This illustration depicts how the region of Cerro de los Batallones in central Spain likely looked nine million years ago when saber-toothed cats and bear dogs shared space and prey during the late Miocene period. (Mauricio Antón)

New research has uncovered how saber-toothed cats and bear dogs managed to cohabitate peacefully more than nine million years ago.

A team of paleontologists from the University of Michigan and the Museo Nacional de Ciencias Naturales in Spain took tooth enamel samples from two species of sabre-toothed cats and one species of bear dog that had been unearthed at sites near Madrid.

By analyzing the enamel and determining what the animals ate, the scientists were able to understand how they lived together in a woodland region.

"What they did to coexist was to avoid each other and partition the resources," said Soledad Domingo, one of the authors of the study published in Proceedings of the Royal Society B and a fellow at the University of Michigan’s Museum of Paleontology.

By analyzing what they ate, researchers surmised the leopard-sized cats and the bear dogs hunted the same prey: wild boar and horses.

However, the cats would have used tree cover to avoid encountering other bigger animals while the dogs hunted in a more open area that rarely overlapped with the cats' territory. The larger bear dogs would have no competition from the cats hunting for those same animals.

During that time, the late Miocene Period, the predators lived in a forested area that had spots of grassland.

The excavated sites in Spain, at Cerro de los Batallones, had an abundance of bones from meat-eating mammals, a situation which offers "a unique window to understand life in the past," Domingo says.

Researchers took the animals' teeth and using a dentist's drill, removed specimens from 27 saber-toothed cats and bear dogs.

Those specimens were run through a stable carbon isotope analysis, which allowed scientists to measure the ratio of carbon 13 molecules to carbon 12.

Both carbon 12 and 13 are present in the carbon dioxide plants ingest during photosynthesis.  When a plant is eaten, it leaves an isotopic signature on teeth and bones.

"This would be the same in your tooth enamel today," says Domingo. "We could have idea of what you eat [if] we sampled [your enamel]."

The carbon isotopes revealed the cats remained in the leafy areas of the habitat instead of venturing into the open areas where the bear dogs were.