Reptile evolution was not a series of sudden jumps, but a slow, steady climb.

Nature · Published 3 October 2026 Swipe more like this →

In short: For 75 years, scientists believed reptile evolution occurred in rapid, dramatic bursts triggered by environmental shifts. A massive new study of 1,000 fossils reveals the truth is far more incremental. Reptiles did not simply explode into diversity; they evolved through a sustained, gradual accumulation of changes over millions of years.

The traditional theory of adaptive radiation, popularized by George G. Simpson in the 1940s, suggested that major biological transitions happened in quick, geologically significant bursts. However, recent research led by Harvard paleontologists has challenged this view. By analyzing a vast database of nearly 1,000 reptilian fossils—collected from over 50 museums across 20 countries—researchers found that extinct reptile lineages from over 250 million years ago evolved through many small, incremental changes over 50 million years, rather than a single sudden event.

This pattern holds true even for the most dramatic transformations. For instance, snakes developed their elongated body plans about 170 million years ago, yet they did not fully lose their limbs for another 105 million years. Similarly, while snakes underwent rapid skull changes between 170 and 165 million years ago to enable their powerful, flexible bites, these anatomical shifts did not coincide with the spikes in species diversity that adaptive radiation theory would predict. This mismatch suggests that rapid anatomical change does not necessarily require a corresponding surge in genetic or taxonomic diversity.

The study also sheds light on how reptiles navigated mass extinctions, including the Permian-Triassic 'Great Dying' about 250 million years ago, which eliminated roughly 90 percent of species. Data shows that reptile evolutionary rates and anatomical differences were nearly as high before this catastrophe as they were after. It took nearly 10 million years for reptiles to recover their previous levels of anatomical diversity, proving that while sudden environmental shifts have massive impacts, the recovery and diversification process is a slow, sustained climb. This research fundamentally shifts our understanding of how life on Earth builds its complexity, moving away from the idea of sudden jumps toward a model of long-term, continuous development.

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