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daggernose shark
The daggernose shark (''Isogomphodon oxyrhynchus'') is a little-known species of requiem shark, in the family Carcharhinidae, and the only extant member of its genus. It inhabits shallow tropical waters off northeastern South America, from Trinidad to northern Brazil, favoring muddy habitats such as mangroves, estuaries, and river mouths, though it is intolerant of fresh water. A relatively small shark typically reaching in length, the daggernose shark is unmistakable for its elongated, flattened, and pointed snout, tiny eyes, and large paddle-shaped pectoral fins.
Daggernose sharks are predators of small schooling fishes. Its reproduction is viviparous, with females give birth to 2–8 pups every other year during the rainy season; this species is capable of shifting the timing of its reproductive cycle by several months in response to the environment. Harmless to humans, the daggernose shark is caught for food and as bycatch in artisanal and commercial fisheries. Limited in range and slow-reproducing, it has been assessed as Critically Endangered by International Union for Conservation of Nature in light of a steep population decline in recent years.
==Taxonomy and phylogeny==
The first scientific description of the daggernose shark, as ''Carcharias oxyrhynchus'', was published by German biologists Johannes Peter Müller and Friedrich Gustav Jakob Henle in their 1839 ''Systematische Beschreibung der Plagiostomen''. They chose the specific epithet ''oxyrhynchus'', from the Greek ''oxys'' ("sharp" or "pointed") and ''rhynchos'' ("nose"). In 1862, American ichthyologist Theodore Gill coined the genius ''Isogomphodon'' for this species, from the Greek ''isos'' ("equal"), ''gomphos'' ("nail" or "peg"), and ''odous'' ("tooth"). However, ''Isogomphodon'' was subsequently relegated to being a synonym of ''Carcharhinus'', until it was resurrected by shark authority Stewart Springer in 1950. Regardless of its taxonomic validity, ''Isogomphodon'', along with the genera ''Nasolamia'' and ''Prionace'', is closely related to ''Carcharhinus''. An extinct relative, ''I. acuarius'', dates back to the Middle Eocene (45 Ma).
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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