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segunda-feira, 19 de novembro de 2012

ORIGEM DO TUBARÃO BRANCO

 [Palaeoichthyology • 2012] Carcharodon hubbelli • Origin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the Upper Neogene Pisco Formation of Peru

Abstract
 The taxonomic origin of the white shark, Carcharodon, is a highly debated subject. New fossil evidence resented in this study suggests that the genus is derived from the broad-toothed ‘mako’, Carcharodon (Cosmopolitodushastalis, and includes the new species Carcharodon hubbelli sp. nov. – a taxon that demonstrates a transition between Chastalis and Carcharodon carcharias. Specimens from the Pisco Formation clearly demonstrate an evolutionary mosaic of characters of both recent C. carcharias and fossil C. hastalis. Characters diagnostic to C. carcharias include the presence tooth serrations and a symmetrical first upper anterior tooth that is the largest in the tooth row, while those indicative of C. hastalis include a mesially lanted third anterior (intermediate) tooth. We also provide a recalibration of critical fossil horizons within the Pisco Formation, Peru using zircon U-Pb dating and strontium-ratio isotopic analysis. The recalibration of the absolute dates suggests that Carcharodon hubbelli sp. nov. is Late Miocene (6–8 Ma) in age. This research revises and elucidates lamnid shark evolution based on the calibration of the Neogene Pisco Formation.
Keywords: Carcharocles;Cosmopolitodus;geochronology;Miocene;Isurus;strontium
2012. Origin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the Upper Neogene Pisco Formation of Peru. DOI: 10.1111/j.1475-4983.2012.01201.x
2009. Exceptional Preservation of the White Shark Carcharodon (Lamniformes, Lamnidae) from the Early Pliocene of Peru
Great whites 'not evolved from megashark'

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