Rare Otter Fossil Found in the Mexican Desert

The newfound teeth may help solve a mystery about how the water-loving mammals made it across the continent six million years ago.

In a surprise to palaeontologists, ancient teeth discovered in the hot scrublands of central Mexico belong to a water-loving otter that roamed North America six million years ago.

Found 120 miles from the nearest coastline, the fossil opens up an entirely new discussion about the movements of mammals across the continent millions of years ago.

The teeth belong to an extinct otter species called Enhydritherium terraenovae, says Jack Tseng at the University of Buffalo, whose team describes the find this week in the journal Biology Letters. This species had previously been found only in coastal regions in Florida and California, suggesting it was dependent on coastal environments like its modern relatives.

A group of northern sea otters gather in Katmai National Park, Kodiak Island, Alaska.
PHOTOGRAPH BY ROY TOFT, NATIONAL GEOGRAPHIC CREATIVE

A sea otter rides the surf in Monterey Bay, California.
PHOTOGRAPH BY PAUL NICKLEN, NATIONAL GEOGRAPHIC CREATIVE

This fossil jawbone found in Mexico belonged to the extinct otter species Enhydritherium terraenovae.
PHOTOGRAPH BY JACK TSENG, UNIVERSITY AT BUFFALO

In March, Tseng and his colleagues were in the land-locked Juchipila Basin in central Mexico, looking for fossils that will help explain a time period beginning around six million years ago when mammals were frequently migrating between North and South America.

While in the field, graduate student Adolfo Pacheco-Castro, from the National Autonomous University of Mexico, came to him with an unusual specimen.

“I knew it was some kind of weasel family member, but otter never crossed my mind,” Tseng says.

Sea otter mother and pup grooming themselves on Moss Landing, Monterey Bay, California.
PHOTOGRAPH BY FRANS LANTING, NATIONAL GEOGRAPHIC CREATIVE

A sea otter finds sanctuary in the Homer boat harbour in Alaska.
PHOTOGRAPH BY PAUL NICKLEN, NATIONAL GEOGRAPHIC CREATIVE

In Alaska, sea otters are dying from toxic algae blooms.
PHOTOGRAPH BY PAUL NICKLEN, NATIONAL GEOGRAPHIC CREATIVE

Finding otter fossils anywhere is already a feat, says Robert Boessenecker, a palaeontologist at the College of Charleston who was not involved with the study.

“Any otter specimens, in general, are as rare as hen’s teeth,” Boessenecker says.

But finding evidence of Enhydritherium in Mexico is even more remarkable. Previous fossils suggest the Americas were seeing massive north-to-south migrations during this time—now, this singular fossil indicates there was possibly some east-to-west movement going on, too.

“Based on what we know about living otters, they need to be close to the water,” Tseng says.

Finding Enhydritherium on both coasts and now in between means this otter may not have been living only in coastal regions but could have used smaller bodies of water to make its way from coast to coast. Tseng points out that the shape of limb bones from Florida specimens suggest the animal was not specially adapted to marine life and had the ability to move easily over land.

A view of the fossil site in the Juchipila Basin in Mexico, where the ancient otter teeth were discovered.
PHOTOGRAPH BY JACK TSENG, UNIVERSITY AT BUFFALO

Sea otters resting in Moss Landing, Monterey Bay, California.
PHOTOGRAPH BY FRANS LANTING, NATIONAL GEOGRAPHIC CREATIVE

Sea otter relaxes near boathouse in Homer, Alaska.
PHOTOGRAPH BY PAUL NICKLEN, NATIONAL GEOGRAPHIC

The discovery also works against a previous hypothesis that the ancient otters took a more circuitous ocean migration route between coasts, Boessenecker adds.

Many more surprises are probably waiting to be uncovered in the rocks of central Mexico, Tseng notes because not much paleontological field exploration has been done there.

“It just goes to shows you how one find can completely change how you interpret the ecology of an extinct species.”

Header Image: A live sea otter finds sanctuary in the Homer boat harbour in Alaska. PHOTOGRAPH BY PAUL NICKLEN, NATIONAL GEOGRAPHIC CREATIVE

Discuss this article

Newsletter

Never miss a Nat Geo moment

Your email address
Submit