Phanerozoic of Pangaea into Laurasia and Gondwana in an extinction known as the Jurassic-Cretaceous extinction. Sea levels rose, destroying fern prairies and creating shallows. Ichthyosaurs became extinct whereas sauropods, as a whole, did not; in fact, some species, like "Titanosaurus", lived until the K-T extinction. The increase in sea-levels opened up the Atlantic sea way which would continue to get larger over time. The divided world would give opportunity for the diversification of new dinosaurs. The Cretaceous is the longest period in the Mesozoic, spans from 145 million to 66 million years ago, and is divided into two epochs: Early Cretaceous,
Early Triassic have revealed that temperatures rose in the first 3 million years of the Triassic, ultimately reaching sea surface temperatures of in the tropics around 249 million years ago. Large and mobile species disappeared from the tropics, and amongst the immobile species such as molluscs, only the ones that could cope with the heat survived; half the bivalves disappeared. On land, the tropics were practically devoid of life. Big, active animals only returned to the tropics, and plants recolonised on land when temperatures returned to normal around 247 million years ago. Early Triassic The Early Triassic is the first of three