The Mosasaurus was a large marine reptile that lived during the late Cretaceous period, around 70 million years ago. It could grow up to 50 feet long and had a long, streamlined body, making it an efficient swimmer. With its powerful jaws and sharp teeth, the Mosasaurus was a top predator in the oceans, feeding on fish, squid, and even other marine reptiles. This creature belonged to a group called mosasaurs, which were closely related to modern lizards and snakes. Fossils of the Mosasaurus have been found in various parts of the world, helping scientists understand the diverse ecosystems of ancient seas.