Sirenosaurus

Sirenosaurus was a large Hadrosaur species that lived in what is now South Dakota and Montana. It was among the few Hadrosaur adapted for swimming and had no rods in its tail, as well as having strong tail muscles as scientists concluded, allowing it to swim away from danger. It lived alongside many types of animals (such as fully terrestrial Hadrosaurs like Edmontosaurus, Parasaurolophus, and among others), but while most of these Hadrosaur species protected themselves against predators like T-Rex by living in large herds, being secure, and by running away from danger, Sirenosaurus, however, was solitary and was semiaquatic, so it defended itself from predators like T-Rex by going into the watery depths for safety. It was also a herbivore that fed on ferns, cycads, and club mosses, but mainly fed on underwater plants, so it only went onto land to rest or to lay eggs. It had possibly went extinct due to the mass extinction caused by an asteroid impact and its effects.