Which mass extinction, about 66 million years ago, eliminated all non-avian dinosaurs?

The Cretaceous–Paleogene extinction eliminated all non-avian dinosaurs about 66 million years ago.

This event marks the boundary between the Cretaceous and Paleogene periods. Around three-quarters of Earth’s species disappeared, including non-avian dinosaurs, ammonites, and many marine and terrestrial organisms. Birds survived because they are the living dinosaur lineage.

The leading cause was the Chicxulub asteroid impact near the present-day Yucatán Peninsula. Evidence includes a worldwide iridium-rich layer, shocked quartz, and the buried impact crater. Volcanism in what is now India’s Deccan region also occurred around this time and may have stressed ecosystems, but the impact is regarded as the decisive trigger of the sudden extinction.