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Acamptonectes
''Acamptonectes'' is an extinct genus of ophthalmosaurid ichthyosaur known from England and Germany. It was collected from the Hauterivian stage of England and Germany and from the Cambridge Greensand Formation, eastern United Kingdom, dating to late Albian or early Cenomanian stage, of the Early Cretaceous-Late Cretaceous boundary. ''Acamptonectes'' was first described by Valentin Fischer, Michael W. Maisch, Darren Naish, Ralf Kosma, Jeff Liston, Ulrich Joger, Fritz J. Krüger, Judith Pardo Pérez, Jessica Tainsh and Robert M. Appleby in 2012 and the type species is ''Acamptonectes densus''.〔
==Description==
''Acamptonectes'' is known from several specimens: the holotype adult, a partial sub-adult, and an additional partial skeleton. The holotype consists of a fragmentary skull roof, a complete mandible, a partial axial skeleton and a partial scapular girdle. ''Acamptonectes'' is similar in morphology to the related but earlier ophthalmosaurids ''Ophthalmosaurus'' and ''Mollesaurus''.
''Acamptonectes'' is morphologically distinct from other ophthalmosaurines in a variety of ways. Its binomial name, meaning "tightly-packed rigid swimmer", refers to the tightly-packed occipital bones and cervical vertebrae that would have allowed little movement in the neck, indicating it must have "shot through the water like a dart."〔 Most of its skeleton appears to be unusually rigid, which would have in effect severely limited the amount of side-to-side motion that was possible in the anterior part of the skeleton. Its snout is also shallower and its teeth more slender-crowned and sharply pointed than related species, and its ribs are also more robust rounded in cross-section, which may be a further adaptation to increase the stiffness of the animal's body, as they were likely more resistant to bending. Like other ichthyosaurs, ''Acamptonectes'' was a predator and probably fed on fish and squid, and its overall body plan would have been similar in appearance to that of a dolphin. It was approximately 3 meters (10 ft) in length.〔
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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