Recent studies indicate that dinosaurs acted as ecosystem engineers, fostering habitat openness during the late Cretaceous period. Their extinction around 66 million years ago likely triggered a significant reorganization of ecosystem structures, profoundly affecting rivers. The emergence of dense forests helped stabilize sediments and created a wide, meandering river surrounding the water.
Dinosaurs functioned as ecosystem engineers, regulating forest growth. Their abrupt extinction resulted in extensive ecological shifts, as illustrated in these artistic renderings. Image credit: Julius Csotonyi.
“When considering how life and the environment evolve over time, it’s typically viewed as climate-driven, causing specific effects on living beings. Alternatively, geographic shifts, like rising mountains, also have a notable impact,” explained Luke Weaver, a paleontologist at the University of Michigan.
“It’s uncommon for life to play a crucial role in altering climate and landscape; the influence isn’t solely one-directional.”
The extinction of dinosaurs followed the impact of a massive asteroid on the Yucatan Peninsula approximately 66 million years ago.
Researchers investigating asteroid evidence discovered that the geological layer above the fallout fragments differed significantly from the underlying rock.
Dr. Weaver and his team began examining this abrupt geological transformation within the Williston Basin, which encompasses the Bighorn Basin across eastern Montana, western North Dakota, and northern Wyoming.
“During my review of previous research, I focused on the Fort Union Formation,” Dr. Weaver mentioned.
“This formation, laid down post-dinosaur extinction, appears to consist of layered rocks in various hues.
“Initially thought to be pond sediments resulting from sea level rise, these formations presented an intriguing contrast to the layer beneath, characterized by poorly developed soils that recall features found along flood plains.”
Researchers then hypothesized a link between these geological alterations and the mass extinction event of dinosaurs, commonly referred to as the end-Cretaceous mass extinction.
They further explored the environments represented by the diverse rock formations.
“Our findings indicated that the striped layers were not sediment from ponds,” Dr. Weaver stated.
“Instead, these are point bar deposits, or sediments from the inner curves of large river meanders.”
“Rather than reflecting a tranquil setting, what we uncovered was a highly dynamic environment within those meandering flows.”
Substantial river sediments are framed by layers primarily comprising lignite, a low-grade coal formed from organic material.
Researchers suggested these formed due to less frequent river activity, attributable to the stabilizing effects of dense forests.
“By stabilizing rivers, these forests curtailed the supply of clay, silt, and sand deep into the floodplain, resulting in an accumulation of mainly organic debris,” Dr. Weaver explained.
What evidence will ascertain whether changes occurred right after the mass extinction?
Fine layers rich in iridium are typically found only from cosmic events.
However, the asteroid impact introduced a mix of elements that settled in thin layers across the globe.
This iridium-rich sediment layer, which defines the Cretaceous-Paleogene boundary, contains about three orders of magnitude more iridium than standard sediments and is recognized as an iridium anomaly.
The researchers subsequently focused on areas of the Bighorn Basin where the boundary was absent.
By analyzing geological shifts between the dinosaur-rich layers and those containing early mammals, they sampled narrow bands of red clay about 1 cm wide.
“These iridium anomalies were perfectly situated at the interface between the two differing geological layers,” Dr. Weaver noted.
“This discovery led us to believe that this phenomenon wasn’t isolated to the Williston Basin; it likely applies across many regions in western North America.”
However, questions linger regarding the reasons for the substantial geological transformations observed before and after the dinosaurs’ extinction.
Later, the team came upon discussions regarding how modern animals, such as elephants, impact their ecosystems.
“This was the moment of clarity that connected all the dots,” Dr. Weaver remarked.
“Dinosaurs were enormous; they must have substantially influenced the vegetation.”
Paleontologists have posited that dinosaurs played a crucial role in facilitating forest growth, trapping sediments, and shaping river structures.
“For me, the most thrilling aspect of our research is the evidence that dinosaurs may have directly influenced their ecosystems,” said Dr. Courtney Splain, a researcher at the University of Florida.
“Notably, the impacts of their extinction may be observed not merely through the disappearance of fossils in the geological record, but also through evident changes in the sediment itself.”
Survey results were published this week in the journal Communication Earth and the Environment.
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ln weaver et al. 2025. Dinosaur extinction can explain the change in continental facies at the Cretaceous-Paleogene boundary. Commune Earth Environment 6, 712; doi:10.1038/s43247-025-02673-8
Source: www.sci.news
