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Biography
For|the band|Sirenia (band)automatic Taxobox| name = Sirenia| fossil_range = Eocene - Recent, Fossil range|55.8|0| image = Manatee.jpg| image_width = 250px| image_caption = West Indian manatee s ( Trichechus manatus )| authority = Johann Karl Wilhelm Illiger|Illiger , 1811| subdivision_ranks = Families| subdivision = Dugongidae
Manatee|Trichechidae
† Prorastomidae
† Protosirenidae
Sirenia (commonly referred to as sea cows ) is an order (biology)|order of fully aquatic, herbivore|herbivorous mammal s that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Four species are Extant taxon|living , in two Family (biology)|families and Genus|genera . These are the dugong (1 species) and manatee s (3 species). Sirenia also includes Steller's sea cow , Extinction|extinct since the 18th century, and a number of taxon|taxa known only from fossil s. The order evolved during the Eocene , more than 50 million years ago.
Sirenia, commonly sirenians , are also referred to by the common name sirens , deriving from the siren s of Greek mythology.ITIS |taxon=Sirenia Illiger, 1811 |id=180676 http://www.sirenian.org/sirenians.html What are sirenians? Sirenian International - Manatee & Dugong Research, Education, & Conservation This comes from a legend about their discovery, involving lonely sailors mistaking them for mermaid s.
"Sea cow" (seekoei) is also the name for a hippopotamus in Afrikaans .
Description
Sirenians have major aquatic adaptation s: forelimbs have modified into arms used for steering, the tail has modified into a paddle used for propulsion, and the hind limbs (legs) are but two small remnant bones floating deep in the muscle. They appear fat, but are wikt:fusiform|fusiform , Hydrodynamics|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 teat s, located under their forelimbs, similar to elephant s. The elephant s are thought to be the closest living relative of the sirenians.
The lungs of sirenians are unlobed.Marine Mammal Medicine, 2001, Leslie Dierauf & Frances Gulland, CRC Press In sirenians, the lungs and diaphragm extend the entire length of the vertebral column. These adaptations help sirenians control their buoyancy and maintain their horizontal position in the water.cite journal| doi = 10.1111/j.1748-7692.1991.tb00111.x| last = Domning| first = Daryl| coauthor = Vivian Buffrenil| title = Hydrostasis in the Sirenia: Quantitative data and functional interpretations| journal =Marine Mammal Science| volume = 7| issue = 4 | pages = 331–368| publisher =| year = 1991cite journal| last = Rommel| first = Sentiel| coauthor = John E. Reynolds| title = Diaphragm structure and function in the Florida manatee (Trichechus manatus latirostris)| journal =The Anatomical Record| volume = 259| issue = 1 | pages = 41–51| publisher =Wiley-Liss, Inc.| year = 2000| pmid = 10760742| doi = 10.1002/(SICI)1097-0185(20000501)259:1<41::AID-AR5>3.0.CO;2-Q
Living sirenians grow between 2.5–4 metres long and can weigh up to 1500& nbsp;kg. Hydrodamalis gigas , Steller's sea cow, could reach lengths of 8 meters.cite book | author=Eldredge, Neal|year=2002|title= Life on Earth: An Encyclopedia of Biodiversity, Ecology and Evolution|publisher= ABC-CLIO| pages= 532|isbn= 1-57607-286-X
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. Steller's sea cow , extinct since 1786, was hunted into extinction by humans. Manatees and the dugong are the only marine mammals classified as herbivore s. Unlike the other marine mammals ( dolphin s, whale s, Pinniped|seals , sea lion s, sea otter s, and walrus es), 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 sirenian is lifted out of the water. The combination of these factors means that sirenians are restricted to warm shallow coastal waters, Estuary|estuaries , and rivers with healthy ecosystem s that support large amounts of seagrass and/or other vegetation.
The Trichechidae species differ from the Dugongidae in the shape of the skull and the shape of the tail.
Classification
See also|Evolution of sirenians|PaenungulataThe order Sirenia has been placed in the clade Paenungulata , within Afrotheria , grouping it with two other orders of living mammal s: Proboscidea , the elephant families, and Hyracoidea, the hyrax es, and two extinct orders, Embrithopoda and Desmostylia .
