The Decline of the Megafuana

Something dramatic happened to a lot of very big animals between 20,000 and 10,000 years ago. During this time period, 34 major groups of large animals died-out. Among those that disappeared, were ten species that weighted more than a ton. Giant sloths, mammoths, mastodons, giant kangaroos, and moa were just a few of the fast-vanishing fauna.

It has long been clear that these large animals, also known as "megafauna", perished in a short period of time. But scientists disagree about what caused their rapid decline. One explanation was that the humans that moved into the area about 13,000 years ago hunted the large animals to extinction. Another eplanation attributes the decline of large animals to an extraterrestrial object hitting the earth about that same time.

To better understand what brought about the demise of large land animals, a team of scientists set out to reconstruct the ecosystems of the past. The team, led by Jacquelyn Gill of the University of Wisconsin, Madison, went to Appleman Lake in Indiana. There they sampled the sediments that lined the lake looking for clues about the animals and ecology that once thrived in that region.

Gill and her colleagues sought three basic artifacts: fungal spores, pollen, and charcoal. Each of these clues held different bits of information. The fungal spores, distributed in the dung of large herbivores, provided a way of estimating how many "mega" animals were present in the region (more spores meant more dung and more dung meant more animals). Pollen grains provided scientists with to reconstruct the type of vegetation that existed in the region. The third clue, charcoal, held information about the fires that raged (or didn't rage) through the region in prehistoric times. More charcoal meant more fires.

The data Gill and her team collected indicated that large animals started to disappear from the region 14,800 years ago. This finding was surprising, archeologists previously thought that humans did not arrive to the region until 13,300 years ago. Gill and her team also showed that the dominant habitat, open savanna, gradually gave way to mixed woodlands. Fires became increasingly more common, a measure of how dramatically the landscape was changing as the megafuana vanished.

Refs:

Gill, J., Williams, J., Jackson, S., Lininger, K., & Robinson, G. (2009). Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America Science, 326 (5956), 1100-1103 DOI: 10.1126/science.1179504

Johnson, C. (2009). Megafaunal Decline and Fall Science, 326 (5956), 1072-1073 DOI: 10.1126/science.1182770

Image courtesy of Barry Roal Carlsen / University of Wisconsin-Madison.