Where have all the megafauna gone? Creatures like mastodons, giant ground sloths, basically the entire Ice Age cast? Scientists know there was a mass extinction in Eurasia and the Americas between 11,000 and 15,000 years ago but the cause of the extinction has remained elusive. Prevailing hypotheses are:
- the animals were hunted to extinction by humans;
- climate change in the form of a brief return to ice-age like conditions killed them off;
- disease brought by humans or their animals when they entered the Americas jumped species and destroyed the beasts;
- a comet impact disrupted the environment to the point that megafauna could not survive.
New evidence points to climate change but with a twist.
A research team, led by scientists from the University of Adelaide, took megafaunal remains with known radiocarbon dates and tested the bones for nitrogen isotope amounts. They then used the isotope amounts to calculate how much water was in the environment when the animals died. By comparing the carbon dates to the amount of environmental moisture, the team was able to conclude there was a huge moisture increase right before the mass extinction. The moisture increase was catastrophic, the team says, because it destroyed grasslands which in turn broke the megafauna food chain.
In a press release, team leader Professor Alan Cooper stated:
“The idea of moisture-driven extinctions is really exciting because it can also explain why Africa is so different, with a much lower rate of megafaunal extinctions and many species surviving to this day.”
”Africa's position across the equator means that grassland zones have always surrounded the central monsoon region. The stable grasslands are what has allowed large herbivores to persist - rather than any special wariness of hunters learned from humans evolving there."
The team published their findings in Nature Ecology & Evolution and it can be found here.