In the history of the earth, were dinosaurs the biggest animals that ever lived?

By far, the largest animal known to exist either today or throughout history is the blue whale. Historically, these giant marine mammals reached up to 100 feet in length and weighed up to 150 tons. These days, thanks to whale hunters targeting the larger members of the species, blue whales generally only grow up to about 80 feet in length. As newborns, these whales start out around 25 feet in length. Nursing calves can drink up to 100 gallons of milk each day.

Blue whales were abundant in nearly all the oceans on earth until the beginning of the twentieth century. For over a century, they were hunted almost to extinction by whalers until protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 blue whales worldwide, in at least five groups.