Tamar Kahn
12 November 2009
Cape Town — Scientists have discovered a new dinosaur species in SA that offers fresh insight into how these ancient creatures evolved from nimble carnivores that walked on two legs to lumbering plant eaters that moved about on all fours.
Researchers unearthed fossil bones from two dinosaurs belonging to the new species, dubbed Aardonyx celestae, on a farm near the town of Senekal in the northern Free State.
"It was an early relative of the sauropod, the largest land animals that ever existed," said University of the Witwatersrand paleontologist Adam Yates, lead author of a paper describing the discovery published this week in Proceedings of the Royal Society B, a London-based peer- reviewed journal.
The fossils, which are estimated to be about 195-million years old, were discovered by a Wits postgraduate student, Marc Blackbeard, who began excavating the sites under Yates's direction five years ago. "We knew there were likely to be some fossils in these 'bone beds' discovered by James Kitching about 20 years ago, but we did not expect to find anything of this magnitude," Yates said.
The team believes Aardonyx walked around on two legs but could drop down onto all fours.
It had a small head, long neck, barrel chest, tree-trunk legs, a whip-like tail and flattened feet with big claws that supported its body weight on the inside of the foot. It stood about 6m high at the hip, and had a widely gaping mouth.
"It gives us a lot of clues about the possible habitat in which sauropods evolved and in which sequence they acquired their characteristics," he said. "The granddaddy of all dinosaurs was a very small animal, probably no more than a metre long and weighing not much more than a turkey. It walked around on two legs and it was a little carnivore.
"Sauropods by contrast were vast plant eaters, the biggest many times larger than a bull elephant, perhaps as long as 40m and weighing 100 tons. That's a pretty big change," Yates said.
This metamorphosis was accompanied by changes to the jaws and teeth to accommodate dinosaurs' need to "stuff enough food down their throats to feed their giant bulk", he said, and their hands evolved from grasping to supporting their great weight.
Dinosaurs also began to slow down as they got bigger.
Until now, scientists believed dinosaurs slowed down only after they became fully fledged quadrupeds, but the foot shape the Aardonyx challenges this idea, he said.
"Our (find) has a very short broad foot, bearing weight on the inside, so there's no way it could be anything but a slow, lumbering plodder," he said.
The researchers suggest the two Aardonyx dinosaurs lived in an oasis on the edge of a desert.
It is not clear how they died, but they were eaten by carnivorous dinosaurs that left some of their teeth behind, Yates said. Carnivorous dinosaurs constantly grew new teeth, as crocodiles do today.
University of Cape Town palaeohistologist Anusha Chinsamy-Turan, who examined the fossil bones' growth rings, said the Aardonyx dinosaurs were not yet fully grown when they died.
"Both were immature individuals under the age of 10," she said.
"It's really quite amazing to think these bones have been buried under the ground for millions of years. I am going to have to update my children's book on African dinosaurs," she said.
Aardonyx means "earth claw" and is derived from the Afrikaans word for earth, aard, and the Greek word for claw, onyx; celestae is named for Yates's wife, Celeste. She was responsible for removing the bones from their casing of concrete-like rock. "She spent over two years and two pregnancies removing the rock," he said.
Yates said the researchers believed they may have stumbled onto a "palaeontological oasis" that might yield further novel species.
With AP and Sapa
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