MARY LOUISE KELLY, HOST:
Tens of thousands of years ago, nearly two dozen kangaroo species vanished, part of a great extinction event. Science reporter Ari Daniel says hundreds of prehistoric teeth may now help paleontologists figure out why.
ARI DANIEL, BYLINE: Kangaroos evolved from a possum-like ancestor. Then, some 8 million years ago...
SAM ARMAN: Australia became quite arid. That was where kangaroos really hit their strides - or I suppose their hops - and diversified into a lot of different groups.
DANIEL: Sam Arman is a paleontologist at Megafauna Central, a natural history museum in Australia. He says there were two major groups of kangaroos - the long-faced ones...
ARMAN: Which is what you still see today, and that includes things like wallabies.
DANIEL: ...And the short-faced ones.
ARMAN: So basically, if you plonked a koala head on top of it, you're basically in the right ballpark - just less fluffy.
DANIEL: Then, in the late Pleistocene, 40 to 65,000 years ago, many of these kangaroos went extinct. And the question is why.
ARMAN: The question has been plaguing paleontology for a couple of hundred years. It really does come down to two arguments.
DANIEL: The first being whether humans, who arrived in Australia around this time, had something to do with it, perhaps by hunting the kangaroos or altering the landscape, or whether it was related to a change in climate.
ARMAN: If these kangaroos were all just feeding on particular sorts of plants, then perhaps climate change came in and wiped out those plants and then they were extinct because of that.
DANIEL: This idea that their food disappeared relies on the kangaroos having been specialized eaters, which some paleontologists believe, based on differences in kangaroos' skull shape and chemistry, that short-faced kangaroos fed primarily on shrubs and long-faced kangaroos mostly on grasses. Arman, however, wasn't so sure.
ARMAN: Adaptation does not necessarily define diet.
DANIEL: So he approached the question of ancient kangaroo extinction by taking a detailed look at the teeth of more than 900 kangaroos, a mix of fossils from a cave in South Australia and modern animals from across the country.
ARMAN: Whenever an animal chews its food, the food leaves marks - microscopic scratches on the surface of the teeth. If we scan them under a very high-resolution microscope, we can then compare what these fossil animals were eating at the time.
DANIEL: Arman and his colleagues found that most of the extinct kangaroos, both the short- and long-faced ones, had mixed diets. That is, he says, they ate both grasses and shrubs, based on what was available. He suggests that starvation brought on by a changing climate may not have wiped them out and the arrival of humans may have.
ARMAN: It doesn't rule out that climate change is involved in some other way, but it's very hard to tell the story without invoking humans in any way.
DANIEL: The research is published in the journal Science.
LARISA DESANTIS: This paper is really helpful in sort of reconstructing what the ecology was, but I think it goes a little bit too far in trying to make the claim that these kangaroos were sort of already well-adapted to variable climate change.
DANIEL: Larisa DeSantis is a paleontologist at Vanderbilt University. She leans towards climate change having more to do with the extinctions, so she says the new research doesn't capture the full picture.
DESANTIS: It's really important to see if we can disentangle the impacts of climate and humans in the past so that we can better understand the impacts that we're having on current ecosystems.
DANIEL: This is a point that Sam Arman agrees with. He hopes the kangaroos that ended their time on Earth in the Pleistocene might help the kangaroos of today escape a similar fate. For NPR News, I'm Ari Daniel.
(SOUNDBITE OF MAC MILLER SONG, "THE MILLER FAMILY REUNION") Transcript provided by NPR, Copyright NPR.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.
