All land animals evolved from sea-dwelling ancestors that left the water and adapted to life on land. Whales are one of several groups of animals that then did the reverse and went back to the sea. They evolved from hoofed land mammals and are distantly related to cows and pigs, while their closest living land relative is the hippopotamus!
THE WALKING WHALE
Ambulocetus, an early member of the whale family, lived more than 50 million years ago. A bit like an otter, it was equally at home on land and in water. Its front feet had small hooves for walking on land, while its back feet served to propel it through the water. Its name means “walking whale.”
The theory that whales are related to hippopotamuses was first suggested in 1870, but most scientists dismissed it as unlikely. More recently, careful comparison of whale DNA and hippo DNA has shown that hippos probably are the closest living relatives of whales.
THE FAMILY TREE
Scientists haven’t found enough fossils to trace the evolution of whales in full. However, a handful of fascinating discoveries from different parts of the whale family tree give us snapshots of evolution in action, with later species ever-better adapted to life in water as their limbs evolved into flippers and their nostrils moved backward to become blowholes:
There are now more than 100 species of whale and dolphin. They are divided into two main types: toothed whales, which hunt fish, and baleen whales, which use plates of bristles in the mouth to sift small animals from the water. The humpback whale is a type of baleen whale.