By 360 million years ago, our ancestors had colonised the land, eventually giving rise to the first mammals about 200 million years ago. These creatures already had a small neocortex - extra layers of neural tissue on the surface of the brain responsible for the complexity and flexibility of mammalian behaviour. How and when did this crucial region evolve? That remains a mystery. Living amphibians and reptiles do not have a direct equivalent, and since their brains do not fill their entire skull cavity, fossils tell us little about the brains of our amphibian and reptilian ancestors.