Study: Kangaroos took unusual evolutionary path to grazing

Thick tooth enamel helped kangaroos chart an unconventional evolution story, compared to herbivores on other continents, an Australian study has found.

The study, published in Science, analyzed fossilized kangaroo teeth spanning millions of years and found that kangaroos, the continent's most diverse and common herbivores, evolved an unusual solution to the challenge of feeding on grass with molars reinforced by thickened enamel, said a statement of Australia's Flinders University released Monday.

The evolutionary history of kangaroos led them to adapt in a very different way to the rise of grasslands compared with hoofed mammals like deer and horses, which dominate most other continents, said study lead author Aidan Couzens, a research associate at Flinders University.

Unlike grazing animals such as horses and deer, which chew side-to-side and evolved high-crowned teeth, kangaroos slice food vertically, Couzens said, adding this chewing style revealed that kangaroos had a conveyor belt of cheek teeth with thick enamel.

"Feeding on grasses wears down teeth more rapidly than other kinds of plants do, because they're often covered in dust and their blades contain thousands of tiny silica particles," Couzens said.

"In some ways, the evolutionary history of herbivorous mammals in Australia is upside down because the vertical chewing herbivores (i.e., kangaroos) win out whereas the reverse occurred on the northern continents," he added.

The study suggests evolution is not always predictable. Competing marsupial herbivores better suited to grazing declined before grasslands spread, leaving the playing field open for kangaroos to take advantage.