manatees additionally do not have incisors or canine teeth. These teeth migrate at a rate of about 1–2 mm/month, based on wear and chewing rates. The Amazonian manatee lacks nails on its flippers, setting it apart from other manatees. 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. Behavior and biology The Amazonian manatee is the only sirenian that lives exclusively in freshwater habitat. The species relies on changes in the peripheral circulation for its primary mechanism for thermoregulation by using sphincters to deflect blood flow from areas of the body in close contact with water. They also rely on subcutaneous fat to reduce heat loss. Manatees have nostrils, not blowholes like other aquatic mammals, which close when underwater to keep water out and open when above water to breathe. Although manatees can remain under water for extended periods, surfacing for air about every five minutes is common. The longest documented submergence of an Amazonian manatee in captivity is 14 minutes. Manatees make seasonal movements synchronized with the flood regime of the Amazon Basin. They are found in flooded forests and meadows during the flood season, when food is abundant. The Amazonian manatee has the smallest degree of rostral deflection (25° to 41°) among sirenians, an adaptation to feed closer to the water surface. It is both nocturnal and diurnal and lives its life almost entirely underwater. Only its nostrils protrude from the surface of the water while it searches river and lake bottoms for vegetation. The Amazonian and West Indian manatees are the only manatees known to vocalize. They have been observed vocalizing alone and with others, particularly between cows and their calves. Diet The manatees themselves