Chapter Thirteen The Early Hominins

The Early Hominins of South Africa An early fossil find was a juvenile skull found at the Taung quarry. It was named Australopithecus africanus by Raymond Dart. Fossils found in the Sterkfontein Valley belong to both Australopithecus africanus and Paranthropus robustus. A. africanus lived earlier than P. robustus.

The Early Hominins of East Africa Olduvai Gorge in Tanzania, associated with the Leakey family, has been the site of finds of Paranthropus boisei and early members of the genus Homo. Species found in the Lake Turkana Basin area include: Paranthropus boisei Paranthropus aethiopicus Australopithecus anamensis Kenyanthropus platyops

The Early Hominins of East Africa (Continued) Hadar in northern Ethiopia was the site of the discovery of “Lucy”, who is a member of the species Australopithecus afarensis. The species Australopithecus garhi is known from the Middle Awash of Ethiopia. Fossilized footprints dating between 3.8 and 3.6 million years B.P. have been found at the site of Laetoli.

The Fossils of Chad A fossil found in northern Chad suggests that the distribution of the early hominins may be greater than that suggested by the better-known south and east African sites. The find has been dated between 3.5 and 3.0 million years B.P. and has been placed in the species Australopithecus bahrelghazalia.

The Species of Australopithecines Although not all paleoanthropologists agree, the following australopithecine species have been identified: Australopithecus anamensis Australopithecus afarensis Australopithecus sediba Kenyanthropus playops Australopithecus bahrelghazalia Australopithecus africanus Australopithecus garhi Paranthropus aethiopicus Paranthropus boisei Paranthropus robustus

Australopithecines as Erect Bipeds The postcranial skeletons of Australopithecus and Paranthropus are those of erect bipeds. Evidence includes: Shape of the pelvis Position of the foramen magnum Presence of a lumbar curve Way the femurs are angled in Anatomy of the foot Laetoli footprints Many hypothesis have been proposed to explain the advantages of erect bipedalism. These benefits include raising the line of sight, freeing the hands, and assisting the body in maintaining a proper body temperature.

Early Hominin Tool Use The earliest hominin tools were probably made of perishable tools such as wood, bark, leaves, and fiber. The evidence for tool use in the archaeological record consists primarily of stone objects. The first concrete evidence of stone tool manufacture comes from a site in Ethiopia dated at 2.6 million B.P. Further evidence for early hominin tool use stems from the anatomy of the hand. The hand anatomy of Paranthropus robustus introduced the possibility that members of this species were capable of a precision grip and complex toolmaking.

Early Hominin Dentition In general, the dentition of Australopithecus and Paranthropus resembles that of Homo. Early species of Australopithecus show many non-hominin features, and Paranthropus evolved rather specialized dentition. Many features of the dentition of A. afarensis are intermediate between that of modern humans and apes. The dentition of Paranthropus is highly specialized for heavy grinding with the back teeth.

The Early Hominin Brain and Skull The cranial capacities of Australopithecus and Paranthropus vary from 400 to 530 cubic centimeters, compared to an average of 1350 for modern humans. The structure of the skull reflects a small cranium associated with large dentition and powerful chewing muscles. The Australopithecus skull shows prognathism and the bones are pneumatized. The expansion of the temporalis muscle is reflected in the presence of a temporal-nuchal crest. The top views shows postorbital constriction. The forehead, behind brow ridges, is low and flat.

Erect Bipedalism and the Human Brain In the evolution of the human pelvis, a repositioning of the sacrum has created a complete bony ring through which the birth canal passes. The need to pass the large human brain through this opening has resulted in the human newborn having a brain less than 30 percent of its adult size. The brains of other animals are almost completely developed at birth. Thus the human infant is very dependent on others for an extended period.

The Paranthropus Skull Paranthropus is characterized by specialized chewing apparatus that includes large premolars and molars associated with a thick, deep mandible. Many features of the skull are related to the development of powerful chewing muscles. The zygomatic arch is long and powerfully built, flaring away from the skull. A small sagittal crest appears on the top of most specimens for attachment of the powerful temporalis muscle.

Ecology and the Early Hominins A major cooling event that took place approximately 2.5 million years ago is associated with the spread of arid and open habitats in east and south Africa. This cooling event is associated with the appearance of new hominin genera, Paranthropus and Homo. Reconstructions of the paleohabitats associated with early hominins suggest several types of habitats.