How kangaroos evolved with a quick jump
Roos' teeth tell the story of changing diet and how that drove evolution. (But we still don't know why they hop). Lyndal Byford reports.
The iconic Aussie kangaroo evolved rapidly and much later than we thought, around 3 million years ago, in response to the spread of grasslands, new research shows.
The researchers examined the teeth of kangaroos and their ancestors from the last 25 million years, in order to understand their diet and how that may have driven evolution.
"If you are a herbivore, diet is a very important thing," lead author Aidan Couzens from Australia's Flinders University, told the Australian Science Media Centre (AusSMC).
"What you do most of the time when you're not sleeping, is eating."
Shorter teeth crowns tend to be found on animals that eat soft plants, while higher teeth crowns tend to be found on animals eating grasses. Around three million years ago, kangaroos' teeth changed.
"The change happened very recently and very rapidly," said Dr Couzens.
"True kangaroos really evolved this very pronounced increase in their crown height, which is very interesting, and suggests it was linked with the origins of grasslands."
The teeth also showed more abrasive wear patterns, typical of animals that eat grasses.
In contrast, the now extinct megafauna-type kangaroos were doing something completely different; they were eating softer plants like the shrubs found on the nullabour plains today.
"This is really good evidence that the origins of grasslands in Australia had a profound effect, and was the primary driver of the radiation of true kangaroos," said Dr Couzens.
This all suggests that kangaroos evolved in a big hop, skip and a jump when the earth was warming, rather than in a slow gradual way over a period when the earth cooled.
Flinders professor Gavin Prideaux said this work was part of a broader study on kangaroo evolution he and his team are conducting to answer some fundamental questions about our most iconic animal.
"When did they descend form the trees? Because they are most closely related to possums that live in trees today, so at some point in the past they moved down onto the ground."
Prideaux also hopes to solve one more the big question in roo research - why do kangaroos hop?
"Believe it or not, we still haven't got a clue as to why kangaroos actually hop," he said.
You can listen to the AusSMC briefing here.