Hominid Origins Introduction Definition of Hominid Dating Methods East African Sites South African Sites Origins of Bipedalism Major Plio-Pleistocene Hominids

I.Definition of Hominid Several characteristics are significant in defining hominids: Large brain size Tool making behavior Bipedal locomotion

II. Dating Methods Paleoanthropologists use two types of dating methods to tell us the age of sites and fossils: A. Relative dating determines only whether an object is older or younger than other objects. B. Chronometric (absolute) dating provides an estimate of age in years based on radioactive decay (usually).

II A. Relative Dating Techniques Stratigrapy is based on the law of superposition, that a lower stratum (layer) is older than a higher stratum. Fluorine analysis applies to buried bones and groundwater seepage. Bones incorporate fluorine during fossilization. Biostratigraphy is related to changes in the dentition of animals. Paleomagnetism is based on the shifting of the geomagnetic pole.

II B. Chronometric Dating Techniques The age of an object can be determined by measuring the rate of disintegration: Potassium/argon (k/Ar) dating involves the decay of potassium into argon gas. K/Ar has a half-life of 1.25 billion years. Carbon-14 is a radiometric method commonly used by archaeologists. Carbon 14 has a half-life of 5730 years. The age can also be determined through techniques such as dendrochronology (tree-ring dating)

III. East African Sites Great Rift Valley (+/- 7mya) May have led to hominid differentiation due to environmental change Volcanic sediments make it possible to chronometrically date the sites. Desert and open rift provide access to deep sediments Provides crucial chronology of human evolution.

III. East African Sites Lothagam – 5.7 mya (protohominid) Aramis – 4.4 mya (Ardipithecus ramidus) Laetoli – 3.7 mya (footprints) Olduvai Gorge - tools, numerous fossils Hadar – 3.5 mya Lucy et al. (A. afarensis) Koobi Fora – 2-3 mya many (100+) individuals

IV. South African Sites Mostly limestone caves and quarries Difficult to date because volcanism is lacking Mostly dated by faunal correlation/biostratigraphy The first australopithecine, a “the missing link” between apes and humans, was at Taung.

V. The Bipedal Adaptation Seems to originate in East Africa, associated with the Great Rift Valley Some Suggestions: Energy Efficiency (over long distances) Predator Identification Carrying Ability Provisioning of Females Heat Dissipation

VI. Plio-Pleistocene Hominids Specimens recovered represent close to 200 individuals from South Africa and more than 300 from east Africa. The specimens have been divided into four broad groupings: Set I Basal Hominids. Set II Early Primitive Australopithecus. Set III Later, more derived Australopithecus. Set IV Early homo.

Set I. Basal Hominids (ca 4.4 m.y.a.) The earliest and most primitive remains are those from Aramis. They have been classified as Ardipithecus ramidus, a different genus from all other Plio-Pleistocene forms.

Set II. Early Primitive Australopithecus (4.2-3.0 m.y.a.) The hominids from Laetoli and Hadar are assigned to Australopithecus afarensis. A. afarensis is so primitive in the majority of dental and cranial features that if it were not for evidence of bipedalism, this primate would not be classified as a hominid.

Set III. Later, More Derived Australopithecus (2.5-1.0 m.y.a.) Two subsets: Robust Australopithecines (aka Paranthropus) Larger body size Small cranial capacities Very large, broad faces Massive back teeth and lower jaws Gracile Australopithecines (Australopithecus) Most of the differences between the two types of australopithecines is in the face dentition

Paranthropus robustus

Australopithecus africanus

Set IV. Early Homo (2.4-1.8 m.y.a.) The earliest appearance of our genus, Homo may be as ancient as the robust Australopithecines. Leakey named these specimens Homo habilis ("handy man") for Olduwan tools Differs from Australopithecus in cranial cavity and dental proportions.

Homo habilis