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''Ankylosaurus'' ( or , meaning "fused lizard") is a genus of thyreophoran dinosaur. Fossils of ''Ankylosaurus'' have been found in geologic formations dating to the very end of the Cretaceous Period, between about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908, and the only species classified in the genus is ''A. magniventris''. A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, ''Ankylosaurus'' is often considered the archetypal member of its group. The largest known ankylosaurid, ''Ankylosaurus'' measured up to in length, in height, and weighed . It was a quadrupedal animal, with a broad, robust body. It had a wide, low skull, with two horns pointing backwards from the back of the head, and two horns below these that pointed backwards and down. The front part of the jaws were covered in a beak, with rows of small, leaf-shaped teeth further behind it. It was covered in armor plates, or osteoderms, with bony half-rings covering the neck, and had a large club on the end of its tail. Bones in the skull and other parts of the body were fused, increasing their strength, and this feature is the source of the genus name. ''Ankylosaurus'' is a member of the family Ankylosauridae, and its closest relatives appear to be ''Anodontosaurus'' and ''Euoplocephalus''. ''Ankylosaurus'' is thought to have been a slow moving animal, able to make quick movements when necessary. Its broad muzzle indicates it was a non-selective browser. Sinuses and nasal chambers in the snout may have been for heat and water balance or played a role in vocalization. The tail club is thought to have been used in defense against predators or in intraspecific combat. ''Ankylosaurus'' has been found in the Hell Creek, Lance, and Scollard formations, but appears to have been rare in its environment. Although it lived alongside another ankylosaur, ''Edmontonia'', their ranges and ecological niches do not appear to have overlapped, and ''Ankylosaurus'' may have inhabited upland areas. ''Ankylosaurus'' also lived alongside dinosaurs such as ''Tyrannosaurus'', ''Triceratops'', and ''Edmontosaurus''. ==Description== ''Ankylosaurus'' is the largest known ankylosaurid dinosaur, estimated to have been up to long, wide, and tall at the hip. This length has been proposed by American palaeontologist Kenneth Carpenter, and is based on the largest known skull (specimen NMC 8880), which is long and wide. The smallest known skull (specimen AMNH 5214) is long and wide, and this specimen is estimated to have been long and around tall.〔 Other authors have proposed a body length of ,〔 ,〔 or more than .〔 The weight of the animal has been estimated at .〔〔 The structure of much of the skeleton of ''Ankylosaurus'', including most of the pelvis, tail and feet, is still unknown.〔 It was quadrupedal, and its hind limbs were longer than the forelimbs.〔 The scapula (shoulder blade) and coracoid (a rectangular bone connected to the lower end of the scapula) of specimen AMNH 5895 were fused, and had entheses (connective tissue) for various muscle attachments. The scapula was long. The humerus (upper arm bone) was short and very broad, and about long in specimen AMNH 5214. The femur (thigh bone) was very robust, and long in AMNH 5214. While the feet of ''Ankylosaurus'' are incompletely known, the hindfeet probably had three toes, as is the case in related animals.〔 The cervical vertebrae of the neck had broad neural spines that increased in height towards the body. The front part of the neural spines had well developed entheses, which was common among adult dinosaurs, and indicates the presence of large ligaments which helped support the massive head. The dorsal vertebrae of the back had centra (or bodies) that were short relative to their width, and their neural spines were short and narrow. The dorsal vertebrae were tightly spaced, which limited the downwards movement of the back. The neural spines had ossified (turned to bone) tendons, which also overlapped some of the vertebrae. The ribs of the last four back vertebrae were fused to them, and the ribcage was very broad in this part of the body. The ribs had scars that show where muscles attached to them. The caudal vertebrae of the tail had centra that were slightly amphicoelous, meaning they were concave on both sides. The interlocked zygapophyses (articular processes) of the caudal vertebrae formed a V-shape when seen from above.〔 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「Ankylosaurus」の詳細全文を読む スポンサード リンク
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