Climate change may have led to the extinction of the largest animals in North America

New study published in Nature Communication suggesting that America’s largest extinct mammals were not moved by extinction by rapidly expanding human populations after they entered America. Instead, the findings, based on a new statistical modeling method, show that large mammal numbers have changed in response to climate change, with a sharp drop in temperature around 13,000 years ago beginning to decline. and the extinction of these great creatures. However, people may have engaged in more complex and indirect ways than simple models of overeating suggest.

Before about 10,000 years ago, North America was home to many large and alien creatures, such as mammals, living earthworms, larger-than-life beavers, and large armadillo-like creatures called glyptodons. But about 10,000 years ago, most North American animals weighing more than 44 kg, also known as megafauna, had become extinct. Researchers from the Max Planck Extreme Incident Investigation Board in Jena, Germany, wanted to find out what caused the extinction. The topic has been hotly debated for decades, with most researchers arguing that overcrowding, climate change, or a combination of the two were to blame. With a new statistical approach, the researchers found strong evidence that climate change was the leading cause of extinction.

Overeating climate change

Since the 1960s, the growing and expanding numbers of people across the continents have been considered when the introduction of “big game” specialty hunters to America has recently taken place. around 14,000 years ago, many large mammals became extinct. The large animals did not have the large anti-predator behaviors to deal with a novel, highly social, machine-driven predator, which made them particularly easy to hunt. Proponents of this “transgender ideology” claimed that humans took full advantage of the predatory prey, destroying animal populations and driving the giant creatures to extinction. -careful.

Not everyone agrees with this idea, however. Many scientists have argued that there is insufficient archaeological evidence to support the notion that megafauna hunting was stable or widespread enough to become extinct. Instead, major climate and ecological changes may have been to blame.

Around the time of extinction (between 15,000 and 12,000 years ago), there were two climate changes. The first was a period of sudden warming that began about 14,700 years ago, and the second was a cold snare about 12,900 years ago when the Northern Hemisphere returned to near-zero conditions. glaciers. One or both of these important temperature exchanges, and their ecological effects, have been implicated in the eradication of megafauna.

“Trying to time megafauna eradication and seeing how they align with human arrival into America or a climate event was a common approach , ”Said Mathew Stewart, co-lead author of the study. “However, extinction is a process – meaning it will expand over time – so to understand the causes of the North American megafauna decline, it is vital that we understand how their numbers changed before they became extinct. these long-term patterns, we see only rough correlations. “

‘Dates as data’

To substantiate these controversial hypotheses, the authors used a new statistical approach developed by W. Christopher Carleton, another co-lead author of the study, and published last year in the Journal of Quaternary Science. The population sizes of prehistoric hunter-gatherer groups and extinct animals cannot be estimated by counting heads or hooves. Instead, archaeologists and palaeontologists use the radiocarbon plaque as a surrogate for past population sizes. The philosophy is that the more animals and people are present in a landscape, the more the colored carbon is left behind, which is then reflected in the archaeological records. and fossils. Unlike established methods, the new method better describes uncertainty in fossil dates.

The main problem with the previous approach is that it mixes the uncertainties associated with radiocarbon dates with the process that scientists are trying to identify.

“As a result, you can see trends in the data that are not real, making this method very unsuitable for capturing changes in population levels in the past. Using simulation studies where we know the true patterns of the data, we have been able to show that the new method does not have the same problems, and as a result our approach can work long. better capture over time changes in population levels using the radiocarbon plaque, “Carleton explained.

The extinction of the North American megafauna

The authors used this new approach to the question of the extinction of the Late Quaternary North American megafauna. Compared to previous studies, the new findings show that megafauna numbers were changing due to climate change.

“Megafauna numbers appear to have been on the rise as North America began to warm up around 14,700 years ago,” says Stuart. “But then we see a trend in the this movement occurred about 12,900 years ago when North America began to cool sharply, and soon after that we begin to see that megafauna has become extinct. “

And while these findings show that a return to conditions near glaciers around 12,900 years ago was to blame for the extinction, the story seems more complicated than this.

“We need to consider the ecological changes associated with these climate changes at a continental and regional level if we are to have a proper understanding of what eradicated extinctions. , “explained the group’s director Huw Groucutt, lead author of the study.” People are also not completely off the hook, as it is still possible that they played a more advanced role in megafauna eradication than simple over-the-counter models. praising. ”

Many researchers have argued that it is an impossible coincidence that megafauna events around the world occurred frequently around the time of human arrival. However, it is important to show scientifically that there was a relationship, and even if there were, the causes may have been much more indirect (such as through habitat change) than the killing frenzy when reached people of an area.

The authors conclude their article with a call to arms, urging researchers to develop larger, more reliable records and robust methods for their interpretation. Only then will we develop a broad understanding of the Late Quaternary megafauna extinction event.

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The Max Planck Events Group “Extreme Events” aims to study the character and impact of extreme events from a multi-perspective perspective. This interdepartmental project will involve research across the three Jena Max Planck Institutes (Chemical Ecology, Biogeochemistry, and Human History Science).