Hippopotamidae

Taxonomy and Evolution

Hippopotamidae is a family of strong mammals that mostly live in water. They have smooth skin and stomachs with three parts. They walk on four toes on each foot and look a bit like pigs. But their closest living relatives are whales and dolphins, known as cetaceans.

There are two living species of hippopotamids. One is the pygmy hippo, which lives in the forests of West Africa. The other is the common hippo, often just called the hippopotamus. The word "hippopotamus" can refer to all hippopotamids, but it is most often used for the common hippo and its group.

Characteristics

Hippopotamids are large mammals with short, stumpy legs and barrel-shaped bodies. They have big heads with broad mouths and nostrils on top of their snouts. They walk on four toes, like pigs, but all their toes are used for walking. Unlike pigs, they don’t have hooves—instead, they have tough pads on each foot. Their stomachs have three parts, but they are not true ruminants.

These animals have smooth skin without special glands for oil or sweat, so they can dry out quickly when not in water. Their teeth are large and strong, especially their canine tusks, which keep growing throughout their lives. Their other teeth are also big and complex, perfect for chewing plants. The number of front teeth can vary, but the general pattern is shown below:

Evolution

Main article: Evolution of hippopotamids

Hippopotamids come from a group of animals called anthracotheres. These animals lived long ago and looked a bit like small hippos. Hippos separated from these ancestors during a time called the Miocene. The oldest hippos we know about lived in Africa and Arabia about 7.4 million years ago. Later, they spread to other places.

Today, there are only two kinds of hippos left: the common hippo and the pygmy hippo. They are the last of two different family lines. In the past, there were many more kinds of hippos, but they are now gone.

The lower teeth of hippos can look similar to the tusks of elephants. Even though hippos and elephants are not closely related, both use these strong teeth when they fight.

Species

The systematics and taxonomy here mostly follows a review by J.-R. Boisserie and the American Society of Mammalogists.

Recent species

• Genus Hippopotamus – true hippopotamuses
  • Hippopotamus amphibius – hippopotamus (Africa)
  • †Hippopotamus lemerlei – Lemerle's dwarf hippopotamus (Madagascar; Holocene)
  • †Hippopotamus madagascariensis – Madagascan dwarf hippopotamus (Madagascar; Holocene)
• Genus Choeropsis – pygmy hippopotamuses
  • Choeropsis liberiensis – pygmy hippopotamus (west Africa)

Fossil species

• Genus Hippopotamus – true hippopotamuses
  • †Hippopotamus antiquus – mainland Europe & British Isles; Pleistocene
  • †Hippopotamus creutzburgi – Crete; Pleistocene
  • †Hippopotamus minor – Cyprus; Pleistocene to Holocene
  • †Hippopotamus melitensis – Malta; Pleistocene
  • †Hippopotamus pentlandi – Sicily; Pleistocene
  • †Hippopotamus laloumena – Madagascar; Holocene
  • †Hippopotamus gorgops – Africa Late Miocene–Middle Pleistocene
• Tentatively placed into Hippopotamus:
  • †Hippopotamus aethiopicus – Kenya & Ethiopia; Pliocene -Pleistocene
  • †Hippopotamus afarensis – Ethiopia, formerly genus Trilobophorus; Pliocene
  • †Hippopotamus behemoth – Israel, Early Pleistocene
  • †Hippopotamus kaisensis – Central Africa; Pliocene
  • †Hippopotamus sirensis – Morocco & Algeria; Pleistocene
• Genus Hexaprotodon – hexaprotodons or Asian hippopotamuses
  • †Hexaprotodon bruneti – Ethiopia; Pliocene
  • †Hexaprotodon coryndoni – Ethiopia; Pliocene
  • †Hexaprotodon crusafonti – Spain; Late Miocene (syn. Hexaprotodon primaevus)
  • †Hexaprotodon hipponensis – Algeria
  • †Hexaprotodon imagunculus – Uganda and Congo; Pliocene
  • †Hexaprotodon iravaticus – Myanmar; Pliocene – Pleistocene
  • †Hexaprotodon karumensis – Kenya and Eritrea; Pleistocene
  • †Hexaprotodon namadicus – India; (possibly same as Hex. palaeindicus)
  • †Hexaprotodon palaeindicus – India;
  • †Hexaprotodon pantanellii – Italy; Pliocene
  • †Hexaprotodon protamphibius – Kenya and Chad; Pliocene
  • †Hexaprotodon siculus –
  • †Hexaprotodon sivajavanicus – Indonesia
  • †Hexaprotodon sivalensis – India
  • †Hexaprotodon sp. (undescribed) – Myanmar
• Genus Archaeopotamus – formerly included in Hexaprotodon
  • †Archaeopotamus harvardi – Arabian Peninsula and Central Africa; Miocene – Pliocene
  • †Archaeopotamus lothagamensis – Kenya; Miocene
• One or two undescribed species
• Genus Saotherium – formerly included in Hexaprotodon
  • †Saotherium mingoz [it] Chad; Pliocene