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Scientists have discovered a new species of dinosaur that had lots of teeth and a body similar to a duck.

The dinosaur has been named Natovenator polydontus, which means "swimming hunter with many teeth", and lived 71 million years ago.

It was much bigger than a duck, walked on two legs, and spent lots of time in water.

But its body has been compared to a duck because it had a streamline shape - meaning it could cut through water easily without any drag to hunt for food.

Streamlined bodies like this have not been seen in the fossils of non flying two-legged dinosaurs before.

In the new study, scientists examined the animals fossilised bones which had been discovered in Mongolia, a country in east Asia.

In studying the fossils, the scientists discovered that the dinosaur's body had several design features that made it perfect for water diving - including ribs that point towards its tail, giving the animal its streamlined body shape.

It also had a long neck similar to modern diving-birds such as geese that can be seen today next to ponds and rivers.

"Its body shape suggests that Natovenator was a potentially capable swimming predator," the study says.

The fossilised bones also revealed an unusual amount of teeth given the size of the animal's jaw.

Scientists expect that this shows the dinosaur had a diet of fish and insects, but said they would need to find fossilised remains of Natovenator's stomach to be sure.