First study to explore how ancient reptiles spread across the Earth after the end-Permian mass extinction.
New research suggests that the ancestors of dinosaurs and crocodiles in the Triassic period were able to migrate across regions of the ancient world that were once thought to be entirely uninhabitable.
In a study published in Nature Ecology and Evolution, scientists from the University of Birmingham and the University of Bristol used a new geographic analysis method to investigate how these early reptiles, called archosauromorphs, spread across the planet after the end-Permian mass extinction—one of the most severe climate events in Earth’s history.
Archosauromorphs defied tropical heat
The earliest archosauromorphs, which resembled modern reptiles and were much smaller than the dinosaurs that followed, were once thought to survive only in limited regions of the world.
Many paleontologists believed that extreme heat across the tropics created a “dead zone” during the earliest Triassic, making those areas uninhabitable for these animals.
Modelling ancient dispersal routes
Using a new modeling technique that combines landscape reconstructions with evolutionary trees, the research team uncovered clues about how these reptiles traveled across the Earth during the Triassic period. This movement took place after a mass extinction event that wiped out more than half of all land animals and 81% of marine species.
The archosauromorphs that survived the extinction event rose to prominence in Earth’s ecosystems in the Triassic, leading to the evolution of dinosaurs. The team now suggests that their later success was in part due to their ability to migrate up to 10,000 miles across the tropical dead zone to access new ecosystems.
Life endured through Earth’s worst climate event
Dr Joseph Flannery-Sutherland from the University of Birmingham and corresponding author of the study said:
“Amid the worst climatic event in Earth’s history, where more species died than at any period since, life still survived. We know that archosauromorphs as a group managed to come out of this event and over the Triassic period became one of the main players in shaping life thereafter.
“Gaps in their fossil record have increasingly begun to tell us something about what we weren’t seeing when it comes to these reptiles. Using our modelling system, we have been able to build a picture of what was happening to the archosauromorphs in these gaps and how they dispersed across the ancient world. This is what led us to call our method TARDIS, as we were looking at terrains and routes directed in space-time.
“Our results suggest that these reptiles were much hardier to the extreme climate of the Pangaean tropical dead zone, able to endure these hellish conditions to reach the other side of the world. It’s likely that this ability to survive the inhospitable tropics may have conferred an advantage that saw them thrive in the Triassic world.”
“The evolution of life has been controlled at times by the environment,” says Professor Michael Benton from the University of Bristol, senior author of the study, “but it is difficult to integrate our limited and uncertain knowledge about the ancient landscape with our limited and uncertain knowledge about the ecology of extinct organisms. But by combining the fossils with reconstructed maps of the ancient world, in the context of evolutionary trees, we provide a way of overcoming these challenges.”
Reference: “Landscape-explicit phylogeography illuminates the ecographic radiation of early archosauromorph reptiles” by Joseph T. Flannery-Sutherland, Armin Elsler, Alexander Farnsworth, Daniel J. Lunt and Michael J. Benton, 11 June 2025, Nature Ecology & Evolution.
DOI: 10.1038/s41559-025-02739-y
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