Crocodiles Survived the Asteroid by Sticking to Warm Places

The asteroid that struck Earth 66 million years ago wiped out the dinosaurs, but crocodiles and their ancient relatives are still here. New research suggests their survival came down to a simple habit: they liked warm places.

The asteroid did not make the whole planet equally hostile

Scientists led by University College London used computer models to work out what Earth's climate and geography looked like after the impact. Their simulations indicated that areas near the equator stayed warm enough for crocodile relatives to keep living there. Those warm pockets acted as refuges, places where surviving populations could hold on and later spread out again.

The same team had previously modelled habitats for the dinosaurs that went extinct and found those areas shrank far more severely after the impact. In the new work, only the most extreme climate simulations wiped out the possible crocodile refuges.

Lead author Dr. Alfio Alessandro Chiarenza, based at University College London's earth sciences department, said the asteroid did not make the whole planet equally hostile to every group. He said crocodiles' long-standing preference for warm environments may have placed survivors exactly where suitable climates held up best, like around the equator.

They followed the warmth for 245 million years

To reach that conclusion, the researchers gathered more than 7,000 fossils and records covering over 400 living and extinct species. They combined that evidence with models that rebuilt Earth's climate and geography across 245 million years.

A pattern held: crocodile relatives moved with the warmth. When the planet heated up, they expanded into new regions, sometimes reaching as far as Antarctica. When it cooled, they pulled back toward the tropics.

About 50 million years ago, during a particularly warm period, global temperatures were roughly 10°C higher than today and the polar regions had no permanent ice. Crocodile relatives lived at high latitudes across North America, Europe and Antarctica. Over the millions of years of cooling that followed, the map of where they could thrive shrank toward warmer tropical regions.

There was at least one exception. Around 94 million years ago, during a spell when global temperatures climbed as much as 14°C above modern levels, one branch of the crocodile family evolved the ability to tolerate hotter conditions than the wider lineage could handle at other times.

The family was far stranger than the animals alive today

Modern crocodiles share many recognisable features with their close relatives, but the wider family tree was wildly varied. It once included heavily armoured plant eaters, predators that hunted entirely on land, and animals weighing more than a metric ton.

One of the most remarkable was Sarcosuchus, nicknamed the "super croc", which could reach 12 metres in length. Another, Postosuchus, was a land-dwelling hunter that could move on either two legs or all four.

Dr. Chiarenza said crocodiles are often called living fossils, but their ancestors and relatives changed enormously, ranging from giants the size of a bus to small animals with the face of a pug. What stayed surprisingly consistent, he said, was their relationship with climate.

The finding offers a possible explanation for how a group that appeared around the same time as the dinosaurs endured two of Earth's five major mass extinctions.