The Palaeozoic began with an explosion of life forms. The Cambrian explosion marks the era with thousands of new life forms in the ancient seas. The era saw many important events, including the development of most invertebrate groups, life's conquest of land, the evolution of fish, reptiles, synapsids (the ancestors of mammals), amphibians, insects, and plants, the formation of the supercontinent of Pangea, and at least two distinct ice ages. The earth rotated faster than it does today so days were shorter, and the nearer moon caused stronger tides.