Sense of Smell Jumpstarted Brain Evolution

Mammals' big brains helped them survive the dinosaur age

May 19, 2011

The fossil of the Jurassic mammal Hadrocodium wui - its skull is only 12 millimeters long and estimated to weigh just 2 grams.

Researchers used computed tomography or CT scans to analyze the skulls of 190-million-year-old mammals found in a Jurassic-era fossil bed in China. These tiny critters, co-existed with the giant, meat-eating dinosaurs and probably survived by being nocturnal.

But to be active at night meant the mammals had to have “very special sensory adaptations," says Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, and a member of the research team that studied the prehistoric mammal skulls.

Jurassic mammals already had a large olfactory bulb for a sophisticated sense of smell.

He says the CT-scans helped the team construct a virtual brain case for two of the ancient mammals. “In this study we have found that the large brain is becoming larger primarily because the olfactory, or the smelling part of the brain, become very big and also the part related to skin tactile sensation also becomes big.”

Luo says the acute sense of smell and touch that helped mammals survive among the predatory dinosaurs is clearly visible in their ancient anatomy.

“So the new evolutionary biology idea from this study of fossils is, maybe, a capacity to smell very well is as important, even more important than hearing and that the tactile sense probably played a big role too.”