How did sharks survive while dinosaurs didn't?

Will - With mass extinctions, it's rarely one thing that is the final act for a particular organism or group of organisms. Let's take the dinosaurs after the impact event. It would've killed off a lot of earth's grasslands. We're talking about the continents right now. There'd have been a lot less vegetation, which is bad news if you're a herbivore, there's less food for you to actually eat. There's more competition for the food that remains, so the herbivores were diminishing in number as a result. That means there's less food for the carnivores and the omnivores. Suddenly it's a very good time to be a bird, with their evolution of those wings, they could cover huge areas and actually find what food remained.

Chris - And birds are warm blooded, of course, which presumably helped?

Will - Yeah, it probably makes them more energy efficient as well. Probably makes them less dependent on actually getting the calories. A reason crocodiles did so well out of the mass extinction event (crocodiles have existed on the planet long before even the dinosaurs, is that they could essentially shut down. They could not require food for months on end. They could essentially afford to go longer without finding their next meal. But if we go to the oceans, sharks, maybe they were just fish generalists. They weren't fussy eaters. It pays not to be a fussy eater during a mass extinction. So they might be able to hoover up what fish remained after the extinction event. Whereas some of their big aquatic reptilian cousins, even despite their size, maybe they were just being out-competed for the same prey.

Chris - Well, I'm glad because I was going to ask you that precise question because there were reptiles living in the ocean alongside the sharks that you'd think, well, why don't they survive if the sharks can? And you think it's because they were a bit too fussy in their eating habits?

Will - The chances are they're going for the same food. We don't actually know which were the apex predators between some of your large Mosasaurs and Ichthyosaurs versus things like sharks. Sharks didn't have size necessarily on their side. They grew into much larger things well after the extinction event that did away the dinosaurs. But at this time, maybe they were just very well coordinated. Maybe they were faster and more agile and were able to actually evade their predators and catch their prey more efficiently and maybe that's what got them through.