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The recently extinct Steller's sea cow was the largest known sirenian to have lived, reaching lengths of 10 metres (33 feet) and weights of 5 to 10 tonnes (5.5 to 11.0 short tons). [ 2 ] Sirenians have a large, fusiform body which reduces drag through the water and heavy bones that act as ballast to counteract the buoyancy of their blubber .
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- Natural history
- Classification and paleontology
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 extinc...
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.
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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.
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
The Sirenia, commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise two distinct families: Dugongidae (the dugong and the now extinct Steller's sea cow) and Trichechidae (manatees, namely the Amazonian manatee, West Indian manatee, and ...
The sirenians range in length from about 9.8 ft (3 m) for the Amazonian manatee to as much as 32.8 ft (10 m) for the extinct Steller's sea cow. Maximum body mass ranges from about 992 lb (450 kg) for the Amazonian manatee to more than 9,920 lb (4,500 kg) for the sea cow. All sirenians are nearly hairless.
Sep 8, 2024 · The Sirenia, commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise the families Dugongidae (the dugong and, historically, Steller's sea cow ) and Trichechidae ( manatees ) with a total of four species.
Jul 28, 2019 · Sirenians (Sirenia), also known as sea cows, are a group of mammals that includes dugongs and manatees. There are four species of sirenians alive today, three species of manatees and one species of dugong. A fifth species of sirenian, the Stellar's sea cow, became extinct in the 18 th century due to over-hunting by humans. The Stellar's sea cow ...
Steller's sea cows (Hydrodamalis gigas) are a recently extinct dugong species, and they were the only sirenians that did not inhabit tropical waters, instead they were found in the subarctic Bering Sea. Steller's sea cows represent the largest known members of Sirenia>; growing up to 10 meters and weighing up to 11,000 kg; whereas the smallest ...
