It’s long been known that mammals have proportionally big brains in comparison to other creatures. Now new scanning technology suggests it may be linked to the sense of smell.

A research project led by Professor Timothy Rowe of the University of Texas at Austin involved scanning the fossilised skulls of two of the earliest known mammals, Morganucodon and Hadrocodium. The former is considered one of the evolutionary links between reptiles and mammals, while the latter is less than two inches long.

The problem in the past has been that it’s difficult to get information on what would have been inside the skull without damaging the fossil, which, to put it mildly, seems a bit of shame for something that’s around 200 million years old.

Now though, Rowe and company were able to use computed tomography, a technique that uses multiple two-dimensions X-rays to produce a three-dimension image. The technique is more commonly known as the CT scan used in medicine.

The data from the scans suggested that when mammal brains first started getting proportionally bigger, it was the areas associated with smell that grew most rapidly, possibly by a factor of 10. It also appeared that the cerebellum, which controls movement, increased in size at a similar time.

Rowe’s theory is that mammal brains didn’t simply grow as a whole, but rather that the process was driven by particular sections growing in response to particular needs. The first of these looks to have been the need to develop a stronger sense of smell in order to hunt at night time rather than go out for food during the day and compete with dinosaurs.