C. l. liberiensis C. l. heslopi The Pygmy Hippopotamus (Choeropsis liberiensis or Hexaprotodon liberiensis) is a large mammal native to the forests and swamps of western Africa (the scientific species classification means "of Liberia", as this is where the vast majority lives). The pygmy hippo is reclusive and nocturnal. It is one of only two extant species in the hippopotamidae family, the other being its much larger cousin the common hippopotamus.
The pygmy hippopotamus displays many terrestrial adaptations, but like its larger cousin, it is semi-aquatic and relies on proximity to water to keep its skin moisturized and its body temperature cool. Behaviors such as mating and birth may occur in water or on land. The pygmy hippo is herbivorous, feeding on whatever ferns, broad-leaved plants, grasses and fruits it finds in the forests.
A rare nocturnal forest creature, the pygmy hippopotamus is a difficult animal to study in the wild; it also lives primarily in countries with a great degree of civil strife. Animals lead mostly solitary lives; they are sometimes seen in pairs or threesomes, but never large pods like the common hippopotamus. They are not known to be territorial.
Pygmy hippos were unknown outside of West Africa until the 19th century. Introduced to zoos in the early 20th century, they breed well in captivity and the vast majority of research is derived from zoo specimens. The survival of the species in captivity is more assured than in the wild: the World Conservation Union estimates that there are less than 3,000 pygmy hippos remaining in the wild. Pygmy hippos are primarily threatened by loss of habitat, as forests are logged and converted to farm land, and are also vulnerable to poaching, hunting, natural predators and war.

Taxonomy and origins
A distinct subspecies of pygmy hippopotamus lived in Nigeria until at least the 20th century. The existence of the subspecies, makes Choeropsis liberiensis liberiensis (or Hexaprotodon liberiensis liberiensis under the old classification) the full trinomial nomenclature for the Liberian Pygmy Hippopotamus. The Nigerian Pygmy Hippopotamus subspecies was never studied in the wild and never captured. All research and all zoo specimens are the Liberian subspecies. The Nigerian subspecies is classified as C. liberiensis heslopi.

Nigerian subspecies

Main article: Hippopotamus#Evolution Evolution
Several species of small hippopotamidae have also become extinct in the Mediterranean in the late Pleistocene or early Holocene. Though these species are sometimes known as "Pygmy Hippopotami" they are not believed to be closely related to C. liberiensis. These include the Cretan Dwarf Hippopotamus (Hippopotamus creutzburgi) of Crete, the Sicilian Hippopotamus (Hippopotamus pentlandi) of Sicily, or the Maltese Hippopotamus (Hippopotamus melitensis) of Malta. There were also several species of pygmy hippo on the island of Madascar (see Malagasy Hippopotamus).

Description
The behavior of the pygmy hippo differs from the common hippo in many ways. Much of its behavior is more similar to that of a tapir, though this is an effect of convergent evolution.

Behavior
Like the common hippopotamus, the pygmy hippo emerges from the water at dusk to feed. It relies on game trails to travel through dense forest vegetation. It marks the trails by spreading feces by vigorously waving its tale while defecating. The pygmy hippo spends about six hours a day foraging for food.

Diet
A study of breeding behavior in the wild has never been conducted; the artificial conditions of captivity may cause the observed behavior of pygmy hippos in zoos to differ from natural conditions. Sexual maturity for the pygmy hippopotamus occurs at between three to five years.

Reproduction
The vast majority of pygmy hippos live in Liberia with smaller populations, mostly clustered around the Liberian border, in Côte d'Ivoire, Guinea and Sierra Leone. Though the range of the pygmy hippo as such has not been significantly reduced, populations are now fragmented. C. liberiensis lives exclusively in rivers running through forested regions.

Conservation
While the common hippopotamus was known to Europeans since classical antiquity, the pygmy hippopotamus was unknown outside of its range in West Africa until the 19th century. Due to their nocturnal, forested existence, they were poorly known within their range as well. In Liberia the animal was traditionally known as a water cow.