The First Bipeds

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Chapter 6

• The First Bipeds

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Chapter Outline

• 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 is the role of bipedalism in human
  evolutionary history?

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Anatomy of Bipedalism

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

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Australopithecus The Earliest Hominine

• Appeared in Africa 4 million years ago.
• From the waist down, fully adapted for
  bipedalism.
• From the waist up, still apelike, with
  intellectual abilities comparable to those of a
  modern-day African ape.

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Foramen Magnum
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Bipedal Gait
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Forms of Australopithecus

• Earliest forms preserve a number of features
  that indicate an apelike ancestor.
• By 2.5 m.y.a. new form with larger chewing
  apparatus and more massive head, while brain
  size remained stable.

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Gracile Australopithecus

• The size of a modern human pygmy.
• Chewed food like humans.
• General appearance resembled an apelike human.
• Size and outward appearance of brain suggest a
  intelligence similar to a modern bonobo,
  chimpanzee, or gorilla.

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Robust Australopithecus

• Shared most of the traits of the Gracile
  Australopithecus.
• Bones were thick with prominent markings where
  muscles attached.
• Skull was thicker and larger with a slightly
  larger cranial capacity.
• Skull possessed a simianlike sagittal crest.

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Species of Australopithecus

• Gracile Species - Location
• A. afarensis - Ethiopia and Tanzania
• A. africanus - South Africa
• A. anamensis - Kenya

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Species of Australopithecus

• Robust Species - Location
• A. aethiopicus - Kenya
• A. boisei - Kenya
• A. gahri - Ethiopia
• A. robustus - South Africa

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Sexual Dimorphism in Canine Teeth
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Bipedalism Drawbacks

• Makes an animal more visible to predators.
• Exposes the soft underbelly.
• Interferes with the ability to change direction
  instantly while running.

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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.

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Fossil Sites in South Africa

• Dirt, bones, and other matter fell down the shaft
  becoming fossilized. In the Pliocene, the earth
  next to the shafts opening provided a shelter
  for trees that may have been used by predators
  for eating without being bothered by scavengers.

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Foot Bones

• A 3- to 3.5-million-year old Australopithecus
• Note how long and flexible the first toe (at
  right) is.

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Vegetation Zones of Africa
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Humans Blood Carries Heat From the Brain
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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
  climb.
• Allowed them to travel far without tiring.

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Reasons for Bipedalism

• Food and water were easier to spot.
• 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
  attackers.