Dispersion and amalgamation of continents, and the evolution of life. The birth of primates. The Mesozoic is the period when dinosaurs reigned at the top of the ecosystem. Stem evolution caused the emergence of new species where the continent split apart, while Crown evolution has led to species diversification through the amalgamation of continents. While dinosaurs spread throughout the world via this process, mammals were also born 250 million years ago, and flourished after dinosaurs went extinct. And primates, leading to the appearance of human beings, were born about 100 million years ago.