For information about the Gothic Metal band, see Sirenia (band)
Sirenia are herbivorous mammals of coastal waters. They have evolved aquatic adaptations: they have arms, which are modified into paddles, but no legs, are fat, and have highly modified skulls with greatly reduced dentition. Their nipples are under their arms (see the picture of a pair of manatees).
The Trichechidae differ from the Dugongidae in the shape of the skull and the shape of the tail.
Paleontological evidence as well as recent biochemical evidence, reveal that Sirenians, together with the Proboscideans (elephants), Hyracoidea (hyraxes) and Tubulidentata (aardvarks) represent four living orders of mammals that are sometimes lumped together as "subungulates", which derived from a primitive ungulate ancestral stock.
The sirenians reached a peak of diversity during the Oligocene and Miocene epochs (55 mya).
Sirenians were most diverse in the Miocene (5-25 mya) when tropical conditions were widespread.
Thereafter during the Pliocene and Pleistocene, sirenians are represented in Florida by abundant remains of fossil manatees (Trichechus sp.).
Stable isotopic analyses were performed on 100 teeth of fossil sirenians and extant Trichechus manatus from Florida in order to reconstruct diets (as determined from [delta]^sup 13^C values) and habitat preferences (as determined from [delta]^sup 18^O values) and test previous hypotheses based on morphological characters and associated floral and faunal remains.
One of the two modern sirenian families, the Dugongidae, with an extant monotypic genus of hypergrazer, the dugong (Dugong augon), is widely distributed in coastal marine waters throughout the subtropical and tropical Pacific and Indian Oceans (Walker 1975; Husar 1978a).
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