Based on its huge thigh bones, it was 40m (130ft) long and 20m (65ft) tall. Weighing in at 77 tonnes, it was as heavy as 14 African elephants, and seven tonnes heavier than the previous record holder, Argentinosaurus.
Scientists believe it is a new species of titanosaur - an enormous herbivore dating from the Late Cretaceous period.
By measuring the length and circumference of the largest femur (thigh bone), they calculatedthe animal weighed 77 tonnes.
This giant herbivore lived in the forests of Patagonia between 95 and 100 million years ago, based on the age of the rocks in which its bones were found.
But despite its magnitude, it does not yet have a name.