Megapterygius (meaning "large wing") is an extinct genus of mosasaurine mosasaur from the Late Cretaceous Toyajo Formation (Hasegawa Muddy Sandstone Member) of Japan.

The Megapterygius holotype specimen, WMNH-Ge-1140240002, was discovered in sediments of the Hasegawa Muddy Sandstone Member of the Toyajo Formation near the peak of Mt.

[1] In 2023, Konishi et al. described Megapterygius wakayamaensis as a new genus and species of mosasaurine based on these fossil remains.

Also like cetaceans, the change in orientation occurs posterior to the center of gravity of the animal, where in Megapterygius, the affected vertebrae are located after the main rib cage.

The femoral head is well-rounded and almost circular in proximal view, which suggests that Megapterygius was capable of rapid pitch control (rotation) and braking.

[1] Skull part around eye socket is slightly wide horizontally, which suggests that had binocular vision that helped it to hunt prey.