65-ton dinosaur feared nothing
Weighing as much as a dozen African elephants and clad in armour-plated skin, Dreadnoughtus - meaning "fears nothing" - would have lived up to its name.
The supermassive dinosaur, whose almost complete skeleton was found in southern Patagonia, Argentina, breaks all records for the largest animal that ever walked the Earth.
It belonged to the family of Titanosaurs that were famous for their size and the bony plates that protected their bodies like a suit of armour.
Dreadnoughtus schrani, which inhabited a temperate forest at the southern tip of South America 77 million years ago, measured 85 feet from its head to tail and tipped the scales at 65 tons.
Like other "sauropod" dinosaurs of its type, it stood on four legs and had a long neck and tail, which may have been used in self defence.
Dr Kenneth Lacovara, from Drexel University in Philadelphia, US, who led the discovery team, said: "Dreadnoughtus schrani was astoundingly huge. It weighed as much as a dozen African elephants or more than seven T. rex.
"Shockingly, skeletal evidence shows that when this 65-ton specimen died, it was not yet full grown. It is by far the best example we have of any of the most giant creatures to ever walk the planet."
Explaining how he chose the dinosaur's name, he added: "With a body the size of a house, the weight of a herd of elephants, and a weaponised tail, Dreadnoughtus would have feared nothing.
"That evokes to me a class of turn-of-the-last century battleships called the dreadnoughts, which were huge, thickly clad and virtually impervious."
To grow so large, Dreadnoughtus would have had to consume colossal quantities of vegetation.
"Imagine a life-long obsession with eating," said Dr Lacovara said. "Every day is about taking in enough calories to nourish this house-sized body. I imagine their day consists largely of standing in one place.
"You have this 37-foot-long neck balanced by a 30-foot-long tail in the back. Without moving your legs, you have access to a giant feeding envelope of trees and fern leaves. You spend an hour or so clearing out this patch that has thousands of calories in it, and then you take three steps over to the right and spend the next hour clearing out that patch."
The skeleton contained 70% of the dinosaur's bones, excluding the skull, and included neck vertebrae over a yard wide, numerous ribs, a six-foot tall thigh bone, and a small section of jaw.
Bones from another, smaller Dreadnoughtus with a less-complete skeleton were also unearthed at the site.
Both animals are thought to have been buried quickly after a river burst its banks, turning the ground into "something like quicksand", said Dr Lacovara.
A description of Dreadnoughtus schrani appears in the journal Scientific Reports, published by the Nature group.