 Furthermore , it appears that Iguanodon became more quadrupedal as it got older and heavier ; juvenile I. bernissartensis have shorter arms than adults ( 60 % of <unk> length versus 70 % for adults ) . When walking as a <unk> , the animal 's hands would have been held so that the <unk> faced each other , as shown by <unk> <unk> and the anatomy of this genus 's arms and hands . The three toed <unk> ( foot ) of Iguanodon was relatively long , and when walking , both the hand and the foot would have been used in a <unk> fashion ( walking on the fingers and toes ) . The maximum speed of Iguanodon has been estimated at 24 km / h ( 15 mph ) , which would have been as a <unk> ; it would not have been able to gallop as a <unk> . 
