Dinosaurs are a group of reptiles that dominated the land for over 140 million years during the Mesozoic era, a period of time which extended from approximately 225 million to 65 million years ago.

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What Made a Dinosaur a Dinosaur?

Many prehistoric reptiles are referred to as 'dinosaurs' by mistake. 

Dinosaurs were a type of reptile known as archosaurs ('ruling reptiles') which included the dinosaurs and the flying reptiles, pterosaurs.

Dinosaurs had a special stance, or way of walking. Their back legs were positioned underneath (perpendicular to) their bodies, instead of sprawling out at the sides, like other reptiles. This gave the an upright stance and allowed them to use far less energy to move than other reptiles (such as crocodiles).

Photo: Fred the Oyster

The dinosaurs ('terrible reptiles') were divided into two main orders, the Saurischia of which some were herbivores and others carnivores, and the Ornithischia which, as far as we know, were all herbivores. The chief difference in structure between the two kinds of dinosaurs was in the pelvis. Saurischians are often referred to as 'lizard-hipped' reptiles and the Ornithischians as 'bird-hipped'.

Dinosaurs also had two holes behind their eye sockets. They had strong jaw muscles that went through the holes to attach directly to the top of their skull. This meant that their jaws were able to open very wide and could bite down with extra force.

Dinosaurs lived on land, not in the sea. Marine reptiles, such as ichthyosaurs, plesiosaurs and mosasaurs are not dinosaurs.

Read More: Birds: The Modern Dinosaurs

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