Crocodiles and their ancient relatives survived the Chicxulub asteroid impact 66 million years ago partly by following warm climates into equatorial refuges, according to a University College London study of more than 7,000 fossils published in Science Advances.
Dinosaurs and crocodilians first appeared roughly 245 million years ago, but their evolutionary paths diverged sharply during Earth’s mass extinctions.
Paleontologists analyzed over 7,000 fossil records representing more than 400 living and extinct species from Pseudosuchia, the crocodile lineage as detailed in Science Advances. The research team combined these anatomical family trees with computer simulations mapping Earth’s changing climate and geography across millions of years.
Crocodiles Tracked Ancient Warmth Across 245 Million Years
The data revealed that ancient crocodile relatives consistently tracked warmth rather than evolving to tolerate dramatic temperature shifts. Around 50 million years ago, when global average temperatures were roughly 10 degrees Fahrenheit higher than today, these reptiles ranged as far north as Europe and Antarctica. As global temperatures subsequently fell, their populations retreated back toward the tropics.
Equatorial Refuges Protected Survivors After the Asteroid Impact
When the Chicxulub asteroid struck 66 million years ago, it triggered prolonged environmental darkness and cooling from atmospheric dust and ash. The researchers tested several post-impact climate scenarios, including reduced sunlight and volcanic carbon dioxide emissions, to see how the lineage fared under sudden stress. Their models demonstrated that with sunlight dimmed by 5 percent or 10 percent, warm equatorial regions remained climatically suitable for crocodile relatives according to the simulation findings.
The asteroid did not make the whole planet equally hostile to every group. Crocodiles’ long-standing preference for warm environments may have placed survivors exactly where suitable climates held up best, like around the equator. These refuges could have sheltered populations that later recovered and radiated out.
Dr. Alfio Alessandro Chiarenza
Only an extreme scenario involving a 15 percent reduction in sunlight eliminated those equatorial habitats entirely. Meanwhile, simulations involving increased atmospheric carbon dioxide were used to examine conditions immediately after the asteroid impact.
Prehistoric Diversity and Modern Vulnerabilities to Climate Change
Although the lineage survived, modern alligators, crocodiles, caimans, and gharials represent only a tiny fraction of a once-massive pseudosuchian diversity. Prehistoric relatives included armored plant-eaters, land-dwelling predators, and massive forms as outlined in the evolutionary records.
Researchers stress that climate preferences alone did not guarantee survival. Smaller body sizes, semi-aquatic habits, flexible diets, and low ectothermic energy requirements all provided critical biological advantages.
However, scientists warn that the very strategy that saved their ancestors now poses a vulnerability in a warming world. Because these reptiles historically coped with climate shifts by migrating toward suitable temperatures, modern habitat fragmentation presents a severe hazard as University College London researchers explained.
These findings have implications for species today. If crocodiles mostly coped with past climate change by moving towards suitable habitats, today’s species will need room to move as the planet warms, and the loss of suitable areas to roads, farms and cities is making that harder.
Professor Philip Mannion
Professor Philip Mannion suggests that these barriers could prevent modern crocodiles from reaching the stable environments they need to survive ongoing global temperature increases.
