Otters as big as lions, there were. As big as grizzly bears.

Atlas Obscura introduces us to Enhydriodon omoensis, a newly classified prehistoric otter that roamed the Omo river valley of Ethiopia, hunting its prey and weighing more than 400 pounds with jaws strong enough to crush bone:

While the study calls the otter “lion-sized,” paleontologist Margaret Lewis of Stockton University in New Jersey, who first analyzed some of the fossils in 2008*, thinks “that’s kind of underselling it.” “Bear otter,” she says, is perhaps a better term to encapsulate just how massive these otters were. Okay, grizzly otter it is.

But the otter’s massive size wasn’t the only thing that surprised the lead author of the study, carnivore specialist Camille Grohé of the University of Poitiers in France. Testing on oxygen and carbon isotopes collected from the otter’s teeth shows that, unlike its semi-aquatic modern descendants, Enhydriodon omoensis lived primarily on land. “I really did not expect that,” says Grohé.

For about three weeks, Grohé worked in the museum’s basement, analyzing the hundreds of Omo carnivore fossils. “I was not just looking at otters,” she says. “I was looking at overall diversity [and] checking if the specimens we had in the database also matched the specimens we had in the drawers.”

Eventually, she came across a “weird” femur, the same one paleontologists uncovered back in the 70s. In a previous study, Lewis had identified that the femur came from a very big prehistoric otter. But that wasn’t the only thing that made this femur a little weird. “It was really, really long and that didn’t really match an aquatic mammal,” which have generally shorter femurs to help the animals swim.

Collaborating with [Columbia University’s Kevin] Uno, Grohé and a team of scientists extracted small amounts of enamel from the Enhydriodon omoensis’s teeth, which they tested for carbon and oxygen isotopes. Grohé was surprised to find that the isotopes were from largely terrestrial sources. “It was feeding on a wide range of [land-based] prey,” says Grohé; the patterns were similar to those found in big cats and hyenas today. But whether the otter was hunting or scavenging, Grohé isn’t sure.

You can read more of Grohé’s study here, in Comptes Rendus Palevol.