'Fluffy and feathery' dinosaur claim sparks debate
25 July 2014 Last updated at 06:10 BST
All dinosaurs were covered with feathers or had the potential to grow feathers, a study suggests.
The discovery of 150-million-year-old fossils in Siberia indicates that feathers were much more widespread among dinosaurs than previously thought.
The find "has completely changed our vision of dinosaurs", the lead researcher told BBC News.
But some experts have doubts, as Pallab Ghosh reports.
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