Wolf-Sized Otter With Powerful Jaws Was Dominant Predator of China Six Million Years Ago

What Siamogale melilutra might have looked like in its environment. Artwork by Mauricio Anton

Otters, whether river- or sea-dwelling, are just so darn cute, we can all agree—but if you were alive 6 million years ago, you might have wanted to consider avoiding a now-extinct Chinese otter named Siamogale melilutra that roamed lakes or swamps. Sure, it looks like any old river otter. Long tail, nice whiskers, cute li'l face, the works. But it weighed 110 pounds, almost as large as a wolf. And look more closely at the bones beneath that face and you'll realize something terrifying: those jaws are meant to crush.

That's according to a study published today in the journal Scientific Reports, which compared the jaws of Siamogale to those of its smaller relatives still living today. To do so, Jack Tseng, an evolutionary biologist at the University at Buffalo, and his colleagues scanned the lower jawbones of 11 different otter species.

Then, they created a 3-D computer model of each jawbone to analyze. That's not the same as working with the actual bones, but for Siamogale, the fossilized jawbone wouldn't act like bone anyway. "It would be essentially meaningless to try to conduct a physical experiment on the fossil because it's turned to rock," said Tseng.

Sea otters today use tools to make up for their weaker jaws. Yoshikazu Tsuno/AFP/Getty Images

So the computer model is the next best thing, and that's what the team used to test their guess that jaw strength would depend on what foods the species prefers. "You don't need to chew fish, you just sort of bite on it and swallow," Tseng said. That means they expected fish-breath otters to have weaker jaws than species that prefer eating things in shells, like molluscs or urchins.

But for the living otters, Tseng and his colleagues saw a totally different pattern: the smaller the jaw, the stiffer it was, no matter what sorts of food the animal eats. Until they looked at Siamogale, which had a jaw six times stronger than the team predicted based just on its size.

That means the giant otters would have been fully capable of crushing large shells, and they could have also snacked on birds and mammals. Tseng and his colleagues think that means Siamogale was a key predator in its ecosystem.

"Studies like this bring to life extinct animals," said Gregory Erickson, a paleontologist at Florida State University who has studied bite force in crocilians and wasn't involved in the study. "This animal was quite a shell-crusher, so to speak," Erickson said.

This sort of project represents a new way to look at fossils, which scientists have traditionally focused on classifying and dating and not much else. "It's a good parameter to understand the working end of an animal," Erickson said. "In paleontology, you're dealing with bones and teeth for the most part, so you don't have much to work with."

But there's no way to quantify exactly how much pressure Siamogale's bite could create. That's because all their measurements were made only on the simulations, so they're limited to comparing the relative strength of each species. While in theory, they'd love to measure live otters snapping down in order to turn that into an absolute strength, the otters are not so excited about the idea.

"Crocodiles are generally very happy to bite anything you put in their mouth," Tseng said. "Mammals are smarter, so they actually don't just bite anything."