What Killed the Great Beasts of North America?

 

 Humans may not have been as involved in the extinction of mammoths and other giant mammals as was believed before.

Until roughly 11,000 years ago, North America was home to a variety of large mammals, including mammoths, giant beavers, and other massive species. In the past, researchers have suggested that these animals eventually died out due to being hunted by the first Americans, known as Paleoindians. However, a new study has indicated that climate change and environmental factors were likely more responsible for their demise. This research could influence future conservation efforts, such as proposals to reintroduce lions and elephants into North America.

The "overkill hypothesis" suggests that humans were responsible for the extinction of the giant mammals, or megafauna, in North America. This idea was first proposed by geoscientist Paul Martin over 40 years ago, as radiocarbon dating seemed to indicate an overlap between the arrival of the first humans and the animals' disappearance. Since then, however, some archaeologists have disputed the hypothesis. They have argued that only two species—mammoth and mastodon—showed signs of having been hunted, while others have pointed to correlations between the extinctions and climate change during the end of the last ice age.

To gain a better understanding of what might have caused the extinction of the megafauna in North America, archaeologists Matthew Boulanger and R. Lee Lyman of the University of Missouri, Columbia, decided to analyze the northeast of North America. This region had received little attention in the past and contains a wealth of prehistoric animal remains, such as the bones of 140 mastodons and 18 mammoths found in New York alone. The researchers hope that their study will provide insights into why the megafauna went extinct and inform future conservation strategies, such as the proposed "rewilding" of lions and elephants into North America.

Boulanger and Lyman collected radiocarbon dates from megafaunal finds and Paleoindian sites in the northeast of North America and examined them for reliability. After filtering out any unreliable dates, they ended up with a sample of 57 megafauna dates from 47 different sites and 25 Paleoindian dates from 22 sites. When they compared the two sets of data, they found that most of the megafauna had already gone extinct before humans came on the scene, indicating that the humans had nothing to do with their demise. This research could have important implications for conservation strategies, such as the controversial proposals for "rewilding" lions and elephants into North America.

Radiocarbon dates indicate that the northeastern megafauna experienced two major declines before going extinct. The first was 14,100 years ago and occurred before humans were in the region, but the population of animals recovered after about 500 years. The second and final population crash began 12,700 years ago, when Paleoindians had just arrived, according to the archaeological record. The team's research, published in the 1 February issue of Quaternary Science Reviews, suggests that even though humans and megafauna coexisted for about 1000 years before the animals went extinct, the animals were already on their way out: Between 75% and 90% of the megafauna were gone before humans ever came. While there was an overlap between humans and animals, there is no evidence of hunting, as neither megafaunal nor Paleoindian sites contained animal bones that had been butchered or modified.  

The authors emphasize that their findings only relate to northeastern North America, not to other places such as the Great Plains and Southwest. Despite the large numbers of megafauna in the northeast, and the absence of evidence of humans being involved in their disappearance, they suggest that overkill could not be the only or even the biggest cause of the extinction of animals across the continent. Climate and environmental changes must have also been important. Researchers observed that the second wave of megafaunal extinction happened 12,700 years ago, which is around the same time as the start of a cold period lasting 1,300 years known as the Younger Dryas. This was followed by the Holocene, which is the warm period where we are still living.

This new research affirms the opinion of many scientists that environmental and climatic factors could be behind the extinction of megafauna. Lisa Nagaoka, a zooarchaeologist from the University of North Texas in Denton, believes that when humans arrived, the megafauna may have already been close to extinction.

Not only did these events take place thousands of years ago, but they also have a relevance to today. Some conservationists are proposing the reintroduction of certain species, such as elephants and African lions, which are related to extinct animals like mastodons and American lions. According to Lyman, this has important implications.  

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This concept has recently been gaining attention in both science and the media. For example, rewilding involves bringing in elephants and Bactrian camels, which are close to extinction in the Gobi Desert, to North America, where they would eat woody plants and weeds that are damaging grasslands in the West. This could create a habitat to help protect these animals from extinction. However, some scientists think this plan is based on an incorrect understanding of ecology, and could end up harming the environment and existing species. 

Lyman says the plan is based on the idea that humans are responsible for saving these animals and restoring their habitats since humans were the ones who caused their disappearance in the first place. However, those who believe in the overkill hypothesis are not convinced by the new study. Gary Haynes, an archaeologist from the University of Nevada in Reno, believes that the authors did not prove or disprove overkill. He thinks humans may have come to the northeast before the time frame indicated by radiocarbon data, but their remains just have not been found yet. Todd Surovell, an archaeologist from the University of Wyoming in Laramie, believes the new study is in line with the idea that humans were the cause of the extinction of the large animals in North America. He suggests that the fundamental question is whether the animals would have gone extinct even without humans arriving.