Manatees (family Trichechidae, genus Trichechus) are large, fully-aquatic marine mammals sometimes known as sea cows.
The name comes from the Spanish manatí, which itself comes from a Carib word meaning "breast." They comprise three of the four living species in the order Sirenia, the other being the dugong, which is native to the Eastern Hemisphere.
The Sirenia is thought to have evolved from four legged land mammals over 60 million years ago, with the closest living relatives being the Proboscidea (elephants) and Hyracoidea (hyraxes).
The Trichechidae differ from the Dugong in the shape of the skull and the shape of the tail.
Dugongs have a forked tail, similar in shape to a whale's, while manatees' tails are paddle-shaped.
They are mainly herbivores, spending most of their time grazing in shallow waters and at depths of 1-2 m (3-7 ft).
Much of the knowledge about manatees is based upon research done in Florida and cannot necessarily be attributed to all types of manatees.
Generally, manatees have a mean mass of 410-545 kg (900-1200 lb), and mean length of 2.7-3 m (9-10 ft), with maximums of 3.6 m and 1775 kg seen (the females tend to be larger and heavier).
When born, baby manatees have an average mass of 30 kg.
On average, most manatees swim about 3 to 5 miles per hour.
However, they have been known to swim up to 20 miles per hour in short bursts.
Manatees inhabit the shallow, marshy coastal areas and rivers of the Caribbean Sea and the Gulf of Mexico (T. manatus, West Indian manatee), the Amazon basin (T. inunguis, Amazonian manatee), and West Africa (T. senegalensis, African manatee).
Florida is usually the northernmost range of the West Indian manatee as their low metabolic rate makes cold weather endurance difficult.
They may on occasion stray up the mid-Atlantic coast in summer.
Half a manatee's day is spent sleeping in the water, surfacing for air regularly at intervals no greater than 20 minutes.
Florida manatees (T. manatus) have been known to live up to 60 years, and they can move freely between salinity extremes; however, Amazonian manatees (T. inunguis) never venture out into salt water.
They have a large flexible prehensile upper lip that acts in many ways like a shortened trunk, somewhat similar to an elephant's.
They use the lip to gather food and eat, as well as using it for social interactions and communications.
Their small, widely spaced eyes have eyelids that close in a circular manner.
Manatees are also believed to have the ability to see in color.
They emit a wide range of sounds used in communication, especially between cows and their calves, yet also between adults to maintain contact and during sexual and play behaviors.