Sabre-toothed cats had weak bites

This article is reposted from the old Wordpress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I'll return with fresh material.

The sabre-toothed cat is one of the most famous prehistoric animals and there is no question that it was a formidable predator, capable of bringing down large prey like giant bison, horses, and possibly even mammoths. The two massive canines - the largest teeth of any mammal - are a powerful visual. But while they were clearly powerful weapons, scientists have debated their use for over 150 years.

Now, a new study shows that Smilodon, the most iconic of the sabre-tooths, had a surprisingly weak bite. They were a precision weapon that were used to deliver a single, final wound to an already subdued victim - the equivalent of an assasin's stiletto rather than a swordsman's blade.

Earlier suggestions pictured Smilodon using its teeth to hang onto the back of large prey, to slash their abdomens open, or to impale them at the end of a flying pouce. One of the most popular theories said that the cat would have used its teeth to sever arteries and airways with a decisive bite to the throat - a quicker technique than the suffocating neck bites used by modern lions.

Working out how strongly Smilodon could bite would go a long way towards deciding on one of these theories and to do that, palaeontologists have studied the animal's fossilised skull. Even then, opinions have gone either way depending on which bit of the skull they looked at. The muscle attachment points suggest it has small jaw muscles, but the bite could have been powered from the neck. The lower jaw is smaller, but strongly built, lending weight to the idea of a powerful bite.

To get some clearer answes, Colin McHenry and colleagues from the University of Newcastle, Australia decided to put Smilodon's skull through a digital crash-test. They used a technique called 'finite element analysis' or FEA, which is typically used in mechanical engineering and crash-testing for cars.

They used a CT scanner to create detailed 3-D models of the skulls of a Smilodon from the famous La Brea Tar Pits in Los Angeles, and a lion from the Taronga Zoo in Sydney. With both predators weighing in fairly equally (the lion was particularly large and the sabre-tooth particularly small), McHenry assumed that they would have tackled similarly sized prey. The team also simulated the jaw and neck muscles of both animals, and put them through a series of simulated bites on the computer.

In terms of skull power, the lion outclassed Smilodon in almost every way. The 'king of beasts' happily chomped down with a force of over 3000N (or 300kg), but a 229kg Smilodon only managed a measly 1000N. It's jaws were remarkably under-powered for a cat of its large size and bulk, biting with the same amount of force as a jaguar about a third of its size. But the powerful neck muscles were factored in, Smilodon's bite force increased to a more respectable 2000N - clearly, this was a predator that bit from the neck.

But even with its restored reputation, McHenry's analysis also found that Smilodon couldn't have bitten prey on the run. Lions will frequently latch onto running buffalo, and its skull is built to handle the massive forces that would push and twist against it. Even with 2000N (200kg) of force pushing sideways on a lion's canines, the teeth experience minimal stress. Not so with Smilodon - subjected to the same forces, it's entire skull experienced tremendous stress and strain. If it tackled large prey that were still on their feet, it would have run a strong risk of snapping its teeth or skull.

The sabre-toothed cat's relatively wussy bite rules out a lot of the theories for its killing style. It couldn't possibly have tackled running prey and slashing at the belly would have left it vulnerable to snapping teeth if the prey tried to get back up. Smilodon's only real option was to use its teeth to deliver a killing bite when there was no chance of the prey actually moving. It was a one-use weapon, reserved for prey that had been brought down and pinned, preferably at the head, by the cat's enormous bulk.

Fortunately, the rest of the animal was superbly adapted for this. Smilodon had a physique that was more bear than cat and it had over-sized 'dew claws' on its 'thumbs'. All of these traits would have given it enough power and inertia to bring down large animals in a way that modern lions simply can't do. Lions often kill with a lengthy suffocating bite that can last for up to 13 minutes. In Smilodon's case, the fate of the downed animal would have been sealed in seconds, especially if the sabre teeth severed the carotid artery.

McHenry speculates that Smilodon's technique could have evolved because of intense competition from other large predators. With fearsome animals like dire wolves, the short-faced bear and the immense American lion on the prowl and ready to fight over a carcass, Smilodon had little time for a long drawn-out kill.

While its bulk and huge teeth would have made it well adapted for hunting large prey, McHenry thinks that that Smilodon, unlike modern cats, would have been woefully inadequate at killing smaller and more agile animals. When the large herbivores of the last Ice Age all died out, Smilodon would have been unable to compete with more versatile killers.

More on finite element analysis: 

• Prehistoric great white shark had strongest bite in history
• Venomous Komodo dragons kill prey with wound-and-poison tactics

Reference: McHenry, Wroe, Clausen, Moreno, & Cunningham. Super-modeled sabercat, predatory behaviour in Smilodon fatalis revealed by high-resolution 3-D computer simulation. 2007. PNAS 104: 10610-10615.