Mass extinctions have played a pivotal role in evolutionary history. While the Permian Period featured the thriving of synapsids, which later became mammals, the largest mass extinction in Earth's history took place at its end. Later, during the Triassic Period, reptiles that had branched off from sauropsids significantly diversified. Lizards, alligators and turtles are some of these reptiles. Ichthyosaurs and pterosaurs appeared in the seas, pterosaurs appeared in the skies, and dinosaurs appeared on land and thrived throughout the Mesozoic Era. Some members of these classes grew quite large. However, most of these diversified reptiles disappeared during the next mass extinction, which occurred at the end of the Cretaceous Period. Birds, which splintered off from maniraptoriformes during the Jurassic Period, broke this trend by successfully weathering this mass extinction and diversifying during the Cenozoic Era.