Belonostomus

Belonostomus (from , 'dart' and 'mouth') is a genus of prehistoric ray-finned fish that was described by Louis Agassiz in 1844. It is a member of the order Aspidorhynchiformes, a group of fish known for their distinctive elongated rostrums.

Fossils of Belonostomus have been found worldwide in marine deposits, although some species are known from freshwater habitats. The oldest known species are from the Upper Jurassic of Germany and England, with the youngest known species from the late Maastrichtian. One specimen has been recovered from the late Paleocene-aged Tongue River Member of North Dakota, which would suggest that this genus was the only aspidorhynchean to survive into the Cenozoic, although it is possible this fossil may have been reworked from earlier formations.