Hominid Origins IntroductionHominid Origins Introduction

I. Definition of HominidII. Dating MethodsIII. East African Sites IV. South African SitesV. Origins of BipedalismVI. Major Plio-Pleistocene Hominids

I.Definition of HominidI.Definition of Hominid

Several characteristics are significant in defining hominids:

Large brain sizeTool making behaviorBipedal locomotion

II. Dating MethodsII. 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 TechniquesII 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 TechniquesII B. Chronometric Dating Techniques1. 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.

2. The age can also be determined through techniques such as dendrochronology (tree-ring dating)

III. East African SitesIII. East African Sites

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

III. East African SitesIII. 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 SitesIV. 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 V. The Bipedal Adaptation

Seems to originate in East Africa, associated with the Great Rift Valley

Some Suggestions:Energy Efficiency (over long distances)Predator IdentificationCarrying AbilityProvisioning of FemalesHeat Dissipation

VI. Plio-Pleistocene Hominids 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.)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.)

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.)

Set III. Later, More Derived Australopithecus (2.5-1.0 m.y.a.)

Two subsets: Robust Australopithecines (aka Paranthropus)

Larger body sizeSmall cranial capacitiesVery large, broad facesMassive back teeth and lower jaws

Gracile Australopithecines (Australopithecus)Most of the differences between the two types of australopithecines is in the face dentition

Paranthropus robustusParanthropus robustus

Australopithecus africanusAustralopithecus africanus

Set IV. Early Homo (2.4-1.8 m.y.a.)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 habilisHomo habilis