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New Clues Rule Out Suspects in the Mammoth Extinction Mystery

Researchers have uncovered evidence that the extinction of large, plant-eating animals preceded and may have contributed to dramatic changes in the composition of prehistoric North American forests. Records preserved in ancient sediments also show that the decline of these animals began long before the emergence of the prehistoric Clovis culture in North America.

Understanding animals' role in maintaining ecological systems can help scientists project the effects of future environmental changes.

The end of the last glaciation marked a period major change in North America: plant communities changed, a wide array of large animals (notably mammoths and mastodonts) disappeared from the continent, and the first prehistoric humans arrived. It is well established that these changes are connected but it has not been clear which happened first, which were causes and which were consequences. The two prevailing hypotheses were 1) that the ecosystem changes were all consequences of the changing climate and that the arrival of humans just helped helped these changes along or 2) that the arrival of humans led to rapid changes in animal populations and plant communities as they altered the landscape.

For this study, researchers looked at fossil pollen, charcoal and a species of dung fungus (Sporormiella) associated with large, grazing animals. They found that:

  •     the decline of the large mammals preceded and may have contributed to changes in the plant community, and
  •     the decline began more than 1,000 years before the prehistoric big-game hunters appeared on the scene

The evidence still does not point out exactly what started the decline of the prehistoric megafauna but it provides a serious challenge to claims that the extinctions were rapid and that they were caused by major climate-driven changes in plant communities.

This study, conducted by a graduate student in the lab of John W. Williams, a professor of geography at the University of Wisconsin, was published in Science and recognized with the Ecological Society of America's William Skinner Cooper Award.

Images (1 of )

  • photo of pollen spores seen through microscrope lens
  • Photo of student researcher examining sediment cores
  • Photo of lake and surrounding trees, grass and plants
Pollen spores preserved in lake sediments, seen here under a microscope, can identify the species that comprised ancient landscapes.
Jacquelyn Gill
A student researcher examines a sediment core for clues to past environmental change.
Jeremy Parker
Sediments accumulated at the bottom of lakes and ponds can preserve pollen grains, fungal spores, and other biological samples from prehistoric landscapes.
Jacquelyn Gill

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