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Hadrosaurids ((ギリシア語:ἁδρός), ''hadrós'', "stout, thick"), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. The family, which includes ornithopods such as ''Edmontosaurus'' and ''Parasaurolophus'', was a common herbivore in the Upper Cretaceous Period of what is now Asia, Europe and North America. Hadrosaurids are descendants of the Upper Jurassic/Lower Cretaceous iguanodontian dinosaurs and had a similar body layout. Hadrosaurids are divided into two principal subfamilies: the lambeosaurines (''Lambeosaurinae''), which had hollow cranial crests or tubes, and the saurolophines, identified as hadrosaurines in most pre-2010 works (''Saurolophinae'' or'' Hadrosaurinae''), which lacked hollow cranial crests (solid crests were present in some forms). Saurolophines tended to be bulkier than lambeosaurines. Lambeosaurines are divided into Aralosaurines, Lambeosaurines, Parasaurolophines and Tsintaosaurines, while Saurolophines include Saurolophus, Brachylophosaurines and Kritosaurines. ==Characteristics== The hadrosaurs are known as the duck-billed dinosaurs due to the similarity of their head to that of modern ducks. In some genera, including ''Edmontosaurus'', the whole front of the skull was flat and broadened out to form a beak, which was ideal for clipping leaves and twigs from the forests of Asia, Europe and North America. However, the back of the mouth contained thousands of teeth suitable for grinding food before it was swallowed. This has been hypothesized to have been a crucial factor in the success of this group in the Cretaceous compared to the sauropods. In 2009, paleontologist Mark Purnell conducted a study into the chewing methods and diet of hadrosaurids from the Late Cretaceous period. By analyzing hundreds of microscopic scratches on the teeth of a fossilized ''Edmontosaurus'' jaw, the team determined hadrosaurs had a unique way of eating unlike any creature living today. In contrast to a flexible lower jaw joint prevalent in today's mammals, hadrosaurs had a unique hinge between the upper jaws and the rest of its skull. The team found the dinosaur's upper jaws pushed outwards and sideways while chewing, as the lower jaw slid against the upper teeth. Hadrosaurs, much like sauropods, are noted for having their manus united in a fleshy, often nail-less pad. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hadrosaurid」の詳細全文を読む スポンサード リンク
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