 Iguanodon were bulky herbivores that could shift from <unk> to <unk> . The only well @-@ supported species , I. bernissartensis , is estimated to have weighed about 3 @.@ 08 tonnes ( 3 @.@ 4 tons ) on average , and measured about 10 metres ( 33 feet ) long as an adult , with some specimens possibly as long as 13 metres ( 43 feet ) . These animals had large , tall but narrow skulls , with toothless beaks probably covered with keratin , and teeth like those of <unk> , but much larger and more closely packed . 
