The geologic era between the Paleozoic and the Cenozoic eras: The Mesozoic is the second of the earth's three major geologic eras of Phanerozoic time and the interval during which the continental landmasses as known today were separated from the supercontinents "Laurasia" (North America and Eurasia) and "Gondwana" by the continental drift.

The Mesozoic is divided into three time periods: the Triassic (245-208 Million Years Ago), the Jurassic (208-146 Million Years Ago), and the Cretaceous (146-65 Million Years Ago).

The Mesozoic occurred before the Cenozoic and after the Palaeozoic periods and was marked by the development of the ancestors of the major plant and animal groups that exist today and the extinction of the dinosaur that suddenly occurred at the end of the Cretaceous period.

Mesozoic means "middle animals", and is the time during which the world fauna changed drastically from that which had been seen in the Paleozoic.

Dinosaurs, which are perhaps the most popular organisms of the Mesozoic, evolved in the Triassic, but were not very diverse until the Jurassic. Except for birds, dinosaurs became extinct at the end of the Cretaceous period. Some of the last dinosaurs to have lived are found in the late Cretaceous deposits of Montana in the United States.

The Mesozoic was also a time of great change with terrestrial vegetation. The early Mesozoic was dominated by ferns, cycads, ginkgophytes, bennettitaleans, and other unusual plants. Modern gymnosperms, such as conifers, first appeared in their current recognizable forms in the early Triassic.

By the middle of the Cretaceous period, the earliest angiosperms had appeared and began to diversify, largely taking over from the other plant groups.