Mosasaurus are a kind of marine reptiles, sometimes called canto dragons. It emerged about 98 million years ago and thrived in the late Cretaceous oceans. Living creatures are closely related to lizards and snakes. It was large (several meters or more) and had fin-like feet and sharp teeth.
Their extinction was triggered by a huge meteorite that fell at the end of the Cretaceous period. As a result, the marine environment changed drastically. The falling point of the meteorite contained a lot of sulfur, and the sulfur that evaporated due to the impact of the impact turned into sulfuric acid gas, which fell as acid rain.