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bigeye sand tiger
The bigeye sand tiger (''Odontaspis noronhai'') is an extremely rare species of mackerel shark in the family Odontaspididae, with a possible worldwide distribution. A large, bulky species reaching at least in length, the bigeye sand tiger has a long bulbous snout, large orange eyes without nictitating membranes, and a capacious mouth with the narrow teeth prominently exposed. It can be distinguished from the similar smalltooth sand tiger (''O. ferox'') by its teeth, which have only one lateral cusplet on each side, and by its uniformly dark brown color.
Inhabiting continental margins and oceanic waters at depths of , the bigeye sand tiger may make vertical and horizontal migratory movements. It feeds on bony fishes and squid, and its sizable eyes and dark coloration suggest that it may spend most of its time in the mesopelagic zone. Reproduction is probably viviparous with oophagous embryos like in other mackerel shark species. This shark is caught incidentally by commercial fisheries, though so infrequently that the International Union for Conservation of Nature (IUCN) cannot yet determine its conservation status.
==Taxonomy and phylogeny==
The first known bigeye sand tiger was a female long caught off Madeira in April 1941, on a longline set for black scabbardfish (''Aphanopus carbo''). The specimen was mounted and later formed the basis for a scientific description authored by German ichthyologist Günther Maul in a 1955 article for ''Notulae Naturae''. He named the species ''noronhai'' in honor of Adolfo César de Noronha, the late Director of the Funchal Museum.〔 Maul assigned his new species to the genus ''Carcharias'', which at the time was used for all members of the sand tiger shark family. When the ''Odontaspis'' came to be recognized as a valid genus separate from ''Carcharias'', the bigeye sand tiger was reassigned as well given its resemblance to the smalltooth sand tiger (''O. ferox'').〔 Until more specimens were examined in the 1980s, some authors speculated that this species represented an extreme variant of the smalltooth sand tiger. Other names for this shark include black sand tiger, oceanic sand tiger, and bigeye ragged-tooth shark.〔〔
Whether the bigeye and smalltooth sand tigers belong in the same family as the superficially similar sand tiger shark (''C. taurus'') has been debated among systematists, with morphological and dentitional studies giving inconsistent results.〔 A 2012 molecular phylogenetic analysis, based on mitochondrial DNA, supported a sister species relationship between ''O. noronhai'' and ''O. ferox'' but not a clade consisting of ''Odontaspis'' and ''Carcharias''. Instead, ''Odontaspis'' was found to be closer to the crocodile shark (''Pseudocarcharias kamoharai''), suggesting that it and ''Carcharias'' should be placed in separate families.〔
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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