Researchers said on Monday the fossils represent a titanosaur species named Ninjatitan zapatai that lived 140 million years ago during the Cretaceous Period.

They identified Ninjatitan as a member of the long-necked plant-eating group that walked on pillar-like all fours.

The dinosaur's incomplete skeletal remains were discovered south of the city of Neuquen.

The researchers said Ninjatitan demonstrated that the titanosaurs as a group first appeared longer ago than previously known.

"It is the oldest record known, not only from Argentina but worldwide," said study lead author Pablo Gallina from the National Council for Scientific and Technical Research of Argentina.

"Titanosaurs are recorded on various sides of the world but the oldest-known records were more modern than this find."

At a length of about 20 metres, Ninjatitan was a large dinosaur, but much smaller than later titanosaurs such as Argentinosaurus that reached a length of around 35m.

The researchers also said the presence of such an early titanosaur in Patagonia supports the idea titanosaurs originated in the Southern Hemisphere.

The findings have been published in the scientific journal Ameghiniana.

Titanosaurs are part of a larger dinosaur group called sauropods that includes others with similar body designs such as Brontosaurus and Diplodocus that lived in North America during the Jurassic Period, which preceded the Cretaceous Period.

A number of the titanosaurs that inhabited Patagonia achieved gigantic proportions such as Argentinosaurus, Patagotitan and Dreadnoughtus.

Jose Luis Carbadillo, another CONICET researcher, told a local publication the age of Ninjatitan's remains could have led people to assume the bones belonged to a dinosaur group pre-dating titanosaurs.

Australian Associated Press