Are birds really dinosaurs?

What you've heard is true: birds really are dinosaurs. Explore this fascinating evolutionary story with us.



Do you want to see a dinosaur? You probably don't need to go far. In the UK alone, there are around 84 million of them. There might be one in your garden or on your street. Pop into the local pet shop and you can take one home with you.

No, this isn't a joke. The science is clear: birds are living dinosaurs.

Sure, the dinosaurs we know and love died in the aftermath of the asteroid strike 66 million years ago. But surviving feathered theropods evolved into the birds all around us today.

That means every bird you see shares direct ancestry with dinosaurs like T. rex – from owls to eagles, from blue tits to buzzards. Bird-watchers are actually training their binoculars on a staggering range of dinosaurs.

This isn't to say all dinosaurs were birds. Just as humans are apes but not all apes are humans, so birds are dinosaurs but not all dinosaurs were birds.

If this is news to you, chances are that your mind is as blown as the Gulf of Mexico all those millions of years ago. But even if you're familiar with this startling fact, there are plenty of details that still have the power to surprise and fascinate.

What connects birds and dinosaurs?

The main thing that connects birds and dinosaurs is ancestry. All birds on Earth today evolved from small, meat-eating theropod dinosaurs.

Theropods were a big, diverse group of dinosaurs. They were mostly carnivorous and had two legs, three-toed limbs, clawed hands and hollow bones.

This group of animals (known as a "clade") included Tyrannosaurus rex and Velociraptor. It's incredible to think that all the world's birds descended from these fearsome beasts. And we mean all of them – from garden birds nibbling at seeds to birds of prey circling the skies.

Fossils such as Archaeopteryx show clearly the link between dinosaurs and birds. This was a kind of bird-like dinosaur that lived around 145 million years ago in present-day Germany. Its fossils show both reptilian and bird-like characteristics.

One of these bird-like features was feathers. Like today's birds, Archaeopteryx used its feathers to fly. Other theropods had feathers that were used for insulation, protection and display, but not flight.

Popular depictions of some classic dinosaurs as scaly reptiles are not quite accurate. In fact, dinosaurs like Velociraptor had feathers all over, while T. rex had scales and patches of feathers.

It's not just feathers that connect birds and dinosaurs. It's also the structure of their skeletons. Like theropods, birds have three-toed feet, hollow bones and similar skull shapes.

Why didn't birds go extinct?

"If birds are dinosaurs," you might be wondering, "why didn't they go extinct with the rest of the dinosaurs?"

Well, some of them did. Bird-like dinosaurs that died out in the mass extinction event included the Enantiornithes, the Ichthyornithes and various toothed, beakless birds.

The fact is that large land animals were hit the hardest by the aftermath of the asteroid strike. It was tiny creatures that mostly survived.

Birds are "generalists". This is a zoological term for a jack of all trades – an animal that can thrive in a wide range of environmental conditions.

Larger dinosaurs died in firestorms or perished from a lack of food. However, small birds hid and lived off seeds and insects that survived the asteroid strike.

Why aren't birds the size of T. rex?

The avian dinosaurs that survived the asteroid strike were mostly small. This helped them survive the firestorms and food scarcity that killed off bigger dinosaurs.

Their evolution since then has been characterised by high metabolic rates and delicate skeletons. These helped them thrive – and the story of evolution is the story of animals that survive because of their adaptations.

In other words, birds haven't grown to the size of a T. rex or other famous dinosaurs because they haven't needed to in order to survive. 

When did birds start singing?