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Santanichthys
''Santanichthys diasii'' is a species of extinct fish that existed around 115 million years ago during the Albian epoch. ''S. diasii'' is regarded as the basal-most characiform, and is the earliest known member of Otophysi. It appears as a small fish, similar in appearance to a modern-day herring no more than 30 centimeters in length. Its most striking characteristic is the presence of a Weberian apparatus, which makes it the most primitive known member of the order Characiformes,〔 the order in which modern-day tetras (including piranhas) are classified in. ''Santanichthys'' has been unearthed from numerous locations throughout Brazil, in rocks dating to the Cretaceous Period. Its presence in this strata is seen as an indicator for the biogeography and evolution of its order.
==Anatomy and morphology==
''Santanichthys'' is a small, characiform fish that would have superficially resembled more advanced tetras or the unrelated herrings. Maximum length appears to be around 30 centimeters standard length. The species possesses a primitive but complete Weberian Apparatus, formed from the first four vertebrae of the spinal column. This is the earliest occurrence of the structure found in any known taxon of fish. Anatomically, the fish is similar to many others within its order. The body is semi-laterally compressed and ovate. The fins are more or less complete for a characiform - ''Santanichthys'' possesses a single dorsal, anal and caudal fin and paired pectoral and pelvic fins. Skeletal-wise, the fish has from 30-40 elongated vertebrae. A complex suspensorium can be found in the taxon. Jaw teeth however, are noticeably absent. Cycloid scales are wholly present throughout the entire body.〔
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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