Early Hominins Chapter 13

Bipedal Adaptation Efficient bipedalism as the primary form of locomotion is seen only in hominins Advantages of bipedalism: Freed hands for carrying objects Wider view of the surrounding countryside Efficient means of covering long distances

Australopithicines (4.2–1.2 mya) Most widely distributed and diverse early African hominins Taxonomy: Made up of two closely related genera Australopithecus (gracile) and Paranthropus (robust) Well established by 3 mya Major features All bipedal Relatively small brains compared to Homo Large teeth (particularly back), thick molar enamel

Australopithecus and Paranthropus anamesnis (4.2-3.9 mya) bahrelghazalia (3.6 mya) afarensis (3.8-3.3 mya) africanus (3-2 mya) garhi (2.5 mya) sediba (1.9-1.7 mya) Kenyanthropus platyops (3.5 -3.2 mya) Paranthropus aethiopicus (2.3-2.5 mya) boisei (2.6-1.2 mya) robustus (2-1 mya) Dates are approximate, evolution is not instant!

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 3.8 and 3.6 mya A. Afarensis

Early South African Hominin Fossils Taung quarry, SA Raymond Dart Taung Child Discovered in 1925 Australopithecus africanus Sterkfontein Valley, SA A. africanus and Paranthropus robustus A. africanus lived earlier than P. robustus

East African Hominin Fossils Olduvai Gorge, Tanzania Leakey family P. boisei and early members of the genus Homo Lake Turkana Basin, Kenya P. boisei, P. aethiopicus, A. anamensis, and K.platyops Hadar, Ethiopia “Lucy”

Chadian Hominin Fossils Australopithecus bahrelghazalia Discovered in 1995 by Michel Brunet Only hominin species found outside of south or east Africa Suggests that the distribution of the early hominins may be greater than that suggested by the better-known south and east African sites

Australopithecus anamensis Northern Kenya (Rift Valley) 4.2-3.9 mya Possible Ardipithecus descendent Possible afarensis ancestor Weighed about 110 lbs Large ape-like canines Large back teeth Bipedal anatomy

Australopithecus afarensis Kenya 3.8-3.6 mya Around 50 individuals discovered between two sites Laetoli Hadar Lucy Donald Johanson 40% complete Valgus knee Pelvic arc more similar to Homo than ape Probable ancestor to all other australopithecines

Paranthropus

Early Hominin Dentition Early Australopithecus show many non-hominin features Many features of the dentition of A. afarensis are intermediate between that of modern humans and apes Paranthropus evolved rather specialized dentition Heavy grinding with the back teeth

The Early Hominin Brain and Skull Cranial capacities Australopithecus and Paranthropus vary from 400 to 530 cc Skull structure Reflects a small cranium associated with large dentition and powerful chewing muscles Prognathism Postorbital constriction The forehead is low and flat Australopithecus – presence of a temporal-nuchal crest suggests large temporalis muscle Paranthropus - skulls are characterized by a small sagittal crest for attachment of the powerful temporalis muscle

The Hominin Brain Evolution of the human pelvis 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

Australopithecine Tool Use Earliest hominin tools Probably made of perishable tools Wood, bark, leaves, and fiber The evidence for tool use in the archaeological record consists primarily of stone objects Paranthropus robustus Hand structure suggests capability of a precision grip and complex toolmaking Australopithecus garhi Garhi means surprise in Afar (Ethiopia) First stone tool manufacturer Dated at 2.6 mya Possible direct ancestor to genus Homo

Australopithecus and Early Homo By 2 mya Early Homo is now a distinct population form late Australopithecus Johanson and White A. afarensis splits into two groups One becomes reproductively isolated Homo habilis Earliest member of the genus Co-existed with late Australopithecines