The dwarf manatee (Trichechus pygmaeus", or mistakenly Trichechus bernhardi) is a possible species of manatee found in the freshwater habitats of the Amazon, though restricted to one tributary of the Aripuanã River. According to Marc van Roosmalen, the scientist who proposed it as a new species, it lives in shallow, fast-running water, and feeds on different species of aquatic plants than the Amazonian manatee, which prefers deeper, slower-moving waters and the plants found there. The dwarf manatee reportedly migrates upriver during the rainy season when the river floods to the headwaters and shallow ponds. Based on its small range, the dwarf manatee is suggested to be considered critically endangered, but at present it is not recognized by the IUCN.
The dwarf manatee is typically about 130 cm (4.3 ft) long, and weighs about 60 kg (130 lb), making it the smallest extant sirenians. It is overall very dark, almost black, with a white patch on the abdomen. It may actually represent an immature Amazonian manatee, but it is reported to differ in proportions and colour. It is, however, at least very closely related, as mtDNA has failed to reveal any difference between the two. Mutation rates in manatees – if the dwarf manatee is distinct – suggests a divergence time of less than 485,000 years. Daryl Domning, a Smithsonian Institution research associate and the world's foremost experts on manatee evolution, has stated that the DNA evidence actually proves that these merely are immature Amazonian manatees.
Disregarding its questionable validity as a species, the proposed name Trichechus pygmaeus is problematic. A formal description using that name was submitted to Nature, but it was rejected and consequently the article has only been published online. This has resulted in the invalidation of the name following chapter 3, article 8.6 of the ICZN Code.
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