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The Amazonian manatee (Trichechus inunguis) is a manatee species endemic to the Amazon Basin, occurring mainly in calm and lentic freshwater rivers and tributaries in Brazil, Peru, Colombia, and Ecuador. This species is the smallest of the sirenians and can be distinguished by its lack of vestigial nails on its flippers. It is known to have a coloration varying from dark gray to black, along with light patches on its ventral region.

Morphology and Physiology
The Amazonian Manatee is the smallest of the sirenians, reaching a maximum length no greater than 275 cm and weighing up to 420 kg. Calves of the species are born weighing between 10-15 kg and 85-105 cm long. The average growth rate for juveniles raised in captivity ranged between 1.6-2.0 mm/day, gaining an average of 1 kg per week. There are no significant size differences between the two sexes.

The general coloration of the Amazonian Manatee can range from dark gray to black with most having white or pink patches on its ventral side. They are cylindrically shaped with forelimbs modified into flippers along with a flat, horizontal paddle-like tail fluke. The Amazonian Manatee lacks nails on its flippers, a distinctive feature exclusive to its species. Their oarlike flippers are used to aid in forward propulsion to counter drag from water resistance, although rare, their flippers can be used for traction on the benthic floor. Accordingly, their flippers are specialized for a more ‘pelagic’ life which concurs with the lack of bottom plants found within their habitat.

Additionally, Amazonian Manatees have the smallest degree of rostral deflection (30.4°), which can be used as an indicator of its specialized feeding within the water column. A small degree of rostral deflection means that the end of the snout is straighter with regard to the caudal portion of the jaw. Animals with a greater degree of deflection, such as D. dugong at about 70° of deflection, are more of a benthic species, feed on the seafloor, and have snouts that point almost completely ventrally. Only T. senegalensis has a smaller rostral deflection of about 25.8°. This is believed to maximize the efficiency of feeding. A small degree of rostral deflection allows Amazonian manatees to feed more effectively at the surface of the water, where much of their food is found.

Amazonian manatees, similar to all living manatee species in the family Trichechidae, have polyphyodont teeth. Their teeth are continuously replaced horizontally from the caudal portion of the jaw to the rostral portion throughout the manatee's life, a unique trait among mammals. Only the closest living relative of order Sirenia, elephants, show a similar characteristic of teeth replacement, but elephants have a limited set of these replacement teeth. As the teeth migrate rostrally in the manatee, the roots will be resorbed and the thin enamel will wear down until the tooth is eventually shed. Referred to as cheek teeth, differentiation of manatee teeth into molars and premolars has not occurred, and manatees additionally do not have incisors or canine teeth. These teeth migrate at a rate of about 1–2 mm/month, based on wear and chewing rates.