Dr Arshad Toosy

Organisms alive today represent only tiny proportion of all the living things that have ever existed. Since life on Earth began, millions of new species have appeared and disappeared, changing through time in a continual process known as evolution. This process occurs largely as a result of natural selection, which favours the survival and reproduction of individuals that are better adapted to their environment than other members of the same species. Indus River dolphins (Platanista minor) are one example of this process.

There are many misconceptions about cetaceans (whales, dolphins, and porpoises), the most common of which is the idea that they re fish. In fact, they are mammals, like you and me. Millions of years ago they lived on land, their bodies were covered with hair, they had external ears, they walked on four legs, and they give birth to live young.

Indus River dolphins are related to all other dolphins, whales, and porpoises. Fossil evidence from the early Eocene epoch indicates that early dolphins (Protocetidae) were already aquatic 45-50 million years ago. Once in the ocean, it took millions of years for what is known as true cetaceans to develop. Early dolphins had little resemblance to the dolphins and whales we know today. According to one theory, primitive early mammals called Mesonychidae roamed across the plains of Africa during the early Eocene epoch. Although long extinct, these early mammals evolved to fill many ecological niches and ranged in size from that of a cat to a bear. It has even been suggested that they may be the antecedent of the modern horse.

By comparing the fossil structure of the jaw and teeth of Mesonychidae with the Protocetidae, scientists believe that a group living on the coast began spending more time foraging for food in the swamps and ocean. Eventually, over millions of years, cetaceans returned to the sea because there was more food and more space than on land. In time they may have become increasingly dependent on the ocean. One can imagine that during the transition between land and ocean, primitive dolphins were like the seals we see today, feeding in the ocean while coming back to the land for breeding. Forty million years ago, the ancestors of dolphins had evolved into Dorudontinae. Eventually, about 30 million years ago, early dolphins split into two main divisions known today as toothed whales (Odontoceti) and baleen whales (Mysticeti). Dorudontiae, the group from which modern dolphins arose, began to appear 25 million years ago.

Because dolphins started to evolve separately some 50 million years ago, their physical structure has had time to develop independently from that of land animals.

Although the fossil record indicates that there was a stage when they were amphibious, once early dolphins became aquatic, it did not take long for their hind limbs to disappear altogether. Cetaceans lost the qualities that fitted them for land existence and gained new qualities for life in water. Their hind limbs disappeared, their body became more tapered and streamlined to enable them to move swiftly through water, and a pair of flukes, which acted like a propeller, replaced the original tail. As part of this streamlining process, the bones in their front limbs fused together until their forelegs became a solid mass of bone and tissue, making very effective flippers. After the cetaceans' hair disappeared, they needed some way to preserve their body heat. This developed in the form of blubber, a thick layer of fat between the skin and the flesh that also acts as emergency source of energy.

Sea dwelling dolphins are thought to have been trapped in the River Indus when the Indus Valley was cut off from the once large Tethys Sea by the joining of the Indian sub-continent with Central Asia. Fossil records provide evidence of how marine dolphins were forced to adapt to their new environment and become the unique and well adapted species we know today. Until recently, they inhabited the entire Indus River, which starts in the Himalayan foothills and runs for about 2,880 km through Pakistan before finally flowing into the Arabian Sea. However, when the increase in human population resulted in the introduction of canal irrigation and cultivation into most areas of the Indus Valley, the destruction of the habitat of dolphins and other animals was inevitable. Because building barrages changed the ecology of the Indus River drastically, the dolphins could no longer move freely throughout the Indus and their population was split into separate groups.

As it is not possible for a single agency to carry out research and protection, co-operative action is needed to ensure the survival of dolphins. It is highly desirable for all relevant organizations and government departments to sue their resources in a coordinated manner to save this unique species from extinction. Otherwise it will become just part of history like the rhinoceros and tigers which used to roam in the Indus riverine jungles.