The sturgeons are related to the paddlefish (family Polyodontidae) in the order Acipenseriformes. Fossils of sturgeons first appear in rocks dating to the Middle Jurassic (about 174 million to 163.5 million years ago). It is thought that sturgeons evolved from an earlier group of fishes called the palaeonisciforms, which appeared at the end of the Silurian Period (about 419 million years ago). The genera Acipenser, Huso, Scaphirhynchus, and Pseudoscaphirhynchus contain living species of sturgeons.
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