And the giant plant eater, named Dreadnoughtus schrani, had not finished growing when it died between 83 million and 66 million years ago. 

"Dreadnoughtus schrani was astoundingly huge," said palaeontologist Kenneth Lacovara, who discovered the fossil skeleton in southern Patagonia and led the excavation and analysis. 

The hefty creature was a titanosaur, a clade of dinosaur that included several members that were the largest land animals to roam the earth.

"[Dreadnoughtus] weighed as much as a dozen African elephants or more than seven T-rex," said Dr Lacovara, an associate professor in Drexel University's college of arts and sciences.

The species, whose name means "fear nothing", had a thigh bone that stood just under two metres and neck vertebrae that were almost a metre wide. The bones at the end of its nine-metre long tail had an unusually large surface area to attach muscles, suggesting it was extremely muscular and powerful.

"With a body the size of a house, the weight of a herd of elephants, and a weaponised tail, Dreadnoughtus would have feared nothing," Dr Lacovara said.

"I think it's time the herbivores get their due for being the toughest creatures in an environment."

Palaeontologist Matthew Lamanna, from the Carnegie Museum of Natural History, said the biggest titanosaurs had remained a mystery because, in almost all cases, their fossils were very incomplete.

But remarkably, more than 70 per cent of theDreadnoughtus' skeleton, excluding its head, has been recovered, making it the most complete giant titanosaur yet discovered.

"It is by far the best example we have of any of the most giant creatures to ever walk the planet," Dr Lacovara said.

The well-preserved skeleton will give scientists unique insights into the anatomy, movement and evolution of these massive creatures.  

Dreadnoughtus' near-complete skeleton also meant scientists could accurately calculate its body weight, using measurements from the animal's thigh bone and upper-arm bone.

A smaller individual, with a less-complete skeleton, was also uncovered at the site. The group has published its discovery in the journal Scientific Reports.