<page_title> List of Global Boundary Stratotype Sections and Points </page_title> <section_title> Cretaceous </section_title> <table> <cell> Maastrichtian <col_header> Epoch </col_header> </cell> <cell> 72.1 <col_header> Stage </col_header> </cell> <cell> Biologic: 12 biostratigraphic criteria Biologic: First appearance of Pachydiscus neubergicus (Ammonite) is just above the boundary. <col_header> GSSP location </col_header> </cell> </table>
In stratigraphy, the First Appearance of Pachydiscus neubergicus was assigned as the defining biological marker for the start of the Maastrichtian Stage of the Cretaceous, 72.1 million years ago.