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''Metaspriggina'' is a genus of chordate initially known from two specimens in the Middle Cambrian Burgess Shale and 44 specimens found in 2012 at the Marble Canyon bed in Kootenay National Park.〔 Whilst named after the Ediacaran organism ''Spriggina'', later work has shown the two to be unrelated.〔 ''Metaspriggina'' is considered to represent a primitive chordate, possibly transitional between cephalochordates and the earliest vertebrates. It lacked fins and had a poorly developed cranium, but did possess two well-developed upward-facing eyes with nostrils behind them. ''Metaspriggina'' also possessed a notochord, along with seven pairs of pharyngeal bars, possibly made of cartilage. The largest specimens are in length. Originally believed to be free-swimming but occasionally found on the sea floor, the fossils from Marble Canyon showing the presence of eyes and their placement suggests it lived as a filter-feeder swimming above the sea floor. The exceptional preservation at Marble Canyon also preserved muscle detail, showing that the animal moved with a side-to-side swimming motion.〔 In ''Metaspriggina'' the myomeral configuration has an additional ventral chevron, and a clear dorsal bend which defines a W-shaped arrangement that is directly comparable to fish.〔 The discovery of pharyngeal bars (gill bars) makes ''Metaspriggina'' the oldest known animal to have this feature.〔 The first pair of pharyngeal bars later evolved to form the upper and lower jaws of vertebrates. ==References== 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「Metaspriggina」の詳細全文を読む スポンサード リンク
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