D. Finnin/© AMNH
Dinosaurs are a group of reptiles that first appeared about 245 million years ago.

They dominated the planet until an extinction event wiped out a large swath of life on Earth about 66 million years ago. But now we know that the Age of Dinosaurs never ended. Instead, a group of dinosaurs gave rise to a new, small airborne form: birds.

Extinction: What happened 65 million years ago?

The leading theory is that a huge asteroid or comet slammed into Earth 65 million years ago, blocking sunlight, changing the climate and setting off global wildfires.

What Happened? »
Rendering of a late-Cretaceous asteroid impact that may have led to the extinction of non-avian dinosaurs. © AMNH