HUMAN EVOLUTION: GENUS AUSTRALOPITHECUS

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HUMAN EVOLUTION GENUS AUSTRALOPITHECUS
PARANTHROPUS
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What is a Hominid?

• Modern humans our direct and indirect ancestors
  (after our lineage split from the chimpanzee)
• In the last decade, the time range of genus
  Australopithecus has been pushed back to 4.2 mya
  its distribution expanded to include regions
  outside E. and S. Africa.
• New finds from 4.5-7 mya are thought to be
  hominids that predate Australopithecines,
  although their status is debated

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Map of Hominid Evolution
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Hominid Sites

• Earliest fossil hominid sites are in Africa
• They now span the latest Miocene to the early
  Pleistocene from about 6-7 mya to about 1.6 mya
• The major groups of sites are

1. Ethiopia Middle Awash valley Hadar
   (Australopithecus afarensis)
2. Kenya Lake Turkana
3. Tanzania Olduvai Gorge
4. South Africa various sites in limestone caverns
   centered around Sterkfontein

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What Makes A Hominid? - Bipedalism

• Primary feature distinguishing hominids from
  other hominoids is walking erect on two legs
  erect bipedalism
• Adaptations for bipedalism in the the partial
  skeleton of Lucy, an australopithecine ( 3.2
  mya) clearly seen in the hip, spine and leg bones

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Why did bipedalism become the primary adaptation
of hominids?

• 1. Carrying behavior
• 2. Reduction of overall heat stress -
  facilitates heat loss through convection by
  exposing body to air currents, only humans have
  sweat glands that produce moisture to cool body
• 3. Most energy efficient way to travel long
  distances
• 4. Allows for better vision in open
  environments defensive action against predators
  by freeing hands to throw objects

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Evidence for Early Bipedalism

• The record of bipedalism is most graphically
  preserved in the fossilized footprints at
  Laetoli, Tanzania, 3.6 mya
• Tracks of 2 individuals were uncovered in
  volcanic ash by Mary Leakey (1978-79)
• Footprints were left by 2 australopithecines in
  damp volcanic ash of Laetoli
• Notice how close the tracks are!

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Laetoli Footprints

• Laetoli footprints clearly show that the
  creatures who made them were fully bipedal
• Big toe hardly diverges from the rest of the
  foot, unlike in apes
• Gait heel-strike followed by toe-off the
  way modern humans walk

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Laetoli Reconstruction

• 2 early hominids walk bipedally across an open
  ash field produced by an erupting volcano.
• Rain wet the volcanic ash footprints filled up
  with more ash, and were thus preserved.
• Footprints reveal that our ancestors walked
  upright with a gait very similar to our own.

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Time-Line of Hominid Evolution5 Adaptive
Radiations

• First Adaptive Radiation 6-7 mya in the late
  Miocene, potential last common ancestors
• Second Adaptive Radiation 4-5 mya in early
  Pliocene, first true hominids
• Third Adaptive Radiation 3-4 mya in middle
  Pliocene, more hominids
• Fourth Adaptive Radiation 2-3 mya in late
  Pliocene, more robust hominids
• Fifth Adaptive Radiation 2-1.8 mya in late
  Pliocene first ice age, genus Homo

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First Adaptive Radiation

• 6-7 mya in the late Miocene, potential last
  common ancestors
• 1. Sahelanthropus tchadensis
• 6-7 mya in Chad (North Central Africa)
• 2. Orrorin tungenensis
• 6 mya in Kenya (East Africa)
• Note We know little about the lifeways of these
  species. However, we do know that they were
  forest adapted.

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1. Sahelanthropus tchadensis

• Discovered in Chad (6-7 mya)
• Most complete cranium from this time period
• Mosaic of ape human-like features, but at the
  ape grade of evolution
• Cranial capacity (320-380 cc)
• U-shaped upper jaw
• Very wide distance between the orbits
• Large, thick continuous brow ridge
• Human-like flat face
• Human-like dentition

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2. Orrorin tungenensis

• Fossils from Tugen Hills in Kenya have been
  dated to about 6 mya
• Earliest Evidence for
• Walking on Two Legs?
• How far back in time does the record of
  bipedalism extend?

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Orrorin tungenensis (cont.)

• Fossils Include upper portion of a femur, lower
  portion of the humerus, some lower jaw fragments,
  teeth
• Arm bone virtually identical to that of a
  chimpanzee
• Femur more human-like, most important for
  showing adaptations for walking on 2 legs
• Was Orrorin a direct human ancestor, or a
  common ancestor of chimps and humans?

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Second Adaptive Radiation

• 4-5 mya in early Pliocene, first true hominids
• 1. Ardipithecus ramidus
• 4.5-5.5 mya in Ethiopia (East Africa)
• 2. Australopithecus anamensis
• 4.2-3.9 mya in Kenya (East Africa)
• Note We know little about the lifeways of these
  species. However, we do know that they were
  forest adapted and fully bipedal.

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1. Ardipithecus ramidus
Earliest True Hominid or Last Common
Ancestor? LAST COMMON ANCESTOR OF CHIMPS HUMANS
MOST LIKELY HAD A MIX OF FEATURES SOME RETAINED
IN CHIMPS, OTHERS RETAINED IN HUMANS!
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Ardipithecus ramidus (cont.)

• Between 4.5 and 5.5 mya from the Middle Awash
  valley site in Ethiopia
• Fossil Remains very fragmentary limb bones, toe
  bones, jaws teeth
• Straight toe bones suggest it may have been
  bipedal
• A mosaic of features seen in later hominids
  modern chimpanzees

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2. Australopithecus anamensis

• Lake Turkana Region of Kenya
• 4.2-3.9 mya
• Probably walked upright
• Teeth enamel thicker than Ardipithecus ramidus,
  so diet included hard foods

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Australopithecus anamensis (cont.)

• Fossil Remains very fragmentary
• Those shown here include
• Jawbone
• part of the front of the face
• parts of an arm bone (radius)
• fragments of a lower leg bone (tibia)

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Third Adaptive Radiation

• 3-4 mya in middle Pliocene, many hominids
• 1. Australopithecus afarensis (Lucy)
• 3-4 mya in East Africa
• 2. Australopithecus africanus
• 2.5-4 mya in South Africa
• 3. Kenyanthropus platyops
• 3.5-3.2 mya in Kenya
• Note We know little about the lifeways of these
  species. However, we do know that they lived in
  open woodlands along wooded streams in the
  savannas, ate fruits and soft foods, maybe had a
  tool-culture like modern chimps

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1. Australopithecus afarensis

• 3-4 mya in East Africa
• Pelvis leg bones resemble modern humans
• Sexual dimorphism (males larger with sagittal
  crest)
• Tree climbers (curved fingers toes)
• Ape-like Features
• Small brain case (430 cc.)
• Prognathic (jutting out) face
• U-shaped palate (v. parabolic shape)

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Australopithecus afarensis
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A. afarensis Skeleton - Lucy
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2. Australopithecus africanus

• 4-2.5 mya in Transvaal region of South Africa
• 1924 1st Australopithicine to be described by
  Raymond Dart!
• Globular cranium, slightly higher ratio of brain
  to body size than A. afarensis
• Face less prognathic than A. afarensis
• Proportions of arm to leg lengths may be more
  ape-like than A. afarensis

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Australopithecus africanus
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Australopithecus africanus
Australopithecus africanus
best known A. africanus cranium (front lateral
views)
Most complete A. africanus skull
Taung Child
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A. afarensis
A. afarensis verses A. africanus
Australopithecus afarensis
Australopithecus africanus
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3. Kenyanthropus platyops

• 3.5-3.2 mya found in 2001 west of Lake Turkana
  in Kenya
• Ape-like features small ear canal, small brain
  case
• Human-like features flat face, small molars
• Importance flat face appeared early in
  evolution, alongside the range of other facial
  forms.
• Evidence that evolution is not linear or
  progressive

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Kenyanthropus platyops
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Fourth Adaptive Radiation

• 1-3 mya in late Pliocene, more robust
  hominids
• 1. Paranthropus boisei
• 2.2-1.2 mya in East Africa
• 2. Paranthropus robustus
• 2-1 mya in South Africa
• 3. Australopithecus garhi
• 2-3 mya in East Africa
• Note We know little about the lifeways of these
  species. However, we do know that they lived in
  open dry woodlands savannas. The robust
  species are famous for eating hard to chew food,
  like seeds, nuts, and roots. May have used tools
  to dig for roots in dry seasons.

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1. Paranthropus boisei

• 2.2-1.2 mya in East Africa Ethiopia, Kenya,
  Tanzania
• Largest teeth found in any hominid!
• Referred to as hyper-robust due to massive
  molars and premolars
• Skull broad, short face with flaring cheek
  bones, relatively small brain, pronounced
  sagittal crest in males
• Skull and dental features are adaptations for
  heavy chewing!

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Paranthropus boisei (KNM-ER 406)
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Paranthropus boisei (KNM-ER 406)
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Paranthropus boisei (KNM-ER 406)
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Paranthropus boisei (OH 5)
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2. Paranthropus robustus

• 2-1 mya in South Africa
• Short, broad face with deep zygomatic arches
  (cheek bones). Larger individuals have sagittal
  crests.
• Large molars covered with thick enamel
• Wear patterns on teeth herbivorous diet of hard
  resistant foods such as seeds, nuts, roots
• Lived in grasslands near rivers and wetlands

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Paranthropus robustus
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3. Australopithecus garhi

• 2-3 mya in East Africa spotty fossil record,
  cranial dental remains found in 1999 in Bouri,
  Ethiopia
• Bones of antelopes, horses, and other animals
  with cut marks made by stone tools butchering
  animals smashing bones for marrow. First meat
  eaters?
• Molars too large to be early Homo
• Ape-like long lower arm, human-like upper arm
  leg
• Mixed traits classified as a new species, maybe
  ancestor of early Homo

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Australopithecus garhi
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Australopithecus garhi
One surprise in the A. garhi skull was enormous
back teeth, instead of smaller ones seen in later
Homo species (Video Image/UC Berkeley)
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Australopithecus garhi

• EARLIEST BUTCHERS
• Signs that hominids scraped smashed animal
  bones, like this antelope tibia, 2.5 mya
• Earliest documented percussion marks made by
  hominids, presumably extracting fatty marrow from
  these bones