Extinct Australian "Lion" Was Big Biter, Expert Says

Bijal P. Trivedi
National Geographic Channel
March 5, 2004
Two million years ago bizarre creatures roamed the Australian
continent—the flesh-eating giant rat-kangaroo, the thunder bird,
the marsupial wolf, and a giant monitor lizard. But these animals have
never taken center stage in the public's imagination or even the
scientific community like the large prehistoric creatures of other
continents—in part, because a poor fossil record revealed few
specimens that looked either large or ferocious.

Now a recent study suggests that one creature—with a bite that may rival that of most predatory mammals—may have been sorely misjudged.

Until it died out about 30,000 years ago, Thylacoleo carnifex—or "pouched lion executioner"—was Australia's reigning mammalian predator. According to a recent study, Thylacoleo was not only a much larger predator than previously believed but also the most specialized mammalian carnivore of all time.

A team of Australian scientists led by Stephen Wroe, a specialist in marsupial carnivore evolution at the University of Sydney, used a new method to estimate the size of this long-extinct predator. A subsequent series of experiments explored its "bite force"—essentially measuring how much pressure its jaws could exert on the head or neck of another creature during a kill. Results suggest few creatures would have survived its bite.

Using about a dozen fossilized skulls from T. carnifex, Wroe and his colleagues determined the species's brain volume, which was used to calculate overall body size. The "lion" was determined to be about 215 pounds (98 kilograms). While that's not as big as a saber-toothed cat or even a living lion or tiger—it is twice as large as previous estimates that pegged T. carnifex as being the size of a leopard. The work was published late last year in the journal Paleobiology.

"Body weight is one of the most significant aspects of an animal's biology—it radically alters how we perceive its role and its impact on the ecology," Wroe said.

Lump of Muscle and Bone

Thylacoleo was an ambush predator—"just a lump of muscle and bone, and powerfully built," Wroe said. "It had a build that was closer to a bear than a cat. It probably preyed on slow but large prey. This creature was built to wrestle—its arm bones were twice as thick as a leopard's, and its skull was as wide as it was long."

Wroe's team recognized that for marsupials (like koalas, wombats, and kangaroos) brain size could be used to estimate overall body weight. (The method is not as effective with placental mammals—like humans—whose evolution has been marked by spectacular brain growth.)

The Thylacoleo weight derived from brain size is consistent with another previous estimate based on measuring the circumference of the femur and humerus—another method used to calculate weight.

"The fact that these methods arrive at approximately the same weight suggests that we have nailed the size of this animal," Wroe said.

"Wroe's paper is impressive," said Ernest Lundelius, a retired paleontologist at the University of Texas at Austin. "It is one of the most thorough reviews on estimating body weight based on material in the fossil record."

A Wimpy Heritage

Thylacoleo's size and position in the pecking order of the Pleistocene epoch has been a point of contentious debate since Richard Owen, a renowned 19th-century paleontologist, first described the animal in 1859. Owen described the "lion" as the "fellest [or fiercest] and most destructive of predatory beasts." But Thylacoleo was descended from plant-eating marsupials, so people doubted its predator status.

"People basically thought it had a wimpy heritage. And it lacked the stereotypical hallmark of a carnivore—namely a set of large canines," Wroe said.

Thylacoleo's carnivore status was finally confirmed in the early 1980s with the discovery of a retractable claw and the simple fact that the animal didn't have the teeth to process plants. "You basically couldn't design a worse skull for eating plants," Wroe added.

But while science acknowledged that Thylacoleo was a carnivore, its size and rank on the food chain was uncertain.

Large warm-blooded predators are scarce in Australia. Some scientists believe this was always the case. "Australia is the flattest, most nutrient-poor continent on Earth—it may have simply been too nutrient poor to support large animals like mammoths," Antoni Milewski said. Milewski is an ecologist who specializes in nutrition and biogeography and is affiliated with the University of Cape Town in South Africa.

Shrinking Lions, Expanding Lizards

In 1994 Tim Flannery, Director of the South Australian Museum and a professor at the University of Adelaide, hypothesized that poor soils and a climate that was erratic for about 20 million years led to a scanty supply of food. That small food supply couldn't provide for big mammalian plant-eaters. In turn, the small size of plant-eaters (which would have been prey to carnivores) stunted the size and diversity of Australian carnivores that evolved. Flannery suggested that giant reptiles—which require less food than their warm-blooded counterparts—filled the niche of top predators.

Perhaps influenced by Flannery's ideas in the last decade, scientists donwgraded the marsupial "lion" into more of a pouched leopard or something the size of a dog—the scientific literature lists a range of weights spanning 44 to 440 pounds (20 to 200 kilograms). Most estimates seemed to hover around 110 pounds (50 kilograms).

Conversely, size estimates of the ruling reptile of the day—a giant monitor lizard called Megalania prisca—seemed to grow. Megalania is often cited, erroneously, to be 2,200 pounds (1,000 kilograms). Wroe has refuted this figure. He believes that Megalania varied between 200 and 330 pounds (90 and 150 kilograms), about the size of a Komodo dragon.

"The [previous Megalania weight figure] has been fitted with a pre-existing theory, and nobody has rocked the boat [until Wroe]—the body mass for Megalania has gone up and the body mass for Thylacoleo carnifex has gone down," Christine Janis said. Janis studies the evolution and paleobiology of vertebrates at Brown University in Providence, Rhode Island.

Wroe's research suggests that Thylacoleo was a formidable predator and a much more robust animal than previously thought, Janis said. "The greater weight of the animal also suggests that we should rethink the idea that you couldn't get large mammalian predators in Australia."

That Thylacoleo was bigger than previous estimates reinforces Wroe's hunch that the animal must have been close to the top of the food chain, Ernest Lundelius said. "I think Thylacoleo is probably competing with Megalania for the top spot—the greater body weight certainly evens the playing field."

Dental Records

Thylacoleo was a committed hypercarnivore—it wasn't a scavenger, it was designed to kill.

Thylacoleo had two types of teeth—one for killing and one for slicing meat. Its carnissials (basically vertical shearing blades) could slice through muscle, hide, and sinew. There was no capacity for bone crunching—a trait of scavengers. Its retractable, switchblade-like claws on its thumbs worked as grappling hooks to bring an animal to the ground, Wroe said.

Fossil evidence even reveals Thylacoleo tooth marks on the bones of Diprotodon optatum—at about 6,200 pounds (2,800 kilograms) Diprotodon was the biggest marsupial in history. While it may not have been able to tackle the adult Diprotodon, Thylacoleo attacked juveniles, evidence shows.

In a series of preliminary experiments Wroe and his colleagues have calculated—using the amount of muscle, the direction in which the muscle pulls, and the length of the jaw—the power of Thylacoleo's bite force.

"This creature had enough power to crush a human skull," Wroe said. "It had a bite force more than two and a half times that of a spotted hyena."

Thylacoleo was a top carnivore that probably occupied a similar niche to a medium-sized saber-toothed cat like Smilodon californicus, which lived in North America in the Pleisocene epoch. Today it would probably be comparable in strength to a lioness, Wroe said.

Milewski disputes the comparison. While he agrees with Wroe's new weight estimates for Thylacoleo, he said that the comparison to a saber-toothed cat is incorrect.

"Marsupials have a slow metabolism, slow growth, and a slow reproduction rate. Thylacoleo may have been the top predator, but it wasn't a superpredator capable of fast ferocious attacks on large prey," Milewski said. "This is not Australia's answer to the saber-tooth cat. The animal didn't have saber teeth. And it certainly doesn't resemble a lioness in its hunting style."

Anyone expecting the lightning-fast attacks of a lion or tiger would be sorely disappointed, according to Milewski. "More likely, these were brauny, thick-set creatures that were not particularly bright and hunted in a very energy-efficient way—perhaps by frightening marsupial mothers into sacrificing their young by tossing them from the pouch."

Regardless of how Thylacoleo hunted, Wroe believes it held its own at the top of the food chain.

For its body size, Thylacoleo probably ate about ten times the amount as Megalania. The lion also had a much greater geographical range. Fossils of Thylacoleo are found throughout Australia, whereas Megalania had a smaller range that was heavily influenced by temperature.

Given its range, the "pouched lion" probably had a much greater impact on the ecology than the monitor lizard or other carnivores of the time. Whether Thylacoleo was a superpredator or not, it was uniquely Australian.

For more on Thylacoleo, watch Extinct!: Super Predators. The episode premieres Monday, March 8, at 9 p.m. ET/10 p.m. PT and is available only on the National Geographic Channel.

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