What is a DINOSAUR?

When many people hear the word dinosaur, they imagine enormous roaring monsters from films. But in science, a dinosaur is something much more specific and far more fascinating.

Dinosaurs were a special group of reptiles that first appeared about 230 million years ago, during a time called the Triassic Period. They are defined not by their size or fierceness, but by particular features of their skeletons. One of the most important clues is how they stood and moved. Unlike modern lizards and crocodiles, whose legs stick out to the sides, dinosaurs had an upright posture with their legs positioned directly underneath their bodies. This allowed them to walk, run and support their weight efficiently and in some cases, grow to extraordinary sizes.

It’s important to know that not all prehistoric reptiles were dinosaurs. Flying reptiles such as pterosaurs and sea dwelling reptiles like plesiosaurs and ichthyosaurs lived at the same time, but they were different groups altogether. They were close relatives in the wider reptile family tree, yet they were not dinosaurs.

Dinosaurs were also incredibly diverse. Some were no bigger than a chicken, while others stretched longer than a blue whale. Some walked on two legs, others on four. There were plant eaters with long necks, horned faces and heavy armour, as well as sharp toothed hunters. Many dinosaurs even had feathers.

Perhaps the most surprising fact of all is that dinosaurs are not completely extinct. Birds are living dinosaurs. Modern birds evolved from small, feathered meat eating dinosaurs. So every robin in the garden and every pigeon in the city is part of the dinosaur story.

In simple terms, a dinosaur is a member of a particular evolutionary group of upright walking reptiles that dominated life on land for over 160 million years and whose legacy is still alive today.

Mesozoic Marvels

According to standard geological dating used by palaeontologists, the Mesozoic Era began around 252 million years ago and ended 66 million years ago.

It started after the great Permian mass extinction the largest extinction event in Earth’s history and ended with the asteroid impact event that caused the extinction of the non avian dinosaurs.

The Mesozoic is divided into three periods:

• Triassic (252–201 million years ago)

• Jurassic (201–145 million years ago)

• Cretaceous (145–66 million years ago)

This era is often called the “Age of Dinosaurs” because dinosaurs evolved early in the Triassic and went on to dominate land ecosystems until the end of the Cretaceous.