260 Mya to 240 Mya
Usage notes: "Mya" means "million years ago" These dates are amazing close approximations, but are subject to adjustments
259. 0.4 Mya, Lopingian, Wuchiapingian: Marking the end of the Permo-Carboniferous glaciation.
254.14 Mya, Paleozoic, Permian, Lopingian, Changhsingian: Land masses unite into supercontinent Pangaea and creating the Appalachian range.
251.9 Mya to 201.3 Mya: Duration of the Triassic Period of the Mesozoic Era. The Triassic Period is between the Permian and Cretaceous Periods.
~ First evidence of mammals occurred in this Period. One was a mouse size critter.
~ This geologic period ended with a mass extinction of species. So, 251,900,000 BP marked a mass extinction of life.
251,900,000 BP to 201,300,000 BP: Triassic Period: This time has been called the Triassic Period. The Triassic Period falls after the Permian Period and before the Jurassic Period. First evidence of mammals appear, a mouse like critter is found to lie within the Period. This geologic period ended with a mass extinction of species.