In popular culture, you’ll often see the high flying Pteranodon and the ocean-going Mosasaurus referred to as “dinosaurs”. However, while both Pteranodon and Mosasaurus were both prehistoric reptiles, were they actually dinosaurs? Nope. Pterosaurs and mosasaurs (and other marine reptiles such as plesiosaurs) were worlds apart from dinosaurs, even if they existed during the same time and in the same places as the so-called “terrible lizards”.
Pterosaurs or “winged lizards” were more closely related to dinosaurs and birds than marine reptiles, since they are clade Avemetatarsalia or “bird metatarsals”, but they certainly were not dinosaurs. And, contrary to the name, they were not lizards either. However, they were the first vertebrates capable of true flight.
On the other hand, mosasaurs and other marine reptiles were hardly related. In addition to mosasaurs, plesiosaurs, icthyosaurs, nothosaurs, placodonts, sea turtles, thalattosaurs, and thalattosuchians also plied the ancient seas. None of these prehistoric marine reptiles were in the same family or order, and only the familiar sea turtles survived the Cretaceous-Paleogene extinction event. The same goes for the pterosaurs. In contrast, while no dinosaurs exist today, some of their descendants, the birds, are still among us.