Trichechus manatus latirostris, like all Sirenians, are non-ruminant herbivores that live in loosely associated social groups (Hartman 1979). The body is massive and fusiform, resembling that of a seal. Body color is generally light to dark gray or brown. Calves are somewhat darker at birth, but lighten gradually within the first month. Adults may reach an average of 3 m (9.8 ft.) in length and 1000 kg (2,200 lbs). The largest adults grow to 4.6 m (15 ft.) and 1,620 kg (3,570 lbs) (Rathbun et al. 1990). Females tend to be larger than males of the same age. Hair is sparse, but distributed all over the entire body surface, with stiff whiskers around the face and muzzle. The upper lip is flexible and lined with bristles on both the upper and lower lip pads. The tail is large, rounded and horizontally flattened. No hind limbs are present but forelimbs are rounded and paddle-like. Females have 2 mammary glands at the axilla of each forelimb. The head is bulbous, with the small eyes set widely apart. Eyes close by contraction of a sphincter muscle around the eye. Orbits are lined with oil glands that bathe the corneas and a nictitating membrane is present. Nostrils are located on the dorsal surface of the snout. Ear openings are small, located immediately behind the eyes, and lack pinnae (USFWS 2001).Bones are massive and heavy, with the ribs and long bones of the limbs lacking marrow cavities (O'Dell 1982). A layer of blubber underlies the skin, and fat deposits are found around the intestines and muscles. Molars designed for crushing are grown continuously in the posterior portion of the jaw and move forward as old teeth wear down (Domning and Hayek 1986). Analysis of ear structure suggests that manatee hearing is not acute, and they may have difficulty in localizing sound that occurs outside of a narrow, low frequency range (Ketten et al. 1992). The brain is small in comparison to other similarly sized mammals.
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