Using MRI scans, researchers have discovered that the brains of small, pug-like dogs have rotated forward in their skulls compared with larger, long-nosed dogs such as Dalmatians and German shepherds. And the olfactory lobe, responsible for smelling, is lower in the brain cavity.

''This is the first systematic example of brain rotation [observed] in any animal,'' said the neuroscientist and study author Michael Valenzuela, who studies brain ageing in humans and animals at the University of NSW.

Pug-like dogs, which look significantly different to the ancestor of domestic dogs, the wolf, were the result of human intervention, he said.

''The very small, pug-like dogs have only come about through selective breeding.''

Brain rotation in these could be an evolutionary trade-off because the length of their skulls had decreased in proportion to the width, said Dr Valenzuela, whose findings have been published in the journal PLoS ONE. ''We speculate that one of the reasons the brain may be rotating in pug-like dogs is that if it hadn't rotated then there would be less space for the frontal lobe to develop,'' he said.

The frontal lobe is an area of the brain responsible for intelligence and problem solving, as well as social behaviour.

Dr Valenzuela said examining the link between brain changes in dogs and their behaviour would be the next step in the research. ''The obvious step forward … is to do more sophisticated cognitive and behavioural tests in dogs and see if there is a relationship between brain rotation [and behaviour].''

The researchers hope to find whether a dog's sense of smell is affected by the repositioning of the olfactory lobe.

"We think of dogs living in a world of smell but this finding strongly suggests that one dog's world of smell may be very different to another's,'' said the veterinarian and study author Paul McGreevy, an associate professor of the University of Sydney.