Desmostylians were bizarre, tusked aquatic mammals that defy simple classification in the animal kingdom.

Nature · Published 3 October 2026 Swipe more like this →

In short: Imagine a creature with the body of a hippo, the teeth of a pipe organ, and a lifestyle that remains a mystery. Desmostylians were the only known extinct order of marine mammals, roaming the North Pacific for millions of years before vanishing into the annals of evolutionary history.

Desmostylia, named for their unique molars that resemble bundles of columns or pipes, were fully aquatic quadrupeds that inhabited the North Pacific from the Early Oligocene to the Late Miocene. Their existence spanned roughly 33.9 to 5.3 million years ago, though phylogenetic models suggest they may have first appeared as early as 47 million years ago. These animals were entirely unlike any living creature, possessing massive limbs, short tails, and a specialized feeding mechanism that involved rooting up plants with tusks and powerful neck muscles before using throat suction to ingest them.

The taxonomic placement of these mammals has been a subject of intense debate for over a century. Traditionally, they were grouped with afrotherian clades like manatees and elephants, but this assignment was always problematic given their exclusive presence along the Pacific Rim. Modern analyses, including a 2014 study, suggest their similarities to sirenians and proboscideans might be a result of convergent evolution, potentially placing them instead as basal perissodactyls. Their skeletal structure, once thought to be semiaquatic, is now widely considered to be fully aquatic, with limbs incapable of supporting their weight on land.

The extinction of the order remains a complex puzzle. While they successfully navigated previous cooling periods, the severe Middle to Late Miocene cooling events likely strained their survival. Furthermore, evidence suggests that competition with sirenians—specifically the genus Hydrodamalis—played a critical role in their terminal decline. As these specialized marine herbivores appeared in the North Pacific, the desmostylians, which shared similar dietary niches, were gradually replaced. By the end of the Miocene, this unique order had disappeared, leaving behind only fossilized remnants of their strange, column-like teeth and robust skeletons.

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