A new species of dinosaur described as Tyrannosaurus Rex's "smaller cousin from the north" has been discovered.

An analysis of 70-million-year-old fossilised skull remains discovered in northern Alaska has shown them to be from a new pygmy Tyrannosaurus, according to research published in the open access journal PLOS ONE.

Scientists examined fragments of the skull roof, maxilla and jaw, and concluded that the species, Nanuqsaurus hoglundi, had an adult skull length of 25in (63.5cm), less than half the size of the 60in (152.4cm) skull of a T Rex, believed to have been the largest of all carnivorous dinosaurs.

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Study co-authors Anthony Fiorillo and Ronald Tykoski, from the Perot Museum of Nature and Science in Texas, said the smaller body size may have reflected an adaption to scarcer resources in the Arctic seasons and the species' partial isolation in the north.

Tyrannosaurs have captured popular imagination since their discovery but the majority of information about them comes from fossils from low to mid-latitudes of North America and Asia.

"The 'pygmy tyrannosaur' alone is really cool because it tells us something about what the environment was like in the ancient Arctic," said Mr Fiorillo.

"But what makes this discovery even more exciting is that Nanuqsaurus hoglundi also tells us about the biological richness of the ancient polar world during a time when the Earth was very warm compared to today."