What’s the News: Mammals’ increased brain size may have come from long-ago natural selection for a better sense of smell, suggests a new study published today in Science. By reconstructing in 3D the skulls of two animals far back on the mammal family tree, the researchers saw that growth of smell-related brain regions accounted for much of the early increase in brain size as mammals developed.

How the Heck:

The researchers looked at fossil skulls of two ancient animals. The 205-million-year old Morganucodon was a proto-mammal: a reptile with some decidedly mammalian characteristics (it looked a bit mouse-like, researchers say), that is thought to be an ancestor of mammals today. The tiny mammal Hadrocodium—imagine a shrew the size of a paperclip—lived 195 million years ago.
Fossil skulls of these species are rare, and the researchers weren’t about to bust them open to examine the brain cavity. Instead, they used high-resolution X-ray computed tomography to make 3D reconstructions of the skulls, inside and out. Based on the size and shape of the skull cavity, and the impressions left by brain tissue, the researchers could make detailed models of the animals’ brains.
Morganucodon‘s ...