[adrian_b]

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.