The Amazon river dolphin is one of the river dolphins formerly included in the superfamily Platanistoidea, making it paraphyletic; it has since been moved to Inioidea. Although not a large cetacean in general terms, this dolphin is the largest freshwater cetacean; it can grow larger than a human. Body length can range from 1.53 to 2.4 m (5.0 to 7.9 ft), depending on subspecies. Females are typically larger than males.[citation needed] The largest female Amazon river dolphins can range up to 2.5 m (8.2 ft) in length and weigh 98.5 kg (217 lb). The largest male dolphins can range up to 2.0 m (6.6 ft) in length and weigh 94 kg (207 lb).
They have unfused neck vertebrae, enabling them to turn their heads 90 degrees. Their flexibility is important in navigating through the flooded forests. Also, they possess long beaks which contain 24 to 34 conical and molar-type teeth on each side of the jaws. In colour, these dolphins can be either light gray or carnation pink.
When the water levels drop, the dolphins move either into the main river channels or into large lakes in the forest, and take advantage of the concentrated prey in these reduced water bodies. They feed on crustaceans, crabs, small turtles, catfish, piranha, shrimp, and other fish.
Adult males have been observed carrying objects in their mouths, objects such as branches or other floating vegetation, balls of hardened clay. The males appear to carry these objects as a socio-sexual display which is part of their mating system. The behaviour is "triggered by an unusually large number of adult males and/or adult females in a group, or perhaps it attracts such animals into the group. A plausible explanation of the results is that object carrying is aimed at females and is stimulated by the number of females in the group, while aggression is aimed at other adult males and is stimulated by object carrying in the group."
The male reaches sexual maturity at about 2 metres (6.6 ft) and the female at about 1.7 metres (5.6 ft). Most calves are born between July and September after a gestation period of 9 to 12 months; they are about 0.81 metres (2.7 ft) long at birth and weigh about 6.8 kilograms (15 lb). The young follow their parents closely for a few months, and often two adults are seen swimming with two or more small juveniles.
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