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Grassland expansion—not human hunting—drove ancient African extinctions

November 23, 2018

By Aylin Woodward

Elephants at a watering hole
Elephants (Loxodonta africana) at a savanna watering hole in Africa. (Photo Credit: John Rowan)

Five million years ago, the Ethiopian savanna boasted some three types of giraffe, two rhinos, one hippo, and four elephant-like species. But today’s East African ecosystem appears very different than its ancient counterpart, with communities having fewer very large mammals.

Some scientists have argued that our hominin ancestors—like Homo erectus and their australopithecine relatives—played a role in driving large mammal extinctions in Africa several million years ago. But that explanation for what happened to most of Africa’s ‘megaherbivores’ (a designation for species that weight more than 2,000 pounds) has remained largely untested, until now.

New research shows that there was indeed a steady decline of megaherbivore diversity—all told, 28 major lineages went extinct—that started around 4.6 million years ago. But according to a team including Paul Koch, distinguished professor of Earth and planetary sciences and dean of the Division of Physical and Biological Sciences at UC Santa Cruz, the demise of these large mammals was mainly due to grassland expansion on the continent that was likely tied to falling atmospheric carbon dioxide levels.

Read the complete article at the UCSC Newscenter.

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