Wroe and his colleagues noted similar adaptations in Australia's extinct marsupial lion.
Previous studies indicate that expanded brain volume in predatory mammals leaves less room for jaw muscles. So does a smaller brain signal a stronger bite force? "As a generality, this is what our findings suggest," Wroe said. "But we need to do more work before we can be sure."
The paleontologist says the brain volume of placental carnivores is about two and a half times larger, on average, than that of pouched carnivores. This may help explain why many marsupials register so high on the study's relative bite scale.
The study lends further weight to Wroe's claim that marsupial lions were far more fearsome than many scientists previously thought.
Thylacoleo carnifex was first described by the distinguished British fossil expert Sir Richard Owen in 1859. Owen, who coined the word dinosaur, believed his latest discovery represented the "fellest [fiercest] and most destructive of predatory beasts."
Scientists later downgraded the catlike animal to the role of a bit player in the Pleistocene food chain, partly because the marsupial lion lacked obviously fanged teeth and had plant-eating ancestors.
More recent work based on fossil evidence done by Wroe and other Australian scientists, however, is now helping to reestablish the ancient lion's fearsome reputation.
"There has been some dispute over interpretations about how Thylacoleo lived [and] what it was related to," said Marcelo Sánchez-Villagra, a paleobiologist at the Natural History Museum in London. "This latest research goes back to Richard Owen's original ideas. These animals were top predators."
Sánchez-Villagra said the South American equivalent of marsupial lions were borhyaenidsmeat-hungry marsupials that resembled present-day hyenas and cats. Borhyaenids had canine teeth adapted for stabbing and flesh-slicing molars. Placental mammals invading from the north later replaced the southern marsupial carnivores.
Wroe, the Australian paleontologist, said it isn't necessarily the size or shape of a predator's canine teeth that's important in gauging the size of their prey. Rather it's the strength of the predator's jaws.
"In fact, when killing very large prey, such as cape buffalo, a lion's teeth often don't even break the skin," he added. "Big prey are killed through slow suffocation."
Wroe said the marsupial lion might well have used "its massive bolt cutter-like cheek teeth to scissor through the windpipe or vital blood vessels of big animals. This would have hastened the demise of the prey, adding rapid major blood loss to asphyxiation."
Bite force can help shed light on the predatory behavior other extinct carnivores, Wroe added. For instance, the extinct saber-toothed cat Smilodon fatalis was shown to have surprisingly weak bite strength relative to its size. This suggests that the predator relied on its formidable fangs to inflict fatal trauma.
The findings of the new study may apply to other living animals. For example, such knowledge may help conservationists to better predict the outcome of interactions between species.
"Previously, body mass has been the single best predictor of direct interaction between competing predators," Wroe noted. "Our results suggest that relative bite force is more accurate still."
Some have proposed reintroducing Tasmanian devils to mainland Australia from Tasmania to help suppress feral fox and cat populations. "In one-to-one situations, our results suggest that the devil would easily prevail and even give dingoes [wild dogs] a run for their money," Wroe said.
When it comes to battles of the biters, don't bet against marsupials delivering the fatal blow.
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