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November 19, 2009

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Poop evidence exonerates humans in mammoth mystery

Nov. 19, 2009
Courtesy Science
and World Science staff

The ques­tion of how huge an­i­mals like the mam­moth, mas­to­don, and ground sloth went ex­tinct—and how their dis­ap­pear­ance from North Amer­i­ca af­fect­ed ecosys­tems—has fi­nally been an­swered with dung, re­search­ers say. 

And it seems hu­mans, or their known po­pu­la­tions at least, have been exon­er­ated.

A woolly mam­moth (Cour­tesy An­te­lope Val­ley In­dian Mu­seum, Ca­lif. State Parks)

In a study that sci­en­tists said sheds light on those roughly 13,000 year-old ex­tinc­tions near the end of the last Ice Age, Jac­que­lyn Gill at the Un­ivers­ity of Wis­con­sin in Mad­i­son and col­leagues an­a­lyzed pol­len, char­coal, and Spo­ro­miel­la—a fun­gus that grows in the dung of large her­bi­vores—from an­cient sed­i­ments in Ap­ple­man Lake, In­di­ana. 

Amounts of Spo­ro­miel­la are cor­re­lat­ed with popula­t­ion size of large her­bi­vores at the time, the in­ves­ti­ga­tors ex­plained. 

They fur­ther cor­re­lat­ed the Spo­ro­miel­la da­ta with records of vegeta­t­ion and fire from the pol­len and char­coal. 

They found that popula­t­ions of these tre­men­dous crea­tures, known as mega­fauna, be­gan shrink­ing more than a thou­sand years be­fore the emer­gence of the Clo­vis peo­ple—the first peo­ple gen­er­ally rec­og­nized to in­hab­it the New World—and be­fore large-scale changes in plant com­mun­i­ties and in­creased fire.

So, where­as re­search­ers had pre­vi­ously be­lieved that Clo­vis hunters and/or such en­vi­ron­men­tal shifts had led to the de­cline of mega­fauna in North Amer­i­ca, it now seems that it hap­pened the oth­er way around, the sci­en­tists said. The slow ex­tinc­tion of megafauna 14,800 to 13,700 years ago would have pre­ced­ed the Clo­vis peo­ple, and would have been a cause—not a re­sult—of vegeta­t­ion changes and in­creased fires. 

The finding al­so rules out an ex­tra­ter­res­tri­al im­pact, pro­posed to have oc­curred 12,900 years ago, as a cause of the ex­tinc­tions, ac­cord­ing to the au­thors of the stu­dy, pub­lished in the Nov. 20 is­sue of the re­search jour­nal Sci­ence.

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The question of how large animals like the mammoth, mastodon, and ground sloth went extinct—and how their disappearance from North America affected ecosystems—has finally been answered with dung, researchers say. In a study that scientists said sheds light on those roughly 13,000 year-old extinctions during the end of the last glacial period, Jacquelyn Gill at the University of Wisconsin in Madison and colleagues analyzed pollen, charcoal, and Sporomiella—a fungus that grows in the dung of large herbivores—from ancient sediments in Appleman Lake, Indiana. Amounts of Sporomiella are correlated with population size of large herbivores at the time, the investigators explained. They further correlated the Sporomiella data with records of vegetation and fire from the pollen and charcoal. They found that populations of these tremendous creatures, known as megafauna, began declining more than a thousand years before the emergence of the Clovis people—the first people generally recognized to inhabit the New World—and before large-scale changes in plant communities and increased fire. So, whereas researchers had previously believed that Clovis hunters and/or such environmental shifts had led to the decline of megafauna in North America, it now seems that it happened the other way around, the scientists said. The slow extinction of megafauna 14,800 to 13,700 years ago would have preceded the Clovis people, and would have been a cause—not a result—of vegetation changes and increased fires. This discovery also rules out an extraterrestrial impact event, proposed to have occurred 12,900 years ago, as a cause of these megafaunal extinctions, according to the authors of the study, published in the Nov. 20 issue of the research journal Science.