‘The origin of mammals’ considers the evolutionary history of mammals using the fossil record to chart their developmental progress. It looks at a group of ‘pre-mammals’, the Synapsids—mammal-like reptiles—including pelycosaurs from 320 mya in the Upper Carboniferous. Then came the therapsids from c.260 mya in the Middle Permian, when the world was increasingly arid. Then 250 mya a mass extinction event wiped out over 90 per cent of animals and plants. Miraculously, a few therapsids survived including the burrowing dicynodont called Lystrosaurus and cynodonts that evolved throughout the Triassic and gave rise to mammals. The earliest mammal was a mouse-sized animal called Morganucodon from 200 mya.