It is named after the city of Saintes in the region of Saintonge, where the original type locality is located.
[7] The base of the Santonian Stage is defined by the appearance of the inoceramid bivalve Cladoceramus undulatoplicatus.
The GSSP (official reference profile) for the base of the Santonian Stage is located near Olazagutia, Spain; it was ratified by the Subcommission on Cretaceous Stratigraphy in 2012.
[7] The Santonian's top (the base of the Campanian Stage) is informally marked by the extinction of the crinoid Marsupites testudinarius.
In the Tethys domain the Santonian is coeval with a single ammonite biozone: that of Placenticeras polyopsis.