The dugong is distinguished from the manatees by its tail which has a straight or slightly concave tail. It is the only truly vegetarian sea-dwelling mammals, manatees are at best only venture into the sea. Dugongs eat vascular sea grasses that are comparable to terrestrial grasses. The roots of the grasses are the most nutritious and prized forage item. Dugongs chew vegetation mainly with rough horny pads which cover the upper and lower palates.
Adults only have a few peg-like molars on the back of their jaw.
Juveniles also have premolars, but these are lost in the first few years. Adult male dugongs have short stubby tusks that evolve from incisor teeth. It is not known what the tusks are used for. A few observations suggest that males use these for guiding their slippery mates in courtship, but there is no scientific evidence to support this idea. Little is known about dugong behavior and ecology of dugongs because of their combination of shyness and curiosity that inhibits observation without disturbance.