 Large three @-@ toed <unk> are known in Early Cretaceous rocks of England , particularly <unk> beds on the Isle of Wight , and these trace fossils were originally difficult to interpret . Some authors associated them with dinosaurs early on . In 1846 , E. <unk> went so far as to assign them to an <unk> he named Iguanodon , and Samuel <unk> noted in 1854 that they looked like bird tracks , but might have come from dinosaurs . The identity of the <unk> was greatly clarified upon the discovery in 1857 of the hind leg of a young Iguanodon , with distinctly three @-@ toed feet , showing that such dinosaurs could have made the tracks . Despite the lack of direct evidence , these tracks are often attributed to Iguanodon . A <unk> in England shows what may be an Iguanodon moving on all fours , but the foot prints are poor , making a direct connection difficult . Tracks assigned to the <unk> Iguanodon are known from locations including places in Europe where the body fossil Iguanodon is known , to Spitsbergen , Svalbard , Norway . 
