Why did the dinosaurs which adapted themselves to marine water not survive?

Dinosaurs that adapted to marine environments, such as plesiOSaurs and ichthyosaurs, were not true dinosaurs but rather marine reptiles. They faced significant challenges, including competition with other marine predators, changes in sea levels, and climate shifts during the late Cretaceous period. The mass extinction event around 66 million years ago, likely caused by an asteroid impact and volcanic activity, drastically altered ecosystems, leading to the extinction of many marine species, including these adapted reptiles. Ultimately, their specialized adaptations may have limited their ability to survive the rapid environmental changes.