Sirenia
Sirenia is an order of fully aquatic, herbivorous mammals that inhabit rivers, estuaries, coastal marine waters, swamps, and marine wetlands. The order evolved during the Eocene epoch, more than 50 million years ago. Sirenians, including manatees and the Dugong, have major aquatic adaptations: forelimbs have modified into arms used for steering, the tail has modified into a paddle used for propulsion, hind limbs (legs) are but two small remnant bones floating deep in the muscle. They appear fat, but are fusiform, hydrodynamic, and highly muscular. Their skulls are highly modified for taking breaths of air at the water's surface and dentition is greatly reduced. The skeletal bones of both the manatee and dugong are very dense which helps to neutralize the buoyancy of their blubber. The manatee appears to have an almost unlimited ability to produce new teeth as the anterior teeth wear down. They have only two teats, located under their forelimbs, similar to elephants. The elephant are thought as the closest living relative of the sirenians.
The three manatee species (family Trichechidae) and the Dugong (family Dugongidae) are endangered species. All four living species are vulnerable to extinction from habitat loss and other negative impacts related to human population growth and coastal development. Already the Steller's Sea Cow has been hunted into extinction by humans. Manatees and the Dugong are the only marine mammals classified as herbivores. Unlike the other marine mammals (dolphins, whales, seals, sea lions, sea otters, and walruses), sirenians eat primarily sea-grasses and other aquatic vegetation and have an extremely low metabolism and poor tolerance for especially cold water. Sirenians have been observed eating dead animals (sea gulls), but their diet is made up primarily of vegetation.  Like dolphins and whales, manatees and the Dugong are totally aquatic mammals that never leave the water  not even to give birth. These animals have been observed eating grass clippings from homes adjacent to water ways, but in this rare occurrence, only the top portion of the sirenia is lifted out of the water.  The combination of these factors means that sirenians are restricted to warm shallow coastal waters, estuaries, and rivers, with healthy ecosystems that support large amounts of seagrass and/or other vegetation.
The Trichechidae species differ from Dugongidae in the shape of the skull and the shape of the tail.
- ORDER SIRENIA
Genus Ishatherium
Ishatherium subathuensis
Family Prorastomidae
Genus Pezosiren
Pezosiren portelli
Genus Prorastomus
Prorastomus sirenoides
Family Protosirenidae
Genus Protosiren
Protosiren minima
Protosiren sattaensis
Protosiren fraasi
Protosiren smithae
Family Dugongidae
Genus ''Sirenotherium
Sirenotherium pirabense
Subfamily Dugonginae
Genus Dugong
Dugong, Dugong dugon
Subfamily Hydrodamalinae
Genus Dusisiren
Dusisiren dewana
Dusisiren jordani
Dusisiren takasatensis
Genus Hydrodamalis
Hydrodamalis cuestae
Steller's Sea Cow, Hydrodamalis gigas
Family Trichechidae
Genus Trichechus
West Indian Manatee, Trichechus manatus
Antillean Manatee, Trichechus manatus manatus
Florida Manatee, Trichechus manatus latirostris
African Manatee, Trichechus senegalensis
Amazonian Manatee, Trichechus inunguis
Dwarf Manatee, Trichechus bernhardi (validity questionable)
- Genus Ishatherium
Ishatherium subathuensis
- Ishatherium subathuensis
- Family Prorastomidae
Genus Pezosiren
Pezosiren portelli
Genus Prorastomus
Prorastomus sirenoides
- Genus Pezosiren
Pezosiren portelli
- Pezosiren portelli
- Genus Prorastomus
Prorastomus sirenoides
- Prorastomus sirenoides
- Family Protosirenidae
Genus Protosiren
Protosiren minima
Protosiren sattaensis
Protosiren fraasi
Protosiren smithae
- Genus Protosiren
Protosiren minima
Protosiren sattaensis
Protosiren fraasi
Protosiren smithae
- Protosiren minima
- Protosiren sattaensis
- Protosiren fraasi
- Protosiren smithae
- Family Dugongidae
Genus ''Sirenotherium
Sirenotherium pirabense
Subfamily Dugonginae
Genus Dugong
Dugong, Dugong dugon
Subfamily Hydrodamalinae
Genus Dusisiren
Dusisiren dewana
Dusisiren jordani
Dusisiren takasatensis
Genus Hydrodamalis
Hydrodamalis cuestae
Steller's Sea Cow, Hydrodamalis gigas
- Genus ''Sirenotherium
Sirenotherium pirabense
- Sirenotherium pirabense
- Subfamily Dugonginae
Genus Dugong
Dugong, Dugong dugon
- Genus Dugong
Dugong, Dugong dugon
- Dugong, Dugong dugon
- Subfamily Hydrodamalinae
Genus Dusisiren
Dusisiren dewana
Dusisiren jordani
Dusisiren takasatensis
Genus Hydrodamalis
Hydrodamalis cuestae
Steller's Sea Cow, Hydrodamalis gigas
- Genus Dusisiren
Dusisiren dewana
Dusisiren jordani
Dusisiren takasatensis
- Dusisiren dewana
- Dusisiren jordani
- Dusisiren takasatensis
- Genus Hydrodamalis
Hydrodamalis cuestae
Steller's Sea Cow, Hydrodamalis gigas
- Hydrodamalis cuestae
- Steller's Sea Cow, Hydrodamalis gigas
- Family Trichechidae
Genus Trichechus
West Indian Manatee, Trichechus manatus
Antillean Manatee, Trichechus manatus manatus
Florida Manatee, Trichechus manatus latirostris
African Manatee, Trichechus senegalensis
Amazonian Manatee, Trichechus inunguis
Dwarf Manatee, Trichechus bernhardi (validity questionable)
- Genus Trichechus
West Indian Manatee, Trichechus manatus
Antillean Manatee, Trichechus manatus manatus
Florida Manatee, Trichechus manatus latirostris
African Manatee, Trichechus senegalensis
Amazonian Manatee, Trichechus inunguis
Dwarf Manatee, Trichechus bernhardi (validity questionable)
- West Indian Manatee, Trichechus manatus
Antillean Manatee, Trichechus manatus manatus
Florida Manatee, Trichechus manatus latirostris
- Antillean Manatee, Trichechus manatus manatus
- Florida Manatee, Trichechus manatus latirostris
- African Manatee, Trichechus senegalensis
- Amazonian Manatee, Trichechus inunguis
- Dwarf Manatee, Trichechus bernhardi (validity questionable)
 extinct