Twenty thousand years ago, North America had a more impressive array of big mammals than Africa does today; by 10,000 years ago, 34 genera of these mammals were gone, including the 10 species that weighed more than a ton.

A new study, published in Science, shows that the decline in Megafauna in North America pre-dates the Clovis culture, or the proposed extraterrestrial impact, by 1000 years. The evidence comes from fungal remains from dung:

Sporormiella is a fungus that produces spores in the dung of large herbivorous vertebrates. Lots of dung means lots of spores, so Sporormiella gives an index of the biomass of large herbivores.

Here’s the chart:

As usual, I’ll now be critical. The study is based on a mere 13 samples – in my opinion not nearly enough to cover 13 genera across a continent – and 4 of those were rejected as being anomalous. By anomalous they decided they were either too old or too young to fit their hypothesis. This is an age-old problem – those that don’t fit are removed, and those that do are not as heavily scrutinised.

Before accepting this study, I’d want to see long-term graphs that indicate a very stable incidence of Sporormiella. Rather than a graph that starts just a few thousand years earlier and even then looks unstable.

I don’t know how they made the above graph from 9 samples, but although the eventual decline is obvious, I’m unsure that it shows the start of the decline as 14,800 years ago. The big drop at roughly 15,700 years ago is not mentioned and is almost as severe.

Finally, I don’t know what to make of this in the summary. After deciding that climate change and extraterrestrial impact were not the cause, the authors state:

What about people? It has long been argued that Clovis artifacts signal the first arrival of people in North America south of the boreal ice sheets and that the Clovis people were specialized big-mammal hunters who caused a crash of megafaunal populations from prehuman abundance to extinction within a few hundred years. This “blitzkrieg” scenario is supported by the fact that terminal dates on megafaunal fossils range from 13,300 to 12,900 years ago, which coincides almost exactly with the Clovis period. But the new data show that the megafaunal decline had begun more than a thousand years earlier. If people were responsible for that decline, they must have been pre-Clovis settlers. The existence of such people has been controversial, but archaeological evidence is slowly coming to light and is consistent with their arrival around the beginning of the megafaunal decline. It is beginning to look as if the greater part of that decline was driven by hunters who were neither numerous nor highly specialized for big-game hunting.

There were not enough hunters, nor did they have the skills, but it was them. Not very convincing!