The Maastrichtian (pronunciation: /mɑːˈstrɪktiən/) is, in the ICSgeologic timescale, the latest age (uppermost stage) of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned the interval from 72.1 to 66 million years ago. The Maastrichtian was preceded by the Campanian and succeeded by the Danian (part of the Paleogene and Paleocene).
At the end of this period, there was a mass extinction known as the Cretaceous–Paleogene extinction event, (formerly known as the Cretaceous–Tertiary extinction event). At this extinction event, many commonly recognized groups such as non-avian dinosaurs, plesiosaurs and mosasaurs, as well as many other lesser-known groups, died out. The cause of the extinction is most commonly linked to an asteroid about 10 kilometres (6.2 mi) wide colliding with Earth at the end of the Cretaceous.