Crocodiles survived the dinosaur-killing asteroid partly by eating leftovers
When an asteroid slammed into Mexico 66 million years ago, about three quarters of species vanished, including every dinosaur except birds. Crocodilians pulled through, likely because they can scavenge and go months without food. The winners were creatures that ate detritus, insects and worms rather than living plants.
The extinction ended the Cretaceous and the whole Mesozoic era and opened the Cenozoic, our own. Almost every land animal heavier than about 25 kg disappeared, except some cold-blooded ones such as sea turtles. All pterosaurs died, as did plesiosaurs, mosasaurs and the ammonites, and plankton, sharks and fish suffered heavy losses. Rocks worldwide record the moment as a thin clay layer unusually rich in iridium, a metal more common in asteroids than in Earth's crust.
The impact explanation, known as the Alvarez hypothesis, gained decisive support in the early 1990s with the discovery of the 180 km Chicxulub crater on the Yucatán Peninsula. The asteroid was probably 10 to 15 km wide. A 2016 drilling project found granite hurled up from deep underground within minutes, and almost none of the gypsum normally found in the local seabed; that sulphur-bearing rock would have vaporised into the atmosphere, prolonging the damage. The main killer was likely an impact winter that shut down photosynthesis. The Deccan Traps volcanism has been proposed as a cause, but 2020 climate modelling favoured the asteroid.
The destruction was global and apparently simultaneous: non-avian dinosaurs appear on every continent right up to the end of the Cretaceous and nowhere afterwards, and fossil pollen shows plant communities wrecked from New Mexico to New Zealand. High latitudes fared somewhat better than the tropics. Neither strict plant-eaters nor strict meat-eaters among mammals seem to have survived. Omnivores, insect-eaters and scavengers did, feeding on invertebrates that lived off dead matter.
Rivers and lakes proved refuges because their food webs run on debris washed in from land. Young crocodilians grow slowly and eat invertebrates and carrion, traits linked to their endurance. Afterwards, emptied niches fuelled bursts of evolution. Mammals radiated into forms such as horses, whales, bats and primates, and a few surviving ground and water birds gave rise to today's birds.
Source: Cretaceous–Paleogene extinction event
