According to paleontology, early hominid skull anatomy was similar to that of their close cousins, the great African forest apes, gorilla and chimpanzee, but they had adopted a bipedal locomotion and freed hands giving them a crucial advantage enabling them to live in both forested areas and on the open savanna at a time when Africa was drying up, with savanna encroaching on forested areas. This occurred 10 million to 5 million years ago.[17]