Sirenia
Overview
 
Sirenia is an order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of fully aquatic, herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

 mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Four species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 are living, in two families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 and genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

. These are the dugong
Dugong
The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

 (1 species) and manatee
Manatee
Manatees are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows...

s (3 species). Sirenia also includes Steller's sea cow
Steller's Sea Cow
Steller's sea cow was a large herbivorous marine mammal. In historical times, it was the largest member of the order Sirenia, which includes its closest living relative, the dugong , and the manatees...

, extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

 since the 18th century, and a number of taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

 known only from fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s. The order evolved during the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

, more than 50 million years ago.

Sirenia, commonly sirenians, are also referred to by the common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

 sirens, deriving from the siren
Siren
In Greek mythology, the Sirens were three dangerous mermaid like creatures, portrayed as seductresses who lured nearby sailors with their enchanting music and voices to shipwreck on the rocky coast of their island. Roman poets placed them on an island called Sirenum scopuli...

s of Greek mythology.
Encyclopedia
Sirenia is an order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of fully aquatic, herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

 mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Four species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 are living, in two families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 and genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

. These are the dugong
Dugong
The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

 (1 species) and manatee
Manatee
Manatees are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows...

s (3 species). Sirenia also includes Steller's sea cow
Steller's Sea Cow
Steller's sea cow was a large herbivorous marine mammal. In historical times, it was the largest member of the order Sirenia, which includes its closest living relative, the dugong , and the manatees...

, extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

 since the 18th century, and a number of taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

 known only from fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s. The order evolved during the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

, more than 50 million years ago.

Sirenia, commonly sirenians, are also referred to by the common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

 sirens, deriving from the siren
Siren
In Greek mythology, the Sirens were three dangerous mermaid like creatures, portrayed as seductresses who lured nearby sailors with their enchanting music and voices to shipwreck on the rocky coast of their island. Roman poets placed them on an island called Sirenum scopuli...

s of Greek mythology. This comes from a legend
Legend
A legend is a narrative of human actions that are perceived both by teller and listeners to take place within human history and to possess certain qualities that give the tale verisimilitude...

 about their discovery, involving lonely sailors mistaking them for mermaid
Mermaid
A mermaid is a mythological aquatic creature with a female human head, arms, and torso and the tail of a fish. A male version of a mermaid is known as a "merman" and in general both males and females are known as "merfolk"...

s.

"Sea cow" is also the name for a hippopotamus
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...

 in South African English
South African English
The term South African English is applied to the first-language dialects of English spoken by South Africans, with the L1 English variety spoken by Zimbabweans, Zambians and Namibians, being recognised as offshoots.There is some social and regional variation within South African English...

.

Description

Sirenians have major aquatic adaptation
Aquatic adaptation
Several animal groups have undergone aquatic adaptation, going from being purely terrestrial animals to living at least part of the time in water. The adaptations in early speciation tend to develop as the animal ventures into water in order to find available food. As successive generations spend...

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 fusiform, hydrodynamic, and highly muscular. Their skulls are highly modified for taking breaths of air at the water's surface and dentition
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...

 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 elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...

s. The elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...

s are thought to be the closest living relative of the sirenians.

The lungs of sirenians are unlobed. 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.

Living sirenians grow between 2.5–4 metres long and can weigh up to 1500 kg. Hydrodamalis gigas, Steller's sea cow, could reach lengths of 8 metres.

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
Steller's Sea Cow
Steller's sea cow was a large herbivorous marine mammal. In historical times, it was the largest member of the order Sirenia, which includes its closest living relative, the dugong , and the manatees...

, extinct since 1786, was hunted into extinction by humans. Manatees and the dugong are the only marine mammals classified as herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

s. Unlike the other marine mammals (dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

s, whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s, seals
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

, sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...

s, sea otter
Sea Otter
The sea otter is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg , making them the heaviest members of the weasel family, but among the smallest marine mammals...

s, and walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

es), sirenians eat primarily sea-grasses and other aquatic vegetation and have an extremely low metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 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, estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

, and rivers with healthy ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

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

The order Sirenia has been placed in the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 Paenungulata
Paenungulata
Paenungulata is a taxon that groups some remarkable mammals, including three orders that are extant: Proboscidea , Sirenia , and Hyracoidea . At least two more orders are known only as fossils, namely Embrithopoda and Desmostylia...

, within Afrotheria
Afrotheria
Afrotheria is a clade of mammals, the living members of which belong to groups from Africa or of African origin: golden moles, sengis , tenrecs, aardvarks, hyraxes, elephants and sea cows. The common ancestry of these animals was not recognized until the late 1990s...

, grouping it with two other orders of living mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s: Proboscidea
Proboscidea
Proboscidea is a taxonomic order containing one living family, Elephantidae, and several extinct families. This order was first described by J. Illiger in 1881 and encompasses the trunked mammals...

, the elephant families, and Hyracoidea, the hyrax
Hyrax
A hyrax is any of four species of fairly small, thickset, herbivorous mammals in the order Hyracoidea. The rock hyrax Procavia capensis, the yellow-spotted rock hyrax Heterohyrax brucei, the western tree hyrax Dendrohyrax dorsalis, and the southern tree hyrax, Dendrohyrax arboreus live in Africa...

es, and two extinct orders, Embrithopoda
Embrithopoda
Embrithopoda is an extinct order of mammals which first appeared in the fossil record during the late Eocene and then died out during the Oligocene....

 and Desmostylia
Desmostylia
Desmostylia is an extinct order of marine mammals which existed from the Arikareean age of the late Oligocene epoch to the Tortonian age of the late Miocene epoch . Their dental and skeletal form suggests desmostylians were amphibious herbivores dependent on littoral habitats...

.

Subdivision

  • ORDER SIRENIA
    • Family †Anthracobunidae
      Anthracobunidae
      Anthracobunidae is an extinct family of primitive proboscideans that lived in the early to middle Eocene period.They resemble the later Moeritheriidae in both size and cheek tooth morphology but lack their characteristic tusks. They are known only from fragmentary remains from Eocene deposits of...

      • Genus †Ishatherium
        • Ishatherium subathuensis
          Ishatherium
          Ishatherium is an extinct genus of early proboscidean from the early Eocene of the Subathu formation in Northwestern India.It is only known from a partial upper molar and was formally classified as a sirenian.- References :...

    • Family †Prorastomidae
      Prorastomidae
      Prorastomidae is a taxonomic family of extinct animals related to the extant manatees and dugong. The family includes two genera:*Pezosiren*Prorastomus...

      • Genus †Pezosiren
        • Pezosiren portelli
          Pezosiren
          Pezosiren portelli is the name given to an early sirenian represented by a Jamaican fossil skeleton, described in 2001 by Daryl Domning, a marine mammal paleontologist at Howard University in Washington, DC...

      • Genus †Prorastomus
        • Prorastomus sirenoides
          Prorastomus
          Prorastomus sirenoides is an extinct species of primitive sirenian that lived during the Eocene Epoch 40 million years ago in Jamaica.-Description:...

    • Family †Protosirenidae
      • Genus †Protosiren
        Protosiren
        Protosiren is an extinct early genus of the order Sirenia. Protosiren existed throughout the Lutetian and Bartonian stages of the Middle Eocene. Its geographic distribution was intercontinental: fossils have been found in the United States , Egypt, France, Hungary, India, and Pakistan...

        • Protosiren minima
        • Protosiren sattaensis
        • Protosiren fraasi
        • Protosiren smithae
    • Family Dugongidae
      Dugongidae
      Dugongidae is a family in the order of Sirenia.The family has one surviving species, the Dugong , one recently extinct species, the Steller's Sea Cow , and a number of extinct genera known from the fossil record....

      • Genus †Nanosiren
        • †Nanosiren garciae
        • †Nanosiren sanchezi
      • Genus †Sirenotherium
        • Sirenotherium pirabense
      • Subfamily Dugong
        Dugong
        The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

        inae
        • Genus Dugong
          Dugong
          The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

          • Dugong dugon
            Dugong
            The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

            , Dugong
      • Subfamily †Hydrodamalinae
        Hydrodamalinae
        Hydrodamalinae is a recently extinct subfamily of the siren family Dugongidae. The Steller's Sea Cow was hunted to extinction by 1760, while the genus Dusisiren is known from fossils dating from the middle Miocene to early Pliocene....

        • Genus †Dusisiren
          • Dusisiren dewana
          • Dusisiren jordani
          • Dusisiren takasatensis
        • Genus †Hydrodamalis
          • Hydrodamalis cuestae
          • Hydrodamalis gigas
            Steller's Sea Cow
            Steller's sea cow was a large herbivorous marine mammal. In historical times, it was the largest member of the order Sirenia, which includes its closest living relative, the dugong , and the manatees...

            , Steller's Sea Cow
    • Family Trichechidae
      • Subfamily †Miosireninae
        • Genus †Anomotherium
          • Anomotherium langewieschei
        • Genus †Miosiren
          • Miosiren canhami
          • Miosiren kocki
      • Subfamily Trichechinae
        • Genus †Potamosiren
          • Potamosiren magdalenensis
        • Genus Trichechus
          • Trichechus manatus
            West Indian Manatee
            The West Indian Manatee is a manatee, and the largest surviving member of the aquatic mammal order Sirenia . The West Indian Manatee, Trichechus manatus, is a species distinct from the Amazonian Manatee, T. inunguis, and the West African Manatee, T. senegalensis...

            , West Indian Manatee
            • Trichechus manatus manatus, Antillean Manatee
            • Trichechus manatus latirostris, Florida Manatee
          • Trichechus senegalensis
            African Manatee
            The African manatee , also known as the West African manatee or seacow, is a species of manatee and is the most endangered of the four species of sirenians. Scientists think they are most similar to West Indian manatees...

            , African Manatee
          • Trichechus inunguis
            Amazonian Manatee
            The Amazonian Manatee is a species of manatee that lives in the freshwater habitats of the Amazon basin. They are found in Brazil, Peru, Colombia, Ecuador, Guyana and Venezuela. Amazonian manatees are aquatic animals of the Sirenia order and are also known as "seacows". Their colour is grey but...

            , Amazonian Manatee
          • Trichechus "pygmaeus"
            Dwarf Manatee
            The Dwarf Manatee is a possible species of manatee that lives in the freshwater habitats of the Amazon, though restricted to one tributary of the Aripuanã River...

            , Dwarf Manatee – validity questionable
      • Genus †Ribodon
        Ribodon
        Ribodon limbatus is an extinct species of Sirenians that lived around South America during the Tortonian....

        • Ribodon limbatus

† extinct

External links

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