Hominid Origins in Africa
Chapter 11
Bipedalism
Human os coxae
Ossa coxae

(a) Homo sapiens. (b) Early hominid (Australopithecus) from
South Africa. (c) Great ape.
Muscles That Extend the Hip

The attachment surface of the gluteus maximus in humans
(a) is farther in back of the hip joint than in a chimpanzee
standing bipedally. (b) In chimpanzees, the hamstrings are
farther in back of the knee.
The spine has two distinctive curves—a backward (thoracic)
one and a forward (lumbar) one—that keep the trunk (and
weight) centered above the pelvis.
The pelvis is shaped more in the form of a basin to
support internal organs; moreover, the ossa coxae are
shorter and broader, thus stabilizing weight
transmission.
Position of the Foramen
Magnum (a) human
(b) chimpanzee
Major Features of Hominid Bipedalism
Lower limbs are elongated, as shown by the
proportional lengths of various body segments
(e.g., in humans the thigh comprises 20% of body
height, while in gorillas it comprises only 11%).
The femur is angled inward, keeping
the legs more directly under the
body; modified knee anatomy also
permits full extension of this joint.
The big toe is enlarged and brought in line with the other toes; in addition, a distinctive
longitudinal arch forms, helping absorb shock and adding propulsive spring.
Early African Hominids

Three major groups:
◦ Pre-australopiths— the earliest and most
primitive hominids (7–4.4 mya)
◦ Australopiths—diverse forms, some more
primitive, others highly derived (4.2–1 mya)
◦ Early Homo—the first members of our
genus (2.4–1.4 mya)
Early Hominid Fossil Finds and Localities
Key Very Early Fossil Hominid Discoveries
(pre-Australopithecus)
Earliest hominids from Africa
 Central Africa

◦ Sahelanthropus tchadensis

East Africa
◦ Orrorin tugenensis

Aramis (Ethiopia)
◦ Ardipithecus ramidus
Pre-Australopiths (7.0–4.4 mya)



A cranium of
Sahelanthropus from Chad,
dating to 7 mya.
The braincase is massively
built, with browridges, a
crest on top, and large
muscle attachments in the
rear.
Combined with these
features is a smallish
vertical face with front
teeth unlike an ape’s.
Key Pre-Australopith Discoveries
Dates
Region
Hominids
Significance
4.4 mya
East
Africa
Ardipithecus
Aramis
Large collection of
fossils, partial
skeletons; bipedal,
bur- derived
5.2–5.8
mya
East
Africa
Ardipithecus
Fragmentary, but
probably bipedal
Key Pre-Australopith Discoveries
Dates
~6.0
mya
~7.0
mya
Region
East
Africa
Central
Africa
Hominids
Significance
Orrorin
Tugenensis
First hominid with
postcranial
Remains
Sahelanthropus
Tchadensis
Oldest hominid;
well preserved
cranium; very
small-brained;
likely bipedal
Australopithecus/Paranthropus from East
Africa



Australopithecus - An early hominid genus,
known from the Plio-Pleistocene of Africa.
Australopithecine - The colloquial name for
members of the genus Australopithecus and
Paranthropus.
Features
 They are all clearly bipedal
 They all have relatively small brains
 They all have large teeth, particularly the back
teeth, with thick to very thick enamel on the
molars.
Earlier More Primitive Australopiths
(4.2–3.0 mya)
Left lateral view of the
teeth of a male patas
monkey.
 Note how the large
upper canine shears
against the elongated
surface of the sectorial
lower first premolar.

Sectorial

Adapted for cutting or shearing; among
primates, refers to the compressed (sideto-side) first lower premolar, which
functions as a shearing surface with the
upper canine.
Australopithecus afarensis from
Laetoli and Hadar

Lucy
◦ A partial hominid skeleton,
discovered at Hadar in 1974.
◦ This individual is assigned to
Australopithecus afarensis.
60-100 individuals
 420 cm3 cranial capacity

Infant A. afarensis Skeleton



An important new find of a
mostly complete infant A.
afarensis skeleton was
announced in 2006.
The discovery was made at
the Dikika locale in
northeastern Ethiopia, near
the Hadar sites.
The infant comes from the
same geological horizon as
Hadar, dating 3.3 mya.
The “Black Skull”


The “Black Skull” dates to
approximately 2.5 mya, is
the smallest for any
hominid known, and has
traits reminiscent of A.
afarensis.
Along with the primitive
traits are a host of derived
ones that link it to
members of the robust
group.
Australopithecus and Paranthropus
from Olduvai and Lake Turkana
Robust vs. gracile species
 Paranthropus aethiopicus
 Paranthropus bosei

Morphology and Variation of the Robust
Australopiths (Paranthropus)
Australopithecus africanus

Australopithecus
africanus adult cranium
from Sterkfontein
Time Line of Early African
Hominids
Early Homo
Homo habilis
 A species of early Homo, well known
from East Africa but perhaps also found in
other regions.
 Handyman

Early Homo Fossil Finds
South African Sites
The first australopithecine “the missing link”
between apes and humans was discovered at a
quarry at Tuang.
 As the number of discoveries accumulated, it
became clear that the australopithecines were
not simply aberrant apes.
 The acceptance of the australopithecines as
hominids required revision of human
evolutionary theory.

Discovery of Child’s Skull From
Taung
The Taung child’s skull,
discovered in 1924.
 There is a fossilized
endocast of the brain in
back, with the face and
lower jaw in front.

Raymond Dart
Raymond Dart, shown
working in his
laboratory.
 Dart published the
story of the discovery
of the Tuang child’s
skull.

Key South African Pliocene and Early
Pleistocene Hominid Discoveries
Swartkrans
Dates
(m.y.a.)
1.8–1.0
Drimolen
2.0–1.5
Paranthropus robustus
Taung
2.5–2.0??
Australopithecus africanus
Sterkfontein
2.2?
Australopithecus africanus; early
Homo?)
Site
Hominids
Paranthropus robustus; early
Homo?
Geology and dating problems in
South Africa

Complex features
◦ Fissures, sink holes, caves, breccia

No volcanic deposits
Steps in Interpreting Homind
Evolutionary Events
1.
2.
3.
4.
Selecting and surveying sites.
Excavating sites and recovering fossil
hominids.
Designating individual finds with
specimen numbers for clear reference.
Cleaning, preparing, studying, and
describing fossils.
Steps in Interpreting Homind
Evolutionary Events
5.
6.
7.
Comparing with other fossil material—in
chronological framework if possible.
Comparing fossil variation with known ranges
of variation in closely related groups of living
primates and analyzing ancestral and derived
characteristics.
Assigning taxonomic names to fossil material.
Estimated Body Weights in PlioPleistocene Hominids
Male
Female
A. Afarensis
45 kg (99 lb)
29 kg (64 lb)
A. Africanus
41 kg (90 lb)
30 kg (65 lb)
South African
“robust”
40 kg (88 lb)
32 kg (70 lb)
Estimated Body Weights in Plio-Pleistocene
Hominids
Male
Female
East African “robust”
49 kg (108 lb)
34 kg (75 lb)
H. Habilis
52 kg (114 lb)
32 kg (70 lb)
Estimated Statures in Plio-Pleistocene Hominids
Male
Female
A. Afarensis
151 cm (59 in.)
105 cm (41 in.)
A. Africanus
138 cm (54 in.)
115 cm (45 in.)
South African
“robust”
132 cm (52 in.)
110 cm (43 in.)
Estimated Statures in Plio-Pleistocene Hominids
Male
Female
East African
“robust”
137 cm (54 in.)
124 cm (49 in.)
H. Habilis
157 cm (62 in.)
125 cm (49 in.)
Estimated Cranial Capacities in Early
Hominids
Early Hominids
Range
(cm3)
Average(s)
(cm3)
Sahelanthropus
~350
Ardipithecus
Not known
Australopithecus afarensis
Not
known
420
Later australopiths
410–530
Early members of genus Homo
631
Estimated Cranial Capacities in Early
Hominids
Contemporary Hominoids
Range
(cm3)
Average(s)
(cm3)
Sahelanthropus
~350
Ardipithecus
Not known
Australopithecus afarensis
Not
known
420
Later australopiths
410–530
Early members of genus Homo
631