Dinosaurs in the valley at mountains . This is a 3d render illustration .
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Dinosaurs had such an immense impact on Earth that their sudden extinction led to wide scale changes in landscapes — including the shape of rivers— and these changes are reflected in the geologic record, according to a University of Michigan study.
Scientists have long recognized the stark difference in rock formations across the western United States dating to the Cretaceous and the Paleocene, but chalked it up to sea level rise, coincidence, or other geological reasons.
But University of Michigan paleontologist Luke Weaver shows that the demise of the dinosaurs 65 million years ago had a profound impact on the landscape, resulting in a sedimentary shift.
Weaver and colleagues suggest that dinosaurs were likely enormous “ecosystem engineers” keeping vegetation down like elephants today. Large sauropods knocking down trees while medium-sized herbivorous dinosaurs feed on shrubs and saplings prevented the establishment of dense forests. Without a protective vegetation cover, runoff increased and rivers traversing this open landscape experienced frequent flooding, branching out in a vast floodplain.
With the dinosaurs gone, forests were allowed to flourish, stabilizing sediment transport, forming ponds and corralling water into rivers with broad meanders.
This shift in the dominating fluvial regimes is reflected by a shift in the deposited sediments, from coarse-grained sand and pebbles to fine-grained clay to layers of coal and plant debris.
“By stabilizing rivers, you cut off the supply of clay, silt and sand to the far reaches of the floodplain, so you’re mostly accumulating organic debris,” Weaver explains.
Artistic rendering showing a typical landscape in the late Cretaceous (below), with a world still dominated by dinosaurs, and the same landscape after they were gone (upper panel).
Julius Csotonyi/University of Michigan
Dinosaurs became extinct after a large asteroid slammed into the Yucatan Peninsula at the transition from the Cretaceous period (K) to the Paleocene period (Pg) about 66 million years ago. After a tsunami flooded most of the North American continent and fires destroyed the rest, glass particles, pulverized rocks and soot settled over much of the planet in a fine layer. This layer can be found between the mapped sediment formations, precisely dating the sudden shift in the geological record.
“The impact of their extinction may not just be observable by the disappearance of their fossils in the rock record, but also by changes in the sediments themselves.” says study coauthor Courtney Sprain of the University of Florida.
The sudden demise of the dinosaurs is also a lesson in how the record of Earth might change in light of human-caused climate change and loss of biodiversity.
“The K-Pg boundary was essentially a geologically instantaneous change to life on Earth, and the changes we’re making to our biota and to our environments more broadly are going to appear just as geologically instantaneous. What’s happening in our lifetimes is the blink of an eye in geologic terms, and so the K-Pg boundary is our best analog to our very abrupt restructuring of biodiversity, landscapes and climate,” Weaver concludes.
The full study, “Dinosaur extinction can explain continental facies shifts at the Cretaceous-Paleogene boundary,” was published in the journal communications earth & environment and can be found here.
Additional material and interviews provided by the University of Michigan.