Final answer:
The most recent mass extinction event, about 65 million years ago, killed off most dinosaur species and allowed for the development of mammals.
Step-by-step explanation:
The most recent mass extinction event, also known as the end-Cretaceous extinction event, occurred about 65 million years ago and resulted in the extinction of most dinosaur species.
Scientists believe that the main cause of this extinction event was the impact of a large asteroid in the present-day Yucatán Peninsula, which caused global climate changes and the release of dust into the atmosphere.
This event marked the end of the dinosaur age and allowed for the development and diversification of mammals.