Mammals first evolved big brains for better sense of smell

May 20, 2011

Skull of Hadrocodium wui (credit: Mark Klingler and Zhe-Xi Luo, Carnegie Museum of Natural History)

Mammals first evolved their characteristic large brains to enable a stronger sense of smell, paleontologists from The University of Texas at Austin, Carnegie Museum of Natural History, and St. Mary’s University in San Antonio have found.

The paleontologists used CT scanners to reconstruct the brains of two of the earliest known mammal species, both from the Jurassic fossil beds of China.

The 3-D scans revealed that even these tiny 190-million-year-old animals had developed brains larger than expected for specimens of their period, particularly in the brain area for smell.

Hadro Skull

T scan of Hadrocodium skull (yellow), showing brain endocast (orange) (credit: Univ. of Texas at Austin)

Other factors leading to larger brains in early mammals included greater tactile sensitivity and enhanced motor coordination, the researchers said. Fossils of some of the earliest mammals, such as Hadrocodium, bore full coats of fur, explaining the need for enhanced tactile sensitivity.

The team CT-scanned more than a dozen early fossil mammals and more than 200 living species over the past 10 years at the High-Resolution X-ray Computed Tomography Facility at The University of Texas at Austin.

Ref: R. Glenn Northcutt, Evolving Large and Complex Brains, Science, 20 May 2011: DOI: 10.1126/science.1206915