Little thylacine had a big bite

In the northeast corner of Queensland lies one of Australia’s great treasures — the Riversleigh World Heritage Area, home to more than 250 sites that are rich in fossils. In that region, some 24 to 11.6 million years ago, as many as five relatives of the extinct Tasmanian tiger, or thylacine, roamed forests along with giant carnivorous rat-kangaroos, marsupial lions, the world’s oldest known venomous snakes and many other long-dead animals. Then, from 11.6 to 5.3 million years ago, the forests dried out and were replaced by shrubs and grasses, and many of those creatures went extinct.

One of those Tasmanian tiger relatives, named Nimbacinus dicksoni, was about the size of a housecat or a fox. Scientists could tell from its teeth that N. dicksoni was a meat eater, but they have been trying to figure out what it ate. There has been conflicting evidence. Some of it indicated that the N. dicksoni could have taken down prey larger than itself, similar to the way that spotted-tail quolls are able to hunt small wallabies. But other evidence indicated that the animals’ diet might have been restricted to small prey, possibly just invertebrates.

To figure out whether N. dicksoni was eating big animals or tiny bugs, Marie R. G. Attard of the University of New South Wales in Sydney and colleagues created a 3-D digital reconstruction of an N. dicksoni skull that had been found at a site in Riversleigh. Then they used a computer program to examine and test the animal’s bite and compare it to several living carnivorous marsupials and the extinct Tasmanian tiger. Their results were published April 9 in PLOS ONE.

The analyses revealed that the N. dicksoni skull was more like that of the spotted-tail quoll than that of the Tasmanian tiger or the northern quoll , which tend to eat smaller critters. N. dicksoni had a powerful bite, the researchers determined, and that would have helped the animals to take down prey larger than itself.

“Potential prey for a fox-sized [N. dicksoni] living in the closed forest communities of Riversleigh likely included many small- to medium-sized birds, frogs, lizards and snakes, as well as a wide range of marsupials,” the researchers write. Those marsupials could have included kangaroos, wombats, dasyurids (a category that includes Tasmanian devils and quolls) and bandicoots. Many of those marsupials are themselves carnivores with powerful bites.

But being able to consume such a variety of prey doesn’t mean that N. dicksoni actually did so, the researchers write. What they ate may have been limited by competition with all those other thylacine relatives that were living in the area at the same time. The various species could have compensated by using different strategies for hunting or settling into different types of habitats. Because researchers haven’t yet analyzed the rest of N. dicksoni’s skeleton, though, they don’t know enough about its body to start hypothesizing about how the animals may have moved and hunted.

In the end, N. dicksoni’s powerful bite couldn’t save the animals when the climate and land around them changed. They went extinct, along with the thylacines that lived alongside them and the others that lived on the Australian continent. That didn’t mean that Australia became predator-free, however. Their disappearance opened up places in the food web and environment, and those spots were soon filled by another type of carnivorous marsupial — the quoll.