Extinct Hippo-Like Creature Discovered Hidden in Museum: 'Sheer Chance'

Evidence of a bizarre hippo-like creature that lived millions of years ago has been discovered "by sheer chance" hidden away in one of the nation's most famous museums.

Paleontologist Kumiko Matsui, affiliated with the Smithsonian National Museum of Natural History in Washington, D.C., uncovered a single uncatalogued tooth in the institution's vast collections.

The tooth turned out to belong to a strange and enigmatic group of extinct marine mammal species known as Desmostylus, according to a study published in the journal Royal Society Open Science. These unusual creatures have primarily been found in the North Pacific, in places such as California and Oregon.

"It is thought to have been a hippopotamus-like animal that lived in the sea," Matsui told Newsweek. But despite the physical similarities to the hippopotamus, these shovel-jawed animals with short tusks may have lived similar lives to sea lions.

"These animals were herbivorous marine mammals that probably ate seaweed like today's dugongs," Matsui said. "Desmostylus lived in a wide variety of shallow sea environments, from cold sea to hot sea."

Among the strangest feature of Desmostylus is its teeth, which are unlike those found in any modern mammal.

The Smithsonian's natural history collection is the largest in the world, holding almost 150 million objects which are used for research and education purposes. The collection consists of plants, animals, fossils, minerals, rocks, meteorites, human remains and human artifacts.

When Matsui began a postdoctoral position at the Smithsonian in the summer of 2021, she took the opportunity to examine some of the cabinets containing fossils.

"Fortunately, while opening the top drawer of one cabinet, I stumbled upon a single unnumbered Desmostylus tooth and a photograph, by sheer chance," Matsui said. "The fossil doesn't have Smithsonian's museum number, but it includes handwritten notes."

From these field notes, Matsui and her Smithsonian colleague, Nicholas Pyenson found that the tooth was discovered during a U.S. Geological Survey expedition in the 1960s conducted in the upper part of the Schooner Gulch geological formation near Point Arena, in northern California. Based on the discovery location, the shape of the fossil and other factors, the researchers identified the tooth as representing the genus Desmostylus.

In addition, the team found that it is among the oldest Desmostylus fossils ever found. This particular specimen is believed to have lived between around 23 million and 22 million years ago, toward the earliest part of the Miocene geological epoch.

The tooth displays characteristics that are primitive within its wider animal family, known as the Desmostylia, according to the authors of the study.

"Our Desmostylus includes only one weird, big molar," Matsui said. "After its death, the body was scattered before the fossilization process."

While the tooth has differences from all other known Desmostylia fossils, it's not currently clear whether this fossil represents a previously documented or undescribed species.

"It's difficult to describe a new species only from a single tooth," Matsui said.

The tooth in question is "huge," measuring around 2.5 inches by 1.5 inches, the researcher said.

"The tooth is dark brown, shiny and heavy," she said. "There are six big, high structures like a column known technically as cusps. Enviably, the enamel is thick and appears to have a low risk of decay."

The latest discovery is significant because while many Desmostylus discoveries have been made across the U.S. West Coast, most of these were found around Southern California and the Portland, Oregon area, according to Matsui.

Most fossils to date have been found in formations dating to the middle of the Miocene period, when the Earth was very warm and suitable for marine mammals, rather than the early part of this epoch.

Correction, 06/19/23, 08:32 a.m. ET: This story was updated to correct the pronouns of Kumiko Matsui.