Evolution and systematics
The oldest sirenians are from the early Eocene and are associated to elephants, hyearaxes, and the extinct desmostylids. The trichechids might have arisen from dugongids within the late Eocene or early Oligocene. The subfamily Trichechinae (fashionable manatees) first appeared in freshwater Miocene deposits in Colombia. It is probably going that a lot of the early developmental historical past occurred in South America. The unfold to North America and Africa was possible within the Pliocene or Pleistocene.
Manatees have a normal physique size of 9–13 ft (3–Four m) and weigh 1,100–3,300 lb (500–1,500 kg) relying on the species. The physique is sort of hairless, sturdy and oval in cross part. Hind limbs are absent however vestigial pelvic bones stay embedded within the pelvic musculature. The tail is a broad, rounded paddle. Forelimbs are brief, versatile, and have tree to 4 nails besides within the Amazonian manatee. Color is grey to brownish and, within the discipline, might depend upon the epiphytes (algae, and so forth.) which might be rising on the pores and skin. The eyes are very small and there's no exterior ear (pinna). The exterior ear canal opening may be very small and troublesome to see. Testes are inside and the male genital opening is anterioventral simply posterior to the umbilicus. Mammary glands are paired and there's a single nipple in every axilla. The higher lips are cut up, coated with stiff vibrissae, and have been described as “prehensile” from the manatee’s capability to manipulate vegetation.
The manatees are discovered on each side of the Atlantic Ocean in tropical and subtropical areas. In West Africa, they vary from Senegal southward to Angola. Along the japanese Atlantic seaboard, they vary from the southeastern United States (primarily Florida) southward all through the Caribbean area to southeastern Brazil plus the Amazon River basin.
Manatees happen in coastal, estuarine and freshwater/riverine habitats. Since two of the species rely extensively on marine vegetation (seagrasses), they not often enterprise into deep waters.
Manatees are usually semi-social. The major social group is the cow-calf pair that will stay intact for 2 years or extra. There is not any pair bonding between women and men. Their reproductive habits has been described as “scramble promiscuity” whereby a number of males compete for mating rights with a single estrous feminine. Manatees might undertake native migrations in response to water temperature, water depth, or to the presence/absence of freshwater. Manatees talk utilizing sound, imaginative and prescient, style and contact. In turbid waters, acoustic communication is vital for sustaining the cow-calf bond. Most manatee sounds are within the 3–5 kHz vary however haven't been nicely studied.
Feeding ecology and weight-reduction plan
The manatees are the one marine mammals which might be herbivorous. However, they aren't obligate herbivores and can eat fish and invertebrates in some areas if they're accessible. The typical manatee weight-reduction plan consists of all kinds of marine and freshwater vascular crops and algae in addition to terrestrial vegetation which may be accessible on shorelines, overhanging and touching the water or floating resembling crimson mangrove propagules. Manatees might feed on backside, mid-water, or floating vegetation they usually might climb partially out of the water to entry shoreline vegetation.
Manatees mature at two to 11 years of age. Females could also be seasonally polyestrus. Gestation is about 12 months however has not been confirmed. Typically, a single calf is born and is 3.3–4.9 ft (100–150 cm) lengthy. Twins are uncommon. The mating system has been described as “scramble competition polygamy or polyandry” or “scramble promiscuity.” Individual estrous females are pursued by as many as 20 or extra males. While males might mature at three to 5 years of age, they is probably not ready to safe mating rights till they're bodily bigger. The typical calving interval is two-and-a-half to three years. There is not any pair bonding. Males play no function in care of the younger. Calves could also be born at any time of the 12 months however there could also be seasonal peaks in components of the vary.
The manatees are listed variously as endangered, threatened, or susceptible beneath worldwide and nationwide laws. The Convention on Trade in Endangered Species of Flora and Fauna (CITES) lists the Amazonian manatee and each subspecies of the West Indian manatee in Appendix I and the West African manatee in Appendix II. The World Conservation Union (IUCN) lists all three species, together with the subspecies, as Vulnerable. The United States Endangered Species Act (ESA) of 1973 lists each subspecies of the West Indian manatee and the Amazonian manatee as “endangered” and the West African manatee as “threatened.” The African Convention for the Conservation of Nature and Natural Resources lists the West African manatee as “protected” beneath Class A. The Florida manatee is protected by the Florida Manatee Sanctuary Act within the State of Florida, United States.
Significance to people
Historically, manatees have supplied people with a meat for food and bones and hides for instruments, implements, and leather-based. Some indigenous peoples might have used manatee components for medicinal and aphrodisiac functions. In Guyana and Florida, manatees have been used to clear vegetation-choked canals and waterways. As of 2003, whereas manatees are protected range-wide, they're nonetheless hunted for food in lots of areas. Ecologically, manatees might profit people not directly by recycling vitamins in seagrass beds, maintaining the vegetation in a continuously regenerating state and sustaining habitat for fish and invertebrates utilized by people. In some areas, particularly in Florida, the manatee is the premise for ecotourism.