Although several other hippopotamus species existed far back in history, only two still remain in the modern day. These two living species are the common hippopotamus (Hippopotamus amphibius) and the pygmy hippopotamus (Choeropsis liberiensis). These tightly linked family members look very much alike physically, although pygmies appear like small scale versions of their significantly bigger cousins.
These herbivorous, semi-aquatic creatures inhabit the central region of Africa, including nations such as Ethiopia, Zambia, Tanzania, Gabon, Chad and the Central African Republic. Common hippos are massive mammals that usually weigh somewhere between 5,000 and 8,000 pounds, according to National Geographic. As far as sustenance goes, common hippos feed on lots of grasses, tender shoots and seeds.
The pygmy hippopotamus has a similarly sturdy and stout physique to the common hippo, but is a lot smaller weight-wise. The typical weight range for pygmy hippos is many, many times smaller than that of the common variety -- usually 352 to 605 pounds, indicates Animal Diversity Web of the University of the Michigan. Another key difference between the two species is lifestyle. Pygmy hippos usually are independent and solitary, while common hippos live in social groups. They live in western Africa in Sierra Leone, Liberia, Guinea and on the Ivory Coast. Like common hippos, they're herbivores. They eat mostly forbs, grasses, fruits, herbs, sedges and ferns.
In history, more hippo species indeed roamed the planet, such as the Malagasy hippopotamus (Hippopotamus lemerlei) of the southeastern African island nation of Madagascar. The European hippopotamus (Hippopotamus antiquus) and Hippopotamus gorgops are both examples of extinct hippos, as well.
Common hippopotamuses are classified as a "vulnerable" species, according to the International Union for Conservation of Nature Red List of Threatened Species in 2008. Pygmy hippopotamuses, however, are in a little more danger with "endangered" status from that same year. Population risks to common hippos include illicit ivory and flesh hunting and loss of available living environment. For pygmy hippos, the problems include both logging activities and hunting. Habitat destruction is also a serious problem for these endangered animals.
- National Geographic: Hippopotamus
- ARKive: Pygmy Hippopotamus
- The IUCN Red List of Threatened Species: Hippopotamus Lemerlei
- The IUCN Red List of Threatened Species: Hippopotamus Amphibius
- The IUCN Red List of Threatened Species: Choeropsis Liberiensis
- Animal Diversity Web: Hexaprotodon Liberiensis
- ARKive: Hippopotamus
- African Wildlife Foundation: Hippopotamus
- San Diego Zoo: Pygmy Hippopotamus
- Wildlife Conservation Society: Common Hippopotamus
- Anup Shah/Photodisc/Getty Images