We now have a complete dinosaur, so we have the data here to compare all the other titanosaurs

Kristina Curry Rogers, Science Museum of Minnesota

The juvenile creature, which lived 65-70 million years ago, was discovered in a quarry in Madagascar.

The Titanosauria were the last surviving sub-group from the giant sauropod dinosaurs, famed for their huge bodies, long necks and tails, but small heads.

And yet, the dearth of fossil skull specimens from these dinosaurs has left scientists wondering what the animals really looked like - face to face. The new creature should help fill in some of the knowledge gaps.

Notoriously incomplete

The fossils were pulled out of soft sandstone in Berivotra in the northwest of Madagascar. They have been detailed in the journal Nature and the animal from which they came called Rapetosaurus krausei.

The bones must have been buried very fast after the creatures died to have allowed such good preservation. Sauropod specimens, in particular, were notoriously incomplete, often with no skull, said Kristina Curry Rogers, from the Science Museum of Minnesota, US, who co-authored the Nature paper.

"Sauropod bones, except for the limb bones, are very fragile," she told BBC News Online. "Because they had such long necks and because they were so enormous, their bones showed a lightening of the skeleton - they were filled with air. And that means they broke apart easily and had only a low chance of being incorporated into the fossil record."

Having now recovered an exceptional specimen, with both head and body intact for the first time, Kristina Curry Rogers said palaeontologists could build a more realistic picture of titanosaurs.

Horsey features

It settled, she said, the argument over whether these animals had a slender-snouted, horsey look with nostrils on top of the head and small teeth positioned to the front of the jaw; or rather a bulldog-shaped head with nostrils on the side.

Rapetosaurus krausei shows the former to be the case.

"That's our key finding here," Kristina Curry Rogers said. "We now have a complete dinosaur, so we have the data here to compare all the other titanosaurs, which are known from only fragmentary specimens. It gives us a benchmark."

The first titanosaur was found in 1842. Since then, their bones have been located on every continent except Antarctica. At least 30 of these herbivores have now been identified.

The largest, Argentinosaurus huinculensis, was found in Patagonia, was more than 40 metres in length and weighed about 90 tonnes. It was one of the largest creatures to ever walk the Earth.

Titanosaurs were the most successful of the sauropods. They survived right up to the mass extinction of species 65 million years ago.

Sauropod skeletons break down quickly