Bones of contention

For 20 years its bones lay forgotten on a university shelf, but now scientists believe they belonged to a dinosaur that was the ancestor of the largest animal ever to walk the earth.

Antetonitrus ingenipes was about 10m long and probably weighed a little less than an adult elephant. But he was a runt compared to what was to come.

A couple of million years later sauropods such as Apatosaurus would grow to more than 23m long and weigh in at about 16t. Apatosaurus, or as it is better known, Brontosaurus, was another giant land animal.

For a long time, palaeontologists did not know much about the evolutionary history of sauropods because the fossil record was scant.

A recent article in the Zoological Journal of the Linnean Society contends that Antetonitrus was firmly on the sauropod family tree and was undergoing major evolutionary transformation. But just where this dinosaur is on the tree is disputed.

In 2003 Wits researcher Adam Yates examined specimens kept in the university's store room. One of them had been collected by famed palaeontologist James Kitching in 1981, near Ladybrand in the Free State and had never been described.

"I saw Antetonitrus sitting on the shelves and it didn't take long to see that it was something special: it had all the sauropod features," said Yates, who now works at the Museum of Central Australia, in Alice Springs.

He still believes that the dinosaur he identified is a true sauropod and is what he calls the "golden spike" on the sauropod family tree, the first of its kind. He believes that the shape of its vertebrae and modifications to its foot gave it the lumbering gait associated withsauropods.

The co-author of the paper, Blair McPhee, from Wits university disagrees: "Antetonitrus wants to be a sauropod, and he is on the family tree but at what place on the tree do you put the name sauropod?"

McPhee believes Antetonitrus was a relatively primitive form that was experimenting with heavy-set locomotion - but its anatomy is not that of the genus.

Just where Antetonitrus lies on the sauropod family tree might soon be cleared up. There are efforts to find more sauropod fossils.

Another author of the paper, Dr Jonah Choiniere, is optimistic further evidence will be found that could explain how this family of dinosaurs dominated the earth for tens of millions of years.