The Cenozoic which follows the Mesozoic is called the Age of Mammals. The Mesozoic is called the Age of Dinosaurs. Before the Mesozoic was the Paleozoic.
The Three Periods of the Mesozoic
The Triassic was the first period of the Mesozoic. Both dinosaurs and mammals evolved during the Triassic. Mammals evolved from the therapsids, also called proto-mammals or mammal-like reptiles. Dinosaurs evolved from archosaurs also called proto-dinosaurs.
In the scientific literature mammals are therapsids and dinosaurs are archosaurs. Similarly birds are dinosaurs, apes are monkeys, and humans didn't evolve from apes, we are apes. Each species is a considered a member of the group from which it evolved.
Neither dinosaurs nor mammals played a prominent role in the Triassic. The central conflict was the competition between their predecessors: the other groups of therapsids and archosaurs.
There were no famous species from the Triassic. Many of you would not know the name of a single dinosaur, mammal, therapsid, or archosaur from the Triassic. If you bought a bag of plastic animals from the Mesozoic it is likely that none would be from the Triassic.
The Jurassic is an age of giant dinosaurs, the long-necked sauropods. The other famous dinosaur from this era was the stegosaurus which had a row of bony plates down it back and spikes on its tail. The spiked tail is called a thagomizer after a fictional caveman, named Thag. In a Far Side comic by Garry Larson it is implied that Thag was killed by a thagomizer. The famous large predators belonged to the genus Allosaurus.
The Cretaceous ended with still another massive extinction. The dinosaurs, except for the birds became extinct. The literature will frequently say the non-avian dinosaurs went extinct. Avian means birds. The birds and mammals lived on into our era, the Cenozoic.
Written April, 15, 2015
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