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Protacanthopterygii
Protacanthopterygii is a ray-finned fish taxon ranked as a superorder of the infraclass Teleostei. They inhabit both marine and freshwater habitats. They appear to have evolved in the Cretaceous or perhaps late Jurassic, originating probably roughly 150 million years ago; fossils of them and the closely related Otocephala are known from throughout the Cretaceous.〔Encyclopædia Britannica Online (2009): Annotated classification – Superorder Protacanthopterygii. ''In:'' (Fish ). Version of 2009-APR-22. Retrieved 2009-SEP-28.
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==Characteristics and origin==
The Protacanthopterygii contain a number of moderately advanced teleosts. Anatomical and other traits commonly found in this superorder are: more than 24 vertebrae, epicentral cartilages, one supraorbital bone, and a mesocoracoid, an adipose fin, and (often prominent) glossohyal teeth. However, they usually lack a protrusible upper jaw, a gular plate, and proximal forking of the intermuscular bones. Most members of this taxon are rather specialized mid-sized to larger predators of smaller animals.〔
As a group, they prefer temperate waters and are far more diverse in the Northern Hemisphere than in the Southern. Some are anadromous migrants and many are quite euryhaline. Thus, they likely originated in nearshore or brackish waters of the Northern Hemisphere – theoretically the original protacanthopterygian might have been a catadromous migrant inhabiting fresh water, but given that the basal Otocephala were very likely marine, this seems not so likely. Given that they are widespread in the Holarctic but reached the Southern Hemisphere in the Pacific region, it is more likely than not that they originated in general region of the Turgai Strait and the nearby Tethys Sea – perhaps towards the Eastern Tethys as they never seem to have settled Africa or Atlantic South America.〔
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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