Which extinction event 66 million years ago wiped out the non-avian dinosaurs?

The Cretaceous-Paleogene extinction event, often abbreviated K–Pg, occurred about 66 million years ago and wiped out the non-avian dinosaurs. It marks the boundary between the Cretaceous and Paleogene periods and is one of the five major mass extinctions in Earth’s history.

The leading explanation is that a large asteroid struck near present-day Chicxulub on Mexico’s Yucatán Peninsula. The impact produced a crater roughly 180 kilometers wide and triggered fires, atmospheric dust, darkness, cooling, and the collapse of many food webs. Evidence includes a worldwide layer enriched in iridium, an element relatively rare in Earth’s crust but common in many asteroids, along with shocked minerals and the Chicxulub crater.

The event did not eliminate every dinosaur: birds are living dinosaurs and survived. It also affected marine reptiles, ammonites, and many plankton groups. The extinction’s aftermath opened ecological opportunities for mammals and birds, helping reshape life during the early Cenozoic. It is sometimes called the K–T extinction in older sources, but K–Pg is the preferred modern abbreviation.