Scientists hope its unusually well-preserved bones will help reveal secrets about some of the largest animals ever to walk the Earth.
The four-legged beast, with a long neck and powerful 29-foot tail, stretched about 85 feet long and weighed about 65 tons. That's more than seven times the weight of even a plus-size male African elephant.
Kenneth Lacovara of Drexel University in Philadelphia, who found the specimen in Argentina's southern Patagonia in 2005, said he can't claim it was the most massive dinosaur known, because the remains of comparably sized beasts are too fragmentary to allow a direct comparison.
But it's the heaviest land animal whose weight during life can be calculated directly with a standard technique that analyzes bones of the upper limbs, he said. And its bones indicate it was still growing when it died.
Lacovara and colleagues describe the plant-eating behemoth in a study released Thursday by the journal Scientific Reports. He said the bones were probably around 75 million to 77 million years old.
The creature got some media attention in 2009 when its excavated remains arrived in a large shipping container at a pier in Philadelphia. Since then, Lacorvara and colleagues have created computerized 3D reconstruction of the bones, and have started making miniaturized physical models of parts of the skeleton to investigate how the animal moved.
The bones will be returned next year to Argentina, where they will be housed permanently at a museum, researchers said.
In the new paper, the researchers named the beast Dreadnoughtus schrani; the second name refers to an American entrepreneur who supported the research. It belongs to a poorly understood group of dinosaurs called titanosaurs.
Experts not connected with the study said the remains were remarkably complete and well-preserved for a titanosaur. While no complete skull was found, the remains reveal more than 70 percent of the rest of the skeleton.
"We're getting a more complete picture of this giant animal than we have for any of the other big titanosaurs that are out there," said paleontologist Kristi Curry Rogers of Macalester College in St. Paul, Minnesota. The bounty of anatomical data should help scientists learn about variation in titanosaurs and their evolution, she said.
"This is pretty big news," Rogers said.
Jeff Wilson of the University of Michigan called the finding "a really great specimen."
Among the questions it can help scientists investigate, he said, is what kind of anatomical features were needed to let a dinosaur grow so huge.
Last May, other scientists announced that another huge dinosaur was being excavated in Patagonia. Wilson, who has seen some of its bones, said its size is comparable to Dreadnoughtus. He said he hopes scientists can determine whether the two beasts are closely related, or whether each came by its huge size independently.
Paul Upchurch of University College London said he thinks the recently announced dinosaur and another species, Argentinosaurus, were more massive than Dreadnoughtus. But he called Dreadnoughtus valuable for its combination of huge size and the completeness of its skeleton.
"If you're interested in super gigantic animals, this is probably the one you want to work on" to study how such beasts walked around, Upchurch said.