The Mesozoic Era 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).
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. 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 in the 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, the earliest angiosperms had appeared and began to diversify, largely taking over from the other plant groups.
Life in the Mesozoic
Dinosaurs and other archosaurs, such as the pterosaurs, dominated the land biota. (Source: University of California Museum of Paleontology)
Cycads and Bennettitaleans were among the dominant land vegetation. (Source: University of California Museum of Paleontology)
The first mammals also arrived on the scene in the Mesozoic, descended from a lineage of so-called "mammal-like reptiles," or synapsids. This is Thrinaxodon, an extinct relative of mammals from the Triassic. (Source: University of California Museum of Paleontology)