Archosaurs are a group of reptiles that includes some of the most famous prehistoric animals, as well as some modern-day creatures. The term “archosaur” means “ruling reptile,” and these animals have indeed ruled the Earth for millions of years.


Archosaurs first appeared about 250 million years ago and quickly became the dominant land animals. This group includes all dinosaurs and pterosaurs, as well as their modern-day descendants: birds and crocodilians. Archosaurs have some special features that set them apart from other reptiles, like holes in their skulls that make their heads lighter and stronger.

The archosaur group is split into two main branches: the bird-line archosaurs (which led to dinosaurs and eventually birds) and the crocodile-line archosaurs (which led to modern crocodiles and alligators). This split happened very early in their history, but both lines were incredibly successful.


Let’s look at a family tree of reptiles. If you follow the branch for archosaurs, you’ll find dinosaurs, pterosaurs, and crocodiles all sitting on different twigs. And at the very tip of one twig, you’ll find birds – the living descendants of dinosaurs!

Fun Fact

Did you know that birds are technically archosaurs? That means when you see a pigeon in the park or a chicken on a farm, you’re looking at a living archosaur – a distant relative of T. rex and Stegosaurus!

People Also Ask

  • What are the main characteristics of archosaurs?
  • Are all dinosaurs archosaurs?
  • What modern animals are archosaurs?

What are the main characteristics of archosaurs? Archosaurs have several unique features. They have openings in their skulls that make their heads lighter and stronger. Many walk with their legs directly under their bodies, unlike other reptiles that have splayed legs. They also have specialized ankle bones and often have air-filled bones or cavities in their skulls.

Are all dinosaurs archosaurs? Yes, all dinosaurs are archosaurs, but not all archosaurs are dinosaurs. The archosaur group includes dinosaurs, pterosaurs, crocodilians, and birds, as well as many extinct groups that aren’t dinosaurs.

What modern animals are archosaurs? The only living archosaurs today are birds and crocodilians (crocodiles, alligators, caimans, and gharials). While they might look very different, these animals are the last living representatives of the once-vast archosaur group.