Tanaocrossus (Ancient Greek for "outstretched fringe", referring to its distinctive dorsal fin) is an extinct genus of primitive freshwater ray-finned fish that inhabited southwestern and eastern North America during the Late Triassic period.

[3][4][5] Indeterminate remains are known from the Dockum Group of Texas and New Mexico (Bull Canyon Formation).

[3][6] A single fragmentary but distinctive fossilized fin from the earlier Carnian-aged Doswell Formation of Virginia, which shares the genus's distinctive fin rays, was long the only record from the eastern United States, but a partial specimen was also later identified from the Manassas Sandstone.

[4][6][7] Morphologically, it can be easily distinguished from other co-occurring fishes by its highly elongated dorsal fin that stretches across its body.

[10][8][11] It was likely a slow-moving fish that inhabited quiet waters, with its dorsal fin allowing for undulation while swimming.