What is the Mesozoic?


A diagram showing the different periods of the Mesozoic and when they started and finished.

The Mesozoic era is a length of time. It started 248 million years ago and ended 65 million years ago. This very long period of time is called an era.

The word ‘Mesozoic’ means middle animals and the types of animals were very different to what came before or after. The middle animals were dominated by dinosaurs, pterosaurs, pliosaurs, plesiosaurs and many other types of animals.

The Mesozoic is divided into three sections called periods:

  • The Triassic Period lasted from 248 to 208 million years ago
  • The Jurassic Period lasted from 208 to 146 million years ago
  • The Cretaceous Period lasted from 146 to 65 million years ago

Although the Mesozoic is often known as the age of dinosaurs, it wasn’t until the Jurassic that dinosaurs became the most common large animals. For most of the Triassic, they were small and uncommon.


Each of the periods had different types of animals than the others. The Triassic is when dinosaurs and mammals are thought to have evolved, as did the pterosaurs and ichthyosaurs.


The Jurassic was the time of the long-necked, or sauropod, dinosaurs and is the time when birds are first seen.


The Cretaceous has some of the most famous dinosaurs like Tyrannosaurus rex and Triceratops but it is also when flowers and flowering plants first evolved. The Cretaceous is also when many of the big dinosaurs died out but dinosaurs live on now as birds.

65 million years ago, a meteor smashed into earth. The sky turned black from all the dust thrown into the sky and, as the dust came back down, it formed black lines. these black lines mark the end of the Cretaceous and the extinction of non-bird dinosaurs.

The End of the Mesozoic marked the beginning of the Cenozoic which is the era we are in now and is often called the age of mammals.

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