Sunday, March 16, 2008

Tasmanian Devil, Most Powerful Bite Myth

I've now seen from several different sources the remarkable claim that the Tasmanian devil's bite force is the strongest of any living mammal. This assertion would be truly extraordinary if it were true. Unfortunately, it is not.

In reality, the bite force of lions, tigers, Grizzly and Polar Bears dwarfs that of the Tasmanian Devil. The Tasmanian Devil's bite is also less powerful than that of the Mountain Lion, Leopard, Gray Wolf and Jaguar and only about half that of the Spotted Hyena. In fact, the idea that a 26 pound marsupial has the strongest bite of any living mammal seems strange indeed. One has to wonder where this odd notion came from. The idea is actually a misunderstanding of a scientific study published in Proceedings of the Royal Society (Series B), Bite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa.

A comparison of bite force from 39 living and extinct species is given in Table 1. The column, CBS (N) is the actual bite force. We can plainly see that the bite force of the Tasmanian Devil, Sarcophilus Harrisii, is 418 which is less than that of, say, Lycaon Pictus, the African Hunting Dog at 428. Both of these are dwarfed by the bite force of the African Lion at 1,768. Clearly, the Tasmanian Devil isn't even in the running for the title of highest bite force for a living mammal.

The confusion comes from the last column, BFQ, Bite Force Ratio. This value is given as CBS (N) / BoM (kg) = BFQ, or Bite Force divided by Body Mass equals Bite Force Quotient. Now, we can see that the Tasmanian devil has a bite force ratio of 181. The African Lion only has a bite force ratio of 112. The Jaguar is closer at 137. The reason why the Tasmanian Devil has such a high bite force ratio is twofold: First, the Tasmanian Devil is a scavenger and needs a strong bite to break bones. Secondly, the Tasmanian Devil has a very large head in proportion to its body. In older adult males the head can be one quarter of the entire body weight. No real predator would be very effective with such a high head ratio. In other words, the large head size of the Tasmanian Devil makes it a poor predator. The enlarged jaw muscles needed to generate the proportionately large bite force of the Tasmanian Devil also interfere with brain size. For example, although the raccoon is similar in size to the Tasmanian Devil the raccoon has a brain 2 1/2 times larger. Although the smaller brain of the Tasmanian Devil makes it less intelligent than the raccoon its oversized olfactory bulbs give it an enhanced sense of smell as would benefit a scavenger in locating carrion.

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