Steller's manatee was the largest vegetarian sea creature that humans have ever encountered: with an estimated body length of up to ten meters, it could probably weigh more than ten tons.

While manatees only inhabit tropical to subtropical waters these days, Steller's manatee, scientifically named

Hydrodamalis gigas , froliced

, on the frigid coasts of the North Pacific.

In 1741, naturalist Georg Wilhelm Steller came across this peculiar marine mammal.

While traveling with Vitus Bering on an expedition in the North Pacific, he was shipwrecked on the way back and stranded on the largest island in the commander group.

There he had to overwinter and endure until the late summer of 1742.

The fact that at least half of the crew survived this time despite the adverse weather was also thanks to the manatees, which were later named after Steller.

They provided tasty meat for the hungry men, and their fat was as good for food as it was for lamp oil.

Steller estimated the population inhabiting the shallow water areas around what is now known as the Bering Island to be around a thousand animals.

In the area surrounding the entire archipelago there must have been no more than a few thousand at that time.

In the years that followed, seal hunters and fur traders repeatedly headed for the Commander Islands in Bering's footsteps.

There they also imitated Steller's manatee so eagerly that the imposing sea mammals were completely exterminated three decades after their discovery.

This ended an evolutionary line in which manatees had also conquered cold sea areas.

Only a few samples of enormously thick skin remain, a few largely complete skeletons, and scattered bones.

At the molecular genetic level, an international team of researchers has now been able to identify adaptations that Steller's manatee had developed for its special habitat: geneticists led by Diana Le Duc from the University of Leipzig, Akhil Velluva from the Max Planck Institute for Evolutionary Anthropology in Leipzig and Molly Cassatt-Johnstone from the University of California at Santa Cruz extracted and analyzed DNA from bones of the extinct manatee.

For comparison, they used the genomes of living manatees and other mammals.

nightmare of ichthyosis

As Le Duc and her colleagues report in the journal Science Advances, it turned out that the genes for two specific lipoxygenases in Steller's manatee stopped working: a premature stop signal prevented the molecular machinery that normally produces the blueprints for these enzymes from doing their job work to complete.

In humans, gene variants that sabotage production of the lipoxygenases in question can cause congenital ichthyosis.

Such skin diseases are characterized by the fact that the top layer of skin, which consists of dead cells, is much thicker than usual.

Those affected suffer from dry, often cracked skin from which clearly visible scales are peeling off.

Steller's manatee apparently presented as a true nightmare of ichthyosis.

Steller, who was the first and only European to study this species alive, compared the top layer of skin with the bark of an old oak tree.

The manatee, which was once also known as the bark animal, probably not only benefited from the fact that the horny layer, which was sometimes more than two centimeters thick, offered a certain degree of protection against heat loss.

Such skin was probably so hard-wearing that the massive animals could venture into rocky shallow water zones with impunity to graze on seaweed.

Even swimming between ice floes probably didn't do them any harm.