Argentinosaurus

The usual answer to "biggest dinosaur," and one of the hardest to pin down. Its story began in 1987 on a farm near Plaza Huincul in Argentina's Neuquén Province, and the giant is still known only from incomplete remains, chiefly back vertebrae and parts of the hips. From those bones, estimates run from about 30 to 35 meters long and 65 to 80 tons, with some published figures higher and some lower. That spread is the honest picture: Argentinosaurus was among the heaviest land animals ever, but a few vertebrae cannot rank it precisely against its titanosaur rivals, and it falls well short of a large blue whale.