The term “sea cow” applies to all members of the Order Sirenia, which includes the dugong and the three species of manatee (West Indian, Amazonian, and West African). These large, herbivorous marine mammals share a common ancestry and a slow-moving, grazing lifestyle in warm, shallow coastal waters. Despite their superficial similarity, dugongs and manatees belong to separate families, Dugongidae and Trichechidae, respectively, having diverged genetically millions of years ago. This evolutionary split resulted in distinct physical forms, geographical ranges, and feeding strategies tailored to their specific environments.
Physical Distinctions
The most immediate visible difference between the two animals is the shape of their tail. Manatees possess a single, rounded, paddle-like fluke that resembles a large spoon or beaver tail. Dugongs, in contrast, have a distinctly notched, fluked tail similar to those found on dolphins or whales.
Their snouts and mouth structures reflect different feeding adaptations. The dugong has a broader, downward-facing, horseshoe-shaped snout, which allows it to root along the seabed for food. Manatees have a shorter snout and a unique, prehensile upper lip split into two sides, enabling them to grasp and manipulate plants. This flexible lip acts almost like a pair of hands for gathering vegetation.
A key difference is found in their dental structure. Adult male dugongs develop a pair of small, tusk-like incisor teeth, which are rarely seen in females or juveniles. Manatees lack incisors, possessing only cheek teeth, but they have a unique system of molar replacement. New molars continuously erupt at the back of the jaw and slowly move forward like a conveyor belt to replace older, worn teeth that fall out at the front.
Geographic Distribution and Habitat
The global ranges of dugongs and manatees are geographically separated. Dugongs are found exclusively in the Indo-Pacific region, inhabiting the warm, shallow coastal waters from East Africa and the Red Sea across to Australia. Large groups are concentrated around places like northern Australia and the Persian Gulf.
Manatees, conversely, are found in the Atlantic Ocean basin and its associated river systems, primarily in the Americas and West Africa. The West Indian manatee inhabits coastal areas from Florida down to Brazil, while the Amazonian manatee is restricted entirely to the freshwater systems of the Amazon River basin. The West African manatee occupies the coastal and inland waters along the western coast of the African continent.
Dugongs are almost exclusively marine mammals and rarely venture into freshwater systems. Manatees, particularly the West Indian and West African species, are comfortable in saltwater, brackish water, and freshwater environments. All manatees are highly sensitive to cold water and must remain in waters above about 68°F (20°C), often migrating long distances to warm springs or power plant outflows during colder months.
Feeding Habits and Ecology
Dugongs are specialized grazers that feed almost entirely on seagrasses, targeting the rhizomes beneath the seabed. They use their downward-pointing snout to efficiently root up entire seagrass plants, leaving distinct feeding trails or furrows in the ocean floor.
Manatees have a much more varied herbivorous diet. They function as generalist browsers, using their flexible, divided upper lip to crop floating vegetation, mangrove leaves, and various aquatic weeds. While they also eat seagrass, their feeding method tends to be less destructive to the root systems than that of the dugong.
The differences in their diets are linked to the abrasiveness of the food they consume. Manatees often ingest plants covered in sand and grit, which led to the evolution of their unique “marching molar” system to compensate for rapid tooth wear. Dugongs focus their grazing on softer rhizomes and have a finite set of molars, using their tusks primarily for social behaviors like fighting during mating season rather than as a feeding tool.