By Sid Perkins
Evidently, my dear Watson, the climate didn’t do it. Scientists weighing in on a cold case open since the end of the most recent ice age — the massive die-offs of North America’s largest mammals — arrived at that conclusion courtesy of some very tiny clues. The spores of a fungus that thrived in and on those creatures’ dung suggest changes in habitat didn’t cause the extinctions. As a result, it’s looking more and more like humans played a major role.
In at least some regions, megafaunal populations apparently began to wane several centuries before changes in vegetation occurred that have been linked to a climatic shift, researchers report in the Nov. 20 Science. In fact, the team argues, die-offs of large herbivores allowed some forms of vegetation previously suppressed by incessant browsing to flourish in a post–ice age world.
Researchers have long debated what triggered the extinctions that struck North American megafauna between 14,000 and 11,000 years ago (SN: 12/4/99, p. 360), and one of the prime candidates has been habitat change caused by a warming climate. The appetites and activities of humans streaming into the continent across a land bridge from Asia provide another possible culprit.