African Megaherbivore Diversity Graphs (image) Arizona State University Share Print E-Mail Caption The decline of African megaherbivore diversity (gray curve) over the last seven million years was driven by falling atmospheric carbon dioxide and the expansion of grasslands, not ancient hominin impacts. The onset of the megaherbivore decline around 4.6 million years ago (red dashed line and shading) occurs well before the appearance of tool-bearing hominin species capable of hunting large prey. Credit John Rowan Usage Restrictions Image to be used in conjunction with media on this research only. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.