PERMIAN

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The final period of the Palaeozoic Age, the Permian (280-248 Ma ) was a time of sharp climatic change. Gone was the warm even climate, the Northern hemisphere was cooling, and ice covered large areas of the world. Earthquakes, volcanoes and mountain formation racked the land, salt lakes formed and seas changed shape and level. Amphibians and reptiles flourished. The cotylosaurs (stem reptiles) such as Pareiasaurus, the first four-footed plant-eater, grew large and ponderous. They still retained the typical reptilian skeletal system, with lower legs at right angles to the body - an inefficient system that requires powerful muscles and thick bones to support large bodies.
Closely related but very different looking were the pelycosaurs such as Dimetrodon and Edaphosaurus, with sails on their backs that may have functioned as heat exchangers to help them control body temperature. These later developed into the therapsida (eg Titanosuchus, Dicynodon, Cynognathus) or mammal-like reptiles from which the mammals of today evolved. They, too, grew large, heavy and slow and became extinct by the mid Triassic .
At the same time as these reptile developments were occurring, insect numbers and species were increasing, with the first flies, grasshoppers and beetles appearing.
At the end of the Permian period land levels changed again, with many seas becoming isolated. Once again the climate began to warm up, and vast deserts formed in the northern hemisphere. Seas increased in salinity, and many groups of animals became extinct. The way was being prepared for the beginning of the Mesozoic Age, during which the dinosaurs would appear and dominate the earth for 140 million years.