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Antarctopelta
''Antarctopelta'' ( ; meaning 'Antarctic shield') was a genus of ankylosaurian dinosaur with one known species, ''A. oliveroi'', which lived in Antarctica during the Late Cretaceous Period. It was a medium-sized ankylosaur, reaching no more than 4 meters (13 ft) in length, and showed characteristics of two different families, making more precise classification difficult. The single known fossil specimen was discovered on James Ross Island in 1986, constituting the first dinosaur remains ever discovered on Antarctica, although it is the second dinosaur from the continent to be formally named.
==Description and classification==
Like other ankylosaurs, ''Antarctopelta oliveroi'' was a stocky, herbivorous quadruped protected by armor plates embedded in the skin. Although a complete skeleton has not been found, the species is estimated to have reached a maximum length of 4 meters (13 ft) from snout to tail tip. Very little of the skull is known, but all of the known skull fragments were heavily ossified for protection. One bone in particular, identified as a ''supraorbital'', included a short spike which would have projected outwards over the eye. The leaf-shaped teeth are asymmetrical, with the majority of the denticles on the edge closest to the tip of the snout. These teeth are also proportionately large compared to those of other ankylosaurs, with the largest measuring 10 millimeters (0.4 in) across. This compares to the much larger North American ''Euoplocephalus'', 6–7 m (20–23 ft) in body length, which had teeth averaging only 7.5 mm (0.3 in) across.
Vertebrae from other sections of the tail were found. Although the tip of the tail did not fossilize, some of the smaller vertebrae recovered would have been situated near the end of the tail in life, and these were associated with ossified tendons on the upper and lower sides. In ankylosaurids, these tendons help to stiffen the end of the tail in support of a large, bony tail club. If such a club existed in ''Antarctopelta'', it has yet to be discovered. Six different types of osteoderms were found along with the skeletal remains of ''Antarctopelta'', but very few were articulated with the skeleton, so their placement on the body is largely speculative. They included the base of what would have been a large spike. Flat oblong plates resembled the ones that guarded the neck of the nodosaurid ''Edmontonia rugosidens''. Large circular plates were found associated with smaller, polygonal nodules, perhaps forming a shield over the hips as seen in ''Sauropelta''. Another type of osteoderm was oval-shaped with a keel running down the middle. A few examples of this fifth type were found ossified to the ribs, suggesting that they ran in rows along the flanks of the animal, a very typical pattern among ankylosaurs. The final group consisted mainly of small bony nodules which are often called ''ossicles'', and were probably scattered throughout the body. Several ribs were also found with these ossicles attached.〔
''Antarctopelta'' shares several features with the nodosaurids, mainly in the teeth and armor, while the possibly-clubbed tail is far more similar to those of ankylosaurids. This mosaic of characters makes assignment to a specific family difficult. It has been designated as Ankylosauria ''incertae sedis'', but has never been subjected to a phylogenetic analysis.〔 A new phylogenetic analysis performed by Thompson ''et al.'', 2011 suggests that ''Antarctopelta'' is the basalmost known nodosaurid.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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