It has long been assumed that the giant mammals that once roamed Africa – giant sloths, colossal elephants, antlered giraffes – were hunted to extinction by early humans. But new research suggests another culprit: climate change. Scientists examined fossil data going back seven million years to get a clear picture of when various species of megafauna disappeared. This showed that the decline of diversity began some 4.7 million years ago – long before humans arrived on the scene – and didn’t accelerate even after early humans capable hunting, such as homo erectus, emerged.

When the team mapped the environmental records for the same period, they could see that the extinctions often followed dips in atmospheric CO2 which would have led to deforestation of the African savannah and the expansion of grasslands. “We know that many of the extinct megaherbivores fed on woody vegetation, so they seem to have disappeared alongside their food source”, said co-author John Rowan, from the University of Massachusetts Amherst.

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