 When they were first described , crested hadrosaurs were thought to be aquatic , an assessment based incorrectly on <unk> that is now known to be padding . The theory was that the animals could swim deep in the water , and use the crest to store air to breath . However , it has now been proven that the crest did not have any holes in the end , and the water pressure at even 3 metres ( 9 @.@ 8 ft ) would be too great for the lungs to be able to <unk> . 
