The Cretaceous Period of Earth history ended with a mass extinction that wiped out numerous species, most famously the dinosaurs. A new study now finds that the structure of North American ecosystems made the extinction worse than it might have been. Researchers at the University of Chicago, the California Academy of Sciences and the Field Museum of Natural History will publish their findings Oct. 29 online in the Proceedings of the National Academy of Sciences.
The mountain-sized asteroid that left the now-buried Chicxulub impact crater on the coast of Mexico's Yucatan Peninsula is almost certainly the ultimate cause of the end-Cretaceous mass extinction, which occurred 65 million years ago. Nevertheless, "Our study suggests that the severity of the mass extinction in North America was greater because of the ecological structure of communities at the time," noted lead author Jonathan Mitchell, a Ph.D. student of UChicago's Committee on Evolutionary Biology.
Mitchell and his co-authors, Peter Roopnarine of the California Academy of Sciences and Kenneth Angielczyk of the Field Museum, reconstructed terrestrial food webs for 17 Cretaceous ecological communities. Seven of these food webs existed within two million years of the Chicxulub impact and 10 came from the preceding 13 million years.
The findings are based on a computer model showing how disturbances spread through the food web. Roopnarine developed the simulation to predict how many animal species would become extinct from a plant die-off, a likely consequence of the impact.
"Our analyses show that more species became extinct for a given plant die-off in the youngest communities," Mitchell said. "We can trace this difference in response to changes in a number of key ecological groups such as plant-eating dinosaurs like Triceratops and small mammals."
The results of Mitchell and his colleagues paint a picture of late Cretaceous North America in whi
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University of Chicago