Australia’s marsupial lion (illustration) has been the subject of much debate.Credit: Peter Schouten

Australia’s largest-ever marsupial predator, Thylacoleo carnifex, probably dined on creatures from densely forested environments, according to a recent analysis.

This exposé of the creature’s culinary habits — presented at the Society of Vertebrate Paleontology meeting in Albuquerque, New Mexico, on 18 October — supports the idea that climate change led to this predator’s eventual extinction 30,000 to 40,000 years ago.

Research leader Larisa DeSantis, a palaeoecologist at Vanderbilt University in Tennessee, says that increasingly dry conditions that began in Australia 350,000 years ago would have shrunk the continent’s forests, causing populations of woodland prey to dwindle. This would have left their predators, such as the marsupial lion T. carnifex, vulnerable to extinction.

Researchers have long puzzled over precisely what T. carnifex ate, and debated the cause of its extinction. Climate change and competition for food or hunting by Australia’s early human inhabitants are the main suspects for the predator’s demise. But the mystery over its dietary preferences has hindered researchers in their quest to understand why it disappeared.

“Its elongate bladed teeth are unlike anything seen in today’s animals, which has made it hard for palaeontologists to infer aspects of its diet and behaviour,” says Matthew McCurry, curator of palaeontology at the Australian Museum in Sydney. Over the years, people have suggested that the marsupial lion fed on everything from carrion to wild cucumbers, he adds, although palaeontologists have long agreed it was a carnivore.

Ambush predator

Most of the research on the marsupial lion — which was about one-third to half the size of the unrelated African lion (Panthera leo) — has focused on its anatomy and the biomechanics of its skull, limbs, claws and teeth. That work suggests the animal was an ambush predator that leapt onto its prey from among the trees. But there have been few other clues as to its diet and lifestyle.

To learn more, DeSantis and her colleagues took 35 fossil teeth from marsupial lions and looked at the ratio of two stable isotopes of carbon in the fossil teeth, which can provide clues about habitat. The team also looked at microscopic pits and scratches on the surface of 106 marsupial lion teeth, which can provide information about the texture of the animals’ diet.

The ratios of these carbon isotopes in plants differ between open and forested environments, DeSantis says. Researchers can detect this chemical signature in the teeth and bones of the herbivores that feed in those habitats, and of the carnivores that then feast on those plant-eaters.

The team’s analysis of wear on the surface of the larger sample of teeth indicated that the marsupial lion had a style of feeding consistent with consuming both bones and meat, much like that of modern African lions, rather than eating flesh alone. The isotopic evidence also suggests that marsupial lions may have preyed on a leaf-eating kangaroo called Protemnodon, which had a similar chemical signature in its teeth to T. carnifex indicating that both creatures fed in a forested habitat.

Hard evidence

Using stable-isotope analysis to show that marsupial lions ate forest animals is an important development, says McCurry, because it provides hard evidence to support previous anatomy-based conclusions about the lion’s diet.

Such analyses help researchers to understand the ecological role of extinct carnivores, adds Gavin Prideaux, who studies prehistoric marsupials at Flinders University in Adelaide, Australia.

But he argues that fossils of T. carnifex are sometimes found in what are thought to have been arid and semi-arid regions, suggesting that the animal was a habitat generalist that lived in a variety of environments. DeSantis’s study relied on teeth collected from eastern Australia, which was probably more dominated by forests than was the more arid western half of the continent. This might have skewed the results, he says.

DeSantis acknowledges the lack of data from Western Australia. But she says that of all the teeth sampled across the eastern states, “every single one demonstrates the consumption of prey from forest environments”, making it clear that in this region, the marsupial lion was a woodland specialist.

The conclusion that climate change made the marsupial lion more vulnerable to extinction is “perfectly reasonable”, says Alistair Evans, a palaeontologist at Monash University in Melbourne, Australia — especially given that researchers already thought that the disappearance of forests may have led to a reduction in populations of marsupial herbivores in the past few hundred thousand years. “The carnivores feeding on those are also going to reduce in population size and perhaps eventually go extinct,” Evans says.

DeSantis notes that there has been a very heated debate about whether humans or climate change are most responsible for the extinction of Australia’s large mammals. “I think that we really need to step back a little bit and better understand the palaeobiology and palaeoecology of a lot of these animals first, before we can really say for certain the potential cause of the extinctions,” she says.