The death of dinosaurs dramatically re-engineered Earth’s landscapes

Changes in rock formations from before and after the mass extinction event 66 million years ago may reflect how dinosaurs acted as ecosystem engineers, shaping vegetation and even the meandering of rivers

By Chris Simms

15 September 2025

Large dinosaurs like titanosaurs would have had a huge impact on their environment

CHRISTIAN JEGOU/SCIENCE PHOTO LIBRARY

The impact dinosaurs had on Earth was so big that their extinction seems to have caused dramatic and wide-ranging changes to the planet’s landscapes, such as shifting rivers.

There is a marked difference between some rock formations in North America before and after the dinosaurs died out in the Cretaceous–Paleogene (K–Pg) extinction event some 66 million years ago, after the Chicxulub asteroid slammed into the Yucatán peninsula.

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For instance, green-grey mudstone of what is known as the Hell Creek formation from the time of the dinosaurs turns into the Fort Union formation’s more colourful pyjama-striped layers that contain lots of lignite, a low-grade form of coal formed from plant matter, as the rise of mammals begins.

The changes have previously been put down to the direct knock-on effects of the asteroid strike, including increased precipitation, but Luke Weaver at the University of Michigan and his colleagues are suggesting a different cause.

They have examined sites – largely river floodplains – in the western US that display the sudden geological changes that occurred around the K-Pg boundary, in Bighorn basin in Wyoming and in the Williston basin, spanning parts of Montana and North and South Dakota.