Dinosaur remains measuring 26 metres long and weighing 59,000 kilos have been uncovered in Argentina.
Scientists found the 77 million year old Dreadnoughtus in southern Patagonia.
They say the fossil was remarkably well-preserved.
Dreadnoughtus weighed more than an adult sperm whale or a heard of African elephants.
While strictly a vegetarian, the dinosaur was of a size that could have clobbered any predator foolish enough to attack it, say scientists.