.