250 million years ago Permian Palaeozoic Earth Paleozoic Era Palaeozoic Earth Palaeozoic Earth Palaeozoic Earth Ordovician Period Paleozoic fossil sharks Paleozoic Era livescience.com Palaeozoic Earth beginning of animal evolution Palaeozoic Earth Paleozoic fossil sharks Permian Paleozoic Era: Facts & Information end-Permian extinction Paleozoic Era Palaeozoic Earth Permian Paleozoic Era http://www.livescience.com/37584-paleozoic-era.html Paleozoic Era: Facts and Information | LiveScience Permian Palaeozoic Earth Palaeozoic Earth