Fig. 6

Cranium of Ouranopithecus macedoniensis. The size of a female gorilla, this genus represents a possible ancestor to the gorilla–chimpanzee–human lineage. A popular hypothesis suggests that fossil apes in Eurasia eventually gave rise to African apes after some group (perhaps Ouranopithecus) migrated back to the Southern continent. This hypothesis is difficult to test, however, because of a poor fossil record from this time period in Africa. Photo courtesy of Eric Delson