Mesozoic Era is classified into 2 groups as:

1. Mesozoic Era which is further divided into 3 groups:
   • Triassic Period: During the Triassic Period, surviving fishes, insects, reptiles, and cone-bearing plants evolved rapidly. About 225 million years ago, the first dinosaurs evolved. The earliest mammals evolved during the late Triassic. Triassic mammals were very small, about the size of a mouse or shrew. Examples: Living Horsetail and Horsetail Fossil
   • Jurassic Period: During the Jurassic Period, dinosaurs became the most diverse land animals. They “ruled” for about 150 million years, but different types lived at different times. One lineage of dinosaurs evolved feathers and ultimately led to modern birds. Archaeopteryx, the first feathered fossil to be discovered, evolved during this time. Example: Pterodactyl Fossil
   • Cretaceous Period: During the Cretaceous Period, Tyrannosaurus rex roamed the land, while flying reptiles and birds soared in the sky. Turtles, crocodiles, and other, now-extinct reptiles like plesiosaurs swam among fishes and invertebrates in the seas. Leafy trees, shrubs, and flowering plants emerged and experienced adaptive radiations. The Cretaceous ended with another mass extinction. More than half of all plant and animal groups were wiped out, including all dinosaurs except the ancestors of modern birds. Example: T. Rex
2. Cenozoic Era which is further divided into 3 groups:
   • Paleogene Period: During the Paleogene Period, climates changed from warm and moist to cool and dry. Flowering plants, grasses, and insects flourished. After the dinosaurs and giant marine reptiles went extinct, mammals underwent a major adaptive radiation. As climates changed, forests were replaced by open woods and grasslands. Large mammals— ancestors of cattle, deer, and sheep and other grazers—evolved and spread across the grasslands. In the sea, the first whales evolved.
   • Neogene Period: During the Neogene Period, colliding continents pushed up modern mountain ranges, including the Alps in Europe and the Rockies, Cascades, and Sierra Nevadas in North America. As mountains rose, ice and snow built up at high elevations and in the Arctic. Falling sea levels and colliding continents created connections between North and South America, and between Africa, Europe, and Asia. Those connections led to great movements of land animals between continents. Climates continued a cooling and drying trend, and grasslands continued to expand. Modern grazing animals continued to coevolve with grasses, evolving specialized digestive tracts to deal with tough, low-nutrient grass tissue.
   • Quaternary Period: During the Quaternary Period, Earth cooled. A series of ice ages saw thick glaciers advance and retreat over parts of Europe and North America. So much water was frozen in glaciers that sea levels fell by more than 100 meters. Then, about 20,000 years ago, Earth’s climate began to warm. Over thousands of years, glaciers melted, and sea levels rose. In the oceans, algae, coral, mollusks, fishes, and mammals thrived. Insects and birds shared the skies. Land mammals—among them bats, cats, dogs, cattle, and mammoths— became common. Between 6 and 7 million years ago, one group of mammals began an adaptive radiation that led to the ancestors and close relatives of modern humans.