The sirenians

Sirenians or “sea cows” are the only aquatic mammals that are exclusively herbivorous; they are seaweed grazers. They live in the world’s warm waters and today are represented by only four species belonging to two families: manatees (Trichechidae, three species), which are found in the coastal waters of the tropical Atlantic and in Amazonia, and dugongs (Dugongidae, a single species), which live on the coasts of the Pacific. A fifth species, the enormous Steller’s sea cow (8 m in length) of the Arctic seas, a skeleton of which can be seen in the Gallery of Comparative Anatomy, was hunted to extinction in the 18th century.

The term “sirenian” was born out of confusion among early observers regarding the dugong and the mermaids of mythology. The sirenians are not related to other marine mammals (cetaceans and pinnipeds). Sea cows are instead related to elephants with whom they form the Tethytheria group.

The oldest known sirenians (Pezosiren, Prorastomus) date to about 48 million years ago and still possess 4 legs suitable for walking on land. They evolve over the course of the Eocene and Oligocene: the fore limbs become robust flippers, the rear limbs reduce in size and the tail is transformed into a powerful horizontal caudal flipper. 

Fossilised sirenian bones have been identified since the days of Buffon, who referred to them as “sea cows”. The Oligocene genus Halitherium, notably Halitherium schinzii, is close to the common ancestor of dugongs and manatees. Metaxytherium cuvieri was named in honor of George Cuvier, who described the first Sirenian fossil from the Loire. Metaxytherium, which was quite common in the Miocene and Pliocene of Europe, is placed close to the origin of dugongs.

Halitherium schinzii
Kaup, 1838
MNHN.F.ALL
Mammalia, Afrotheria, Paenungulata, Tethytheria, Sirenia, Halitheriinae
Oligocene, Approximately 30 million years ago
Azey, Rhineland-Palatinate, Germany

This sirenian skeleton belongs to a stem group close to the common origin of dugongs and manatees. It has been reconstructed from several fossil bones discovered in Germany.

Halitherium lived in the warm coastal waters to the west of the European archipelago, in the ancient Tethys Ocean.

Donated by Mr Lepsius, Director of Darmstadt Museum.

Metaxytherium cuvieri
Christol, 1832
MNHN.F.FS
Mammalia, Afrotheria, Paenungulata, Tethytheria, Sirenia, Dugongidae
Miocene, 20 to 15 million years ago
Doué-la-Fontaine, Maine-et-Loire, France

This almost complete fossil skeleton of a sirenian was discovered at Doué-la-Fontaine in the Maine-et-Loire, France. In 1921 it was presented to the Muséum national d’Histoire naturelle and named Metaxytherium cuvieri in honour of George Cuvier who described the first sirenian fossil from the Loire.

Metaxytherium cuvieri lived in the Mediterranean Sea and in the Paratethys. Metaxytherium is an extinct genus close to the origin of dugongs. Fairly common in the European Miocene and Pliocene, it is represented by numerous widely distributed species.

Donated by Marcel and Victor Chatenay.