Johnson suggests the fungus research is superb evidence for when the decline began, but it is not as good at confirming exactly when the extinction was completed, especially over larger areas where sparse populations might have persisted. The DNA finds, on the other hand, can detect late survivors, he says, “maybe very close to the actual time that the last individuals were alive, at least in Alaska.” The bones analyzed from the period roughly in between show that the extinction process afflicted many species simultaneously. Those fossils came from the contiguous U.S., which back then was separated from Alaska by the massive Laurentide and Cordilleran ice sheets and so, Faith notes, could explain why the pattern of extinction differed up there.
So what caused the decline? The jury’s still out, says Willerslev’s collaborator Ross MacPhee of the American Museum of Natural History in New York City. Johnson notes that archaeologists are turning up evidence of humans in the New World before Clovis, and he suggests they overhunted the megafauna. The beautifully crafted fluted spear points linked with the Clovis might reflect strategies that developed once the giants became rare and harder to hunt, Johnson adds.
Even if scientists cannot definitively finger the killer, research into the megafauna disappearance “is directly relevant today because we are in the middle of a mass extinction and one for which we know the cause—us,” Gill says. “Large animals are among the most threatened today,” she points out, and no one wants Africa to follow the ancient experience of the Americas.
This article was originally published with the title Lost Giants.