Ancient Hippo-Sized Mammal Was A Suction Feeder

2862 Ancient Hippo-Sized Mammal Was A Suction Feeder
Discovery of the new genus and species from Unalaska indicates the desmostylians were a successful group that were larger and more diverse than previously known. Artwork by Ray Troll

A toothy, hippo-sized mammal who ate like a vacuum cleaner ambled North Pacific shorelines about 23 million years ago. Called Ounalashkastylus tomidai, the new genus and species belonged to the order Desmostylia, the only order of marine mammals to ever go completely extinct. The findings were published this month in Historical Biology.

The fossils, which came from at least four individuals, were recovered from an Aleutian island called Unalaska. The animal had a long snout with tusks, and their tooth and jaw structure indicate that they were vegetarians that ripped out marine algae, sea grass, and other near-shore plants – and then literally sucked them up into their mouths. “The new animal – when compared to one of a different species from Japan – made us realize that desmos do not chew like any other animal,” Southern Methodist University’s Louis Jacobs says in a statement. “They clench their teeth, root up plants and suck them in.” 


They would buttress their lower jaw with their columnar teeth against their upper jaw, while big muscles in the neck powered the tusks and big muscles in the throat helped with suction. “No other mammal eats like that,” Jacobs adds. “The enamel rings on the teeth show wear and polish, but they don’t reveal consistent patterns related to habitual chewing motions.”

The stocky-limbed animals likely swam in a similar way to polar bears with their powerful forelimbs. And on land, they probably lumbered along like sloths. “Ounalashka,” means “near the peninsula” in the Aleut language, and “stylus” is Latin for “column,” referring to the shape of the cusps of their teeth. The species name honors a Japanese vertebrate paleontologist. Also, a group of desmostylians is called a troll, a designation that honors artist Ray Troll. 

Unalaska is the farthest north any desmo has ever been found. The group is only known from the North Pacific: from Baja California, up along the west coast of North America, around the Alaska Peninsula and the Aleutian Islands, and over to Russia’s Kamchatka Peninsula and Sakhalin Island and the Japanese isles. 

One of the fossils of this newest desmo belonged to a baby. “The baby tells us they had a breeding population up there,” Jacobs explains. “They must have stayed in sheltered areas to protect the young from surf and currents.” Adults were big enough to be safe from predators. Study co-author Anthony Fiorillo from the Perot Museum of Nature and Science adds: “The baby also tells us that this area along the Alaska coast was biologically productive enough to make it a good place for raising a family.”


However, unlike all other marine mammal orders, this one went totally extinct. Every single desmostylian lived and died between 33 million and 10 million years ago. While short-lived, they were a successful group with greater biodiversity than we previously thought.

Image Credit: Ray Troll




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