New York, March 27 (IANS): Side-to-side movement of the teeth and jaw bones of mammals, especially cows, helped our earliest ancestors to grind food with their molars and eat a more diversified diet, researchers have found.

The findings, led by researchers at the University of Chicago, showed that these changes may have been a contributing factor to their survival of the mass extinction at the end of the Cretaceous Period 66 million years ago.

Almost all modern mammals, including placental mammals, like humans and deer, and marsupials, like kangaroos and opossums, share similarities in their jaw structures and musculature that allow for both pitch -- basic up and down movement -- and yaw movements -- side-to-side, crosswise motion. 

This allows mammals to have especially diverse diets today, from cutting pieces of meat to grinding tough plants and vegetables. 

For early mammals, these characteristics meant they could be more resourceful during tough times, the researchers said, in a paper published in the journal Scientific Reports.

"If you have a very specialised diet you're more likely to perish during a mass extinction because you're only eating one thing. But if you can eat just about anything and 90 per cent of your food goes away, you can still live on scraps," said David Grossnickle, graduate student at the University of Chicago. 

For the study, the team used two-dimensional (2-D) images of early mammal fossils and three-dimensional (3-D), to analyse the structure of teeth, jaw bones, and how the muscles that control them were attached to the skull. 

The results showed that as species began to develop a projection on the upper molars that fit into a corresponding cup or basin on their lower counterparts, the musculature of the jaw also changed to provide greater torque for side-to-side yaw movements. 

This way the animal could grind its food between the molars like a mortar and pestle, as opposed to cutting it with simple up and down pitch movements.