Blue Whale is known as Earth's largest Animal

The blue whale is a marine mammal belonging to the suborder of baleen whales (called Mysticeti). At 30 metres (98 ft) in length and 180 metric tons (200 short tons) or more in weight, it is the largest known animal to have ever existed. The endangered blue whale can eat some 4 to 8 tons (3.6 to 7.3 metric tons) of krill per day. The heart of a blue whale is as big as a car, and it's tongue is as long as an elephant. Average lifespan of blue whale is estimated at around 80 to 90 years.
Blue whales look true blue underwater, but on the surface their coloring is more a mottled blue-gray. The blue whale has a broad, flat head and a long, tapered body that ends in wide, triangular flukes.
Blue whale calves enter the world already ranking among the planet's largest creatures. After about a year inside its mother's womb, a baby blue whale emerges weighing up to 3 tons (2.7 metric tons) and stretching to 25 feet (8 meters). It gorges on nothing but mother's milk and gains about 200 pounds (91 kilograms) every day for its first year.
Blue whales live in all the world's oceans occasionally swimming in small groups but usually alone or in pairs. They often spend summers feeding in polar waters and undertake lengthy migrations towards the Equator as winter arrives.