Grandemarinus is an extinct genus of gar from the Late Cretaceous of Morocco.

The genus name honors evolutionary biologist Lance Grande and references the species' apparent marine nature, while the specific epithet references Oued Gheris, a wadi near the type locality.

[1][2][3][4] The Akrabou Formation preserves a largely pelagic ecosystem, indicating that Grandemarinus was an entirely marine species, in contrast to extant gar, which are found in mostly freshwater and brackish ecosystems, but similar to what is thought to have been the ancestral condition for gars.

It has an unusually short-snouted appearance akin to that of the basal fossil gar Masillosteus and Cuneatus, but its anatomy indicates that it is more closely related to the extant Lepisosteus and Atractosteus.

The short snout was likely evolved as a specialized trait for catching certain pelagic fish.