Search results
Sirenians are classified in the clade Paenungulata, alongside the elephants and the hyraxes, and evolved in the Eocene 50 million years ago (mya). The Dugongidae diverged from the Trichechidae in the late Eocene or early Oligocene (30–35 mya). [3][4]
- Overview
- 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.
Britannica Quiz
Wild Words from the Animal Kingdom Vocabulary Quiz
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
Jan 4, 2021 · They live in swamps, rivers, estuaries, marine wetlands, and coastal marine water. Sirenians have no dorsal fin. No need, really, when you can navigate calm freshwaters instead of strong ocean waves.
All extant sirenians are found in shallow waters along coastlines and inlets. Manatees are found along tropical coastlines on both sides of the Atlantic Ocean and in the Amazon Basin. Dugongs are found off of coastal eastern Africa, along the shores of the Indian Ocean, and on the northern coast of Australia.
Jul 28, 2019 · Sirenians are large, slow-moving, aquatic mammals that live in shallow marine and freshwater habitats in tropical and subtropical regions. Their preferred habitats include swamps, estuaries, marine wetlands, and coastal waters.
Sea Cow. The sea cow is a group of marine mammals that contains famous marine creatures like the Dugong and Manatee. Physical Characteristics. Length: 10 to 13 feet (3 to 4 m) Weight: 800 and 1,200 pounds (360 to 540 kg) Lifespan: Up to 40 to 60 years. Key Information. Scientific name: Trichechus.
People also ask
Where does a sirenian live?
Are sirenians sea cows?
How many species of sirenians are there?
How long does a sirenian live?
Where did sirenians come from?
What does a sirenian do?
They have a large, rotund body shape and are found in warm coastal waters and rivers in the Caribbean, Gulf of Mexico, and the Amazon basin in South America, as well as the Indian and western Pacific Oceans. They are herbivores that primarily feed on seagrass and other aquatic plants.
