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."
