The biggest biodiversity extinction is Cretaceous - Paleogene event which devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton.

 At the end of the Cretaceous era, the empire of dinosaurs was spread all over the world. But the impact of meteorite to the Yucatan Peninsula of Mexico brought the end of this empire 65 million years ago.

Although it is generally accepted that the meteor impact caused extinction, other theories continue to be put forward in order to explain the extinction. The common volcanism at the end of the period and the climatic changes caused by the separation of the continents are just a few of these theories. Pterosaurs, Ichthyosaurs, Mosasaurs, Plesiosaurs were reptile groups that disappeared together with dinosaurs. Most primitive birds, half of the marine invertebrate groups including rudist mytilus, belemnit and ammonites, many foramifer species, include many marine plankton including microorganisms. About 35% of land plants have been destroyed. About 70% of all species disappeared. 

After the K–Pg extinction event, biodiversity required substantial time to recover, despite the existence of abundant vacant ecological niches.

This extinction, known as the Cretaceous-Tertiary extinction, caused the Mesozoic period to be closed. In the new ecosystem, which was established after extinction, reptiles lost their importance and mammals became dominant. So, the Cenozoic period started.