The History of Our Tribe Hominini Textbook Part III Pliocene Epoch Chapter 9 Gracile Australopiths

PART III EPOCH THE EPOCH ( Figure fauna of North America . by Jay is in the public domain . The Epoch ( was characterized by global cooling and weather disruptions due to the formation of the Panama land bridge and resultant changes in ocean currents . The polar ice caps were expanding and sea levels had already begun to drop , as the Epoch ( kya ) approached . The geologic record shows us that Africa was subject to cooling and drying trends , with sons becoming more pronounced . Grasslands were expanding and thus forest cover was shrinking . wet and dry periods changed the African landscape . Lakes formed and dried and filled once again . All of the and most went extinct during this epoch and by . genus Homo appeared in the fossil record . The most tantalizing question with regard to the earliest members of our genus is what drove the process . By the time of the more derived ( and ( and genus Homo ( 22 ) cranial capacity had increased and 200 , respectively , from the earlier . It has generally been hypothesized that competition for resources was the driving force , and while that may be so , recent research has just how radical climatic changes were in East Africa . The film Becoming ( 2009 , Discovery Communications ) provides a nice overview of how scientists have pieced together the ment of that region of the world from the local geology . 75

, Foraging in South African grasslands . Artwork by Walter . Figure The Epoch can be considered the time of the great adaptive radiation of the , when more than a dozen species evolved in the corridor from Ethiopia to South Africa . While the died out , concurrent with the reduction in forest cover during the late and early , many came and went over the course of almost of the . The lineage may the there is possible material ( possibly or ) from the late from several sites ( and ) for which no designation has been established . While there is debate as to how much time spent outside of forested environments , they certainly filled distinctive niches , as evidenced by changing morphology as well as more versatile hands that afforded them greater manipulative abilities . As we discover more about limb morphology , it is apparent that some were more adapted to an arboreal environment whereas others were less so . Of even greater interest is that the East African ( and ) may represent a different than those from South Africa ( and ) The East African species may have been more adapted to a terrestrial environment , while the South African forms may have retained or reverted to more primitive climbing adaptations . The various species may have walked differently as well . The question remains from which group are we descended ?

Some researchers have suggested that Au . from South Africa may be part of our lineage this confounds matters for some researchers as to how the older East African species were seemingly less primitive in some ways than the more recent South African forms . We need to realize that we are only seeing part of the picture . Just as the ape population levels exploded on three continents in the , the same was apparently true for African in the . Discoveries of new species of African apes and are accelerating . We need to break out of our linear mindset and realize that there were numerous species adapting to localized , so we should not expect to see uniform changes across time and geographic space . In addition , the same may hold true for grouping and mating practices . We should not jump to conclusions or get too caught up in how the various species were related and who begat whom ! While everyone would like to be the person who found one of our long lost relatives , the history of paleoanthropology is fraught with those claims and . 76

Gorge . Panoramic view of Gorge by is licensed under . Figure Modem landscape of Upper morphology suggests that retained adaptations for climbing trees that were likely used for food and safety . However , when on the ground , they were habitual bipeds , albeit with some from ourselves

. Gracile Figure fossil sites . Map of the fossil sites of the early by and Sting is licensed under . Genus ( southern ape ) was first used in 1924 by Raymond Dart for the Child , a juvenile Au . specimen from the quarry site of , in South Africa . Au . and ( depending on the evolutionary schema of individual ) are known as gracile , due to their more gracile masticatory apparatus relative to the robust . 79

Figure An outlook . By Taylor , 80 The History of Our Tribe