Belgian researcher Pascal Godefroit and his team compared the anatomy of the newly discovered dinosaur fossil to a variety of birds and dinosaurs to determine their relationship.

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But the researchers say the new fossil shows the Alvarezsauridae group split from birds much earlier on the evolutionary tree than was thought.

BBC: New dinosaur discovery solves evolutionary bird puzzle

Prof Barnosky and colleagues compared the rates of known species extinctions in mammals, birds and amphibians during the last five centuries with those estimated from the fossil record during the previous Big Five die-outs of the geological past.

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Findings from the second fossil were even more revealing - inside were the preserved remains of two primitive crow-sized birds, called Confuciusorni.

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