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.