Hominid Origins Introduction
I.Definition of Hominid
Definition of Hominid
Dating Methods
III. East African Sites
IV. South African Sites
V. Origins of Bipedalism
VI. Major Plio-Pleistocene Hominids
Several characteristics are significant in defining
hominids:
II. Dating Methods
II A. Relative Dating Techniques
Paleoanthropologists use two types of dating
methods to tell us the age of sites and fossils:
Ø
I.
II.
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).
Large brain size
Tool making behavior
Bipedal locomotion
Ø
Ø
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II B. Chronometric Dating
Techniques
1.
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)
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.
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.
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III. East African Sites
IV. South African Sites
Ø Lothagam – 5.7 mya (protohominid)
Ø Mostly limestone caves and quarries
Ø Aramis – 4.4 mya (Ardipithecus ramidus)
Ø Difficult to date because volcanism is lacking
Ø Laetoli – 3.7 mya (footprints)
Ø Mostly dated by faunal correlation/biostratigraphy
Ø Olduvai Gorge
- tools, numerous fossils
Ø Hadar – 3.5 mya Lucy et al. (A. afarensis)
Ø Koobi Fora – 2-3 mya many (100+) individuals
Ø The first australopithecine, a “the missing link”
V. The Bipedal Adaptation
VI. Plio-Pleistocene Hominids
Ø Seems to originate in East Africa, associated
Ø Specimens recovered represent close to 200
with the Great Rift Valley
Ø Some Suggestions:
Energy Efficiency (over long distances)
Predator Identification
Carrying Ability
Provisioning of Females
Heat Dissipation
Set I. Basal Hominids (ca 4.4 m.y.a.)
Ø The earliest and most primitive remains are those
z
from Aramis.
They have been
classified as
Ardipithecus ramidus,
a different genus from
all other PlioPleistocene forms.
between apes and humans, was at Taung.
individuals from South Africa and more than 300
from east Africa.
Ø 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 II. Early Primitive
Australopithecus (4.2-3.0 m.y.a.)
Ø The hominids from Laetoli and Hadar are
assigned to Australopithecus afarensis.
Ø 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.
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Set III. Later, More Derived
Australopithecus (2.5-1.0 m.y.a.)
Paranthropus robustus
Two subsets:
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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
Australopithecus africanus
Set IV. Early Homo (2.4-1.8 m.y.a.)
Ø The earliest appearance of our genus, Homo
may be as ancient as the robust
Australopithecines.
Ø Leakey named these specimens Homo habilis
("handy man") for Olduwan tools
z
Differs from Australopithecus in
cranial cavity and dental
proportions.
Homo habilis
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