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 Sirenia comprise the families Dugongidae (the dugong), Trichechidae (manatees), Protosirenidae (Eocene sirenians), and Prorastomidae (terrestrial sirenians). Currently, four species of sirenians exist. Sirenians are classified in the clade Paenungulata, alongside the elephants and the hyraxes, and evolved in the Eocene 50 million years ago. The Dugongidae diverged from the Trichechidae in the late Eocene or early Oligocene.