Why did crocodiles, turtles, lizards and birds survive the Cretaceous-Palaeogene extinction event, but non-avian dinosaurs didn’t?
Mike Follows
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Sutton Coldfield, West Midlands, UK
The Cretaceous-Paleogene (K-Pg) extinction event that occurred 66 million years ago is believed to have been caused by an asteroid crashing into Earth just off the Yucatan peninsula in south-eastern Mexico. The event caused catastrophic environmental changes, including firestorms, tsunamis, darkness from soot and dust, global cooling and ecosystem collapse.
While many species went extinct, certain groups were better adapted to survive. The survival of crocodiles, reptiles and avian theropod dinosaurs (the ancestors of modern birds) can be attributed to several key factors.
The asteroid impact would have lifted dust into the stratosphere, where it would have stayed for an extended period because this layer is above the weather systems and the rain that would normally carry it back down to the ground. With the dimming of the sun, photosynthesis would have been compromised, reducing the total biomass that could be supported on the planet.
Larger animals like non-avian dinosaurs required vast amounts of food and would have succumbed quite early to this disruption in food supply. Smaller species like crocodiles, lizards and birds had a distinct advantage.
After an asteroid hit Earth 66 million years ago, crocodiles and turtles would have been able to seek refuge in water
Lizards could also shelter in burrows while firestorms raged above, and crocodiles and turtles could seek refuge in water, which would have buffered them from temperature extremes and atmospheric disruptions. Smaller species often reproduce faster, with shorter gestation periods, enabling them to generate larger populations and adapt more quickly to new conditions.
With a less specialised diet, avian dinosaurs could forage for a wider range of food and migrate to favourable habitats, helping them survive the extreme conditions of the period.
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