Introduction to Mesozoic This era is divided to three periods; 1.Triassic (240 to 205 million years ago), 2.Jurassic (205 to 138 million years ago) and Cretaceous (138 to 65 million years ago). Mesozoic means middle life or the era of middle animals and it is an era in which plant fossils varies from Paleozoic. Dinosaurs are the most famous animals in this era and they appeared from Mesozoic. They did not change significantly up to Mesozoic. Dinosaurs extinguished in late Cretaceous excluding birds. Some of the last dinosaurs have been found in the sediments of Montana 's late Cretaceous. This period was also a big change for land plants. Early Mesozoic was captured by cycads, ginkgophytes and bennettitaleans. Advanced ginkgophytes, such as primitive pines rose in a clear form in early Mesozoic. In middle Cretaceous, primitive angiosperms appeared, changed and replaced by other plants.