The research traces 66 million years of mammal diversity

When trying to understand the present, it is helpful to look at history. New research from the University of Nebraska-Lincoln examined the fossil record going back 66 million years and tracked changes in mammalian ecosystems and species diversity on the North American continent.

The study, led by Alex Shupinski, who earned her PhD in May, and co-authored by Kate Lyons, an associate professor in the School of Biological Sciences, provides a comprehensive look at how species diversity changed over the first 65 million years. the Cenozoic Era – until the arrival of humans – and how climate and other environmental factors, including changing landscapes, affected animal life on the continent.

Findings published in Proceedings of the Royal Society B they also provide insight into how mammals bounced back after the last mass extinction – the eradication of the non-avian dinosaurs.

“About 66 million years ago, we go from a completely subtropical environment across North America to grasslands to a frozen savannah and finally into an ice age,” Shupinski said. “It shows how species have changed over time, through many ecological, environmental and climatic changes, and allows us to make comparisons across these events and at different spatial scales.”

The researchers sliced ​​the fossil record from the Cenozoic era into million-year increments and used three indices of functional diversity — which quantify changes in community structures using mammalian traits — to examine mammal communities at local and continental scales.

For most of the Cenozoic Era, local and continental rates of functional diversity varied, but surprisingly during the first 10 million years of this era, immediately after the extinction of the non-avian dinosaurs, all rates of functional diversity both locally and across the continent increased.

“It was fascinating to see that for most of the Cenozoic, functional diversity was separated across temporal and spatial scales, except for this one,” Shupinski said.

“For 10 million years, all scales change in the same way. Then, about 56 million years ago, we see a massive immigration of mammals into North America from other continents, and at that point we see a divergence of functional diversity.” .

“Communities change at different times, at different rates and in different directions,” she said. “We can observe that locally the diversity of roles is increasing, but continentally they are decreasing.”

Lyons said that some changes among mammal species can be explained by environmental changes, including periods of cooling and warming or when heavily forested areas were usurped by grasslands, but that large-scale environmental changes did not reach the level of disruption caused by the dinosaur mass extinction.

“Therefore, this could potentially be a way to identify areas of the world or communities that are under particular stress,” Lyons said.

“We may be entering a sixth mass extinction event, and if so, we can expect the communities at the forefront of this extinction to respond in a similar way based on the patterns we see after the extinction of the non-avian dinosaurs.” .”

In the field of conservation paleobiology, tracking past changes in ecosystems over long periods of time helps scientists and the public better understand the biodiversity crises that are happening today, and this current study offers a thorough analysis of the age of mammals and hints at what may come next.

“If we look at modern (crises) and see a similar response in the functional diversity of modern community structures, this can be a conservation tool because we can highlight some of these communities that are experiencing the most disruption and that are at the highest risk of change and disruption to their ecological services and functions,” Shupinski said.

Additional authors of the study are Peter Wagner, professor of earth and atmospheric sciences at Nebraska, and Felisa Smith of the University of New Mexico, Albuquerque.