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Mammals' large brains evolved for smell

A highly developed sense of smell kick-started the development of mammals' big brains.

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The researchers scanned the fossilised skulls of tiny, very early mammals

Scientists used very high-resolution scanning to study the skulls of two of the earliest known mammal species.

Comparing the shape of their brain cases to those of slightly earlier animals, or "pre-mammals", revealed that the first brain areas to over-develop were those associated with the sense of smell.

The findings are published in Science.

An improved sense of smell may have allowed our tiny, furry ancestors to hunt at night.

The researchers were able to create 3D images of prehistoric animals' brains using the latest computed tomography, or CT, scanning methods.

"Before CT, one had to break open a fossil to get to the internal anatomy," explained Professor Timothy Rowe from the University of Texas at Austin, one of the researchers involved in the study.

"[This technique] is non-destructive, so we can measure internal anatomy in ways that were never before possible."

Evolution timeline
Mammals, and humans in particular, have the largest brains in the animal kingdom, relative to the size of their bodies. So the scientists wanted to work out why mammal brains evolved to become so very large and complex.

To do this, they studied the earliest known mammals - the tiny fossilised skulls of 190-million-year-old Morganucodon oehleri and Hadrocodium wui, both of which were discovered in China.

By comparing these skulls to those of more primitive animals, and to living mammals, they were able to build a sequence of events in the evolution of mammal brains.

The team found that, in early mammals, the brain regions associated with smell were much larger than in more primitive or "pre-mammal" ancestors.

Read on



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