Imagine a manatee walking around on land. Let that image sink in for a moment. It's ridiculously adorable, the plump mammal seemingly out of its element. But back in the Eocene, over 40 million years ago, we know that early relatives of manatees were doing just that. That's because we've found walking sirenians.

Paleontologists have known about walking manatee ancestors for a while. The most famous of all is Pezosiren, named in 2001 from fossils found in Jamaica. But this sirenian wasn't the only one, and now paleontologist Ester Díaz-Berenguer and colleagues have named the first quadrupedal dugong relative from the roughly 40 million-year-old strata of the Bay of Biscay.

Known from a skull and osteological elements of at least six individuals, Sobrarbesiren cardieli is a beast of two worlds. Parts of the skeleton, like the cranium, are the spitting image of their modern counterparts. And some of the bones of Sobrarbesiren are denser than those of purely terrestrial mammals, a condition that acted as bone ballast to help this mammal achieve neutral buoyancy in water. But Díaz-Berenguer and coauthors also found enough of the front and rear limbs to know that Sobrarbesiren still had legs capable of support this ancient mammal on land. This was an amphibious manatee, able to shuffle between water and the shore. If only we could have seen them in life. Perhaps then we'd have the Calming Stem Sirenian to help us get through the work week.

Sirenian
The skull of Sobrabesiren. Credit: Díaz-Berenguer et al 2018

Name: Sobrarbesiren cardieli

Meaning: Sobrarbesiren means "siren from Sobrarbe", in reference to where the mammal was found, and cardieli honors its discoverer Jesús Cardiel Lalueza.

Age: Eocene, about 40 million years old.

Where in the world?: Huesca, Spain. 

What sort of organism?: A sirenian, or relative of today's manatees and dugongs.

How much of the organism’s is known?: A skull and skeletal elements of at least six individuals.

Reference:

Díaz-Berenguer, E., Badiola, A., Moreno-Azanza, M., Canudo, J. 2018. First adequately-known quadrupedal sirenian from Eurasia (Eocene, Bay of Biscay, Huesca, northeastern Spain). Scientific Reports. doi: 10.1038/s41598-018-23355-w

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