Argentine paleontologist Juan Porfiri and Brazilian researcher Alexander Kellner said they were fortunate to find most of the animal's bones, around 70%, as usually archaeologists can only locate around 10%.
Scientists said the dinosaur's neck was unique in both its structure and size at 17 meters (56 feet), allowing them to claim the discovery of a new species from the largest plant-eating dinosaurs.
The researchers also said the giant herbivore, which lived approximately 88 million years ago in northern Patagonia in the late Cretaceous period, was between 32 and 34 meters (105 to 111 feet) in length, and as tall as a four-story building.
The creature was named Futalognkosaurus Dukei and is a member of the Titanosauria group.
"The first part of the name is indigenous Mapuche language for 'giant chief of the lizards', while the second part comes from Duke Energy Corp, the company that paid for the excavation," the agency said.
"This is one of the biggest in the world and one of the most complete of these giants that exist," Jorge Calvo from Argentina's National University of Comahue said.
The fossil bones were retrieved from other animal remains, as well as extremely well preserved leaves, which was evidence that the climate in Patagonia was warm and humid allowing rainforests to flourish.
Remains of other giant herbivores have been found in Argentina's Patagonia region, including the largest known dinosaur, Argentinosaur, measuring 37 meters (120 feet) long, and Puertasaurus, estimated to be between 35 and 40 meters (115 to 131 feet).