Mesozoic Era, one of the major divisions of geologic time. It is sometimes called the Age of Reptiles.
| Mesozoic Era | |||
| Period | Began | Lasted | Animal life |
| Triassic | 250 million years ago | 38 million years | The first turtles, crocodiles, dinosaurs, sea reptiles, flying reptiles, and mammals appeared. The huge supercontinent began to break up into separate continents. |
| Jurassic | 213 million years ago | 68 million years | The first birds appeared. Dinosaurs reached their greatest size. Insects were plentiful. Ammonites flourished in the sea. A few small mammals lived on land. |
| Cretaceous | 145 million years ago | 80 million years | Horned and armored dinosaurs became common. Flowering plants developed. Dinosaurs, flying reptiles, and giant sea reptiles died out at the end of the period. |
