Dreadnoughtus unearthed in Argentina (AAP)

A dinosaur seven times the size of T-rex and with a weaponised tail would fear nothing.

That's why a new titanosaur unearthed in Argentina by Kenneth Lacovara, from Drexel University in the US, and colleagues has been named Dreadnoughtus schrani.

"That evokes to me a class of turn-of-the-last century battleships called the dreadnoughts, which were huge, thickly clad and virtually impervious," Associate Professor Lacovara says in a statement about the study, which is published in the journal Scientific Reports.

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

It belongs to a group of big-bodied herbivores, called titanosaurs, that lived about 66-100 million years ago. Their sizes were estimated with incomplete fossils.

But now, after field seasons from 2005 through 2009, these scientists have 45.3 per cent of a skeleton and can say this dinosaur was about 59.3 metric tonnes and 26 metres long.

"It weighed as much as a dozen African elephants or more than seven T. rex," Lacarova says.

"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."

Lacovara said it probably was obsessed with eating in its temperate forest at the southern tip of South America some 77 million years ago, and wouldn't have had to move much.

"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."

Efforts to understand this dinosaur's body structure, growth rate, and biomechanics are ongoing areas of research within Lacovara's lab.

Prior to the description of this Dreadnoughtus schrani specimen, another Patagonian giant, Elaltitan, held the title of dinosaur with the greatest calculable weight at 47 tons.

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