The dinosaurs and the mammals appeared during the Triassic period, roughly 225 million years ago. The dinosaurs went extinct 65 million years ago.

The Mesozoic Era lasted about 180 million years, and is divided into three periods, the Triassic, the Jurassic, and the Cretaceous. Each of these periods is divided into many epochs and ages. Mesozoic means "Middle Animal" and is sometimes called the age of reptiles. The term Mesozoic was coined John Phillips in 1840.

The world's life forms were very different during the Mesozoic than either before or after. During the Mesozoic, dinosaurs dominated the Earth. After the Mesozoic, the Cenozoic or the "Age of Mammals" began. Forty percent of the known dinosaurs date from the last 15 million years of the Cretaceous period.

1. The earliest period of the Mesozoic Era was the Triassic period (248 - 208 million years ago), in which the first small dinosaurs and mammals developed. The Triassic began after a major extinction had wiped out most of the life forms on Earth. The end of the Triassic was also marked by a worldwide extinction, although minor in comparison.
2. The second period was the Jurassic period (208-146 million years ago), in which the dinosaurs began to flourish. Giant sauropods appeared along with many other dinosaurs. The first primitive birds and flowering plants (angiosperms) appeared.
3. The third Mesozoic period was the Cretaceous period (146-65 million years ago),

which saw the height of the dinosaurs and the development of flowering plants. It ended with another extinction and the demise of the dinosaurs and many other prehistoric animals.

The Age of Reptiles (The Mesozoic Era -248 - 65 million years ago)

Triassic Period 248 - 208 million years ago (One super continent, Pangaea.)

Jurassic Period 208-146 million years ago (In mid-Jurassic, Pangaea began to break apart, into Laurasia and Gondwana)

Cretaceous Period 146-65 million years ago ( Continental drift continued at a fast pace, with accompanying volcanic activity. The continents are similar to now. )