what is one event that marks the end of mesozoic era

The event that marks the end of the Mesozoic era is the extinction of dinosaurs.

The Mesozoic era is actually known as the era of dinosaurs, where many types of very large reptiles, as well as dinosaurs and many other types of giant beasts inhabited the Earth. However, near the end of this era, dinosaurs were wiped out which marked the end of the entire era.

the dinosaurs died out at the end of the Mesozoic Era