Create a list of articles to read later. You will be able to access your list from any article in Discover.
You don't have any saved articles.
Our brief introduction to dinosaurs reveals a key feature that gave them an advantage over other prehistoric reptiles.
Dinosaurs are a group of reptiles that dominated the land for over 140 million years (more than 160 million years in some parts of the world). They evolved diverse shapes and sizes, from the fearsome giant Spinosaurus to the chicken-sized Microraptor, and were able to survive in a variety of ecosystems.
One of the reasons for dinosaurs' success is that they had straight back legs, perpendicular to their bodies. This allowed them to use less energy to move than other reptiles that had a sprawling stance like today's lizards and crocodiles.
With their legs positioned under their bodies rather than sticking out to the side, dinosaurs' weight was also better supported.
Many dinosaur species became extinct around 66 million years ago, but a group of living dinosaurs are still with us today: birds.
Dinosaurs are archosaurs, a larger group of reptiles that first appeared about 251 million years ago, near the start of the Triassic Period.
Some other non-dinosaur reptiles are also archosaurs, including pterosaurs (the now-extinct flying reptiles) and modern crocodiles and their ancestors.
These and many other types of ancient reptiles are often wrongly called dinosaurs.
Marine reptiles, such as ichthyosaurs, plesiosaurs and mosasaurs are not dinosaurs. Nor is Dimetrodon or other reptiles in the same group (previously called 'mammal-like reptiles' and now called synapsids).
None of these other extinct groups shared the characteristic upright stance of dinosaurs.