Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch (or, in chronostratigraphy: the fifth of six stages in the Upper Cretaceous series). The Campanian spans the time from 83.6 ± 0.7 Ma to 72.1 ± 0.6 Ma (million years ago). It is preceded by the Santonian and it is followed by the Maastrichtian.
Marsupites
The International Commission on Stratigraphy (ICS) has assigned the extinction of "Marsupites testudinarius" as the defining biological marker for the start of the Campanian Stage of the Cretaceous, 83.6 ± 0.2 million years ago.