The Paleozoic and Mesozoic ERAS are two of the three major divisions of geologic time. The Paleozoic Era began about 541 million years ago and ended about 252 million years ago. It is characterized by the emergence of life in the oceans, the evolution of fish and other aquatic animals, and the colonization of land by plants and animals. The Mesozoic Era followed the Paleozoic and lasted from about 252 million years ago to 66 million years ago. During this time, dinosaurs were the dominant land animals, and the first birds and mammals appeared. The Mesozoic also saw the emergence of flowering plants and the breakup of the supercontinent Pangaea.