Most people think of crocodilians as living fossils—stubbornly unchanged, prehistoric relics that have ruled the world’s swampiest corners for millions of years. But their evolutionary history tells a different story.

Despite their dominance, once the end-Triassic extinction hit, no non-crocodylomorph pseudosuchians survived. Whereas hyper-carnivore crocodylomorphs appeared to also die off, the terrestrial generalists made it through. The authors hypothesize that this ability to eat almost anything allowed them to survive, while so many other groups went extinct.

“After that, it goes bananas,” said Melstrom. “Aquatic hypercarnivores, terrestrial generalists, terrestrial hypercarnivores, terrestrial herbivores—crocodylomorphs evolved a massive number of ecological roles throughout the time of the dinosaurs.”

Something happened during the Late Cretaceous Period that set crocodylomorphs on a decline. The lineages specialized for diverse ecologies began to disappear, even the terrestrial generalists.

By the end-Cretaceous mass extinction event (punctuated by the meteor that killed the non-avian dinosaurs), most of the survivors are semiaquatic generalists and a group of aquatic carnivores. Today’s 26 species of living crocodilians are nearly all semiaquatic generalists.