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The BBC iPlayer app is currently available in the following countries: Austria, Australia, Belgium, Canada, Denmark, Finland, France, Germany, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain, Sweden and Switzerland. Please note, not all programming is available in all countries.

From a tiny hatchling just 30 centimetres long to fully grown dinosaur requires a huge food intake. But just how did Big Al and his fellow dinosaurs feed such fantastic growth? Scientists turn to the dinosaur's two closest living relatives - the crocodile and alligator - to find out. Fascinating clip from the BBC natural history programme Walking with Dinosaurs: The Ballad of Big Al. Watch more high quality videos on the new BBC Worldwide YouTube channel here: http://www.youtube.com/bbcworldwide