A sirenian is any of four species of large, aquatic mammals that live primarily in tropical waters where aquatic plants are abundant. They are believed to be the basis for the mermaid myth and are named after the Sirens of Greek mythology. Modern sirenians have two front limbs in the form of flippers but no hind limbs. The three species of manatee occupy warm latitudes of the coastal Atlantic and associated rivers, and the dugong inhabits the coastlines of the Indian and Pacific oceans. The extinct Steller’s sea cow also belonged to the dugong family. Sirenian populations are vulnerable to depletion from hunting, drowning in nets, collisions with boats, and habitat degradation.

Where do sirenians live?

Sirenians, which include manatees and dugongs , are large aquatic mammals that live primarily in tropical waters where aquatic plants are abundant. Manatees inhabit warm latitudes of the coastal Atlantic and associated rivers. The Antillean manatee lives in nearshore waters, lagoons, estuaries, and rivers of eastern Mexico, down the Central American coast, and across northern South America. The Amazonian manatee inhabits the Amazon River, while the West African manatee is found in coastal areas and slow-moving rivers from Senegal to Angola. Dugongs inhabit the warm coastal waters of the Indian and Pacific Oceans.

What do sirenians eat and how do they find their food?

Sirenians, including manatees and dugongs , primarily consume aquatic plants in tropical waters. Manatees use their prehensile lips and sensory bristles (vibrissae) to discriminate between and manipulate food plants. Dugongs also use thick bristles (vibrissae) on their broad snouts to detect, discriminate, and manipulate food. Both dugongs and manatees are selective feeders, analyzing their environment before feeding.

How are sirenians adapted to living in water?

Sirenians, which include dugongs and manatees , have several adaptations for aquatic life. Their bodies are round and taper to a horizontal, flattened tail that provides propulsion. They have two front limbs shaped like flippers, but no hind limbs. Nostrils on the upper snout act as valves to keep water out. Sirenian bones are dense, lacking marrow, which assists with maintaining neutral buoyancy. They also have thick, tough, nearly hairless skin, except for sensory hairs called vibrissae on the muzzle, and small eyes and ears.

What are some threats to sirenians, and why are they considered vulnerable or endangered?

Sirenians, including dugongs and manatees , face several threats that contribute to their vulnerable or endangered status. These long-lived animals can fall victim to hunting, habitat degradation, drowning in nets, and collisions with boats. Dugongs, for example, are classified as a vulnerable species since 1982 due to excessive hunting and habitat degradation. Their low reproductive rates cannot compensate for increased mortality from habitat deterioration, loss of seagrass, entanglement in fishing nets, and boat collisions. Sirenian populations are easily depleted by human activities.

sirenian

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Features of dugongs and manatees compared.

An illustration of Steller's sea cows (Hydrodamalis gigas) swimming and feeding on kelp near the shore, with two people in traditional clothing observing from a wooden boat above the water.

World map showing the geographic ranges of the four living species of the order Sirenia: the West Indian manatee (highlighted in yellow along the southeastern US, Gulf of Mexico, Caribbean, and northeast South America), the Amazonian manatee (in green within the Amazon River basin), the African manatee (in pink along the west coast and rivers of West and Central Africa), and the dugong (in purple along coastal waters from East Africa through the Indian Ocean to northern Australia and parts of So

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Related Topics:: manatee; Trichechidae; Caribbean manatee; West African manatee; Dugongidae

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sirenian

mammal

Also known as: Sirenia

Written by

Thomas O'Shea

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History

Top Questions

What is a sirenian?
A sirenian is any of four species of large, aquatic mammals that live primarily in tropical waters where aquatic plants are abundant. They are believed to be the basis for the mermaid myth and are named after the Sirens of Greek mythology.

Modern sirenians have two front limbs in the form of flippers but no hind limbs. The three species of manatee occupy warm latitudes of the coastal Atlantic and associated rivers, and the dugong inhabits the coastlines of the Indian and Pacific oceans. The extinct Steller’s sea cow also belonged to the dugong family. Sirenian populations are vulnerable to depletion from hunting, drowning in nets, collisions with boats, and habitat degradation.
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2. siren
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What kinds of animals are included in the sirenian group?
The sirenian order includes four living species within two families: Trichechidae (manatees) and Dugongidae (dugong). The three species of manatees, belonging to the genus Trichechus, are found in the warm coastal Atlantic and associated rivers. The dugong (Dugong dugon) inhabits the coastlines of the Indian and Pacific oceans. The Steller’s sea cow (Hydrodamalis gigas) also belonged to the dugong family, but humans hunted them to extinction less than 30 years after their scientific description in 1741. The term "sea cow" is sometimes used to refer to sirenians collectively.
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Where do sirenians live?
Sirenians, which include manatees and dugongs, are large aquatic mammals that live primarily in tropical waters where aquatic plants are abundant. Manatees inhabit warm latitudes of the coastal Atlantic and associated rivers. The Antillean manatee lives in nearshore waters, lagoons, estuaries, and rivers of eastern Mexico, down the Central American coast, and across northern South America. The Amazonian manatee inhabits the Amazon River, while the West African manatee is found in coastal areas and slow-moving rivers from Senegal to Angola. Dugongs inhabit the warm coastal waters of the Indian and Pacific Oceans.
3 Britannica Sources
1. sirenian
2. dugong
3. manatee
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What do sirenians eat and how do they find their food?
Sirenians, including manatees and dugongs, primarily consume aquatic plants in tropical waters. Manatees use their prehensile lips and sensory bristles (vibrissae) to discriminate between and manipulate food plants. Dugongs also use thick bristles (vibrissae) on their broad snouts to detect, discriminate, and manipulate food.

Both dugongs and manatees are selective feeders, analyzing their environment before feeding.
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How are sirenians adapted to living in water?
Sirenians, which include dugongs and manatees, have several adaptations for aquatic life. Their bodies are round and taper to a horizontal, flattened tail that provides propulsion. They have two front limbs shaped like flippers, but no hind limbs. Nostrils on the upper snout act as valves to keep water out. Sirenian bones are dense, lacking marrow, which assists with maintaining neutral buoyancy. They also have thick, tough, nearly hairless skin, except for sensory hairs called vibrissae on the muzzle, and small eyes and ears.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some threats to sirenians, and why are they considered vulnerable or endangered?
Sirenians, including dugongs and manatees, face several threats that contribute to their vulnerable or endangered status. These long-lived animals can fall victim to hunting, habitat degradation, drowning in nets, and collisions with boats.

Dugongs, for example, are classified as a vulnerable species since 1982 due to excessive hunting and habitat degradation. Their low reproductive rates cannot compensate for increased mortality from habitat deterioration, loss of seagrass, entanglement in fishing nets, and boat collisions. Sirenian populations are easily depleted by human activities.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

sirenian, (order Sirenia), any of four large aquatic mammalian species now living primarily in tropical waters where food plants grow. The three species of manatee (genus Trichechus) occupy warm latitudes of the coastal Atlantic and associated rivers, and the dugong (Dugong dugon) inhabits the coastlines of the Indian and Pacific oceans. The extinct Steller’s sea cow (Hydrodamalis gigas), formerly of the Bering Sea, also belonged to the dugong family, but all were killed off by humans less than 30 years after they were first scientifically described in 1741. Steller’s sea cow was the largest sirenian and one of the few sirenians to occupy cold water. The term sea cow is now sometimes used to refer collectively to sirenians.

Natural history

The order Sirenia was named after the Sirens of Greek mythology, and sirenians are believed to be the basis for the mermaid myth. Modern sirenians have two front limbs in the form of flippers but no hind limbs; even the pelvis is vestigial, and there are no skeletal remnants of leg or foot bones at all. Sirenian bodies are basically round in cross-section and taper toward the tail, which is flattened horizontally and provides propulsion. Dugong tails are deeply notched, similar to those of whales, whereas in manatees the tail is rounded outward like a paddle. Sirenians in general are slow-moving but capable of short bursts of speed. There are no marked differences between the sexes; females have two inconspicuous mammary glands with one teat near the base of each flipper. Both dugongs and manatees have thick tough skin (that of Steller’s sea cow was even tougher). All sirenians are nearly hairless except at the muzzle, where there are thick sensory hairs called vibrissae. The upper lip is enlarged and muscular and serves to grasp and manipulate food plants. The eyes are small, and the external ears consist only of tiny pits. Nostrils on the upper surface of the snout function as valves to exclude water. Sirenian bones are exceptionally dense, most of them lacking marrow. This adaptation is thought to help maintain neutral buoyancy.

Manatees and dugongs differ in a number of traits besides the shape of the tail. Manatees lack incisor teeth, but incisors do occur in dugongs, erupting as tusks in the males. Manatees grow a never-ending series of molars that continuously move forward in the jaw to replace those that wear and fall out at the front. Dugongs, on the other hand, have a finite number of six molars and premolars in each jaw, and they are not replaced; in older individuals only two remain. Manatees have six neck vertebrae instead of the seven typical of mammals. Dugongs are exclusively marine, but manatees inhabit both marine and freshwater systems.

Dromedary camels (Camelus dromedarius). Animals, mammals.

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Sirenian populations are easily depleted by activities of people, often falling victim to hunting, drowning in nets, collisions with boats, and habitat degradation. They are protected by law and international agreements in almost all countries, but in many areas populations remain very low or are extirpated as a result of past and present human activities.

Classification and paleontology

Sirenians arose from terrestrial hoofed mammals (tethytheres) during the Paleocene Epoch (65 million to 54.8 million years ago) in what is now the Old World. Tethytheres also gave rise to elephants (order Proboscidea), and early sirenians spread to shallow waters throughout the tropics. The family Dugongidae, which eventually included Steller’s sea cow, was an early offshoot, giving rise to the Trichechidae about 40 million years ago.

Order Sirenia (sea cows)
Four living species in two families
- Family Trichechidae (manatees)
  - Genus Trichechus
    Three species
- Family Dugongidae
  Two genera, one now extinct
  - Genus Dugong (dugong)
    One species
  - Genus Hydrodamalis (Steller’s sea cow)
    One species hunted to extinction

Thomas O'Shea

sirenian

Natural history

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Classification and paleontology