Gyrosteus is an extinct genus of ray-finned fish from the family Chondrosteidae that lived during the Lower Jurassic. It has a single species, G. mirabilis.
There could be a "second" species, G. subdeltoideus. However, not much data has been gathered on it, but it is known from otoliths.
This large fish had a sturgeon-like body, reaching 6 metres (20 ft) to 7 metres (23 ft) long.
Gyrosteus is only known from incomplete fossil specimens.