Prehistoric mammals wouldn't have messed with this huge otter

The wolf-size otter lived in a shallow swamp surrounded by thick vegetation. (Mauricio Antón)

Six million years ago, the shallow swamps of what's now southern China may have been dominated by massive, 110-lb. (50 kilograms) otters that have since gone extinct.

And now, researchers have found that these hefty otters had more than size on their side. Turns out, this animal had a powerful bite, six times stronger than was expected from size alone and strong enough to crush big mollusk shells or the bones of birds and small mammals, the researchers noted in a new study.

"None of the modern otters are top predators," said Jack Tseng, the lead researcher on the study and a functional anatomist at the University at Buffalo. "They don't attack large prey, because physically, they're not that big. We think this fossil otter was like the bear of its environment — one of the top predators," he told Live Science. [See images of the fearsome wolf-size otter]

Fossil fragments of the otter, Siamogale melilutra, were discovered several years ago, but it was only recently that Tseng and his colleagues scanned and ran computational models on the digitally reconstructed skull. The objective: to figure out how this wolf-size otter lived.

According to Tseng, that's one of the two big questions that paleontologists try to answer: "What is it?" and "How did it live?" (Although Tseng often goes into the field to find new fossils, he wasn't involved in the expedition that uncovered S. melilutra.)

To figure out the strength of the otter's jaw, Tseng's team ran computational simulations to see how biting would strain its jaw. They did the same for modern otters, and found that smaller otters had stiffer — and, therefore, more powerful — jaws, and larger otters had more flexible jaws. Based on these findings, they calculated that the ancient otter was an abnormal powerhouse, having a jaw strength that was six times what would be estimated based on the animal's body size.

"When we observed other animals, we saw that living species still followed the trend," said Tseng, who expanded his models to include information from other predators, such as bears and wolves. "So, in this case, the sea otter stood out."

Only one other animal broke from the link between body size and jaw stiffness: another extinct predator called Kolponomos newportensis, an aquatic bear that lived in the Pacific Northwest 20 million years ago. Even though the two animals were separated by the Pacific Ocean, the habitats of both predators were abundant with hard-shelled mollusks, Tseng explained. "So that's one line of evidence pointing to this fossil otter being a large consumer of mollusks with its jaw size and strength," he said.

But Tseng's models can't definitively explain how the prehistoric otter lived. Rather, they provide some possibilities of what it might have been capable of doing. For example, Tseng said, fossils of the animal show that its jaws were strong enough to break open mollusks, but that doesn't mean it didn't also hunt smaller mammals or fish. Because the fossil wasn't found with prey in the animal’s mouth, there's no direct evidence indicating what the creature ate.

To figure out exactly where the fossilized otter fit into the food web, researchers would need to run a chemical analysis of the otter's tooth enamel. That analysis could reveal whether it was an apex predator or a predator somewhere in the middle of the food web, Tseng said. That analysis would involve grinding the teeth down into a fine powder — and the fossil is so rare that researchers aren't willing to do that.

"We don't want to risk it," Tseng said.

The researchers detailed their findings today (Nov. 9) in the journal Scientific Reports.

Original article on Live Science.