The blue whale is the largest known animal to have ever lived, far bigger than any of the dinosaurs. An adult blue whale can grow to about 30m long and weigh more than 180,000kg, equivalent to around 40 elephants, 30 Tyrannosaurus rex dinosaurs, or about 2,670 average-sized men.
But it started as something far smaller. Like all other whales, the blue whale, Balaenoptera musculus, evolved from a four-legged mammal that lived on land some 48 million years ago and grew just 1.8m long. This common ancestor, called Pakicetus, foraged in streams and some of its descendants became adapted to living in the water. This eventually resulted in a completely aquatic creature called Dorudon, which lived 37 million years ago and grew 4.5m long. In Dorudon, we see the beginnings of what makes whales so special. Its nostrils had moved back from its snout to the top of its head. Its forelimbs had become stiff flippers, its trunk was elongated, its hind limbs were virtually non-existent and its tail had evolved into two rubbery flukes, which propelled the animal forward through the water as they were wafted up and down, rather than the side-to-side motion of a fish’s tail.
Then something extraordinary began to happen. Because these mammals were floating in the sea, supported by the buoyancy of the saltwater, they escaped the limitations of gravity and could become bigger and bigger, with the blue whale out-monstering every other cetacean species. Turn the page for some amazing facts about this extraordinary mammal.