how the canines of carnivorous mammals evolved into super-killers

Carnivorous animals come in all shapes and sizes, from the 500 gram quoll to the 500 kilogram polar bear. This disparate group of mammals share a common characteristic: canines in the front of their jaws.

The canines are long and pointed, with a sharp point and, in some cases, blade edges. These formidable weapons are what make carnivores such effective killers. In fact, our new research released today reveals how evolution has shaped dogs into unique shapes suited to the lifestyle of each predator.

We applied state-of-the-art 3D methods to measure the canines of more than 60 predators, including lions, cheetahs, grizzly bears, dingoes and Tasmanian devils. The research represents the first comprehensive analysis of canine tooth shape in predatory mammals.

We have found that canine teeth have evolved in special ways to help each species kill and eat their favorite prey, helping to make mammals one of nature’s most efficient predators.

Born to kill

When carnivorous mammals growl, they reveal four long canines in the front of their jaws – two at the top and two at the bottom. These teeth are the first point of contact between predator and prey, and are used to stab, kill, and dismember a socket.

Not all carnivores have the same diet. Grizzly bears eat meat, fruits, and plants, while meerkats feed primarily on invertebrates like scorpions and beetles. Big cats, like cheetahs, stick to meat.

Carnivores can kill in multiple ways as well. Tigers smother their prey with a targeted bite to the throat, while wolves use multiple sharp bites to tear their prey apart. Small canids such as the red fox scramble and violently shake their prey, while wolverines can kill with a single crushing skull bite.

There has been little research on the associations between the shape, function and evolution of canine teeth. Our research aimed to determine which canine shapes are best for each predator diet.

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A bite worse than its bark

We scanned and compared the canines of over 60 carnivores, including tigers, coyotes, polar bears, wolverines, raccoons, and even quolls. We then examined the association between canine shape and function.

We have found that the shape of the teeth varies depending on the types of food a carnivore bites in on a regular basis, just as we choose different kitchen knives based on what we want to cut.

Big cats such as lions, tigers, and cheetahs have some of the sharpest canines in the animal kingdom. These long, dagger-like weapons are used to stab – bite deep into the throats of prey to bring them down.

Take a 3D look at a cheetah’s canines in the interactive below.

Other species, such as the coyote and the red fox, have slender, curved canines. These teeth act as hooks to help hold small prey and prevent them from sliding out of the mouth when shaking.

Animals that eat a lot of “soft” prey, or those that bite the throat, often have thin, pointed canines. The sharp tips make a crack in the prey and when the animal bites, the long, sharp edges of the tooth help to penetrate deep into the socket.

Species with harder or more varied diets have strong, sturdy teeth that do not break when cracking bones or other hard foods. These species include scavengers such as the Tasmanian devil and generalists such as the honey badger.

The bluntest upper canine tips we have examined belong to the crab-eating mongoose. As the name suggests, the species feeds on crabs and other hard prey such as reptiles, snails, and insects.

We have also found canine teeth with blunt tips and edges in animals that kill their prey with crushing skull bites, such as the American swallow or wolverine. Blunt tips are better able than sharp tips to withstand the stresses produced by such heavy force.

Something to chew on

Research is helping to make new connections between tooth shape and ecology that may shed light on the diet and behavior of extinct species.

For example, the thylacine (or Tasmanian tiger) had curved canines, suggesting that it may have grabbed and shaken smaller prey. This supports recent research on thylacine skull shape which found that, unlike previous theories, thylacine likely hunted small preys rather than large ones.

By studying canine teeth closely, we discovered how evolution has shaped even the smallest animals to fit the niches they fill in nature.

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