Mammals may owe their large brains to the development of more acute senses, such as smell and touch, in their extinct ancestors.

Timothy Rowe at the University of Texas in Austin and his co-authors made computed tomography scans of the intact fossil skulls of two species that preceded the first mammals. Compared with those of its predecessors, the brain of Morganucodon oehleri — which roamed the Earth some 200 million years ago — was larger relative to the size of its body. Much of the difference is attributable to the growth of brain areas involved in sensing and processing smell and touch, as well as movement coordination.

Another mammalian ancestor from the same period, Hadrocodium wui (pictured), also showed brain growth, particularly in regions attuned to smell. The authors suggest that an improved sense of smell might have laid the neural groundwork for the ability to deal with different types of environmental information.

Credit: KLINGER & LUO, CARNEGIE MUSEUM OF NATURAL HISTORY

Science 332, 955–957 (2011)