Although partial skeletons of potentially larger cousins have been found before, Dreadnoughtus is the largest land animal for which a body size can be accurately estimated.
"It is by far the best example we have of any of the most giant creatures to ever walk the planet," said Dr Kenneth Lacovara of Drexel University in Philadelphia, who made the discovery.
Examination of the 77 million-year-old specimen - from the cretaceous period - suggested it may not even have been fully grown at the time it died, he writes in the Scientific Reports journal.
The bones unearthed in southern Patagonia between 2005 and 2009 included most of the vertebrae from the 10m tail, which could have acted like a heavy whip for defence, a neck vertebra measuring more than a metre across, and a thigh bone which, at almost 2m, is taller than the average man.
Also included were a shoulder blade, several ribs, toes, a claw, a small section of jaw and a tooth, along with most bones from both forelimbs and hindlimbs, adding up to 70 per cent of bone types and 45 per cent of the total skeleton.
The discovery of the thigh and upper arm bones in particular were crucial in allowing experts to calculate Dreadnoughtus' size.
"Titanosaurs are a remarkable group of dinosaurs, with species ranging from the weight of a cow to the weight of a sperm whale or more," said Dr Matthew Lamanna, another of the researchers. "But the biggest titanosaurs have remained a mystery because, in almost all cases, their fossils are very incomplete."
Another, known as Argentinosaurus, was of a similar size to Dreadnoughtus and could have been even larger, but its measurements remain a mystery with only half a dozen vertebrae, a shin bone and some other fragments ever recovered.
Lacovara said he had chosen the name "Dreadnoughtus" because the species reminded him of the "virtually impervious" battleships of the early 20th century.
"With a body the size of a house, the weight of a herd of elephants and a weaponised tail, Dreadnoughtus would have feared nothing," he said.
The creatures must have spent every day battling to take in enough calories.
"I imagine their day consists largely of standing in one place," he said.
"You have this 37 feet-long [11.3m] neck balanced by a 30 feet-long [9.1m] 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."
