During the Mesozoic era the dominant life forms were reptiles. The land form was full of reptiles. The small dinosaurs intruded during the Triassic period. The appearance of large species of dinosaur was during the Jurassic and Cretaceous period. As the Mesozoic era progressed mammals and birds came into existence. Gymnosperms were dominant in the Mesozoic era. Angiosperm appeared in the Cretaceous period. After the mass extinction of dinosaurs, mammals and angiosperms were prevalent throughout the Cenozoic era.