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 carnivorenamely 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 Earthit 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 reptileswhich require less food than their warm-blooded counterpartsfilled 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 dogthe 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 daya giant monitor lizard called Megalania priscaseemed 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 spotthe greater body weight certainly evens the playing field."
Thylacoleo was a committed hypercarnivoreit wasn't a scavenger, it was designed to kill.
Thylacoleo had two types of teethone 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 crunchinga 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 optatumat 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 calculatedusing the amount of muscle, the direction in which the muscle pulls, and the length of the jawthe 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 wayperhaps 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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National Geographic Channel
The 'Extinct' Series Airing on the National Geographic Channel