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A British paleontologist has discovered not one, but two new species of dinosaur while studying fossils in a Canadian museum.

Dr Nick Longrich was examining fossilised bones from two horned dinosaurs, which had been kept in the Canadian Museum of Nature for 75 years.

And he found that, while they had previously been classified as a species from Canada, they more closely resembled dinosaurs from the American south west - suggesting they are a new species.

This illustration shows Pentaceratops aquilonius, a new species of dinosaur discovered by a British paleontologist in a Canadian museum. Dr Nick Longrich was examining fossilised bones from two horned dinosaurs, which had been kept in the Canadian Museum of Nature for 75 years, when he made the finding

The fossils had previously been classified as Anchiceratops and Chasmosaurus, species known to be from Canada, but now that classification may need to be changed.

One represents a new species of Pentaceratops, said Dr Longrich, named Pentaceratops aquilonius - a buffalo-sized plant-eating dinosaur from around 75 million years ago.

The second appears to be a new species of Kosmoceratops, a dinosaur with an ornate skull from Utah, though more complete fossils are needed to confirm this.

Dr Longrich, from the University of Bath, said his find revealed dinosaur species from the region were much more diverse than previously thought.

'We thought we had discovered most of the species, but it seems there are many undiscovered dinosaurs left,' said Dr Longrich, from the university's Department of Biology & Biochemistry.

'The total dinosaur diversity must have been extraordinarily high. 

'We've really only just scratched the surface.'

Pentaceratops was a smaller cousin of Triceratops, belonging to a group of large, horned dinosaurs with a long brow horn and elongate frills called the Chasmosaurinae.

The dinosaurs were based in western North America at the end of the Cretaceous Period, around 75 million years ago.

Up until now, ten Chasmosaur species have been recognised from that period, with distinct species occurring in the northern and southern parts of the continent.

Dr Longrich believes that, although distinct northern and southern provinces existed, there was contact between them.

Dinosaurs would spread from one part of the continent to the other, then diverge to form new species.

Competition between the different species then prevented the dinosaurs from moving between the northern and southern regions.

Pictured here is the fossil previously believed to be Anchiceratops ornatus at the Canadian Museum of Nature, Ottawa, Ontario. But Dr Longrich said it may have been classified incorrectly

This image shows what was previously thought to be Chasmosaurus russelli. Dr Longrich said his find revealed dinosaur species from North America were much more diverse than had been previously thought

'The distribution of dinosaur species was very different from the patterns seen in living mammals,' Dr Longrich said.

'In living mammals, there tend to be relatively few large species, and they have large ranges. With Cretaceous dinosaurs, we see a lot of large species in a single habitat.

'They also tend to be very regional - as you move from one habitat to another you get a completely different set of species.'

The patterns help explain why paleontologists keep finding more species, as they discover them when examining different habitats.

Dr Longrich believes such patterns are caused by dinosaur biology.

'In this sense, dinosaur biology seems quite different from mammal biology,' he said.

'It could be that mammals are more intelligent and so they tend to have more flexible behaviour, and adapt their behaviour to their habitat

'On the other hand, dinosaurs may have had to adapt themselves physically to survive in a different habitat, and evolved new species.'

Dr Longrich's study appears in the academic journal Cretaceous Research.