I'm self-employed order aralen Other hadrosaurs are known to have had hollow bone structures on their heads, whereas pterosaurs had smooth crests made of keratin - the hard fibrous proteins responsible for beaks, horns and fingernails. 必須 2000文字以内 [bbs:youtube:(Youtubeの動画ID)]と書くとYoutubeの動画が貼れます。(例:[bbs:youtube:OQThUAQ0UN0])