Dinosaurs are a group of reptiles that dominated the land for over 160 million years. They evolved diverse shapes and sizes, from the fearsome giant Spinosaurus to the turkey-sized Microraptor, able to survive in a variety of ecosystems.
One of the reasons for the dinosaurs’ success is that they had straight legs, perpendicular to their bodies. This allowed them to move faster than other reptiles that had a sprawling stance like today’s lizards and crocodiles.
Most dinosaur species became extinct around 65 million years ago, but the descendents of one dinosaur group, birds, are still with us today.
Dinosaurs are descended from archosaurs, a large group of reptiles that appeared about 250 million years ago.
Archosaurs also gave rise to non-dinosaur reptiles such as the pterosaurs (flying reptiles), now extinct, and the ancestors of modern crocodiles.
These and many other types of ancient reptiles are often wrongly called dinosaurs.
Stegosaurus, showing the upright stance shared by all dinosaurs