Why did crocodiles survive the asteroid that killed dinosaurs? New study of 7,000 fossils points to warmer climates

Archosauria, which consisted of two major species around 250 million years ago, including dinosaurs and crocodilians, once ruled the land where we live today. But while the behemoth dinosaurs were extinct, possibly with subsequent asteroid strikes 65 million years ago, somehow their relatives, crocodiles, which go by many names like gharials, alligators, and caimans, found almost all the continents, excluding Europe and Antarctica.

A new study published on October 21 in Science Advances pointed to the secret of crocodiles’ survival as location and temperature. Led by paleontologist Dr. Alfio Alessandro Chiarenza from University College London and others, the researchers analyzed over 7,000 fossils of more than 400 species, both living or extinct, from pseudosuchia, a larger group that includes crocodilians.

They then compared the records to computer simulations that reconstructed Earth’s evolving climate for 245 million years ago to map out the global history of the group.


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They found out that with the changing climate, the crocodiles survived by moving to warmer areas. Fifty million years ago, when Earth’s temperature was around 10 degrees Fahrenheit warmer on average, the reptiles ranged as far north as Europe and Antarctica.

Then the Earth cooled, and they retreated to the tropics, where most of the species now live. Lead author Dr. Chiarenza said in a statement published in phys.org, “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,” he added.

Following the impact of the Chicxulub asteroid that killed most dinosaurs, the researchers also examined climate changes tens to hundreds of years later. They tested several scenarios, including dimming of the sun caused by ash and dust, and increased carbon dioxide due to volcanic eruptions.

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“At 5% and 10% reduced sunlight, warm regions around the equator stayed suitable for crocodile relatives, but not at 15% less,” the researchers noted in the statement, explaining that this extreme scenario is now unlikely. “Other scenarios, such as increased carbon dioxide, did not affect climate suitability for crocodiles.”

The authors went on to say that climate change alone did not explain why crocodiles survived. “Smaller body size, semiaquatic lifestyles, flexible diets and the low energy needs of ectothermic ("cold-blooded") animals probably also helped,” University College London (UCL) wrote in the statement.

Professor Philip Mannion, who was also part of the study, said, “These findings have implications for species today. If crocodiles mostly coped with past climate change by moving toward 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.”

Although crocodiles survived the mass extinction that killed the dinosaurs, they lost most of their diversity. Long ago, Earth was full of ancient crocodile relatives, including long-legged land-dwellers, “super croc” that could grow up to 40-foot-long, and Postosuchus, which hunted solely on land and could move on two legs as well as on all fours. Today, only a small number of crocodile species remain compared to their diverse past.

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Chiarenza concluded, “Crocodiles are often called living fossils, but their ancestors and relatives changed enormously throughout their history, ranging from giants the size of a bus that could have devoured a T. rex, to small, cute animals with the face of a pug.”

“Our study shows that, despite all this diversity, what stayed surprisingly consistent was their relationship with climate,” he added.