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Lambeosaurus ( ; meaning "Lambe's lizard") is a genus of hadrosaurid dinosaur that lived about 76 to 75 million years ago, in the Late Cretaceous period (Campanian) of North America. This bipedal/quadrupedal, herbivorous dinosaur is known for its distinctive hollow cranial crest, which in the best-known species resembled a hatchet. Several possible species have been named, from Canada, the United States, and Mexico, but only the two Canadian species are currently recognized as valid. ''Lambeosaurus'' was belatedly described in 1923 by William Parks, over twenty years after the first material was studied by Lawrence Lambe. The genus has had a complicated taxonomic history, in part because small-bodied crested hadrosaurids now recognized as juveniles were once thought to belong to their own genera and species. Currently, the various skulls assigned to the type species ''L. lambei'' are interpreted as showing age differences and sexual dimorphism. ''Lambeosaurus'' was closely related to the better known ''Corythosaurus'', which is found in slightly older rocks, as well as the less well-known genera ''Hypacrosaurus'' and ''Olorotitan''. All had unusual crests, which are now generally assumed to have served social functions like noisemaking and recognition. ==Description== ''Lambeosaurus'', best known through ''L. lambei'', was quite similar to ''Corythosaurus'' in everything but the form of the head adornment. Compared to ''Corythosaurus'', the crest of ''Lambeosaurus'' was shifted forward, and the hollow nasal passages within were at the front of the crest and stacked vertically. It also can be differentiated from ''Corythosaurus'' by its lack of forking nasal processes making up part of the sides of the crest, which is the only way to tell juveniles of the two genera apart, as the crests took on their distinctive forms as the animals aged. In build, ''Lambeosaurus'' was like other hadrosaurids, and could move on both two legs and all fours, as shown by footprints of related animals. It had a long tail stiffened by ossified tendons that prevented it from drooping. The hands had four fingers, lacking the innermost finger of the generalized five-fingered tetrapod hand, while the second, third, and fourth fingers were bunched together and bore hooves, suggesting the animal could have used the hands for support. The fifth finger was free and could be used to manipulate objects. Each foot had only the three central toes. The most distinctive feature, the crest, was different in the two well-known species. In ''L. lambei'', it had a hatchet-like shape when the dinosaur was full-grown, and was somewhat shorter and more rounded in specimens interpreted as females.〔 The "hatchet blade" projected in front of the eyes, and the "handle" was a solid bony rod that jutted out over the back of the skull. The "hatchet blade" had two sections: the uppermost portion was a thin bony "coxcomb" that grew out relatively late in life, when an individual neared adulthood; and the lower portion held hollow spaces that were continuations of the nasal passages.〔 In ''L. magnicristatus'', the "handle" was greatly reduced, and the "blade" expanded,〔Lull, pp. 193–194.〕 forming a tall, exaggerated pompadour-like crest. This crest is damaged in the best overall specimen, and only the front half remains. The Canadian species of ''Lambeosaurus'' appear to have been similar in size to ''Corythosaurus'', and thus around 9.4 m long (31 ft).〔Lull, pp. 227–228.〕 Impressions of the scales are known for several specimens; a specimen now assigned to ''L. lambei'' had a thin skin with uniform, polygonal scutes distributed in no particular order on the neck, torso, and tail.〔Lull, pp. 112–117.〕 Similar scalation is known from the neck, forelimb, and foot of a specimen of ''L. magnicristatus''.〔 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「Lambeosaurus」の詳細全文を読む スポンサード リンク
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