mosasaurs

Sharks, dolphins, ichthyosaurs… makes sense that some faster mosasaurs would evolve in that direction too.

Jurassic-Cretaceous marine crocodiles (like also ichthyosaurs and mosasaurs) looked like sharks, i.e.

The pterosaurs, plesiosaurs and mosasaurs are all extinct as best as we can tell.

Marine reptiles like mosasaurs, plesiosaurs and ichthyosaurs were not dinosaurs.

Beyond ichthyosaurs and cetaceans, carcharhinification (shark-like convergent evolution) also occurred in plesiosaurs, mosasaurs, certain teleost fish like barracuda, and even the extinct thalattosuchian crocodylomorphs.

The mosasaurs also developed a caudal fin (vertical, like sharks and ichthyosaurs, not horizontal like whales and dolphins) and eventually they became quite shark-like, though not as fish-like as ichthyosaurs.

And while we are at it, pterosaurs, which are not dinosaurs, and mosasaurs, likewise.

Between ichthyosaurs (who evolved in Triassic) and mosasaurs (who evolved in Cretaceous) there existed also a group of marine crocodiles (Metriorhynchidae; who evolved in Jurassic), which also had caudal fins and were quite shark-like.

Consequently, the Cretaceous–Paleogene extinction event which wiped out the dinosaurs and other related reptiles never happened, leaving the way clear for an intelligent species to eventually evolve from mosasaurs, a family of Late Cretaceous marine lizards closely related to the modern monitor lizards.

Besides the theropod dinosaurs there have been some extinct crocodilians, some mosasaurs, some pliosaurs, some phytosaurs, a few ichthyosaurs, some rauisuchians (these are triassic predators) and also a few saber-toothed synapsids that belong to the ancestors of mammals.

It also destroyed myriad other terrestrial organisms, including some mammals, birds,[21] lizards,[22] insects,[23][24] plants, and all the pterosaurs.[25] In the oceans, the K–Pg extinction killed off plesiosaurs and mosasaurs and devastated teleost fish,[26] sharks, mollusks (especially ammonites, which became extinct), and many species of plankton.

From the wikipedia page: "Other prehistoric animals, including mosasaurs, ichthyosaurs, pterosaurs, plesiosaurs, and Dimetrodon, while often popularly conceived of as dinosaurs, are not taxonomically classified as dinosaurs.

There was also a very recent UK find of a large Pliosaur (Plesiosaur), which coexisted with Mosasaurs, and at 10m might have eaten this Japanese one for lunch.