Gryponautilus
Gryponautilus is a genus of Upper Triassic nautilids belonging to the trigonoceratacean family Grypoceratidae, characterized by involute, inflated shells, which at maturity develop narrowly rounded keel-like venters. Venters on inner whorls are truncated and broadly convex to concave.
Immature forms bear a resemblance to Grypoceras.