Family Dugongidae (Dugong)

[Extract] The Dugongidae is one of four families within the Sirenia, a mammalian order with a long evolutionary history extending back more than 50 million years. The sirenians are ancestrally related to a superficially dissimilar grouping of other mammals known as the Afrotheria. The afrotherians contain some modern families such as Proboscidea (elephants), Afrosoricida (golden moles and tenrecs), Tubulidentata (aardvarks), Hyracoidea (hyraxes), and Macroscelidea (elephant shrews). The closest contemporary relatives of sirenians are the elephants and hyraxes, and the three groups have been linked together as the clade Paenungulata. At least 35 named species of sirenians have existed through time, ranging in mass from small sea cows weighing an estimated 150 kg to the extinct Steller's Sea Cow (Hydrodamalis gigas) estimated to have weighed more than 10,000 kg. Some early sirenians walked on land with sturdy hindlimbs but fed on aquatic vegetation. Later forms evolved a variety of foraging strategies, adapting to changing climatic, geologic, oceanographic, a n d biological conditions within the bounds of aquatic megaherbivory. Today only two sirenian families remain: the Trichechidae, containing the three species of manatees that occur on both sides of the Atlantic, and the Dugongidae, with one species, tl1e Dugong, which occurs in the Indo-West Pacific. The ancestors of these families diverged 25-40 million years ago. The dugongids were by far the most diverse group of sirenians. The family Dugongidae is divided into three subfamilies: the Halitheriinae, the Dugonginae, and the Hydrodamalinae. The extinct Halitheriinae was the basal group of the dugongids. The Dugonginae arose from them and diversified in the Caribbean and western Atlantic in the Oligocene. They dispersed to other tropical waters of the world in the late Oligocene and early Miocene. A partial postcranial skeleton (vertebrae and ribs) of an indeterminate sirenian has recently been described from a cave in the Hindenburg Range, Western Province of Papua New Guinea. These fossils represent the earliest evidence (c.11·8 million years ago) of Sirenia in Australasian coastal marine ecosystems