Many people learn that dinosaurs died out 66 million years ago. But that is only half true. Birds came from a group of dinosaurs about 150 to 165 million years ago.

Scientists now say that birds are dinosaurs. Some big dinosaurs, like a relative of Tyrannosaurus, had feathers. Today, more than 10,000 kinds of birds are alive. The pigeon in the park is a living dinosaur!

We often hear that dinosaurs became extinct 66 million years ago, but modern biology says this is only partly true. According to a 2015 review, birds evolved from theropods, the group that includes Tyrannosaurus and Velociraptor, during the Jurassic period. Bird-like features such as feathers, light bodies and wings appeared gradually over tens of millions of years.

Since the 1990s, many fossils of feathered dinosaurs have been found in China. In 2012, scientists described Yutyrannus, a relative of Tyrannosaurus about nine meters long, which had long feathers. In 2008, a study of protein fragments from a T. rex bone suggested it was closer to birds than to alligators. So birds are not just descendants of dinosaurs. They are dinosaurs.

The familiar claim that dinosaurs died out 66 million years ago is, strictly speaking, inaccurate. In modern classification, a group includes an ancestor and all of its descendants, and because birds arose from within the theropods, the lineage that also produced Tyrannosaurus and Velociraptor, they must be counted as dinosaurs. A 2015 review by Brusatte and colleagues dates the origin of birds to the Jurassic, roughly 165 to 150 million years ago, and stresses that bird-like traits such as feathers, wings and lightweight bodies were assembled piece by piece over tens of millions of years.

Although the end-Cretaceous mass extinction devastated dinosaurs, some birds survived and later diversified into more than 10,000 living species. Fossil discoveries have strengthened this picture. Feathered dinosaurs have been unearthed in China since the 1990s, and in 2012 Xu Xing's team described Yutyrannus, an estimated nine-meter relative of Tyrannosaurus covered in long filament-like feathers. Molecular evidence points the same way: collagen fragments recovered from a T. rex bone grouped it closer to chickens and ostriches than to alligators, although the sequences were incomplete and their authenticity was debated. The result therefore fits the anatomical evidence without proving it.