The heaviest animal in the world is the blue whale, which can weigh as much as 150 to 200 tons and can measure 100 feet from head to tail. Females usually weigh more than males. At birth, blue whale calves are about 25 feet long and weigh about 3 tons.
Blue whales are the largest animals that have ever lived on Earth. One of the largest known land dinosaurs, the sauropod Argentinosaurus, weighed only an estimated 180,000 pounds, about half the weight of the blue whale.
Although blue whales have few marine predators, aggressive whaling between 1900 and the mid-1960s significantly reduced their numbers. As of 2014, an estimated 10,000 to 25,000 blue whales remain.