Extinct walrus-like mammal that sucked prey in prehistoric times discovered

Fossil evidence has led to the identification of a new prehistoric mammal with similarities to modern walruses.

The fossil, which dates from 1.7 to 2.2 million years ago, was discovered in Lower Pleistocene layers of the North Atlantic.

A team of paleontologists led by Mathieu Boisville of the University of Tsukuba (Japan) discovered that the fossil belonged to a previously unknown species.

The newly identified fossilized species has been named Ontocetus posti. Interestingly, this new species shares striking feeding similarities with modern walrus (Odobenus rosmarus) .

“Ontocetus has been identified as close relatives/cousins of the modern walrus. A unique feature of the modern walrus is that it uses the suction-feeding technique,” Boisville told Interesting Engineering (IE) .

Boisville added: “The evolutionary history of walruses is shaped by their specialization in suction-feeding, particularly within the small group (the tribe Odobenini) to which the modern walrus belongs.”

Suction-feeding technique

The walrus has evolved a specialized feeding way that allows it to efficiently extract food from hard-shelled prey.

Ontocetus had four post-canine teeth, a bigger lower canine, and a fused, shorter jaw, which was strikingly similar to its present-day relatives.

These features indicate Ontocetus posti was a suction feeder, but less specialized than modern walruses.

“Modern walrus uses its lips to capture the mollusk and employs its tongue like a piston to extract the flesh from the shell and suck it in. The walrus’s palate is arched to facilitate the pressure and the amount of water in its oral cavity. The fact that the modern walrus has a fused mandible and reduced teeth allows it to minimize the tensile and compressive forces that the oral cavity—and therefore the skull and mandible—undergo during suction-feeding,” explained Boisville.

Similar feeding styles in Ontocetus and contemporary walruses suggest convergent evolution.

Species extinct due to global cooling

As per the press release , the fossils of this new species were discovered in Norwich, United Kingdom, and Antwerp, Belgium.

Initially, the fossils were identified as belonging to another extinct walrus species, Ontocetus emmonsi. However, a detailed inspection of the jawbones revealed that they belonged to a new species.

The Ontocetus genus traveled from the Pacific to the Atlantic around the Mio-Pliocene period. Ontocetus embarked on an epic journey through the Central American Seaway to conquer the Atlantic.

“ Ontocetus posti was probably restricted to the North Sea basin. Ontocetus (and Ontocetus emmonsi ) migrated from the western Pacific (coast of Japan) around 5.3 million years ago and colonized the North Atlantic very shortly afterward, probably via the Central American Seaway. After colonizing along the east coast of the USA, they migrated towards the North Sea and Morocco during the late Pliocene, undoubtedly dictated by successive glacial-interglacial cycles,” he explained to IE.

Ontocetus faced insurmountable obstacles when glacial cycles intensified, Arctic ice increased, and mollusk distribution changed as a result of global cooling. This eventually led to the extinction of the species.

The rise of the modern walrus can be traced back to these turbulent times. As Ontocetus disappeared, the walrus thrived and diversified due to its greater adaptation to colder temperatures.

This study highlights how environmental shifts influenced walrus evolution and marine mammal survival.

“The beautiful thing about walruses (which include Ontocetus posti ) is that they are one of the lineages of marine mammals (along with cetaceans) that can tell us about past climate change,” Boisville concluded.

Although reduced to a single species today, the walrus lineage was once remarkably varied, occupying vast regions for millions of years. Their sensitivity to climate change makes them valuable indicators of past environmental conditions.

The findings have been reported in the journal PeerJ Life & Environment .