Trichechus, Dugong, Dusisiren, Sobrarbesiren and Prorastomus

Prorastomus sirenoides (Owen 1855; Middle Eocene, 40 mya; 1.5m in length) is a basal sirenian with four legs of even length, a short tail and more teeth. Derived from Moeritherium and Castoroides, a giant beaver.

Sobrarbesiren cariedli (Díaz-Berenguer 2018; Eocene, 47mya) is a basal sirenian with four legs, a short tail and teeth. The anterior dorsals are taller and the pelvis is longer. The caudal vertebrae have ventral processes. The cervicals are shorter. The forelimbs are larger than the hind limbs.

Dusisiren reinharti (Donning 1978) is a recently extinct dugong adapted to cold waters. Tusks and hind limbs are absent here. This was a slow-swimming herbivore, derived from beavers and Moeritherium.

Trichechus manatus (Liinneaus 1758) is the extant manatee dugong adapted to warm waters of the Carribbean and Atlantic coast of the Americas. Note the large number of cheek teeth here colorized with three molars, but all have molar shape and the new one replaces the old one from back to front, as in elephants, which they greatly resemble in the skull.

Dugong dugon (Lacépède 1799) is the extant dugong, native to SE Asian waters. Note the small number of cheek teeth.

Díaz-Berenguer E et al. 2018. First adequately-known quadrupedal sirenian from Eurasia (Eocene, Bay of Biscay, Huesca, northeastern Spain. Scientific Reports. 8 (1): 5127.

Domning DP 1978. Sirenian evolution in the North Pacific Ocean. University of California Publications in Geological Sciences 118:1-176.

de Lacépède BGE 1799. Tableau des divisions, sous-divisions, ordres et genres des mammifères. Paris: Plassan. [Originally issued as a pamphlet dated “L’An VII de la République”

Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

Owen R 1855. On the fossil skull of a mammal (Prorastomus sirenoïdes, Owen) from the island of Jamaica. The Quarterly Journal of the Geological Society of London 11:541-543.

Self-Sullivan C. Evolution of the Sirenia.

wiki/Dusisiren
wiki/Prorastomus
wiki/Evolution_of_sirenians
wiki/Sobrarbesiren
wiki/Manatee
wiki/Dugong