The world of dinosaurs: fossils, evolution and ecosystems

Dinosaurs were a diverse branch of archosaurs whose fossils record changing bodies, habitats and evolutionary relationships.

Dinosaurs were not a single uniform group of giant reptiles. Their fossil record includes many body plans, sizes and ecological roles, and it spans environments that changed over geological time. These guides connect dinosaur anatomy and classification with fossils, trackways, growth and the ecosystems researchers reconstruct from them.

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Frequently asked questions

What makes an animal a dinosaur?

Dinosaurs are a defined evolutionary group within Archosauria. Similar age or appearance alone does not make a fossil animal a dinosaur; pterosaurs and many marine reptiles belonged to other groups.

Were all dinosaurs enormous?

No. Dinosaur body sizes varied widely. The smallest known forms and the largest sauropods represent very different ends of that range, and incomplete fossils can make size estimates uncertain.

What can footprints tell us about dinosaurs?

A trackway records foot placement and movement at a particular place and time. It can preserve behaviour-related evidence, but usually cannot identify the trackmaker as a named species on its own.

Are birds part of the dinosaur group?

Yes. Birds are living theropod dinosaurs. The word non-avian dinosaurs is used for the dinosaur lineages outside modern birds.