Thylacoleo carnifex, the marsupial lion, was the largest meat-eating mammal known from Australia, approaching the weight of a lioness. It was no lion. Its ancestors ate plants, its closest living relatives are koalas and wombats, and it had almost no canine teeth. It lived across the whole continent, was a top predator for nearly 2 million years, and disappeared about 40 000 years ago.
A carnivore from a family of leaf-eaters
Owen named it in 1859 from a damaged skull and called it among the most destructive of predators. Few agreed. Its skull and teeth were laid out like those of koalas and wombats, so Flower took it for a plant-eater, and it was later credited with diets of crocodile eggs, carrion, cycad nuts and native cucumbers. Broom answered that an animal with no grinding teeth could not have lived on plants. Skeletons found since 1966 have settled it as a specialist meat-eater. Its family tree is still moving: a 2025 collagen study placed it closer to the koala than to anything else sampled, a result its authors call a novel hypothesis.
Blades instead of fangs
The true canines were stubby. In their place the first incisors grew large, the lower pair lying almost horizontal, and the third premolars became long shearing blades, relatively larger than the cheek teeth of any other mammalian carnivore. In a 2005 model by Wroe and colleagues, a 109 kg Thylacoleo bit with about 1 692 N at the front of the jaw, close to the 1 768 N of a 295 kg lion. For its size that was the highest of any large predator studied. A 2018 university summary is lower, at about 80 per cent of a large lion, and all these figures are calculated from skulls, not measured.
How it used the teeth is disputed. The Australian Museum describes stabbing incisors. Janis argued that the upper incisors wore blunt and met tip to tip, so they could grip skin but not pierce it. The blades may have opened wounds, or the jaws may have delivered a crushing or suffocating throat bite.
The thumb
Each hand had a semi-opposable thumb bearing a hooked claw in a sheath, on an arm whose elbow combined weight-bearing with wide rotation of the forearm, a mix not seen in living placental carnivores. The Australian Museum suggests the claw may have disembowelled prey. Wroe and Sansalone are sceptical: they put it at no more than 28 mm, too short to kill large animals, and say it looks big mainly because the other finger claws were small. Janis still judged Thylacoleo able to bring down prey larger than itself, hunting alone. A Diprotodon forearm bone from near Glen Innes, New South Wales, has blade-like tooth marks, which could mean predation or scavenging.
Claw marks in the dark
Tight Entrance Cave in south-western Australia shows how it moved. It used the cave off and on between about 140 000 and 51 000 years ago, and thousands of claw marks cover steep rock faces up to 3.3 m high. Most seem to come from young animals, and Arman and Prideaux concluded in 2016 that marsupial lions climbed well and raised their young in caves. A near-complete skeleton from Moree, New South Wales, fits: an adult female found with a pouch baby and an older juvenile. Of more than 10 000 bones in the cave, few if any carry its tooth marks.
In 2018 Wells and Camens described the first complete tail, almost half the length of the backbone, and a rigid lower back. They compared the build to a Tasmanian devil’s and pictured a stealth hunter and scavenger that braced on its tail to free its forelimbs. No one has proposed it as a habitual tree dweller.
A forest hunter in a drying land
Among its youngest reliably dated fossils are bones from South Walker Creek in Queensland, 40 100 ± 1 700 years old, from the same deposit as the last megalania and Diprotodon. Tooth chemistry offers the most specific account of its end. A study led by DeSantis, presented at a conference in 2018, found from 35 samples from eastern Australia that it hunted mainly in forests rather than open country, which suits an ambush predator. Australia began drying about 350 000 years ago, and on this reading the hunter lost its cover as forests thinned, outlasting the arrival of people but not the climate. Others read the habitat differently: Nullarbor finds suggest open, arid country, and the role of people remains debated. Whether people painted it is contested too. Akerman and Willing reported a striped animal in Kimberley rock art as Thylacoleo in 2009, while Welch and Lewis conclude such figures are probably thylacines.
