One of the first details noted about Iguanodon was that it had the teeth of a herbivorous reptile , although there have not always been consensus on how it ate . As Mantell noted , the remains he was working with was unlike any modern reptile , especially in the toothless , scoop @-@ shaped form of the lower jaw symphysis , which he found best compared to that of the two @-@ toed sloth and the extinct ground sloth Mylodon . He also suggested that Iguanodon had a prehensile tongue which could be used to gather food , like a giraffe . More complete remains have shown this to be an error ; for example , the hyoid bones that supported the tongue are heavily built , implying a muscular , non @-@ prehensile tongue used for moving food around in the mouth . The giraffe @-@ tongue idea have also been incorrectly attributed to Dollo via a broken lower jaw .