Sirenia

The Sirenia ( ), commonly referred to as sea cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The extant Sirenia comprise two distinct families: Dugongidae (the dugong and the now extinct Steller's sea cow) and Trichechidae (manatees, namely the Amazonian manatee, West Indian manatee, and West African manatee) with a total of three species.

species of extinct mammal

Dugongidae is a family in the order of Sirenia. The family has one surviving species, the dugong (Dugong dugon), one recently extinct species, Steller's sea cow (Hydrodamalis gigas), and a number of extinct genera known from fossil records. thumb|Dugong skeleton displayed at Philippine National Museum

Trichechidae is a family of sirenians that includes all living manatees and several extinct genera.

development from a Tethytherian ancestor and radiation of species

REDIRECT Dugongidae

thumb|Skull dome of Stegoceras (AMNH 5450) showing cross-section thickness