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spadenose shark
The spadenose shark (''Scoliodon laticaudus'') is a species of requiem shark, and part of the family Carcharhinidae. It is common in the tropical Indian and western Pacific Oceans, where it forms large schools in shallow water. A small shark reaching a length of , the spadenose shark is named for its distinctively flattened, triangular snout. It is a predator of small bony fishes and invertebrates. This species exhibits the most advanced mode of viviparity of any fish, in which the developed embryos form a highly complex placental connection to the mother at a very small size. Females breed year-round, giving birth to six to 18 pups after a gestation period of five to six months. The spadenose shark is harmless to humans and is valued by artisanal and commercial fishers for its meat and fins. Its abundance ensures it forms a significant component of many fisheries in South and Southeast Asia. The International Union for Conservation of Nature has assessed this species as Near Threatened.
==Taxonomy and phylogeny==
The first scientific description of the spadenose shark was published in 1838 by the German biologists Johannes Peter Müller and Friedrich Gustav Jakob Henle, in their ''Systematische Beschreibung der Plagiostomen''. The holotype is presumed to be a -long stuffed specimen in the Zoologisches Museum of Berlin. The generic name ''Scoliodon'' is derived from the Greek ''skolex'' ("worm") and ''odon'' ("tooth"), while the specific epithet ''laticaudus'' comes from the Latin ''latus'' ("broad" or "wide") and ''cauda'' ("tail"). Other common names used for this species include Indian dog shark, sharp-nosed shark, trowel-nose shark, and yellow dog shark.
Phylogenetic analyses based on morphological and molecular data indicate the spadenose shark is one of the most basal members of its family, along with the related genus ''Rhizoprionodon'' and ''Galeocerdo'', the tiger shark. In addition, anatomical similarities suggest this species to be the closest living relative of the hammerhead sharks, which diverged from the other carcharhinids some time before the Middle Eocene (48.6–37.2 Ma).〔Martin, R.A. (Hammerhead Taxonomy ). ReefQuest Centre for Shark Research. Retrieved on August 30, 2009.〕
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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