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Chaos in the Cretaceous!

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Rob Barber/AMNH
Eocene (Orohippus scene).

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Rob Barber/AMNH
Cretaceous (Mongolian scene).

You've probably heard how dinosaurs went extinct: They were all killed one terrible day when a huge object from outer space--a comet or asteroid the size of at least 100,000 Superdomes--slammed into Earth around 65 million years ago. But this description is not quite right.

Yes, a meteorite did pack an enormous punch, but current research indicates that the extinction of dinosaurs is a much more complicated story. First of all, dinosaurs are not extinct. Birds are living dinosaurs--survivors of the turmoil that wiped out their relatives like T. rex. So what caused the chaos 65 million years ago? There's no doubt a comet or asteroid hit Earth around that time and no doubt the impact had deadly consequences for life on Earth. But other factors, including massive volcanic eruptions and changing sea levels may have also played a role in wiping out at least half of all species alive at the time.

Look closely: At extinct animals

A wide range of plants and animals, both on land and in the sea, went extinct 65 million years ago. The ferocious Tyrannosaurus rex was one of the last species of nonavian dinosaurs. The ancient mollusks known as ammonites disappeared quite suddenly 65 million years ago. The closest living relatives of ammonites include squid and the chambered nautilus.

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