Tail shape is the main physical difference between a manatee and dugong. The tail of a manatee is rounded, whereas a dugong has a forked tail. Another difference is that male dugongs have tusks while manatees do not.
Manatees and dugongs are the only two living mammal species that belong to the Sirenian animal order. Although these two mammals are in the same family, they live oceans apart. Manatees inhabit shallow waters near the Atlantic Ocean coastline, whereas dugongs reside in the shallows near the Pacific and Indian Ocean coastlines. These mammals prefer shallower water because neither have the capability of breathing underwater. Both manatees and dugongs can only hold their breath for two to four minutes while diving and thus rarely dive deeper than 10 feet.