Plus ça change, plus c'est la même chose.

There's something about extinctions that are still somewhat puzzling: although the causes of three of the largest mass extinction events are now pretty much agreed upon, it's still unclear why some organisms survive - flourish, even - while others vanish. For example, the Mesozoic sea was full of Ammonites and Belemnites: two types of cephalopod molluscs. Their fossils are about the most familiar of all: I'd bet they were the first collected by many of us on our holidays to Dorset. Yet the K-T event that wiped out the dinosaurs, pterosaurs, mosasaurs, ichthyosaurs, plesiosaurs and so on accounted for them too. And yet... 

Another family of cephalopods - the nautiluses - managed to survive. Fossil examples from the Cretaceous are pretty much identical to the few modern species.