Ethiopia once had lion-sized otters

In the 19th century, paleontologists collected many bones and teeth that they could not identify. Some of them came from rich Ethiopian deposits deposited up to 4.5 million years ago. Now, after 150 to 180 years in storage, some of these fossils have been identified as coming from giant otters that weighed over 200 kilograms (440 pounds) and co-existed in the region with our ancestors.

The new species took so long to identify itself because we are very far from having a complete skeleton. An article in the French journal Palevol Reports brings together two partial jaws, a few teeth, and a leg bone to describe a new species which the authors named Enhydriodon omoensis, while assigning other scattered otter bones found at the same location to the genus Torolutra.

Giant otters are a long-established feature of the Pliocene and Late Miocene eras. Enhydriodon dikikaea resident of the Afar region in Africa, was already described as having the size of a lion when it was scientifically described in 2011, but E.omoensis is even bigger.

A reconstruction of E. omoensis compared to the silhouettes of living otters, a modern human female, and an Australopithecus. Image credit: © Sabine Riffaut, Camille Grohé / Palevoprim / CNRS – University of Poitiers

The most familiar of the 13 surviving otters might be the Eurasian otter, but the subfamily spans a surprising range of sizes. Eurasian otters typically weigh up to 17 kilograms (37.5 pounds), but the Asian small-clawed otter weighs only 2 to 6 kilograms (4.4 to 13.2 pounds), while the sea otter from the North Pacific can reach 45 kilograms (99.2 pounds).

The extinct genus Enhydriodon has been found in many places across eastern Africa and sometimes beyond, with at least six species living in the eastern rift system. E.omoensis was found in the Lower Omo Valley, Ethiopia, north of Lake Turkana, where the oldest stone tools were made 3.3 million years ago.

Fossils of Australopithecines have been found in the same Omo Formation, and subsequently early humans also lived in the area; Homo sapiens may even have evolved there. E.omoensis would have been a competitor to Australopithecines for food, and possibly early humans if it had survived a bit longer, even if it hadn’t eaten them directly.

Moreover, it was not a fearsome beast that our ancestors could avoid by staying out of the water.

“What is special, in addition to its massive size, is that [isotopes] in its teeth suggest that it was not aquatic, like all modern otters,” said Dr Kevin Uno from Columbia University in a statement. “We found out that he had a diet of land animals.”

The conclusion is based on the fact that plants store different ratios of carbon isotopes depending on their growing conditions and photosynthetic pathways. Herbivores incorporate the proportions of the plants they feed on, which in turn go into making carnivores, including their bones and teeth.

Uno and his co-authors are convinced that the other bones found in the same formation belong to the genus Torolutra, which resembled modern river otters and lived primarily on fish. They also describe a bone fragment they believe to be from a large Enhydriodon, but cannot identify the species.

Charles P. Patton