Thylacosmilus atrox – an extinct, bizarre, marsupial super-predator that roamed South America about 4 – 3 million years ago – had huge saber-like teeth but its bite was weaker than that of a domestic cat, says new research reported in the open-access journal PLoS ONE.

“Thylacosmilus looked and behaved like nothing alive today,” said lead author Dr Stephen Wroe, a paleontologist with the University of New South Wales.

“To achieve a kill the animal must have secured and immobilized large prey using its extremely powerful forearms, before inserting the saber-teeth into the windpipe or major arteries of the neck – a mix of brute force and delicate precision. The iconic North American saber-toothed ‘tiger’, Smilodon fatalis, is often regarded as the archetypal mammalian super-predator.”

“However, Smilodon – a true cat – was just the end point in one of at least five independent ‘experiments’ in saber-tooth evolution through the Age of Mammals, which spanned some 65 million years.”

Thylacosmilus atrox is the best preserved species of one of these evolutionary lines – pouched saber-tooths that terrorized South America until around 3.5 million years ago. For its size, its huge canine teeth were larger than those of any other known saber-tooth.

Smilodon‘s killing behavior has long attracted controversy, but paleontologists now mostly agree that powerful neck muscles, as well as jaw muscles, played an important role in driving the saber-teeth into the necks of large prey. Little was known about the predatory behavior in the pouched Thylacosmilus.

Dr Wroe with colleagues constructed and compared sophisticated computer models of Smilodon and Thylacosmilus, as well as a living conical-toothed cat, the leopard. These models were digitally ‘crash-tested’ in simulations of biting and killing behavior.

“We found that both saber-tooth species were similar in possessing weak jaw-muscle-driven bites compared to the leopard, but the mechanical performance of the saber-tooths skulls showed that they were both well-adapted to resist forces generated by very powerful neck muscles,” Dr Wroe explained.

“But compared to the placental Smilodon, Thylacosmilus was even more extreme.”

“Frankly, the jaw muscles of Thylacosmilus were embarrassing. With its jaws wide open this 80-100 kg super-predator had a bite less powerful than a domestic cat. On the other hand – its skull easily outperformed that of the placental Smilodon in response to strong forces from hypothetical neck muscles.”

“Bottom line is that the huge sabers of Thylacosmilus were driven home by the neck muscles alone and – because the saber-teeth were actually quite fragile – this must have been achieved with surprising precision.”

“It may not have been the smartest of mammalian super-predators – but in terms of specialization – Thylacosmilus took the already extreme saber-tooth lifestyle to a whole new level,” Dr Wroe concluded.

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Bibliographic information: Wroe S et al. 2013. Comparative Biomechanical Modeling of Metatherian and Placental Saber-Tooths: A Different Kind of Bite for an Extreme Pouched Predator. PLoS ONE 8 (6): e66888; doi: 10.1371/journal.pone.0066888