Did Dino’s Make Rivers Wind?

Dinosaurs had been the architects of whole ecosystems on Earth. Leaf-munching, ground-trampling, and soil-uprooting by herds of enormous herbivores like Tricerotops and Edmontosaurus saved Cretaceous forests in test, serving to to keep up open savannas that might in any other case have been thick with timber. This in flip probably had a profound impact on how rivers flowed throughout landscapes, each whereas the dinosaurs had been alive and after they went extinct in an asteroid apocalypse.

When the large reptiles had been alive, rivers tended to movement straight, overflow their banks, and unfold throughout the panorama. After their demise, forests grew again, and rivers established meandering paths. These are among the many findings of a brand new study, revealed this week in Nature Communications Earth & Environment by a staff of scientists from the University of Michigan.

“The disappearance of these dinosaur megafauna fundamentally rearranged and reconfigured landscapes and ecosystems as we know them today,” says Luke Weaver, a paleontologist on the University of Michigan and the examine’s lead writer. “An extinction event, which is biological, can have dramatic consequences for the non-biotic aspects of the landscape.”

After the dino’s demise, forests grew thick, and rivers established meandering paths. 

The newly proposed hyperlink between dinosaurs and rivers was the results of shut scrutiny of layers of sediment laid down earlier than and after the dino-killing Chicxulub meteorite hit Earth 66 million years in the past. The best-known marker for this boundary between the age of dinosaurs and the age of mammals—generally known as the Cretaceous-Paleogene boundary—is a skinny layer of sediment enriched in iridium that was delivered by the meteorite and scattered across the globe. But the strata on both aspect of this boundary additionally register an abrupt shift at many rocky outcrops present in historical floodplains.

Below the boundary, sediment tends to be thick with silt and sand, says Weaver. This is indicative of rivers that commonly overflowed their banks and delivered sediment throughout the floodplain. Above the boundary, there’s a lot much less silt and sand and much more coal—the carbonized detritus of historical vegetation. This sample means that the riverbanks started to stabilize, corralling sediment into vast and established meandering channels.

Geologists had already proposed explanations for this shift, none of which needed to do with dinosaurs. One concept is that within the early Paleogene, Earth was merely wetter normally, because of extra precipitation or rising seas, which raised the water desk. Fires ignited by the meteorite impression might even have modified what sediment was flowing via the rivers. But Weaver and his colleagues suspected these explanations had been lacking an essential a part of the story: dinosaurs. “These things are an absolutely enormous presence on the landscape,” he says.

The disappearance of dinosaurs basically rearranged landscapes as we all know them at present.

To get a greater view, the researchers checked out outcrops throughout western North America that clearly present strata earlier than and after the Cretaceous-Paleogene boundary, together with 5 newly recognized boundary websites in Montana and Wyoming. They discovered a change within the sediment file from sand and silt to coal is constant throughout western North America and persists for greater than 1,000,000 years after the impression. In their examine, they argue a shift of this scale is greatest defined by an abrupt and dramatic regrowth of forests, which had been beforehand saved in test by hungry dinosaurs.

“With that hot and humid landscape there is no reason you shouldn’t have dense forests being formed, unless you have something preventing them from coming in,” says Weaver. Within simply a long time to some centuries after the devastation incited by the meteorite, he says the forests would have grown again to type closed canopies not in contrast to at present’s temperate rainforests of the Pacific Northwest. These forests would then have rooted soil in place and stabilized rivers anyplace such timber might develop. “This is a first step toward testing a really big idea,” says Weaver, including that extra paleobotanical proof for the way forests modified would assist strengthen the story.

Other analysis does help the concept that forests quickly grew again after the dinosaurs disappeared, says Scott Wing on the Smithsonian National Museum of Natural History, who was not concerned within the analysis. For occasion, he has discovered a rise within the measurement of seeds present in sediment after the dino-mammal period boundary. These bigger seeds counsel vegetation had been adapting to a denser forest surroundings, as a result of bigger seeds can survive longer with out daylight earlier than germinating. The hyperlink with rivers “is a new line of evidence. It’s a different way of looking at the problem,” he says.

The new principle additionally brings the dinosaurs into the a lot bigger story of how vegetation have formed the movement of rivers since they emerged on land 450 million years in the past, says Mathieu Lapôtre at Stanford University, who additionally didn’t take part within the examine. “Once plants evolved there were a bunch of things that changed the distribution of vegetation on Earth.”

In the brand new dinosaur-free forests, small mammals started their rise. Eventually the primates got here alongside, a couple of of whom would come to reshape the planet’s rivers on an excellent grander scale. “It’s a story that is important for all of Earth’s history from the first land plants to today,” says Lapôtre.

Lead picture: Catmando / Shutterstock

• James Dinneen

  Posted on September 16, 2025

  James Dinneen is a science and surroundings journalist from Colorado, primarily based in New York. Find extra of his work at jamesdinneen.wordpress.com.