Experts piece together dinosaur with 1,000 teeth and a permanent smile

A dinosaur with a permanent smile and jaws packed with 1,000 teeth has been unearthed in an African desert by scientists who describe it as one of the most bizarre animals ever to walk on four legs.

The discovery of the long-necked dinosaur with a skull shaped like a hammer-head shark was made in the same area of Niger where scientists last year found a giant crocodile that was so big it could eat a dinosaur for breakfast.

Nigersaurus, a leaf-eating sauropod that lived between 90 million and 100 million years ago, is nearly unique in that it had a jaw bones that ran across its face from side to side, rather like the mouth of Wallace the Plasticine cartoon character.

Paul Sereno, a palaeontologist from Chicago University and one of the world's leading dinosaur hunters, said yesterday that Nigersaurus was probably the most bizarre dinosaur he had tried to classify.

"It's a bit of an alien-looking creature," Dr Sereno told the annual meeting of the American Association for the Advancement of Science in Boston.

"When we first pried the jaw-bone from the rock, we knew we had the end of a neck and a skull with the bones pretty much teased apart. When we first prepared it I disowned it as belonging to the dinosaurs.

"Eventually we cleaned it off, the light bulb went on and we understood that we had oriented the jaw as we would have a normal dinosaur, fore and aft, and that was a mistake. It was, in fact, oriented completely transversely."

More surprising was the number of enamel-covered teeth, 1,000 of them, that Nigersaurus would use to eat its vegetarian diet. The tiny teeth are in "batteries", side by side, like soldiers on parade.

"The teeth were narrow, needle-shaped, not bigger than a few millimetres in width and packed into an open groove in the jaw such that they were all supporting each other and growing out in unison," Dr Sereno said.

"There were stacks of as much as eight or 10 teeth in a single line erupting from a single point in the jaw. They are all in a straight line, side by side and this has never been seen before in any herbivore that I know of.

"It looks like a hammer-head shark on legs. I've never seen anything like it. It's going to be a shocker when we eventually get this thing together."

In Nigersaurus's time, a period known as the Mesozoic, grasses did not exist and the landscape was dominated by giant ferns, which was probably what the beast browsed on, Dr Sereno said.

"It's a plant-eater; it's got teeth that have wear facets and it's definitely designed to crop plants and when you look at it you say, 'Jesus this is the Mesozoic lawnmower'.

"I really imagine this animal with a jaw seven or eight inches across up front and in a straight line. My suspicion is that it was a ground-feeder specialised in mowing down ferns.

"We tend to think that because sauropods had such long necks they must have been like giraffes. Well, that's probably not true for a good number of them. They were probably using their necks for a radius, allowing them to stand in one place or walk slowly and take vegetation from a wider range of spots."

At 45 feet from head to tail, with hips rising to about 10 feet high, Nigersaurus was not particularly big for the sauropods. But what it lacked in size, it made up for in novelty.

"It's really a remarkable animal," Dr Sereno said. "The bones are so thin that I can't actually cast and mould them and reconstruct the skull using the bones themselves. I'm going to have to scan the bones because some of them are paper-thin."

When the scientists, led by Dr Sereno, finish reconstructing the animal's bones, they will be able to draw a sketch of how it appeared at a time when the part of the barren Niger landscape in which it roamed was a lush river valley, filled with meandering streams.

Dr Sereno said Nigersaurus would have been the sort of animal preyed upon by the giant supercrocodile, sarchosuchus, which lived in the same area at the same time.

"I would not doubt for a minute that those two encountered each other, and I'm sure it was not favourable for Nigersaurus," he said. "The crocodile, I think, would have something to watch out for along the river banks.

"Nigersaurus is a fairly lightly built, delicate and ponderous plant-eater and they would have been an easy prey for sarchosuchus to drag in."