There's one animal that exists today that measures up to the ancient behemoths. The blue whale can measure up to 100 feet in length and weigh as much as 150 tons. Today most blue whales only reach lengths of 75 to 80 feet because whale hunters tend to target the largest of the species, according to experts. About 50 people could stand on the tongue of an adult blue whale. Even a baby blue whale is gigantic — a newborn calf can be as long as 25 feet and drink as much as 100 gallons of its mother's milk a day. Endangered since the mid-1960s, only 10,000 blue whales are believed to still exist.