Rhinoceroses and hippopotamuses look superficially similar. If you were to squint at the two animals side by side, you might think the hippo is simply a rhino missing its horn. Both are large, heavy, thick-set herbivores with thick skin, pillar-like legs and enormous heads.
What's the difference between rhinos and hippos?
Both can be found in Africa, often in the same region. But despite their looks, they have a number of key physical, ecological and behavioural differences. And it turns out that they are not closely related at all. Here is all the information you need to tell a rhino from a hippo.
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Are hippos and rhinos related?
Though they are both mammals, rhinoceroses and hippopotamuses have followed very different evolutionary paths for tens of millions of years. Rhinoceroses are Perissodactyls – aka 'odd-toed ungulates'.
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Their nearest relatives are horses and tapirs (mammals from South and Central America that resemble pigs with nose trunks).
Hippos are Artiodactyls – aka 'even-toed ungulates', a group of animals that includes pigs, antelopes, sheep, goats, camels, giraffes and cattle. It's hard to believe but the hippo's closest living relatives are the cetaceans: whales and dolphins. They evolved from a common ancestor called anthracotheres – a semi-aquatic pig-like creature – but their evolutionary paths diverged some 50 million years ago.
There are just two species of hippopotamus: the common hippopotamus and the pygmy hippopotamus. Both are found in sub Saharan Africa. Two species of rhino are also found in similar regions of Africa, the white and black rhino respectively. However, there are three rhino species in Asia: the great one horned or Indian rhino (in India), the Javan rhino and the Sumatran rhino.
Where do rhinos and hippos live?
In Africa, white and black rhinoceroses are found in open savannah and grass plains of eastern and southern Africa while the black rhino also lives in semi-desert and forests. The three Asian species of rhino prefer dense jungle.
Hippos are amphibious, spending much of their time in waterholes, rivers and lakes. They have sensitive skin and the water protects them from the sun. It is also a refuge from terrestrial predators such as lions, hyenas and wild dogs. But they do not feed in the water – instead, under the cover of night, they leave the water to find suitable grazing.
Are hippos and rhinos the same size?
The largest common hippos are male and can, in exceptional circumstances, reach 5m long, 1.6m tall and weigh over 4000kg. Pygmy hippos stand only 1m tall, are less than 2m long and weigh just 250kg.
The largest rhino, the white rhinoceros, may reach a similar weight, height and length to a common hippo.
The Sumatran rhinoceroses is the smallest of the five rhino species. And while slightly shorter than a common hippo, it can be up to 3m long and weigh up to 1000kg.
Are they sociable?
Individuals of most rhinoceros species tend to be loners outside of the breeding season. Males will seek out mates when it is time to breed and mothers will stay with their young. But for the rest of the time, the rhino lives alone. White rhinos, however, are more sociable and may sometimes be found in small groups (the collective noun for rhinos is a 'crash' of rhinos).
Hippos are far more likely to be seen in groups, in water at least. Here they gather in protective gatherings known as pods or bloats of up to 30 individuals and naturalists have observed a social hierarchy and fairly complex communications and interactions. On land hippos tend to forage on their own.
How do they defend themselves?
Both rhinoceroses and hippopotamuses will defend themselves when threatened. Despite their bulk, they are nimble and can charge opponents with terrifying power. The hippo can open its mouth enormously wide and can bite an enemy, such as a crocodile, with the largest canine teeth of any land mammal, reaching over 50cm (and in extreme cases over 1m) in length.
The larger rhinos can use their horns for self-defence and it can be a deadly weapon with 3000-4000kg of angry rhino behind it. Both males hippos and rhinos use their teeth and horns respectively in battles with rivals during the breeding season.
Do hippos and rhinos have the same diet?
Rhinoceroses have fairly broad diets, but different species have their own feeding adaptations. White rhinos have squared mouths for getting close to the ground for grazing. Black rhinos have more pointed mouths for browsing leaves, twigs and fruit. The three Asian rhinos are somewhere in between, eating twigs and leaves but also tucking into grass and even aquatic plants whenever they find them.
Hippos are most similar to the white rhino, grazing on short grass. They will eat fallen fruit if they come across it. Occasionally, they will eat meat in the form of small mammals or reptiles that are unfortunate enough to cross a hungry hippo's path.
Are either of them at risk of extinction?
Hippos are much more common than rhinoceroses. There are between 120000-150000 hippos in Africa, with 2000-3000 belonging to the smaller species, the pygmy hippo.
The five species of rhinoceros comprise fewer than 27,000 animals in total, with just under 16,000 of these being white rhinos. The population of the rarest species, the Javan rhino, may comprise just under 80 individuals left in the wild.
Are they deadly to humans?
Rhinos and hippos do not attack humans willingly but may become aggressive if they feel threatened, particularly if they have young.
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The hippo is responsible for 500-1000 human deaths every year, usually people travelling in small boats through hippo territories. It's thought that the hippos mistake the boats for crocodiles, which they fear and often attack on sight.
This death toll makes hippos among the most dangerous large animals on earth.
There are occasional reports of rhinos charging and killing humans. In India between 1 and 3 people are thought to be killed by rhinos each year.
