July 2, 2013
Ancient Sabre-Like Toothed Predator Had Weaker Bite Than Domestic Cat
April Flowers for redOrbit.com - Your Universe Online
Millions of years ago, a bizarre, pouched super-predator terrorized South America with huge saber-like teeth. New research from the University of New South Wales (UNSW), however, shows the Thylacosmilus atrox had a bite weaker than that of a domestic cat.
Marsupials in Australia and America are among the closest living relatives of the extinct T. atrox, which had tooth roots extending rearwards almost into its small braincase. "Thylacosmilus looked and behaved like nothing alive today," says UNSW palaeontologist Dr. Stephen Wroe, who led the research team.
"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."
Smilodon fatalis, the iconic North American saber-tooth "tiger" is often regarded as the archetypal super-predator mammal.
A true cat, Smilodon, however, was just the end result of at least five independent experiments in saber-toothed evolution during the Age of Mammals that lasted some 65 million years.
Of those five evolutionary lines, the Thylacosmilus atrox is the best preserved species of the pouched saber-tooths that terrorized South America until about 3.5 million years ago. The huge canine teeth of the Thylacosmilus were larger than those of any other known saber-toothed animal for its size.
There has been a long-standing controversy surrounding Smilodon's killing behavior, but recently scientists have begun to agree that the powerful neck and jaw muscles played an important role in driving the saber-teeth into the necks of large prey. In contrast, the predatory behavior of Thylacosmilus was fairly unknown.
Dr. Wroe and his international team of researchers constructed and compared sophisticated computer models of Smilodon and Thylacosmilus, along with a living conical-toothed cat, the leopard, to shed light on this super-predator mystery. The computer models were digitally "crash-tested" in simulations of biting and killing behavior, and the results were published in a recent issue of PLoS ONE.
"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," says Dr Wroe. "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 [175-220 lb.] '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."
Dr. Wroe says the bottom line is that the huge saber teeth of Thylacosmilus were driven home by the neck muscles alone. Because saber-teeth were actually quite fragile, Wroe suggests this must have been achieved with surprising precision.
"For Thylacosmilus - and other saber-tooths - it was all about a quick kill," said Wroe. "Big prey are dangerous -- even to super-predators -- and the faster the kill the less likely it is that the predator will get hurt -- or for that matter attract unwanted attention from other predators.
"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," says Dr Wroe.