A species
Blue whale
Balaenoptera musculus
The biggest animal known, living on tiny krill.
You and the blue whale last shared an ancestor about 95 million years ago (on 23 December, if life's history were one year).
The blue whale is the largest animal known to have lived, heavier than the largest dinosaurs, yet it feeds almost entirely on tiny krill. Surprisingly, apart from other whales, its closest living relatives are hippos. Its ancestors were four-legged land animals with hooves that left the land, moved into the sea and became swimmers.
The largest adults can grow to about 29 metres long, as long as three buses in a row, and weigh up to about 180 tonnes. Its back is mottled blue-grey with paler marks, while its belly is paler. It has no teeth. Instead, long grooves under its throat let its throat stretch very wide to scoop up mouthfuls of tiny shrimp-like krill and seawater, then strain the water out through a filter of baleen.
It lives in the open ocean around the world, from warm seas to the edge of polar ice. It stays out of the Arctic and enclosed seas such as the Mediterranean. Most blue whales travel between cold waters rich in food and warmer waters where calves are born. They are often alone or in pairs. One giant mouthful can give as much energy as about 200 days of food for an adult.
A tongue as heavy as an elephant
Its tongue weighs about as much as an elephant and is so large that a football team could stand on it.
Huge babies
A newborn calf is already about 7 to 8 metres long. It feeds on its mother's rich milk for about six to eight months, drinking about 200 litres each day.
Hunted almost to nothing
Antarctic blue whales fell from about 200,000 animals to fewer than 2,000 at their lowest point, less than 1% of their original number.