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The First Bipeds


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Title: The First Bipeds

Chapter 7
  • The First Bipeds

Chapter Preview
  • What Is the Anatomy of Bipedalism, and How Is It
    Preserved in the Fossil Record?
  • Who Were the Australopithecines, and What Were
    They Like?
  • What Role Did Bipedalism Play in Human
    Evolutionary History?

  • Controversial Finds The
    Earliest Bipeds?

One of the main derived traits that mark hominids
as different from apes is bipedalism.
Sahelanthropus tchadensis
  • dated to 6-7 million years ago
  • found in Chad (Central Africa)
  • brain size of approximately 350 cc
  • possibly bipedal (due to position of the foramen
    magnum underneath the skull)
  • Ape-like features brow ridges hominid-like
    features small canine teeth

  • Sahelanthropus tchadensis

  • Orrorin tugenensis
  • dated to about 6 million years ago
  • found in Kenya (East Africa)
  • fossils include fragmentary arm and thigh bones,
    lower jaws, and teeth
  • possibly adapted to both bipedality and tree
  • the femur indicates possible bipedality

  • Orrorin tugenensis

  • Ardipithecus ramidus
  • dated to 5.8-4.4 million years ago
  • found at the Aramis site in Ethiopia (East
  • its teeth are small, have thin enamel, and are
    intermediate in form between those chimpanzees
    and australopithecines
  • its deciduous molar (baby tooth) resembles a
    chimpanzee tooth
  • possibly bipedal

  • Ardipithecus ramidus

The Anatomy of Bipedalism and Its Preservation in
the Fossil Record
Why is bipedalism so important in distinguishing
hominids from apes?

- Remember, the term hominid bipedal ape -
Bipedalism has a number of anatomical
consequences - These traits can be used to
identify bipedalism in hominoid fossils and
thus, can be used to distinguish apes from
Why is bipedalism so important in distinguishing
hominids from apes?

- We now recognize the bipedalism is the first
human-like trait to evolve among apes - Prior
to the 1950s, this was not the case. Scholars
had assumed that larger brains had developed
first. - The best example of the persistence
of this kind of thinking is the Piltdown Hoax.
Piltdown Hoax
  • Many scientists of the 1920s believed the
    ancestor to humans had been found in the Piltdown
    gravels of Sussex, England, in 1910.
  • The Piltdown specimens consisted of a humanlike
    skull and an apelike jaw that seemed to fit
    together though the joints connecting the two
    were missing.
  • They were discovered along with the bones of
    other animal species known to be extinct.

Piltdown Hoax
  • The Piltdown Hoax was accepted as ancestral to
    humans because it fit with expectations that the
    missing link would have a large brain and an
    apelike face.
  • No one knows how many of the scientists who
    argued that this specimen was the missing link,
    were involved in the forgery.

Anatomy of Bipedalism
  • Forward position of the large opening in the base
    of the skull (foramen magnum)
  • Series of curves in the spinal column
  • Basin-shaped structure of the pelvis
  • Angle of the lower limbs from the hip joint to
  • Shape of the foot bones

Foramen Magnum
  • Bipedalism can be inferred from the position of
    the foramen magnum, the large opening at the base
    of the skull.
  • Note its relatively forward position on the human
    skull (left) compared to the chimp skull (right).

Skeletons and Locomotion Humans and Chimps
Upper Hip Bones and Lower Limbs
  • Compare the upper hip bones and lower limbs of
    (from left) Homo sapiens, Australopithecus, and
    an ape.
  • The similarities of the human and
    australopithecine bones are indicative of
    bipedal locomotion.

The Bipedal Gait
  • The bipedal gait is really more like serial
    monopedalism or locomotion using one foot at a
    time through a series of controlled falls.
  • Note how the bodys weight shifts from one foot
    to the other as an individual moves through the
    swing phase to heel strike and toe off.

Laetoli The Fossil Record of Bipedalism
  • Fossilized footprints were preserved in volcanic
    ash at the 3.6-million-year-old Tanzanian site
    of Laetoli.
  • The foot of a living human fits inside the
    ancient footprint, which shows the characteristic
    pattern of bipedal walking.

The Australopithecines
Australopithecus afarensis
  • dated to 3.5-2.6 million years ago
  • found in Tanzania and Ethiopia (East Africa)
  • males (5 ft. tall) appear to have been much
    larger than those of females (3.5-4 ft. tall)
  • More evidence of sexual dimorphism males have
    larger canines
  • Possessed a protruding face with a low forehead

  • Australopithecus afarensis
  • Post-cranial anatomy and the Laetoli footprints
    indicate striding bipedalism
  • ape-like features curved fingers (adapted for
    arboreal life?)

Lucy an A. afarensis fossil
  • A 40 complete skeleton of Lucy, indicates
    that australopithecine ancestors were bipedal.
  • This adult female was only 31/2 feet tall.
  • Paleoanthropologists reconstructed the entire
    skeleton from the remains that were discovered.

  • Australopithecus afarensis
  • had a small brain case and cranial capacity (380
    and 530 cc) - similar to that of modern

Lucys Child a juvenile A. afarensis fossil
Sexual Dimorphism in Canine Teeth
Australopithecus afarensis should marked
differences in the size of canine teeth among
males and females.
Trunk Skeletons
  • Compare the trunk skeletons of modern human, A.
    afarensis, and chimpanzee.
  • In its pelvis, the australopithecine resembles
    the modern human, but its rib cage shows the
    pyramidal configuration of the ape.

Upper Jaws
  • Upper jaws of an ape, Australopithecus, and
    modern human show differences in the shape of the
    dental arch and the spacing between the canines
    and adjoining teeth.

Australopithecus vs. Piltdown
  • The Taung child, discovered in South Africa in
    1924, was the first fossil specimen placed in the
    genus Australopithecus.
  • In the early 20th century scientists were
    expecting the ancestors to humans to possess
    large brains and an apelike face and to originate
    from Europe or Asia rather than Africa.

Later Forms of Australopithecus
  • The earliest forms preserve a number of features
    that indicate an ape-like ancestor.
  • By 2.5 million years ago, new forms with a larger
    chewing apparatus and more massive head appeared,
    although brain size remained stable.

Australopithecine Fossil Locations
  • Australopithecine fossils have been found in
    South Africa, Malawi, Tanzania, Kenya, Ethiopia,
    and Chad.
  • Most have been found in the Great Rift Valley of
    East Africa. Why?

Australopithecine Fossils and Rifting
  • In the Miocene, the Eurasian and African
    continents made contact at the eastern and
    western ends of what is now the Mediterranean
  • As these land masses met, rifting occurred,
    gradually raising the elevation of the eastern
    third of Africa.
  • The dryer climates that resulted may have played
    a role in human evolution in the distant past and
    provided excellent geological conditions for
    finding fossils.

Fossil Sites in South Africa
  • Many of the fossil sites in South Africa were
    limestone caverns connected to the surface by a
  • Over time, dirt, bones, and other matter that
    fell down the shaft accumulated in the cavern,
    becoming fossilized.

Species Of Australopithecus
Species Location Dates Features/Fossil Specimens
A. anamensis Kenya 3.94.2 mya Oldest australopithecine
A. afarensis Ethiopia Tanzania 2.93.9 mya Well represented in fossil record.
A. africanus South Africa 2.33 mya First discovered, gracile, well represented in fossil record.
Species Of Australopithecus
Species Location Dates Features/Fossil Specimens
A. aethiopicus Kenya 2.5 mya Oldest robust australopithecine (Black Skull)
A.bahrelghazali Chad 33.5 mya Only australopithecine from central Africa
Species Of Australopithecus
Species Location Dates Features/Fossil Specimens
A. boisei Kenya 1.22.3 mya Later robust form co-existed with early Homo (Zinj)
A. garhi Ethiopia 2.5 mya Later East African australopithecine with humanlike dentition
A. robustus South Africa 12 mya Robust co-existed with early Homo
  • Kenyanthropus platyops
  • dated between 3.5 and 3.2 million years ago
  • found in Kenya (East Africa)
  • skull has a broad flat face and small teeth
  • the brain size is similar to that of
  • the lack of prognathism (like Sahelanthropus)
    may indicate its close relation to genus Homo
  • it may be another australopithecine

  • Kenyanthropus platyops

Gracile Australopithecines
  • Members of the genus Australopithecus possessing
    a more lightly built chewing apparatus.
  • Best known example Australopithecus africanus

Robust Australopithecines
  • Several species within the genus
    Australopithecus, who lived from 2.5 and 1.1
    million years ago in eastern and southern Africa.
  • Known for the rugged nature of their chewing
    apparatus (large back teeth, large chewing
    muscles, and a bony ridge on their skull tops for
    the insertion of these large muscles).

Robust Australopithecines
  • Also known by the alternative genus -

Gracile and Robust Australopithecines Compared
Robust Australopithecines The Sagittal
  • A crest running from front to back on the top of
    the skull along the midline to provide a surface
    of bone for the attachment of the large temporal
    muscles for chewing.

Foot Bones of Later Australopithecines
  • Drawing of the foot bones of a 3- to
    3.5-million-year-old Australopithecus from
    Sterkfontein, South Africa, as they would have
    been in the complete foot.

Australopithecus garhi
  • In 1999, Ethiopian paleoanthropologist Y. Haile
    Selassie discovered fossil material placed into
    the new species Australopithecus garhi.

Australopithecus garhi
  • a possible ancestor of genus Homo
  • possessed an arched dental arcade and a ratio
    between front and back teeth more like humans and
    gracile australopithecines

Our Possible Evolutionary Relationship to
Later Australopithecines and Early Homo
  • The gracile and robust forms of australopithecus
    appear to have developed in response to
    deforestation and the progressive drying of the
  • These forms were ideally suited for plant
  • Predators posed a major problem and the yielding
    sticks, stones and bones as defensive weapons
    (manuports) may have paved the way for stone tool
    making among early Homo

Later Australopithecines and Early Homo
  • When two closely related species compete for the
    same niche, one will out-compete the other,
    bringing about the latters extinction law of
    competitive exclusion.
  • early Homo and later Australopithecus did not
    compete for the same niche and appear to have
    co-existed for 1.5 million years

The Genus Homo
Homo habilis
  • dated to 2.5 1.8 million years ago
  • found in East and South Africa
  • believed to have mastered the Oldowan stone tool
  • there is ample fossil evidence that H. habilis
    was a major staple in the diet of large
    predatory animals so it was probably not a

Homo habilis
  • its brain size is slightly larger than
    australopithecines, 500 - 650 cc
  • its face is less prognathic than

Homo habilis
Compare the feet of apes (left), H. habilis
(middle), and modern humans (right). How are
they similar how are they different?
Homo habilis
Compare the digits of apes (left), H. habilis
(middle), and modern humans (right). How are
they similar how are they different?
The Role of Bipedalism in Human Evolution
Bipedalism Drawbacks
  • Makes an animal more visible to predators.
  • Exposes the soft underbelly.
  • Interferes with the ability to change direction
    instantly while running.

Bipedalism Drawbacks
  • Quadrupedal chimpanzees and baboons are 30 to 34
    faster than bipeds.
  • Frequent lower back problems, hernias,
    hemorrhoids, and other circulatory problems.
  • Consequences of a serious leg or foot injury
    seriously hinders a biped and they are an easy
    meal for some carnivore.

Reasons for Bipedalism
  • A way to cope with heat stress.
  • Allowed them to gather food and transport it to a
    place of safety for consumption.
  • Mothers were able to carry their infants safely.
  • They could reach food on trees too flimsy to
  • Allowed them to travel far without tiring.

Reasons for Bipedalism The Savanna
  • Food and water were easier to spot Savanna
  • More likely to spot predators before they got too
    close for safety.
  • Hands freed from locomotion provided protection
    by allowing them to brandish and throw objects at

Reasons for Bipedalism The Carrying
  • Hands freed from locomotion provided protection
    by allowing them to brandish and throw objects at

Reasons for Bipedalism The Sexual
Selection Model
  • Advanced by Owen Lovejoy
  • Hands freed from locomotion provided males the
    ability to carry more food to attract more mates
  • Hands freed from locomotion provided females with
    another means to carry and protect infants.

Explaining Bipedalism A Word of
When trying to explain the evolution of
bipedalism we have to beware of teleological
thinking (i.e. confusing a consequence of
bipedalism for its cause). Review the previous
hypotheses explaining bipedalism can you find
evidence of teleological thinking? Can you think
of counter-evidence from modern primate behavior?
Bipedalism and Environmental Change
  • Since the late Miocene, the vegetation zones of
    Africa have changed considerably.
  • The presence of bipedalism in the fossil record
    without a savannah environment indicates that
    bipedalism appeared without any particular
    adaptive benefits at first, likely through a
    random macromutation.

The Aquatic Ape Theory For Class
  • Argues that bipedalism developed within estuaries
    and water holes where hominids congregated to
    avoid predators.
  • Since apes have lower levels of body fat, those
    who were bipedal did not drown and were able to
    move to deeper water.
  • Can you spot any problems with this hypothesis?