How mammals have evolved over 66 million years

Recent research from the University of Nebraska–Lincoln has provided significant insights into mammalian ecosystems and species diversity in North America by examining the fossil record from 66 million years ago. 

The study, led by Alex Shupinski and co-authored by Kate Lyons, was published in the Proceedings of the Royal Society B. 

Mammalian species diversity 

The research delves into how mammalian species diversity has evolved over the first 65 million years of the Cenozoic era, up until the arrival of humans, and investigates how climate and environmental changes have influenced animal life on the continent.

“Beginning 66 million years ago, we go from a completely sub-tropical environment across North America to grasslands to a frozen savanna, and finally, reaching the Ice Age,” said Shupinski. 

“It’s showing how species changed through time, through many ecological, environmental and climatic changes and it allows us to compare across those events and at different spatial scales.”

Functional diversity of mammals 

The researchers divided the fossil record into million-year increments and used three indices of functional diversity to examine mammalian communities on local and continental scales. Functional diversity quantifies changes in community structures using mammalian traits. 

The study revealed that, for most of the Cenozoic era, local and continental measures of functional diversity differed. However, during the first 10 million years of the era, immediately following the extinction of non-avian dinosaurs, all measures of functional diversity, both locally and across the continent, increased.

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

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

“Communities are changing at different times, at different rates and in different directions. We might see locally, the diversity of roles increasing, but continentally, they’re decreasing.”

Changes among mammalian species

Lyons pointed out that some changes among mammalian species can be attributed to environmental changes, such as cooling and warming periods or the transition from forested areas to grasslands. However, these changes were not as disruptive as the mass extinction of dinosaurs. 

“That is why this could potentially be a way to pinpoint areas of the globe or communities that are under particular stress.”

Lyons further noted that we may be entering a sixth mass extinction event, and if so, we might expect to see communities that are on the vanguard of that extinction respond in a similar way, based on the patterns we see after the extinction of the non-avian dinosaurs.

Insights for mammal conservation 

The study offers a thorough analysis of the age of mammals, which is valuable for the field of conservation paleobiology. 

Tracking past changes in ecosystems over long periods helps scientists and the public better understand the current biodiversity crisis. 

“If we are looking at the modern (crises) and we see a similar response in the functional diversity of modern community structures, it may be a conservation tool as we can highlight some of these communities that are experiencing the most disturbance and that are at highest risk of change and disturbance in their ecological services and function,” Shupinski said.

Resilience of mammalian communities 

The research highlights the resilience and adaptability of mammalian communities in the face of environmental challenges and mass extinction events. 

By examining the fossil record and understanding how species diversity has evolved, scientists can gain insights into how current and future biodiversity crises might unfold and develop strategies to mitigate their impacts.

The study’s findings underscore the importance of understanding historical biodiversity patterns to better address present and future ecological challenges. 

By investigating the fossil record and analyzing changes in species diversity, researchers can provide valuable information that informs conservation efforts today. 

The work of Shupinski, Lyons, and their colleagues serves as a reminder of the dynamic nature of ecosystems and the ongoing need to study and preserve the diversity of life on Earth.

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