The documentary series reaches the Jurassic period, when the first giant killers stalked Earth and lurked in the seas. North America was dominated by the allosaurus, an ambush hunter with a lethal bite, allowing it to bring down even the heavily armoured stegosaurus. Life in the oceans was just as deadly - a fossil found in the Arctic in 2008 turned out to be a colossal marine reptile. Named Predator X, the creature was 50ft long, weighed 45 tons and had a bite force unmatched by anything in the Jurassic seas