The name hippopotamus is the combination of two Greek words “hippo” and “potamos”. Hippo means horse and potamos means river. Thus, hippopotamus is a horse living in or near bodies of water like, rivers, lakes, etc., and is generally known as the river horse.

It is the only living genus of the order artiodactyls (even-toed animals) of amphibious (living both on land and in water) nature, presently living in Africa and south Sahara.

It is characterised by its big head and mouth, broad snout, and massive jaw with 38-42 teeth. The skin is smooth with almost no hair, a unique adaptation to an aquatic life. Hippos stay in water during most of the day and at night they come out to search for food which consists of grass and plants. Hippos are good divers but do not actually swim. They move much faster under water by sinking to the bottom.

With short legs, the height is about 1.5 metres; however, it is one of the largest and the heaviest living mammals which weigh about four tonnes, half tonne less than the average weight of the heaviest living land mammal of the world — the elephant.

In herds of 25-30, male hippos compete with one another to establish their supremacy. The average age of the hippo is 40 years; they normally give birth to one calf at a time; however, there are some cases of twins also reported. The calf (baby hippo) at the time of birth is about 27-50 kg and after one year, it is about 250 kg.
Hippos possess a lot of commercial importance and are mostly hunt because of that — for instance, an adult hippo contains about 90 kgs of fat , the ivory of its teeth is superior and its hide.

Presently the hippopotami are confined to Africa. In the geologic past they were common in the old world. About one million ago, they were present in Africa, Europe, Mediterranean islands, and Madagascar. About four million year ago, the hippos were present in the Mediterranean and the region that is now Pakistan and India.
The rocks of continental origin, known as Siwaliks, are famous for their fossil mammals, including hippos and these rocks are well distributed in India, Pakistan and Kashmir.

The Geological Survey of Pakistan in collaboration with the Howard University, USA has collected the fossils hippo from Bhittani-Marwat Range, NWFP; Bun Khurma and Samwal areas to the South of Mirpore, Azad Kashmir. Another team from the Geological Survey of Pakistan and British Archaeologist Mission in Pakistan also collected the remains of the hippo from Pabbi Hills, Punjab.

In Bhittani-Marwat Range the fossils are encountered in 2.5 to two million years old rocks whereas, in Samwal and Bun Khurma areas the fossils hippo range from 3.4 to two million years old. In Pabbi Hills the elements of hippo have been found in 3.8 to 2.5 million years old rocks. No fossil hippo older than 3.8 million years has so far been reported from Pakistan.

The youngest fossils are however, reported from the Bhittani-Marwat Range and Samwal areas in about two million years old rocks. The hippopotamid material collected from the above mentioned areas is referred to hexaprotodon. The name was given to the fact that six incisor teeth were present in the maxilla.

The subcontinental hippos were more primitive and had a set of six incisors (anterior teeth) of equal size, three in each half of maxilla rather than four as present today in the modern form, hippopotamus amphibious.

Fossils provide important evidence about the environment in which the animal lived. Based on hippo`s mode of living (aquatic habitat) and diet (soft water vegetation) it can be said that the above mentioned areas during the period from 3.8 to two million years ago were occupied by a system of small rivers in which the hippos lived.
Later on, hippos became rare or absent. Maybe due to the rivers became shallow and dry causing the disappearance or the retreat of the hippo from these areas.

The remains of these million years old hippos can be seen in the museum of the Geological Survey of Pakistan Headquarters office Quetta, where they are on display along with other material.