Hominid Origins in Africa

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Chapter 11

• Hominid Origins in Africa

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Bipedalism
Human os coxae
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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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The spine has two distinctive curvesa backward
(thoracic) one and a forward (lumbar) onethat
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.
Position of the Foramen Magnum (a) human (b)
chimpanzee
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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).

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.
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Early African Hominids

• Three major groups
• Pre-australopiths the earliest and most
  primitive hominids (74.4 mya)
• Australopithsdiverse forms, some more primitive,
  others highly derived (4.21 mya)
• Early Homothe first members of our genus
  (2.41.4 mya)

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Early Hominid Fossil Finds and Localities
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Key Very Early Fossil Hominid Discoveries
(pre-Australopithecus)

• Earliest hominids from Africa
• Central Africa
• Sahelanthropus tchadensis
• East Africa
• Orrorin tugenensis
• Aramis (Ethiopia)
• Ardipithecus ramidus

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Pre-Australopiths (7.04.4 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 apes.

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Key Pre-Australopith Discoveries
Dates Region Hominids Significance
4.4 mya East Africa Ardipithecus Aramis Large collection of fossils, partial skeletons bipedal, bur- derived
5.25.8 mya East Africa Ardipithecus Fragmentary, but probably bipedal
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Key Pre-Australopith Discoveries
Dates Region Hominids Significance
6.0 mya East Africa Orrorin Tugenensis First hominid with postcranial Remains
7.0 mya Central Africa Sahelanthropus Tchadensis Oldest hominid well preserved cranium very small-brained likely bipedal
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Australopithecus/Paranthropus from East Africa

• Australopithecus - An early hominid genus, known
  from the Plio-Pleistocene of Africa.
• Australopithecine - The colloquial name for
  members of the genus Australopithecus and
  Paranthropus.
• Features
• They are all clearly bipedal
• They all have relatively small brains
• They all have large teeth, particularly the back
  teeth, with thick to very thick enamel on the
  molars.

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Earlier More Primitive Australopiths (4.23.0 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.

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Sectorial

• Adapted 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.

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Australopithecus afarensis from Laetoli and Hadar

• Lucy
• A partial hominid skeleton, discovered at Hadar
  in 1974.
• This individual is assigned to Australopithecus
  afarensis.
• 60-100 individuals
• 420 cm3 cranial capacity

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Infant 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.

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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.

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Australopithecus and Paranthropus from Olduvai
and Lake Turkana

• Robust vs. gracile species
• Paranthropus aethiopicus
• Paranthropus bosei

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

• Australopithecus africanus adult cranium from
  Sterkfontein

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Time Line of Early African Hominids
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Early Homo

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

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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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Discovery of Childs Skull From Taung

• The Taung childs skull, discovered in 1924.
• There is a fossilized endocast of the brain in
  back, with the face and lower jaw in front.

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Raymond Dart

• Raymond Dart, shown working in his laboratory.
• Dart published the story of the discovery of the
  Tuang childs skull.

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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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Geology and dating problems in South Africa

• Complex features
• Fissures, sink holes, caves, breccia
• No volcanic deposits

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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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Estimated Body Weights in Plio-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)
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Estimated Body Weights in Plio-Pleistocene
Hominids
Male Female
East African robust 49 kg (108 lb) 34 kg (75 lb)
H. Habilis 52 kg (114 lb) 32 kg (70 lb)
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Estimated Statures in Plio-Pleistocene Hominids
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.)
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Estimated Statures in Plio-Pleistocene Hominids
Male Female
East African robust 137 cm (54 in.) 124 cm (49 in.)
H. Habilis 157 cm (62 in.) 125 cm (49 in.)
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Estimated Cranial Capacities in Early Hominids
Early Hominids Range (cm3) Average(s) (cm3)
Sahelanthropus Not known 350
Ardipithecus Not known Not known
Australopithecus afarensis Not known 420
Later australopiths Not known 410530
Early members of genus Homo Not known 631
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Estimated Cranial Capacities in Early Hominids
Contemporary Hominoids Range (cm3) Average(s) (cm3)
Sahelanthropus Not known 350
Ardipithecus Not known Not known
Australopithecus afarensis Not known 420
Later australopiths Not known 410530
Early members of genus Homo Not known 631