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''Cladoselache'' is a genus of extinct shark. It appeared in the Devonian period. This primitive shark grew to be up to long and roamed the oceans of North America. It is known to have been a fast moving and fairly agile predator due to its streamlined body and deep forked tail. ''Cladoselache'' is one of the best known of the early sharks in part due to the well preserved fossils that were discovered on the 'Cleveland Shale' on the south shore of Lake Erie. In addition to the skeleton, the fossils were so well preserved that they included traces of skin, muscle fibres, and internal organs, such as the kidneys. ==Appearance== ''Cladoselache'' exhibited a combination of derived and ancestral characteristics. It had anatomical features similar to the current mackerel sharks of the family Lamnidae. It had a streamlined body, from five to seven gill slits, and a short, rounded snout that had a terminal mouth opening at the front of the skull.〔 It had a very weak jaw joint compared with modern-day sharks, but it compensated for that with very strong jaw-closing muscles. Its teeth were multi-cusped and smooth-edged, making them suitable for grasping, but not tearing or chewing. ''Cladoselache'' therefore probably seized prey by the tail and swallowed it whole. Its sturdy but light-weight fin spines were composed of dentine and enamel.〔 ''Cladoselache'' also had a blade-like structure which was positioned in front of the dorsal fins. These anatomical features made swimming easier and faster. Unlike most sharks, ''Cladoselache'' was almost entirely devoid of scales with exception of small cusped scales on the edges of the fins, mouth and around the eyes. It also had powerful keels that extended onto the side of the tail stalk and a semi-lunate tail fin, with the superior lobe about the same size as the inferior.〔 This combination helped with its speed and agility which was useful when trying to outswim its probable predator, the heavily armored long placoderm fish ''Dunkleosteus''. 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「Cladoselache」の詳細全文を読む スポンサード リンク
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