52-580: See Text Trichechidae is a family of sirenians that includes all living manatees and several extinct genera. Trichechidae This article about a mammal is a stub . You can help Misplaced Pages by expanding it . Sirenians The Sirenia ( / s aɪ ˈ r iː n i . ə / ), 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 extant Sirenia comprise two distinct families : Dugongidae (the dugong and
104-438: A muscular hydrostat , a biological structure that relies on muscular pressure and muscle contractions to manipulate and move food. The manatee uses its large upper perioral bristles to carry out a grasping motion: it performs a flare that tightens the muscular hydrostat while the large upper bristles get pushed out and the lower jaw drops and sweeps the vegetation in by closing. The primary bristles used for vegetation ingestion are
156-564: A petrosal bone was found in Tunisia, dating back to approximately the same time as Prorastomus . This is the oldest sirenian fossil to be found in Africa and supports molecular data suggesting that sirenians may have originated in Africa. Prorastomidae and Protosirenidae , the earliest sirenian families , consisted of pig-like amphibious creatures who died out at the end of the Eocene. With
208-492: A female first gives birth is disputed, ranging anywhere from 6 to 17 years. The time between births is unclear, with estimates ranging from 2 to 7 years. In Sarasota, Florida, 53 females under observation produced at least 55 calves during a five-year period. Manatees can reach sexual maturity as early as two to five years of age. Manatee gestation is around one year, and then they lactate for one to two years. West Indian manatees and African manatees can breed year-round, and
260-464: A female will mate with multiple males. Amazonian manatees have a breeding season, usually mating when the river levels begin to rise, which varies from place to place. Manatees may be taken into captivity after being found stranded to facilitate their recovery, and there are many instances of manatees being successfully rehabilitated and released into the wild. As all extant sirenian species are rated as Vulnerable, these rehabilitation programs present
312-458: A few times during their lives and invest considerable parental care in their young. Dugongs generally gather in groups of less than a dozen individuals for one to two days. Since they congregate in turbid waters, little is known about their reproductive behavior. The males are often seen with scars, and the tusks on dugongs grow in first for males, suggesting they are important in lekking. They have also been known to lunge at each other. The age when
364-557: A maximum of 300 grams (11 ounces), about 0.1% of the animal's body weight. The bodies of sirenians are sparsely covered in short hair ( vibrissae ), except that it becomes denser on the muzzle, which may allow for tactile interpretation of their environment. Manatees are the only known organism with uniformly vascularized corneas. This may be the result of irritation from or protection against their hypotonic freshwater environment. Sirenians are referred to as "sea cows" because their diet consists mainly of seagrass . Dugongs sift through
416-521: A preferred diet for the dugongs. To ensure the abundance of favored seagrasses, dugongs exhibit sustained grazing pressure on seagrass patches up to a month or more. The grazing maximizes the presence of species preferred by the dugongs at the expense of less nutritious and less favored species. This grazing method also encourages rapid recovery of seagrass meadows- the dugongs graze in meandering, single trails that leave uncropped patches of seagrass. This ungrazed reserve with their surviving rhizomes are key to
468-678: A profound study of palaeontology, particularly of vertebrates,' in 1962. In 1966, Simpson received the Golden Plate Award of the American Academy of Achievement . At the University of Arizona , Tucson , the Gould-Simpson Building was named in honor of Simpson and Minnesota geologist and polar explorer Lawrence M. Gould , who, like Simpson, also accepted an appointment as Professor of Geosciences at
520-421: A protein source, oils, and a stabilizing agent. This concoction is supplemented with vitamins. During intake, young manatees might require electrolytes via intravenous hydration or even tube feeding if they continuously reject the bottle. After six months, they will be introduced to solid foods like romaine and iceberg lettuce, pumpkin, and root vegetables. After a year and a half, the weaning process will begin and
572-421: A useful means to support these species. However, the vulnerability of these animals also means that the taking of manatees from the wild for commercial purposes is a conservation issue. Manatees tend to do well in a captive environment and have been known to thrive. However, it can be difficult to replicate the conditions of their natural environment to the extent necessary to maintain a manatee at its healthiest;
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#1732772623515624-600: Is found in waters above 18 °C, and its range spans Senegal to Angola. The dugong ( Dugong dugong ), the closest living relative of Steller's sea cow, lives in the Indo-West Pacific Ocean in more than 40 different countries. They are coastal animals supported by wide protected sea grass meadows. Steller's sea cow was discovered in 1741 around islands in the Bering Sea and was specialized for cold subarctic temperatures. It ranged from Alaska through
676-414: Is often caused by direct hunting by humans or other human-induced causes, such as habitat destruction , entanglement in fishing gear , and watercraft collisions . Steller's sea cow was driven to extinction due to overhunting in 1768. Sirenia, commonly sirenians , are also referred to by the common name sirens , deriving from the sirens of Greek mythology . Sirenians are classified within
728-459: The Amchitka and Aleutian Islands , and even to Japan. Steller's sea cow was reported to have congregated in shallow, sandy areas along coastline and mouths of rivers and creeks to feed on kelp. The evolution of sirenians is characterized by the appearance of several traits that are found in all sirenians. The nostrils are large and retracted , the upper-jaw bone contacts the frontal bone ,
780-695: The American Museum of Natural History from 1945 to 1959. He was Curator of the Museum of Comparative Zoology at Harvard University from 1959 to 1970, and a Professor of Geosciences at the University of Arizona from 1968 until his retirement in 1982. Simpson was elected to the American Philosophical Society in 1936 and the United States National Academy of Sciences in 1941. In 1943 Simpson
832-531: The New World . In Western Europe the first and oldest sirenian remains have been found in a new paleontological site , in Santa Brígida, Amer (La Selva, Catalonia , Spain ). One of the earliest aquatic sirenians discovered is Prorastomus , which dates back to 40 million years ago, and the first known sirenian, the quadruped Pezosiren , lived 50 million years ago. An ancient sirenian fossil of
884-579: The cohort Afrotheria in the clade Paenungulata , alongside Proboscidea (elephants), Hyracoidea (hyraxes), Embrithopoda , Desmostylia , and Afroinsectiphilia . This clade was first established by George Gaylord Simpson in 1945 on the basis of anatomical evidence, such as testicondy and similar fetal development . The Paenungulata, along with the Afrotheria, are one of the most well-supported mammalian clades in molecular phylogeny. Sirenia, Proboscidae, and Desmotylia are grouped together in
936-484: The diaphragm , these extend the entire length of the vertebral column, helping the animals control their buoyancy and reducing tipping in the water. Extant sirenians grow to between 2.5 and 4 metres (8.2 and 13.1 ft) in length and can weigh up to 1,500 kilograms (3,300 lb). Steller's sea cow was the largest known sirenian to have lived, and could reach lengths of 9 metres (30 ft) and weight of 8 to 10 tonnes (8.8 to 11.0 short tons). A dugong's brain weighs
988-566: The sagittal crest is missing, the mastoid fills the supratemporal fenestra (an opening on the top of the skull), there is a drop-like ectotympanic (a bony ring that holds the ear drum ), and the bones are pachyosteosclerotic (dense and bulky). Sirenians first appeared in the fossil record in the Early Eocene and diversified throughout the epoch . They inhabited rivers, estuaries, and nearshore marine waters. Sirenians, unlike other marine mammals such as cetaceans , lived in
1040-752: The Caribbean, South America, and Central America and frequent drowned cays, mangroves, lagoons, and sea grass beds. The Amazonian manatee ( T. inunguis ) has been documented in all parts of the Amazon River Basin in South America. River channels that connect allow easy travel to other waterways where food may be plentiful. The Amazonian manatee lives only in freshwater. The West African manatee ( T. senegalensis ) lives in murky isolated inland mangroves and coastal flats in West Africa. It
1092-508: The Trichechidae in the late Eocene or early Oligocene (30–35 mya). Sirenians grow to between 2.5 and 4 metres (8.2 and 13.1 feet) in length and 1,500 kilograms (3,300 pounds) in weight. 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). Sirenians have a large, fusiform body which reduces drag through
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#17327726235151144-496: The U2 and L1 fields. Dugongs and trichechids differ in how they use the U1 and U2 bristle fields during feeding. Dugongs use a medial-to-lateral motion for U2 bristles, while trichechids use a prehensile, lateral-to-medial grasping motion. These divergent feeding behaviors allow dugongs to exploit benthic foraging, including rhizome consumption, more effectively than trichechids. Food handling
1196-416: The animal forward, or twisted to turn. The forelimbs are paddle-like flippers which aid in turning and slowing. Unlike manatees, the dugong lacks nails on its flippers, which are only 15% of a dugong's body length. Manatees generally glide at speeds of 8 kilometres per hour (5 mph), but can reach speeds of 24 kilometres per hour (15 mph) in short bursts. The body is fusiform to reduce drag in
1248-473: The appearance of the Dugongidae at this time, sirenians had evolved the characteristics of the modern order, including an aquatic, streamlined body with flipper-like fore limbs and no hind limbs, and a powerful tail with horizontal caudal fins which uses an up-and-down motion to move them through the water. The last of the sirenian families to appear, Trichechidae , apparently arose from early dugongids in
1300-410: The back of the jaw. Adults lack incisors, canines, and premolars, and instead have 8 to 10 cheek teeth . Manatees have an unlimited supply of teeth moving in from the back and shedding in the front; these are continuously formed by a dental capsule behind the tooth row. These teeth are constantly worn down by the abrasive vascular plants they forage, particularly aquatic grasses. Unlike those of manatees,
1352-770: The clade Tethytheria . On the basis of morphological similarities, Tethytheria, Perissodactyla , and Hyracoidea were previously thought to be grouped together as the Altungulata , but this has been invalidated by molecular data. Procaviidae [REDACTED] Trichechidae [REDACTED] Dugongidae [REDACTED] Elephantidae [REDACTED] Orycteropodidae [REDACTED] Macroscelididae [REDACTED] Chrysochloridae [REDACTED] Potamogalidae [REDACTED] Tenrecidae [REDACTED] † = Extinct Family Dugongidae : Family Trichechidae : †Family Protosirenidae : †Family Prorastomidae : Distribution The warm shallow waters of
1404-457: The densest bones in the animal kingdom. These may act as ballast , countering the buoyancy of their blubber and helping them remain suspended slightly below the water's surface. Manatees do not possess blubber per se, but rather have thick skin and consequently are sensitive to temperature changes. They often migrate to warmer waters whenever the water temperature dips below 20 °C (68 °F). The lungs of sirenians are unlobed; along with
1456-459: The dugong's teeth do not continually grow back via horizontal tooth replacement. The dugong has two tusks which emerge in males during puberty, and sometime later in life for females after reaching the base of the premaxilla . The number of growth layer groups in a tusk indicates the age of a dugong. Sirenians exhibit pachyostosis , a condition in which the ribs and other long bones are solid and contain little or no bone marrow . They have among
1508-599: The equator have been the center of Sirenian habitation. The northernmost living population, the Florida subspecies of the West Indian manatee ( T. manatus latirostris ), inhabits the coast and frequents freshwater springs, power plants, and canals in Florida to stay warm during the winter. Individuals may migrate north in the warm summer months, some up to 1,000 kilometers (about 621.37 mi) from their winter range. The Antillean subspecies ( T. manatus manatus ) occurs in
1560-606: The expansion and restoration of seagrasses. Seagrasses respond to cropping by increasing nitrogen levels and decreasing lignin. Cultivation grazing allows dugongs to increase both nutritionally superior seagrasses, but the overall nutritional quality of the seagrasses. By maintaining the seagrasses in an immature state, dugongs ensure the highest level of nutrition. Despite being mostly solitary, sirenians congregate in groups while females are in estrus . These groups usually include one female with multiple males. Sirenians are K -selectors ; despite their longevity, females give birth only
1612-454: The feeding ecology. Dugongs are constrained in their feeding by their rudimentary dentition and limited nitrogen abundance in seagrasses. To counter this, they use a strategy called "cultivation grazing". This grazing can alter the composition of seagrass communities and favor species. Early and rapidly growing species will succeed over slow-growing species. Oftentimes, these "pioneer" species can be high in nitrogen and low in fibre, making them
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1664-547: The juvenile manatees will be offered less and less milk during feeding times, slowly transitioning to a completely solid food diet. The three extant manatee species (family Trichechidae) and the dugong (family Dugongidae) are rated as Vulnerable on the IUCN Red List of Threatened Species . All four 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 1768,
1716-476: The late Eocene or early Oligocene. In 1994, the family was expanded to include not only the subfamily Trichechinae ( Potamosiren , Ribodon , and Trichechus ), but also Miosireninae ( Anomotherium and Miosiren ). The African manatee and the West Indian manatee are more closely related to each other than to the Amazonian manatee. Dugongidae comprises the subfamilies Dugonginae and Hydrodamalinae and
1768-524: The manatee to graze for several hours per day. By contrast, 10% of the diet of the African manatee is fish and mollusks . Manatees have been known to eat small amounts of fish from nets. As opposed to bulk feeding , dugongs target high-nitrogen grasses to maximize nutrient intake, and, although predominantly herbivorous , dugongs will occasionally eat invertebrates such as jellyfish , sea squirts , and shellfish . Some populations of dugongs, such as
1820-549: The manatee's diet is marine or estuarine plants. When compared to the captive diet, aquatic plants have more dry matter and soluble neutral detergent fiber, and less digestible nutrients. Although more easily digestible nutrients may seem to represent a better diet, a manatee's gastrointestinal tract is adapted to the wild diet through microbial processes of fermentation. Rescue and rehabilitation efforts often involve orphaned infant manatees. In captivity, young manatees will be bottle-fed an amino acid-based milk formula that includes
1872-520: The now extinct Steller's sea cow ) and Trichechidae ( manatees , namely the Amazonian manatee, West Indian manatee, and West African manatee) with a total of four species. The Protosirenidae (Eocene sirenians) and Prorastomidae (terrestrial sirenians) families are extinct. 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
1924-481: The oil of the African manatee can cure ailments such as ear infections, rheumatism , and skin conditions. Hunting is the largest source of mortality in Amazonian manatees, and there are no management plans except in Colombia. Amazonian manatees, especially calves, are sometimes illegally sold as pets, but there are several institutions that care for and rescue these orphans, with the possibility of releasing them into
1976-640: The one in Moreton Bay , Australia, are omnivorous, feeding on invertebrates such as polychaetes or marine algae when their supply of seagrasses is low. In other dugong populations in western and eastern Australia, there is evidence that dugongs actively seek out large invertebrates. Populations of Amazonian manatees become restricted to lakes during the July–August dry season when water levels begin to fall, and are thought to fast during this period. Their large fat reserves and low metabolic rates—only 36% of
2028-461: The paraphyletic Halitheriinae. The tusks of modern-day dugongs may have originally been used for digging, but they are now used for social interaction. The genus Dugong probably originated in the Indo-Pacific. The tail fluke of a dugong is notched and similar to those of dolphins , whereas the tail fluke of manatee is paddle-shaped. The fluke is pumped up and down in long strokes to move
2080-552: The seafloor in search of seagrasses, using their sense of smell because their eyesight is poor. They ingest the whole plant, including the roots, although they will feed on just the leaves if this is not possible. Using its divided upper lip, the West Indian manatee is known to consume over 60 different freshwater and saltwater plants, such as shoalweed , water lettuce , muskgrass , manatee grass , and turtle grass . An adult manatee will commonly eat up to 10–15% of its body weight, or 50 kilograms (110 lb), per day, which requires
2132-416: The species of plants consumed, as reflected in the mean feeding cycle length. Thus, Florida manatees adapt their feeding behavior depending on the characteristics of the plants they consume. They exhibit different food handling strategies and efficiencies based on the plant species, with faster consumption observed for plants with tubular stems and numerous branches. This research provides valuable insights into
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2184-430: The surface, sometimes standing on their tails to do so. They typically inhabit warm, shallow, coastal waters, or rivers. They are mainly herbivorous, but have been known to consume animals such as birds and jellyfish. Males typically mate with more than one female and may gather in leks to mate. Sirenians are K -selected , displaying parental care . The meat, oil, bones, and skins are commercially valuable. Mortality
2236-551: The typical diet fed to captive manatee populations may contain insufficient quantities of the nutrients they need. Manatee captive-fed diets vary greatly from the manatee's diet in the wild. In captivity manatees are fed 70–80% leafy green vegetables, 10–20% dried forage, and 5% vegetables and fruits. Dried forage is foods such as hay and timothy grass, which are often used as horse and cattle feed. The vegetables and fruits that are fed to manatees include romaine lettuce, carrots, and apples. In their natural habitat approximately half of
2288-678: The usual placental mammal metabolic rate—allow them to survive for up to seven months with little or no food. Perioral bristles are not only used to sense things, but can be used to grasp and manipulate food. Of the 6 distinct fields of bristles on upper and lower lips, the perioral fields have distinct length-to-diameter ratios, defining their boundaries. Macrovibrissae are used to detect food by its size and microvibrissae to manipulate food. They can be used to break off leaves and undesirable parts while feeding. Sirenians use their elaborate facial musculature along with perioral bristles to acquire, manipulate, and ingest aquatic vegetation. The snout makes up
2340-580: The water and heavy bones that act as ballast to counteract the buoyancy of their blubber . They have a thin layer of blubber and consequently are sensitive to temperature fluctuations, which cause migrations when water temperatures dip too low. Sirenians are slow-moving, typically coasting at 8 kilometres per hour (5.0 miles per hour), but they can reach 24 kilometres per hour (15 miles per hour) in short bursts. They use their strong lips to pull out seagrasses , consuming 10–15% of their body weight per day. While breathing, sirenians hold just their nostrils above
2392-454: The water. Like those of cetaceans, the hind limbs are internal and vestigial . The snout is angled downwards to aid in bottom-feeding . Sirenians typically make two- to three-minute dives, but manatees can hold their breath for up to 15 minutes while resting and dugongs up to six minutes. They may stand on their tails to hold their heads above water. Much like elephants, manatees are polyphyodonts , continuously replacing their teeth from
2444-607: The wild. The body parts of dugongs are used as medicinal remedies across the Indian Ocean. George Gaylord Simpson George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist . Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis , contributing Tempo and Mode in Evolution (1944), The Meaning of Evolution (1949) and The Major Features of Evolution (1953). He
2496-500: The word hypodigm in 1940, and published extensively on the taxonomy of fossil and extant mammals. Simpson was influentially, and incorrectly, opposed to Alfred Wegener 's theory of continental drift , but accepted the theory of plate tectonics (and continental drift) when the evidence became conclusive. He was Professor of Zoology at Columbia University , and Curator of the Department of Geology and Paleontology at
2548-461: Was an expert on extinct mammals and their intercontinental migrations. Simpson was extraordinarily knowledgeable about Mesozoic fossil mammals and fossil mammals of North and South America. He anticipated such concepts as punctuated equilibrium (in Tempo and Mode ) and dispelled the myth that the evolution of the horse was a linear process culminating in the modern Equus caballus . He coined
2600-836: Was awarded the Mary Clark Thompson Medal from the National Academy of Sciences . For his work, Tempo and mode in evolution , he was awarded the academy's Daniel Giraud Elliot Medal in 1944. He was elected to the American Academy of Arts and Sciences in 1948. He was awarded the Linnean Society of London 's prestigious Darwin-Wallace Medal in 1958. Simpson also received the Royal Society 's Darwin Medal 'In recognition of his distinguished contributions to general evolutionary theory, based on
2652-431: Was hunted to extinction by humans. The meat, oil, bones, and skin of manatees have commercial value. In some countries, such as Nigeria and Cameroon, African manatees are sold to zoos, aquariums, and online as pets, sometimes being shipped internationally. Though hunting of them is illegal, lack of law enforcement in these areas allows poaching . Some residents of West African countries, such as Mali and Chad, believe that
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#17327726235152704-561: Was measured by observing the length of cyclic movements (feeding cycles) of the manatees' perioral bristles used to introduce food into their mouths. Mean feeding cycle lengths varied based on the manatees' body size and the species of plant being consumed. Rates of food introduction, derived from mean feeding cycle lengths, were comparable to chewing rates reported in other studies. Manatees consumed plants with tubular stems and numerous branches more quickly than plants with flat blades. Food handling time using perioral bristles differed depending on
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