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Sirenia Fossil range: Early Eocene - Recent
West Indian Manatees (Trichechus manatus)
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Infraclass: Eutheria Superorder: Afrotheria Order: Sirenia Illiger, 1811
Families
Dugongidae Trichechidae †Prorastomidae †Protosirenidae

For information about the Gothic metal band, see Sirenia (band)

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 Stellar'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 only eat sea-grasses and other aquatic vegetation and have an extremely low metabolism and poor tolerance for especially cold water. Like dolphins and whales, manatees and the Dugong are totally aquatic mammals that never leave the water — not even to give birth. 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
  • Family †Prorastomidae
  • Family †Protosirenidae
  • Family Dugongidae
    • 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
      • African Manatee, Trichechus senegalensis
      • Amazonian Manatee, Trichechus inunguis

† extinct

• Shoshani, Jeheskel (November 16, 2005). in Wilson, D. E., and Reeder, D. M. (eds): Mammal Species of the World, 3rd edition, Johns Hopkins University Press, 92-93. ISBN 0-801-88221-4. 
• Garrison, Tom - Oceanography 5th Edition
• The Paleobiology Database

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Sirenia

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Sirenia

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Sirenia

• http://www.sirenian.org/ Sirenian International - Manatee & Dugong Research, Education, & Conservation
• The earliest known Sirenian is Pezosiren portelli.
• http://www.savethemanatee.org/ Save The Manatee - Help protect this endangered species.