Discovery of Ontocetus posti: An Ancient Marine Mammal and Its Evolutionary Significance

The Discovery of Ontocetus posti: An Ancient Marine Mammal

Approximately two million years ago, a sizable mammal made its way through the North Atlantic Ocean, eventually hauling its substantial body onto a beach, its stomach filled with clams. At first glance, one might think this creature resembled a walrus. However, the extinct animal belonged to an entirely different genus of marine mammals, showcasing evolutionary distinctions as stark as those between a fox and a dog.

In a groundbreaking study published in the journal PeerJ Life & Environment, researchers reveal that despite the significant evolutionary differences, this walrus relative may have employed a remarkably similar foraging technique known as suction feeding. Mathieu Boisville, a paleontologist from the University of Tsukuba in Japan and one of the authors of the study, remarked that it is quite rare to observe two large marine animals developing such analogous adaptations, a phenomenon referred to as convergent evolution.

The creature, named Ontocetus posti, belongs to a group of marine mammals that originated around five million years ago along the Pacific Coast of North America, later dispersing into the Atlantic Ocean through the yet-to-close seaway connecting North and South America.

While most fossils from this group are primarily located along the southeastern shores of the United States, over the years, both amateur fossil hunters and professional paleontologists have unearthed fragments of skulls and lower jaws along the North Sea’s coasts and seabed. These significant finds were primarily around the areas of Antwerp in Belgium and Norwich in England. Initially, these remains were categorized as a distinct species, known as Ontocetus emmonsi.

Upon closer examination of the fossils, Boisville and his team identified that the jaw structure bore a striking resemblance to that of modern walruses, rather than their southern relatives. Similar to its close relatives, Ontocetus posti possessed an array of teeth, which included lower incisors and a prominent lower canine. Notably, its robust chin bones were fused together, mirroring the anatomical features of contemporary walruses.