The Sirenia order contains two families, the dugongs and the manatees, two modern taxons and four species. The sirenians are marine mammals, which dwell in the warm coastal waters of the Atlantic, Indian and Pacific oceans. They feed on seaweed, marine grass, various other aquatic plants and silt. They never come ashore; they live and die in the water.
Externally the sirenians slightly resemble the seals, but they don't have hind flippers, only the front ones, but they got a tail fluke: rounded (in the manatees) or whale-like (in the dugong), it is positioned not vertically, as the fishes tails, but horizontally, as in the case of the whales. The skeleton of the hind limbs is reduced almost completely. Only two or four bones remain from the hips. The skin is thick, up to 5 cm, in folds, almost hairless, with only sparse bristles scattered over it.
The canines are absent (they were present in some extinct species), the upper incisors, which slightly resemble tusks (up to 20 cm), are present only among the male dugongs. The manatees have up to ten molars in each half of the jaw, upper and lower, and the dugongs usually have only three. As in case of the elephants, as the teeth wear out, the front ones fall out, and the new ones grow from behind. The females have two teats, as the elephant cows do. Those, as well as other morphological traits, especially prominent in the extinct sirenians, show their and the elephants mutual ancestry from the ancient even-toed mammals, in whose memory some of the manatees still bear rudimentary `nails' on their front flippers.
THE DUGONGS AND THEIR KIN
Underwater, surrounded by marine flora and fauna, the female dugong gave birth to its' only calf and immediately, so that the flabby lung walls of the newborn would absorb their first breath of air, it positioned the calf onto its back, bringing it to the surface. The female swam so for about an hour, carrying the calf on its back and did not submerge. And then it dived carefully for a couple of hours, adjusting the calf to the element in which it was destined to live for the rest of its life.
And it fed the calf milk (underwater!). The father dugong was nearby, but it did not give the calf rides, didn't feed it anything, its' importance in protection against predators wasn't large, only attraction and sentimental feelings, but not responsibility, kept the male close to the family.
The dugongs are large animals, but are harmless and helpless. And quite boring, in the opinion of many observers. They eat all day long; sating themselves on eelgrass, swallow it almost without chewing. They feed underwater, where they dwell, without surfacing to breathe, for 10 minutes. The length of the biggest, exactly measured males from the nose to the tip of its tail - two meters ninety centimetres. The weight of the heaviest ones - 200-300 kilograms. 56 litres of fat can be extracted from such a blimp! Fat, meat, 'tears' of the dugong (the fatty lubricant that drips in the corners of their eyes when the captured dugong is dragged ashore) - all, in the local superstitions, promise luck or healing from various ills. Therefore the dugongs are hunted with spears and with nets, and that is why they are rare now.
The dugongs dwell in the coastal waters of the Red sea, in the Indian Ocean at the eastern coast of Africa, alongside the coastline and the islands of the Bengal bay, Sri Lanka, Indonesia, Northern Australia, Moluccas and Philippines.
And along the western shores of Africa, in the tropical zone, live the manatees - members of the sirenian family that is different from the dugongs'. They swim from the seas into rivers, have reached even the Chad Lake in some mysterious fashion and have settled there. Their close relatives found a habitat that is right for them on the other side of the Atlantic, at the eastern shores of America. They are the common manatee (from North Carolina to northeast South America) and the Brazilian manatee: the rivers of the Orinoco and Amazon watersheds.
Externally the manatees differ from the dugongs only by the rounded tail fin and a more hare-lipped upper lip, whose halves can move independently of each other. However, the dugongs are bigger than the manatees. The old males' measure up to four and a half meters and weigh up to 680 kilograms. But such specimens are rare now; two- and three-meter-long are more common. The old travellers used to tell about even seven-meter-long manatees, but in our days, nobody has seen such beasts.
The manatees are also different because of their shorter pregnancies - five-six months long (eleven for the dugongs). There can be two calves, they live for about two years with their parents, of which one and a half they suckle their mother. It feeds the calf underwater, lying horizontally with the belly downwards, without supporting it with a fin, nor standing vertically chest-high out of the water, as it often happens with the dugongs, people say.
It is strange, but exactly this rumoured sirenian 'humanoid' method of calf feeding has spawned, apparently, the legends, fairy tales and myths about the mermaids. The examiners of these legends believe so. However, it is possible that the dugongs do not feed their calves by pressed them to their chests with their flippers and raising their heads above water. Still, it is currently unknown. Yet the breast-feeding manatees were observed many times in aquariums and zoos and nobody has seen anything like it.
The natural history of the sea cows is quite ordinary, their behaviour is not renowned by manifestations of particular intelligence, and their way of life is monotonous. But their supernatural, mythical history is quite romantic, and its primeval roots lead far into the depths of the millennia - to the kingdom of the ancient Babylon. From there the myths of the fishtailed mermaids (initially - mermen!), changing their form and content, migrated to Phoenicia, ancient Greece, and later on to the other countries.
Two hundred years ago the sirenians (natural, not the fairy tale ones) lived in our seas as well, having able to adapt to quite cool waters of northern Pacific Ocean. For the manatees and the dugongs live only in warm water, no lower than 20 degrees, but even that is too cold for them. They just doze in it, spending the winter and waiting for the summer, when the salt and fresh waters at the northern end of their habitat will grow warmer.
The Commodore sirenians, or Steller's sea cows, have been discovered in 1742 by Bering's expedition. The name 'Steller's' they received in honour of the young explorer, the 'adjunct of natural history' and the doctor of that expedition, Georg Steller, who had first described the cabbage-eaters - so the Russians had called the Commodore sirenians, who fed on brown seaweed, the sea cabbage in the local language. But not only the natural preference of the cool waters (and some morphological traits) had distinguished the cabbage-eaters from their exotic relatives, but also their size: they were up to nine meters in length and four tonnes in weight.
'And from one single cow the meat for thirty-tree men could be easily given as food for one month' (Peter Yakovlev, ober-gitenforvalter).
They were! The fur trappers, who went to the Commodore islands soon after Bering's expedition, killed them all. The last one, they say, was eaten by a certain Popov with his cohorts in 1768.