A study published in August in the journal Cell has shed light on the evolutionary history of the rhinoceros.
The rhinoceros family belongs to the Rhinocerotidae clade, which also includes the tapirs.
A clade includes species from a single common ancestor. The rhinoceros family diverged from the tapir family some 55-60 million years ago.
The family then evolved into over a hundred species distributed across the world, but only nine of them survived to the Late Pleistocene age (14 to 12000 years ago). Subsequent extinctions resulted in five extant species – the black, white, Sumatran, Indian, and Javan rhinoceroses – and four extinct ones – the Siberian, Merck, narrow-nosed and woolly rhinoceroses.
There are primarily three theories governing the story of rhinoceros evolution.
One theory, known as the ‘horn hypothesis’, emphasises horn morphology, and puts the Sumatran, the black, and the white rhinoceros species together for they have two horns. The ‘geographical hypothesis’ clubs species according to their geographical origins; for e.g., it puts the Sumatran, Javan, and Indian species together. The third hypothesis puts Sumatran rhinoceros with the other extant species.
