Dinosaur eggs discovered

The dinosaurs belong to the group called sauropods, among the largest to walk the planet

Six eggs containing the fossils of baby dinosaurs have been found in Argentina.

The skulls, which are remarkably well preserved, provide clues to how dinosaurs' heads developed and evolved.

The fossils were found at Auca Mahuevo, a site that has previously yielded similar fossils, dating back to about 65-145 million years ago.

The dinosaurs are titanosaurs - members of the group of long-necked, long-tailed plant-eaters called sauropods.

Click here to see the fossil skull

The first titanosaur was found in 1842. Since then, their bones have been located on every continent except Antarctica and Australasia.

Yet, very few skull specimens have been found, because the bones of the skeleton, except the limbs, are very fragile.

The nearly complete foetal skulls shed light on the evolution of some of the most notable cranial features of sauropod dinosaurs

Luis Chiappe and co-authors

These skulls - a few centimetres across - are so well preserved that even the teeth are visible, developing in the jaw.

The team behind the find - led by Luis Chiappe from the Natural History Museum of Los Angeles County - say the discovery could help explain certain evolutionary events in dinosaurs.

"The nearly complete foetal skulls shed light on the evolution of some of the most notable cranial features of sauropod dinosaurs," they write in the journal Science.

It is not clear precisely what type of titanosaur the dinosaurs belong to. They possess features of at least three different species.

At least 30 sauropods have now been identified. The largest, Argentinosaurus huinculensis, 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.

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Fossil skull: The eye socket is located in the centre, and the snout pointing to the left. Image: Science