Hominid Origins in Africa

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Chapter 11

• Hominid Origins in Africa

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Chapter Outline

• The Bipedal Adaptation
• Early Hominids from Africa (Pre-Australopithecus
  Finds)
• Australopithecus/Paranthropus from East Africa
• Early Homo

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Chapter Outline

• South African Sites
• Interpretations What Does It All Mean?
• Seeing the Very Big Picture Adaptive Patterns of
  Early African Hominids

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Plio-Pleistocene

• Pertaining to the Pliocene and first half of the
  Pleistocene, a time range of 51 mya.
• For this time period, numerous fossil hominids
  have been found in Africa.

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Morphological

• Pertaining to the form and structure of organisms.

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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.

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Human os coxae
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The Human Pelvis
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Ossa coxae

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

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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.

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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).

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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).

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Major Features of Hominid Bipedalism

• The spine has two distinctive curvesa backward
  (thoracic) one and a forward (lumbar) onethat
  keep the trunk (and weight) centered above the
  pelvis.

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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.

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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).

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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.

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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.

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Question

• Which skeletal modification was NOT necessary for
  bipedalism?
• Development of a second (longitudinal) arch on
  the foot.
• Repositioning of the foramen magnum.
• Shortening and broadening of the pelvis.
• Shortening of the femur.

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Answer d

• Shortening of the femur was not necessary for
  bipedalism.

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Early Hominid Fossil Finds and Localities
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Position of the Foramen Magnum

• (a) a human and (b) a chimpanzee.
• Note the more forward position in the human
  cranium.

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Key Very Early Fossil Hominid Discoveries
(pre-Australopithecus)
Site Dates(m.y.a.) Hominids
East Africa Middle Awash (Ethiopia five localities) 5.85.2 Ardipithecus
East Africa Aramis (Ethiopia) 4.4 Ardipithecus ramidus
Central Africa Tugen Hills 6.0 Orrorin tugenensis
Central Africa Toros-Menalla 7.0 Sahelanthropus tchadenis
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Estimated Body Weights and Stature in
Plio-Pleistocene Hominids
Body Weight Body Weight Stature 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 Africanrobust 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.
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Australopithecus

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

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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.

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Australopithecine

• The colloquial name for members of the genus
  Australopithecus and Paranthropus.
• The term was first used as a subfamily
  designation, but its now most often used
  informally.

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Lucy

• A partial hominid skeleton, discovered at Hadar
  in 1974.
• This individual is assigned to Australopithecus
  afarensis.

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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
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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
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Key East African Australopithecine and Early Homo
Discoveries
Site Dates(m.y.a.) Hominids
Olduvai 1.851.0 Australopithecines, early Homo
Turkana 1.91.3 3.51.6 Many australopithecines several early Homo Paranthropus also Kenyanthropus 2 nearly complete crania 3 jaw fragments, isolated teeth 1 nearly complete skeleton (H. erectus)
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Key East African Australopithecine and Early Homo
Discoveries
Site Dates(m.y.a.) Hominids
Bouri 2.5 Australopithecines (A. garhi)
Hadar 3.53.0 Many early australopithecines (A. afarensis)
Laetoli 3.63.4 Early australopithecines (A. afarensis) well-preserved footprints
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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.

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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.

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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.

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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.

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Question

• Which of the following is the site where a 75
  foot long trail of hominid footprints was found?
• Olduvai
• Laetoli
• West Lake Turkana
• Aramis

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Answer b

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

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Question

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

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Answer c

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

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Homo habilis

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

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Early Homo Fossil Finds
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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.

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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 brains size and surface features.

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Little Foot

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

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Key South African Pliocene and Early Pleistocene
Hominid Discoveries
Site Dates(m.y.a.) Hominids
Swartkrans 1.81.0 Paranthropus robustus early Homo?
Drimolen 2.01.5 Paranthropus robustus
Taung 2.52.0?? Australopithecus africanus
Sterkfontein 2.2? Australopithecus africanus early Homo?)
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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.

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Steps in Interpreting Homind Evolutionary Events

1. Comparing with other fossil materialin
   chronological framework if possible.
2. Comparing fossil variation with known ranges of
   variation in closely related groups of living
   primates and analyzing ancestral and derived
   characteristics.
3. Assigning taxonomic names to fossil material.

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Swartkrans, Geological Section
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Time Line of Plio-pleistocene Hominids
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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