New research suggests that the ancestors of alligators and crocodiles stayed loyal to a warm climate through mass extinctions and hothouse worlds, a loyalty that may have helped them survive the asteroid that killed the non-avian dinosaurs.
A crocodylian surviving the dinosaur extinction. Image credit: Davide Bonadonna.
“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,” said University College London’s Dr. Alfio Alessandro Chiarenza, lead author of the study.
“Our study shows that, despite all this diversity, what stayed surprisingly consistent was their relationship with climate.”
Dr. Chiarenza and colleagues traced the climate preferences of a group of crocodile-line animals called Pseudosuchia.
They combined a family tree of more than 400 fossil and living species, more than 7,000 fossil occurrences, and 130,000 records of living crocodylians.
They then used climate simulations to project where suitable habitat existed across 245 million years.
The pseudosuchians once included land-dwelling, marine, giant and even plant-eating forms, and ranged as far as the poles.
Yet the study authors found that its temperature and rainfall preferences stayed within tight limits.
Their models suggest the group’s ancestral temperature optimum was around 23 degrees Celsius (about 73 degrees Fahrenheit), and living crocodylian lineages sit between 26 and 30 degrees.
When the world warmed, the animals spread toward the poles; when it cooled, they retreated toward the equator.
According to the researchers, these creatures were following a stable climate niche as it moved across the globe, rather than adapting to new conditions.
The analysis flagged two exceptions: (i) around 94 million years ago, during one of the most extreme hothouse episodes of the dinosaur age, the thermal optimum shifted upward, to roughly 35 degrees, in an early branch of the group that includes modern crocodylians; (ii) about 34 million years ago, as the planet dried out, one Australasian lineage of now-extinct crocodile relatives shifted toward drier conditions, a change the scientists link to the progressive aridification of that continent.
The authors also tried to answer a long-running question: why crocodile relatives survived the asteroid impact 66 million years ago when non-avian dinosaurs did not.
They ran climate simulations of the aftermath, with sunlight dimmed, ash blanketing North America and volcanic carbon dioxide rising.
In nearly every scenario, warm refuges persisted near the equator and in the subtropics. Only the most extreme case, a 15% drop in sunlight, erased suitable climate everywhere.
Earlier work by some of the same authors found that the climate habitat of non-avian dinosaurs collapsed in comparable experiments.
However, the climate was only part of the story: smaller body size, a semi-aquatic lifestyle that offered access to food chains less disrupted by the collapse of plant productivity, a generalist diet and a cold-blooded metabolism probably all helped.
“The asteroid did not make the whole planet equally hostile to every group,” Dr. Chiarenza said.
“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.”
“These findings have implications for species today,” said University College London’s Professor Philip Mannion, senior author of the study.
“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.”
The findings appear today in the journal Science Advances.
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Alfio Alessandro Chiarenza et al. 2026. Climatic niche conservatism shapes the macroevolution, extinction, and survivorship of crocodile-line archosaurs. Science Advances 12 (43); doi: 10.1126/sciadv.aeg2217
