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.

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.

So there have been at least 4 groups of amniotes that looked like sharks, cetaceans among mammals and at least 3 groups of diapsids.

However all these marine predators looked like sharks from the point of view of locomotion, but none of them had the kind of teeth specialized for cutting that are characteristic for sharks. Teeth resembling those of sharks are found only among some other fish, e.g. piranhas, whose bodies do not resemble sharks.

I guess we’ll see if they have the endurance. Sharks have been around for a while after all. But, Orca have surpassed sharks in terms of badassery, right? And it isn’t that close. They aren’t evolving into sharks, they are the upgrade!

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.

Jurassic-Cretaceous marine crocodiles (like also ichthyosaurs and mosasaurs) looked like sharks, i.e. they depended mostly on their caudal fin for swimming.

On the other hand, there was no resemblance between sharks and plesiosaurs or pliosaurs. The latter swimmed using their lateral fins, somewhat like marine turtles and penguins, not like sharks. Also the dentition of plesiosaurs and pliosaurs had no similarity to sharks, so except for being big predators there were no resemblances between them.