Saber teeth in predators evolved many times. Did it lead to their extinction?

In the history of teeth, perhaps no tooth is as famous as the saber tooth.

These long, blade-like canines seem almost perfectly optimized to kill prey. They've evolved at least five times in mammals, most notably in the saber-tooth cat Smilodon, who sported serrated sabers that could measure nearly one foot long.

But behind the fearsome appearance of saber teeth lies a conundrum.

"They're probably really fragile," says paleontologist Emily Rayfield, of the University of Bristol. "In some animals these extremely elongate canines were really sharp, but they're probably also quite prone to breakage."

Generally speaking, canines have two main jobs that can sometimes be at odds.

"They need to be sharp enough to puncture and slice things. But on the other hand, they need to be strong enough to avoid breakage when they're doing that job," says Rayfield. Saber teeth took this tradeoff to the extreme, Rayfield and her colleagues report in Current Biology, becoming about as good as they could be at puncturing prey, ultimately sacrificing durability.

That peak performance may have ultimately led to the downfall of saber-toothed predators, the researchers suggest.

The research team came to this conclusion after analyzing nearly 100 canine teeth that spanned the super-sharp to super-sturdy spectrum, including saber-toothed cats, snow leopards, wolverines and panda bears. First, they tested each tooth's durability using the same sort of computer modeling that engineers use to test the strength of different materials.

"Whereas you can do this for cars and bridges, you can also do it for teeth," says Rayfield.

To measure puncture performance, the team turned to actual experiments. They created a stainless steel 3D model of each tooth, which then "bit" down into gel, allowing them to measure the force required for each bite.

"It's kind of like a really stiff Jell-O," says Rayfield. "You can imagine that really sharp teeth don't need much force to go through the gel, whereas really blunt teeth need a lot of force to go through the gel."

Combined, these data revealed the relative strength and puncture performance of all these teeth. Saber teeth, it turned out, were stretched to extremes for puncture performance

"They'd all evolved towards this shape which made them really good at puncturing, but probably to the point where they were as good as they could be, to resist breakage," says Rayfield. "Any increase in resisting breakage would mean their puncture performance would got worse."

Given saber teeth's strengths and relative weakness, saber-toothed predators likely targeted soft tissues, Rayfield suggests. Those advantages helped saber-toothed cats, including Smilodon, to become apex predators of their time. But the specialization that brought them to such heights may have ultimately led to their downfall, Rayfield suspects, as no saber-toothed creatures exist today.

The results "made us think about whether they'd actually kind of reached a sort of pinnacle in performance that meant that when the environment changed or when there were new predators on the scene, like humans, for example, these animals were simply not able to adapt and change," she says.

In some ways, saber teeth represent an evolutionary pinnacle, the optimal design for a canine tooth to puncture prey, says Rayfield. But they also show how getting too good at one thing can sometimes be an evolutionary dead end.