The dwarf manatee (Trichechus pygmaeus, sometimes mistakenly referred to as Trichechus bernhardi) is a hypothetical species of manatee that is said to inhabit freshwater areas in the Amazon Basin, specifically limited to a tributary of the Aripuanã River. Marc van Roosmalen, the biologist who suggested it as a new species, claims it resides in shallow, fast-flowing waters and feeds on a different selection of aquatic plants than the Amazonian manatee, which prefers deeper, slower-moving rivers.
According to reports, the dwarf manatee migrates upstream during the rainy season, moving toward headwaters and shallow ponds as the rivers flood. If it is indeed a distinct species, its limited distribution would warrant classification as critically endangered. However, it is not currently recognized by the IUCN.
This manatee is said to measure about 130 cm (4.3 ft) in length and weigh around 60 kg (130 lb), which would make it the smallest living member of the sirenian order. It is described as being nearly black in color with a white patch on its underside. Some scientists speculate that it may simply be a juvenile form of the Amazonian manatee, although reported differences in body shape and coloration suggest otherwise. Despite this, mitochondrial DNA analysis has found no genetic differences between the two. If the dwarf manatee is a separate species, mutation rate estimates place their divergence at less than 485,000 years ago. However, Daryl Domning, a leading authority on manatee evolution and a research associate at the Smithsonian Institution, argues that the genetic data supports the idea that these animals are actually young Amazonian manatees, not a distinct species.