4.6 million years

That’s how long ago Africa’s once-plentiful giant herbivores started going extinct, according to a new study published in the journal Science. That’s more than a million years before the first evidence of animal meat consumption by early human ancestors. In other words, it wasn’t us.

Africa now has only five species of herbivores over 2,000 pounds — elephants, giraffes, hippopotamuses, and two kinds of rhinoceros — but once had far more. Some scientists had speculated that the earliest human ancestors may have hunted many of these giant plant-eaters to extinction. The new study, conducted by a research team that included UMass Amherst scientist John Rowan and was led by Tyler Faith of the University of Utah, found that the decline in megaherbivore lineages began far earlier. Moreover, the rise of humans did not change the rate of extinctions.

Instead, the authors suspect that an expansion of grasslands caused by a changing climate left fewer food sources for large animals that had previously survived on woody vegetation.

— DANTE RAMOS