The question of how mammals evolved their exceptionally large brains has intrigued researchers for years, and although many ideas have been put forward, none has provided a clear answer. Now a team of palaeontologists suggests that the mammalian brain evolved in three distinct stages, the first of which was driven by an improvement in the sense of smell. Their evidence, published in tomorrow’s issue of Science, comes from two fossilized skulls, each measuring little more than 1cm in length.
Mammals emerged during, or just before, the early Jurassic period, some 200 million years ago. We know that the earliest mammals were small, nocturnal animals that fed on insects, but there is very little in the way of details about how their brains might have looked, because fossils are scant, consisting mostly of isolated jaws and teeth. A few skulls have been found but until now studying the brain involved damaging the fossils which, given their rarity, was out of the question.