The last dinosaurs are generally believed to have existed around 65.5 million years ago, at the end of the Cretaceous Period. This time marks the Cretaceous-Paleogene (K-Pg) extinction event, also known as the Cretaceous-Tertiary (K-T) extinction, which is thought to have been caused by a combination of environmental changes and the impact of a large asteroid or comet near what is now the Yucatán Peninsula in Mexico.
This event led to a mass extinction, wiping out about three-quarters of the Earth’s plant and animal species, including most dinosaurs. Some avian dinosaurs, however, survived and evolved into the birds we know today.
It’s worth noting that the exact timing and speed of the extinction event are still topics of research and debate among scientists. Some research suggests the extinction may have occurred more gradually over a longer period of time, rather than happening suddenly.