Chapter 11Chapter 11Hominid Origins in Africa

Bipedalism Bipedalism

Human os coxae

Ossa coxae Ossa coxae

(a) Homo sapiens. (b) Early hominid (Australopithecus) from South Africa. (c) Great ape.

Muscles That Extend the HipMuscles 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.

Position of the Foramen Magnum (a) human (b) chimpanzee

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.

Major Features of Hominid Major Features of Hominid BipedalismBipedalism

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 HominidsEarly African HominidsThree 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 Early Hominid Fossil Finds and LocalitiesLocalities

Key Very Early Fossil Hominid Key Very Early Fossil Hominid Discoveries (pre-Discoveries (pre-Australopithecus)Australopithecus)Earliest hominids from AfricaCentral Africa

◦Sahelanthropus tchadensisEast Africa

◦Orrorin tugenensisAramis (Ethiopia)

◦Ardipithecus ramidus

Pre-Australopiths (7.0–4.4 Pre-Australopiths (7.0–4.4 mya)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 Key Pre-Australopith DiscoveriesDiscoveries

Dates Region Hominids Significance

4.4 myaEast

AfricaArdipithecus

Aramis

Large collection of fossils, partial

skeletons; bipedal, bur- derived

5.2–5.8 mya

East Africa

ArdipithecusFragmentary, but probably bipedal

Key Pre-Australopith Key Pre-Australopith DiscoveriesDiscoveriesDates Region Hominids Significance

~6.0 mya

East Africa

OrrorinTugenensis

First hominid with postcranialRemains

~7.0 mya

CentralAfrica

SahelanthropusTchadensis

Oldest hominid; well preserved cranium; very small-brained; likely bipedal

Australopithecus/Paranthropus Australopithecus/Paranthropus from East Africafrom East AfricaAustralopithecus - An early hominid

genus, known from the Plio-Pleistocene of Africa.

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

FeaturesThey are all clearly bipedalThey all have relatively small brainsThey all have large teeth, particularly the

back teeth, with thick to very thick enamel on the molars.

Earlier More Primitive Earlier More Primitive Australopiths (4.2–3.0 mya)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.

SectorialSectorialAdapted for cutting or shearing;

among primates, refers to the compressed (side-to-side) first lower premolar, which functions as a shearing surface with the upper canine.

Australopithecus afarensis Australopithecus afarensis from Laetoli and Hadarfrom Laetoli and Hadar

Lucy◦ A partial hominid skeleton,

discovered at Hadar in 1974.

◦ This individual is assigned to Australopithecus afarensis.

60-100 individuals420 cm3 cranial

capacity

Infant A. afarensis SkeletonInfant 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”

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 Australopithecus and and Paranthropus Paranthropus from Olduvai from Olduvai and Lake Turkanaand Lake TurkanaRobust vs. gracile speciesParanthropus aethiopicusParanthropus bosei

Morphology and Variation of the Morphology and Variation of the Robust Australopiths Robust Australopiths (Paranthropus)(Paranthropus)

Australopithecus africanusAustralopithecus africanus

Australopithecus africanus adult cranium from Sterkfontein

Time Line of Early African Time Line of Early African HominidsHominids

Early Early HomoHomoHomo habilisA species of early Homo, well

known from East Africa but perhaps also found in other regions.

Handyman

Early Early HomoHomo Fossil Finds Fossil Finds

South African SitesSouth African SitesThe 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 Discovery of Child’s Skull From Taung 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 DartRaymond 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 Key South African Pliocene and Early Pleistocene Hominid DiscoveriesPleistocene 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?)

Geology and dating Geology and dating problems in South Africaproblems in South AfricaComplex features

◦Fissures, sink holes, caves, brecciaNo volcanic deposits

Steps in Interpreting Homind Steps in Interpreting Homind Evolutionary Events 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 Steps in Interpreting Homind Evolutionary Events 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.

Estimated Body Weights in Estimated Body Weights in Plio-Pleistocene HominidsPlio-Pleistocene 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-Estimated Body Weights in Plio-Pleistocene HominidsPleistocene 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 Estimated Statures in Plio-Pleistocene HominidsHominids

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 Estimated Statures in Plio-Pleistocene HominidsHominids

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 Estimated Cranial Capacities in Early HominidsEarly Hominids

Early HominidsRange (cm3)

Average(s) (cm3)

Sahelanthropus

Not known

~350

Ardipithecus Not known

Australopithecus afarensis 420

Later australopiths 410–530

Early members of genus Homo 631

Estimated Cranial Capacities in Estimated Cranial Capacities in Early HominidsEarly Hominids

Contemporary HominoidsRange (cm3)

Average(s) (cm3)

Sahelanthropus

Not known

~350

Ardipithecus Not known

Australopithecus afarensis 420

Later australopiths 410–530

Early members of genus Homo 631