At the beginning of the Phanerozoic, we witness what is called the “Cambrian explosion of Life”; virtually all modern phyla make their appearance. Some groups typical of the period are presented: in the sea, echinoderms (hedgehogs and sea stars, crinoids and related forms); on the continents, we witness the differentiation of insects and the establishment of close relationships between these animals and plants. The chapter ends with the largest biological crisis to ever hit Earth. However, such crises are important for the evolution of biodiversity, because they allow certain groups, who have lived in the shadow of dominant forms, to stand out and to thrive.