Chapter 11

Hominid Origins in Africa

Chapter Outline

• The Bipedal Adaptation• Early Hominids from Africa (Pre-

Australopithecus Finds)• Australopithecus/Paranthropus from East

Africa• Early Homo

Chapter Outline• South African Sites• Interpretations: What Does It All Mean?• Seeing the Very Big Picture: Adaptive Patterns

of Early African Hominids

Plio-Pleistocene

• Pertaining to the Pliocene and first half of the Pleistocene, a time range of 5–1 mya.

• For this time period, numerous fossil hominids have been found in Africa.

Morphological

• Pertaining to the form and structure of organisms.

Bipedalism

• Bipedalism as the only form of hominid terrestrial locomotion.

• Since major anatomical changes in the spine, pelvis, and lower limb are required for bipedal locomotion, once hominids adapted this mode of locomotion, other forms of locomotion on the ground became impossible.

Human os coxae

The Human Pelvis

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.

Line of Weight Transmission

• The line over which a significant weight load is carried.

• In a bone structure, the portion of the bone carrying the load will usually be reinforced (i.e., thicker/buttressed).

Major Features of Hominid Bipedalism

• The foramen magnum (shown in red) is repositioned farther underneath the skull, so that the head is more or less balanced on the spine (and thus requires less robust neck muscles to hold the head upright).

Major Features of Hominid Bipedalism• 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.

Major Features of Hominid Bipedalism

• 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.

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%).

Major Features of Hominid Bipedalism

• The femur is angled inward, keeping the legs more directly under the body; modified knee anatomy also permits full extension of this joint.

Major Features of Hominid Bipedalism

• 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.

Question

• Which skeletal modification was NOT necessary for bipedalism?

a) Development of a second (longitudinal) arch on the foot.

b) Repositioning of the foramen magnum.

c) Shortening and broadening of the pelvis.

d) Shortening of the femur.

Answer: d

• Shortening of the femur was not necessary for bipedalism.

Early Hominid Fossil Finds and Localities

Position of the Foramen Magnum

• (a) a human and (b) a chimpanzee.

• Note the more forward position in the human cranium.

Key Very Early Fossil Hominid Discoveries (pre-Australopithecus)

SiteDates

(m.y.a.)Hominids

East Africa

Middle Awash (Ethiopia;

five localities)5.8–5.2 Ardipithecus

Aramis (Ethiopia) 4.4Ardipithecus

ramidus

Central Africa

Tugen Hills ~6.0 Orrorin tugenensis

Toros-Menalla ~7.0Sahelanthropus

tchadenis

Estimated Body Weights and Stature in Plio-Pleistocene Hominids

Body Weight Stature

Male Female Male Female

A. afarensis 99 lb 64 lb 59 in. 41 in.

A. africanus 90 lb 65 lb 54 in. 45 in.

South African“robust”

88 lb 70 lb 52 in. 43 in.

East African “robust”

108 lb 75 lb 54 in. 49 in.

H. habilis 114 lb 70 lb 62 in. 49 in.

Australopithecus

• An early hominid genus, known from the Plio-Pleistocene of Africa, characterized by bipedal locomotion, a relatively small brain, and large back teeth.

Features of Australopithecus

1. They are all clearly bipedal (although not necessarily identical to Homo in this regard).

2. They all have relatively small brains (i.e., at least compared to Homo).

3. They all have large teeth, particularly the back teeth, with thick to very thick enamel on the molars.

Australopithecine

• The colloquial name for members of the genus Australopithecus and Paranthropus.

• The term was first used as a subfamily designation, but it’s now most often used informally.

Lucy

• A partial hominid skeleton, discovered at Hadar in 1974.

• This individual is assigned to Australopithecus afarensis.

Abbreviations Used for FossilHominid Specimens

Abbreviation Explanation

AL Afar locality

LH Laetoli hominid

OH Olduvai hominid

KNM-ER(or simply ER)

Kenya National Museums, East Rudolf

Abbreviations Used for FossilHominid Specimens

Abbreviation Explanation

KNM-WT(or simply WT)

Kenya National Museums,West Turkana

Sts Sterkfontein, main site

Stw Sterkfontein, west extension

SK Swartkrans

Key East African Australopithecine and Early Homo Discoveries

SiteDates

(m.y.a.)Hominids

Olduvai 1.85–1.0 Australopithecines, early Homo

Turkana 1.9–1.3

3.5–1.6

Many australopithecines; several early Homo Paranthropus; also Kenyanthropus 2 nearly complete crania; 3 jaw fragments, isolated teeth; 1 nearly complete skeleton (H. erectus)

Key East African Australopithecine and Early Homo Discoveries

SiteDates

(m.y.a.)Hominids

Bouri 2.5 Australopithecines (A. garhi)

Hadar 3.5–3.0 Many early australopithecines (A. afarensis);

Laetoli 3.6–3.4 Early australopithecines (A. afarensis); well-preserved footprints

Laetoli

• Dated at between 3.5 and 3.7 m.y.a.• Fossilized hominid footprints were found

in an ancient volcanic bed. • Despite agreement that these individuals

were bipedal, some researchers feel they were not bipedal in the same way as modern humans.

Hadar (Afar Triangle)• Dating suggests a range from 3.9 to 2.3 m.y.a.• Recovered:

"Lucy" an Australopithecus afarensis female, was recovered here.

Group of bones representing 13 individuals, including 4 infants, suggest a social unit died at the same time.

Some stone tools may be 2.5 million years old, making them the oldest cultural evidence yet found.

Koobi Fora (East Lake Turkana)

• This site yielded the richest assemblage of Plio-Pleistocene hominids from the African continent.

• Most of the hominids date to 1.8 m.y.a., others date back to 3.3 m.y.a.

• 150 hominid specimens recovered at Koobi Fora represent at least 100 individuals.

West Turkana

• Two important discoveries: Discovery of a nearly complete 1.6

m.y.a. Homo erectus adolescent. Discovery of “the black skull”, a

well-preserved 2.4 million year old skull which caused a major reevaluation of Plio-Pleistocene evolution.

Question

• Which of the following is the site where a 75 foot long trail of hominid footprints was found?

a) Olduvai

b) Laetoli

c) West Lake Turkana

d) Aramis

Answer: b

• Laetoli is the site where a 75 foot long trail of hominid footprints was found.

Question

• The early primitive (4.2-3.0 m.y.a.) hominids from East Africa have been named:

a) Orrorin.

b) Paranthropus.

c) Australopithecus.

d) Ardipithecus.

Answer: c

• The early primitive (4.2-3.0 m.y.a.) hominids from East Africa have been named Australopithecus.

Homo habilis

• A species of early Homo, well known from East Africa but perhaps also found in other regions.

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.

Taung Child• Discovered in 1924. • The endocast is in back,

with the fossilized bone mandible and face in front.

• An endocast is a solid impression of the inside of the skull, often preserving details relating to the brain’s size and surface features.

Little Foot

• Paleoanthropologist Ronald Clarke carefully excavates an australopithecine skeleton, nicknamed “Little Foot,” from the limestone matrix at Sterkfontein cave.

Key South African Pliocene and Early Pleistocene Hominid Discoveries

SiteDates

(m.y.a.)Hominids

Swartkrans 1.8–1.0 Paranthropus robustus; early Homo?

Drimolen 2.0–1.5 Paranthropus robustus

Taung 2.5–2.0?? Australopithecus africanus

Sterkfontein 2.2? Australopithecus africanus; early Homo?)

Steps in Interpreting Homind Evolutionary Events

1. Selecting and surveying sites.

2. Excavating sites and recovering fossil hominids.

3. Designating individual finds with specimen numbers for clear reference.

4. Cleaning, preparing, studying, and describing fossils.

Steps in Interpreting Homind Evolutionary Events

5. Comparing with other fossil material—in chronological framework if possible.

6. Comparing fossil variation with known ranges of variation in closely related groups of living primates and analyzing ancestral and derived characteristics.

7. Assigning taxonomic names to fossil material.

Swartkrans, Geological Section

Time Line of Plio-pleistocene Hominids

Groups of Plio-Pleistocene Hominids

• Specimens represent 200 individuals from South Africa and more than 300 from East Africa.

• Divided into four broad groupings: Set I. Pre-Australopithecus/basal

hominids Set II. Australopithecus/Paranthropus. Set III. Early Homo