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Nagi
>>216576
This, for the most part. The Chicxulub impact and whatever-the-hell-else happened at the end of the Cretaceous (Deccan Traps, etc.) that killed off most of the land life on the planet also mucked with the aquatic ecosystem. A global drop in sea levels dumping shallow sea top predators into deep sea top predators' ecosystems didn't help matters. The ground-up unsettling of the food chain combined with native and foreign top predators now fighting it out for similar territory killed off all the top marine reptiles of the time.
The reason sharks survived is because, well, they weren't the apex predators in the Mesozoic. Pliosaurs were in the Jurassic, and mosasaurs were in the Cretaceous. Sharks were opportunists that usurped the throne once the marine reptiles were all gone. And what happened when sharks did claim the apex marine predator throne? Megalodon happened. And then another ever-so-slight change in marine ecosystems killed him off in the blink of an eye, too, because apex predators are the most fragile niche out there to fill.
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