Semionotiformes

order of fishes

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July 13, 2026

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The Semionotiformes are an order of primitive bony fishes that are now extinct, with the exception of the gars, which are their modern descendants. These fish were abundant during the Mesozoic Era.1

The family Semionotidae, within the Semionotiformes, is characterized by deep bodies, small mouths with grinding teeth, and rhomboid scales. They are considered ancestral to present-day gars. The gars themselves, belonging to the family Lepisosteidae, are known for their elongated snouts filled with needle-like teeth and their bodies covered in thick, diamond-shaped scales.21

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fish
Annotated classification
Order Semionotiformes (gar and fossil relatives) 3 (2 extinct and 1 living) families of widely divergent fishes; probably independent of the Amiiformes but with typical holostean characters; length to about 3 metres (roughly 10 feet). Late Permian to present. Infraclass Teleostei (advanced bony
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Order Semionotiformes (gar and fossil relatives) 3 (2 extinct and 1 living) families of widely divergent fishes; probably independent of the Amiiformes but with typical holostean characters; length to about 3 metres (roughly 10 feet). Late Permian to present. Infraclass Teleostei (advanced bony
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holostean
Skeletal features
…infraclass Holostei includes the orders Semionotiformes, Pycnodontiformes, and Amiiformes. In these orders the preoperculum (an L-shaped bone anterior to the operculum, or gill cover) is tied to the palatal elements and provides part of the originating area for the adductor mandibulae muscle.
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…infraclass Holostei includes the orders Semionotiformes, Pycnodontiformes, and Amiiformes. In these orders the preoperculum (an L-shaped bone anterior to the operculum, or gill cover) is tied to the palatal elements and provides part of the originating area for the adductor mandibulae muscle.
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