Blue whales are the largest animals ever known to have lived on Earth. These magnificent marine mammals rule the oceans at up to 100 feet long and upwards of 200 tons. Their tongues alone can weigh as much as an elephant. Their hearts, as much as an automobile. 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 and stretching to 25 feet. It gorges on nothing but its mother's milk and gains about 200 pounds every day for its first year.

Source: National Geographic