Editing Amazonian manatee (section)

==Physical characteristics==
[[File:Stamp_of_Brazil_-_1979_-_Colnect_263982_-_Amazonian_Manatee_Trichechus_inunguis.jpeg|left|thumb|Brazilian stamp from 1979 illustrating an Amazonian manatee]]
The Amazonian manatee is the smallest member of the manatee family and can be distinguished by its smoother rubbery skin and lack of vestigial nails on its flippers.<ref name="Edge" /> Ranges of body weight and size observed are {{cvt|7.5|–|346|kg|lb}} and {{cvt|76.0|–|225|cm|ftin}} for captive males, {{cvt|8.1|–|379|kg|lb}} and {{cvt|71.0|–|266|cm|ftin}} for captive females, and {{cvt|120.0|–|270|kg|lb}} and {{cvt|162.0|–|230|cm|ftin}} for free-ranging manatees, respectively.<ref name="Amaral" /> The maximum actual Amazonian manatee weight reported is {{convert|379|kg|lb}}.<ref name="Amaral" /> Calves of the species are born weighing {{cvt|10|–|15|kg|lb}} and {{cvt|85|–|105|cm|in}} long.<ref name="Amaral" /> The Amazonian Manatees increase in length approximately 1.6-2.0&nbsp;mm per day. This length is measured along the curvature of the body so absolute length can differ between individuals. As calves, they gain an average of 1 kilogram per week.<ref>{{cite journal |last1=Rosas |first1=Fernando Cesar Weber |title=Biology, conservation and status of the Amazonian Manatee Trichechus inunguis |journal=[[Mammal Review]] |date=1994 |volume=24 |issue=2 |pages=49–59 |doi=10.1111/j.1365-2907.1994.tb00134.x |bibcode=1994MamRv..24...49R}}</ref>

Amazonian manatees are large, cylindrically shaped mammals, with forelimbs modified into flippers, no free hind-limbs, and the rear of the body in the form of a flat, rounded, horizontal paddle.<ref name = "AnimalInfo" >{{cite web |title=Animal Info - Amazonian Manatee |url=http://www.animalinfo.org/species/tricinun.htm |website=Animal Info |publisher=animalinfo.org |access-date=23 October 2014}}</ref> The flexible flippers are used for aiding motion over the bottom, scratching, touching, and even embracing other manatees, and moving food into and cleaning the mouth.<ref name="AnimalInfo" /> The manatee's upper lip is modified into a large bristly surface, which is deeply divided.<ref name="AnimalInfo" /> It can move each side of the lips independently while feeding.<ref name="AnimalInfo" /> The general coloration is grey, and most Amazonian manatees have a distinct white or bright pink patch on the breast.<ref name="AnimalInfo" />

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 [[Anatomical terms of location#Cranial and caudal|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&nbsp;mm/month, based on wear and chewing rates.<ref name="Domning">{{cite journal |last1=Domning |first1=D.P. |last2=Hayek |first2=L.-A.C. |s2cid=83985834 |title=Horizontal tooth replacement in the Amazonian manatee (Trichechus inunguis) |journal=[[Mammalia (journal)|Mammalia]] |date=1984 |volume=48 |issue=1 |page=105 |doi=10.1515/mamm.1984.48.1.105 |url=https://www.degruyter.com/document/doi/10.1515/mamm.1984.48.1.105/html|url-access=subscription }}</ref>

The Amazonian manatee lacks nails on its flippers, setting it apart from other manatees.<ref name="Canisius"/> Additionally, Amazonian manatees have a very small degree of rostral deflection (30.4°), which can be used as an indication of where in the water column the animal feeds. A small degree of 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.<ref name="Domning 1982">{{cite journal |last1=Domning |first1=D.P. |last2=Morgan |first2=G.S. |last3=Ray |first3=C.E. |title=North American Eocene Sea Cows (Mammalia: Sirenia) |journal=Smithsonian Contributions to Paleobiology |issue=52 |pages=1–69 |date=1982 |doi=10.5479/si.00810266.52.1 |url=https://www.archive.org/download/northamericaneo52domn/northamericaneo52domn.pdf}}</ref>