Colours of Wildlife: Hippos
Created | Updated Apr 16, 2013
Hippos
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
This time I feature a truly iconic African mammal species, the Hippo, Hippopotamus amphibius. Its scientific name means 'Amphibious River Horse' although it is not closely related to horses. Hippos are artiodactyls – even-toed hoofed mammals – and currently it seems they are quite closely related to whales! More on that later.
Today there are only two hippo species: the big one, and the Pygmy Hippo, Choeropsis liberiensis which is rare and only occurs in west African rainforests. I will dedicate a separate article to that one sometime. The common hippo occurs all over sub-Saharan Africa, wherever there are large rivers and not too much disturbance by humans. Hippos stay mostly in the water during the daytime; their sensitive skins can easily dry out. Their eyes, nostrils and ears are positioned at the tops of their heads so these parts can stick out while the rest of their bodies are under water. When they submerge their nostrils close up. They are graceful swimmers, being able to dive and 'walk' along the bottom of the river. They mate and give birth (to a single baby) in the water. Hippo calves can also suckle underwater, folding their tongues around their mother's nipples. Sometimes hippos will bask in the sun on the riverbank. Their skins secrete a pinkish fluid, which offers protection against sunburn and moisturizes and conditions the skin. In old days people thought that hippos sweat blood!
But hippos are not fully aquatic; they are at home on land as well as in the water. Hippos emerge from the water at nighttime and feed. They graze on the riverbanks on lush grass, sometimes moving away into the surrounding savannah. These giant living lawnmowers keep the grass in check; after being grazed by them it sends up fresh, new leaves. This also prevents the grass from becoming old and dry, limiting the risk of fires. Hippos also fertilize the riverbanks with their dung.
Hippos have the largest jaws with the widest gape of all land mammals – they can open their mouths to almost 180 degrees. When they 'yawn' they're actually displaying their fearsome teeth. This may be a territorial display or intended to intimidate inferiors. Hippos have enormous canine teeth, those in the lower jaw being larger and sharper than those in the upper. These teeth are hidden by the huge, fleshy lips when a hippo's mouth is closed, but the yawning display shows them clearly. The lower canines can reach 50 cm/20” in length and have enormously long roots embedded in the jaw. With these hippos can inflict severe injuries on each other during territorial fights, or on animals like crocodiles in self-defense. Hippos also kill humans; indeed hippos kill more people than any other African mammal. Where hippos and people co-exist, the greatest danger to people is when they go fetching water at rivers in the early morning and risk getting between a hippo returning from a night's grazing and its water refuge. Hippos have also been known to attack people in boats, canoes or rafts.
Although they can be very aggressive, hippos are peaceful most of the time. They live in herds, with bulls, cows and calves of various ages mixed together. Most of the time yawning is enough to settle disputes. Hippos have a very deep bellowing call which they utter in a variety of situations. They also use scent marking for territorial and social purposes, the most notorious manifestation of which is the way they scatter their dung over the water or the riverbank, rapidly flicking their tails from side to side to splatter it widely in all directions.
This habit is the inspiration for a folk tale told among the San or Bushmen of Southern Africa. According to this tale the hippo, after its creation, asked if it could live in the water. The Creator, because of the hippo's size and appetite, feared that it would eat all the fish. So the hippo swore that it would come out of the river to eat grass instead of fish. As proof it said that it would always scatter its dung so that it could be inspected for the presence of fish bones.
Another tale, this one by the Ndebele, tells that the hippo once had long and beautiful hair. But the hare became jealous of it and set it on fire; the hippo then dove into a river to douse the flames but its hair had burnt off, and it was so ashamed of its hairless skin that it stayed in the water ever since.
Few people are aware that hippos used to be not exclusively African. Even in historic times they occurred in the Middle East, and not very long before that they occurred all over Europe and in Asia as well. The two European species, Hippopotamus antiquus and Hippopotamus gorgops (the latter found in Africa too) were bigger than the present-day hippo and were found even in Britain. But there were also European dwarf hippos. These were not related to the modern Pygmy Hippo, instead having been descended from big European hippos that got isolated on islands in the Mediterranean. There were several different species, living on islands like Malta, Sicily, Cyprus and Crete. Over the course of the Ice Ages the sea level changed, becoming lower during times of maximal ice extent and then rising up again in the interglacial periods. In times of low sea levels many of the islands were connected to the mainland or separated only by narrow straits over which hippos could swim. Then when the sea level rose again they became trapped on the islands and started changing. To cope with the limited food the islands offered they became smaller.
Asian hippos were generally on the small side and probably included a variety of forest-living types similar to the present pygmy hippo. In Africa there also used to occur a much greater diversity … about a million years ago no less than eight different species lived at the same time. In some lakes of East Africa numerous species existed alongside each other, avoiding competition by having different feeding behaviours and staying in different regions of the lakes. Also not long ago several hippo species occurred on the island of Madagascar. They were likely descended from hippos that had managed to swim across the sea strait separating the island from Africa, and diversified there into at least three different species, these also being quite small. None of the native Madagascan hippos survive today. The living pygmy hippo seems however to belong to an ancient lineage separate from the big hippos, perhaps one that goes back many millions of years.
But hippos pose an interesting evolutionary puzzle. For long they were regarded as being close relatives of pigs. And yet there are no fossils of very primitive pig-like forms. The fossils we have don't go back very far, the earliest good fossils (of the genus Kenyapotamus) being only about 16 million years old and already quite hippo-like. A group of extinct artiodactyls that show hippo-like features are the Anthracotheres, the earliest known members existing about forty million years ago. It might be that hippos are descendants of anthracotheres. More recently some very puzzling genetic evidence has emerged linking hippos with whales! What is strange about this is that the first true whales were already wading into the oceans fifty-five million years ago. If whales and hippos are more closely related to each other than either are to other artiodactyls it means that hippos must have a separate lineage going back at least as far as the earliest whale ancestor. This means there is a very long history of evolution that has not been preserved as fossils. This reminds us that there is much more going on than what we know about. Currently it is thought that hippos are indeed descendants of anthracotheres, and therefore these, too, have a very ancient pedigree and have split away from the other artiodactyls, including pigs, probably about sixty million years ago.
At present hippos are still numerous in Africa but declining, mostly as a result of conflict with humans. Provided they and the rivers and lakes they live in are protected, their future would be secure. Hippos can live as long as 60 years.
