text: what is the largest mammal indigenous to the amazonian rainforest?   well, since you did not specify terrestrial or aquatic, then:  the tapir (a grazer animal) is the largest terrestrial mammal of the amazon weighing up to ~650 lbs.     however, as far as the aquatic mammals are concern, there are two species of large indigenous dolfins and the rare amazon "manatee" which is arguably the largest of all indigenous amazonian mammals period.