Cronopio Dentiacutus - new mammal discovery in south america

The animal displays a host of features that appear to have no parallel among living or extinct mammals, says Prof Guillermo Rougier from the University of Louisville, Kentucky, US.

"The back teeth, the molars, are the kind of teeth that you will find in an insectivore, an animal that eats insects of different kinds, and even very small invertebrates, so perhaps small lizards, which were present in the same place," he told BBC News.

"But we have no idea why he needed such huge canines. Those tusks are a big surprise."

It is possible Cronopio used them to skewer certain insect prey, but it is clear the canines could not have been deployed with much force.

The slender nature of the snout and of the teeth themselves mean that to have bitten down hard, or to have wrestled another creature with its mouth, would have invited almost certain injury.

Cronopio is what is termed a dryolestoid. These were a group of primitive, extinct mammals belonging to the lineage leading to modern marsupials and placental mammals.

They are known mainly from teeth and jaws found in North America and Europe from the Jurassic Period (145-200 million years ago). To now have relatively complete dryolestoid skulls form South America in the form of Cronopio is therefore a boon to scientists trying to study the spread and diversity of mammals through Earth history.