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Hominid Evolution

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Probably developed between 8 and 4 million years ago in Africa, but we are still ... Saggital crest and temporo-nuchal crest across lower back of skull 'Apelike' face ... – PowerPoint PPT presentation

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Title: Hominid Evolution


1
Hominid Evolution
  • Part 1

2
Trends in Hominid Evolution
  • Bipedalism
  • Larger Brains
  • Smaller face teeth and jaws

3
Bipedalism
  • Probably developed between 8 and 4 million years
    ago in Africa, but we are still unsure of the
    exact time
  • Between 16 and 11 mya, there was a drying period
    in Africa.
  • During this time, tropical forest cover was
    replaced in some parts of the continent by
    tropical grasslands, called savannah,
    interspersed by dense forest.

4
Why bipedalism
  • Bipedalism may have been an adaptation to living
    in the savanna. If this is the case, however,
    why are baboons not bipedal?
  • Better dispersion of body heat.
  • The ability to use the hands, to carry food for
    instance, while the legs are moving (walking or
    running).
  • Making, carrying and using tools for gathering
    plants foods, hunting and weapons

5
Why bipedalism
  • Fitted a scavenger lifestyle because it was an
    efficient way to cover long distances walking at
    a slow pace.
  • Scavenging would have encouraged the use of tools
    to cut meat efficiently and quickly.
  • Ultimately we cannot know why bipedalism
    developed, we can only speculate.

6
Disadvantages of bipedalism
  • Bipedal walking has benefits but also costs. The
    benefits had to outweigh the costs for these
    animals to become and remain bipedal.
  • One cost is that blood flow to the brain becomes
    harder to sustain.
  • Bipedal posture puts enormous pressure on the
    back, hips and pelvis, especially for females
    when pregnant.

7
Skeletal changes to support bipedalism
  • Skullforamen magnum position placed skull over
    the spinal column
  • Pelvisrounded rather than flat and long as in
    apes
  • Knock-kneed legs helps us move our legs when
    walking and running and maintain the centre of
    balance at the mid-line of our bodies.
  • Hominid feet have a robust heel and ankle bones
    as well as an arch.
  • See http//www.becominghuman.org/

8
Brain size increases
  • Brain size as seen through cranial capacity has
    increased over time
  • Australopithecus africanus 440 cc
  • Homo erectus 1000 cc
  • Homo sapiens 1300 cc
  • Bipedalism came first and then brain development.
  • Some of the increase in brain size is due to
    increase in over all body size.

9
Brain size
  • Between 4 mya and 2 mya the relative size of the
    brain did not increase but between 2 mya and the
    present it doubled in relative size and tripled
    in actual size.
  • Brain size increase due to
  • Tool use?
  • Language development?
  • Increased lifespan?

10
Brain size
  • The size of human brains is limited by the size
    of the female pelvis.
  • As brains became larger, children were born less
    developed and more dependant on their parents,
    particularly their mothers.

11
Reduction of face, teeth and jaws
  • After 2 mya we see substantial changes in face,
    teeth and jaws
  • Australopithecines had
  • Large molars relative to their body size
  • Large and strong jaw bones
  • Large faces that projected below the eyes
  • These features may well have been related to
    their food supply, mostly plants food requiring
    chewing and grinding

12
Reduction of face, teeth and Jaws
  • Smaller faces, teeth and jaws in various Homo
    species after 2 mya
  • Probably related to
  • tool use
  • greater dependence on meat as a food source
  • use of fire

13
Dates to remember
  • 4 million years ago
  • Clear evidence of bipedalism with
    Australopithecus afarensis
  • 2.5 million years ago
  • First stone tools which have been associated with
    Homo habilis, the first of the genus Homo
  • 1.8 to 1.6 million years ago
  • Earliest evidence for Homo erectus

14
The Sivapithecines
  • 18-8 mya found during the Miocene Epoch
  • East Africa and Eurasia (China, Hungary,
    Pakistan)
  • Hominoids (possibly hominids)
  • Ancestral to orangutans and probably chimpanzees,
    gorillas and humans.
  • By 8 mya the hominid line had probably branched
    off.

15
Sahelanthropus tchadensis
  • 7 mya
  • Chad
  • Also called Toumai
  • Discovered July 2002 by member of French team

16
Sahelanthropus tchadensis
  • DNA evidence from modern apes and humans suggest
    a single ancestral species at about 6-7 mya
  • Environment would have been partially wooded
    savanna
  • Mix of ape-like and hominid features
  • Cranial capacity of 350cc

17
Sahelanthropus tchadensis
  • Because of short face, massive brow ridge, mouth
    and jaw that protrude less than apes and small
    canines, face considered relatively
    modern-looking, even more modern than Lucy A.
    afarensis at 3.6-2.9 mya

18
Sahelanthropus tchadensis
  • But dental remains almost identical to
    Ardipithecus
  • Could Toumai be a direct ancestor of H habilis
    making Australopithecines a hominid branch that
    became extinct?
  • - Was this animal bipedal? Difficult to tell
    because no post-skeletal material.

19
Ardipithecus ramidus
  • 4.4 mya during the Pliocene Epoch (Pliocene
    begins 5.2 mya and ends 1.6 mya)
  • Subsequent finds date to 5.8-5.2 mya (Miocene era)

20
Ardipithecus ramidus
  • Ethiopia, Awash region
  • Found in early 1990s (1992, 1993, 1994)
  • Represented by the pieces of 17 individuals with
    finds that show almost a complete skeleton

21
Ardipithecus ramidus
  • Has apelike relatively small molars and large
    canines, like a chimpanzee
  • Latest finds of bones form lower part of body
    such that it was semi-bipedal
  • Seems to be a precursor to Australopithecus

22
Ardipithecus ramidus
  • The environment in which Ardipithecus ramidus
    lived would have been tropical forest
  • Since this animal was semi-bipedal, this find
    suggests to some paleoanthropologists that
    bipedalism was not an adaptation to savannah
    environments as previously thought.

23
Australopithecus anamensis
  • 4.2-3.9 mya found during the Pliocene Epoch
  • Kenya (East Africa)

24
Australopithecus anamensis
  • Small number of finds including upper and lower
    jaws, cranial fragments, and the upper and lower
    parts of a leg bone (tibia) found in 1995 when
    the species was named as well as an armbone
    (humerus) found in 1965.

25
Australopithecus anamensis
  • Apelike jaw with shallow palate and large canines

26
Australopithecus anamensis
  • Older than A. afarensis but has a similar
    shinbone which suggests bipedalism
  • Seems to be a bridge between Ardipithecus and A.
    afarensis

27
Australopithecus afarensis
  • 4-3 mya
  • East Africa
  • (Ethiopia, Tanzania and Kenya)
  • The East African Rift Valley
  • Hadar and Laetoli

28
Australopithecus afarensis
  • Lucy (AL 288-1) with bones from all parts of a
    partial skeleton
  • Dates to 3.2 million year ago
  • Found by D. D. Johanson at Hadar, Ethiopia in
    1974.

29
Australopithecus afarensis
  • First family
  • Thirteen individuals of all ages and both sexes
  • Hadar in Ethiopia
  • Found in 1975 by Johanson
  • Dates to 3.2 mya

30
Australopithecus afarensis
  • Laetoli footprints in fossilized volcanic ash at
    Laetoli site in Tanzania
  • Found by Mary Leaky in 1976
  • Shows that these ape like Australopithecines
    walked like us at 3.5 mya.
  • Heel strike.
  • A well-developed arch.
  • Big toe, in front of the ball of the foot and
    parallel to the other toes.
  • A deep impression for the big toe shows toe-off.
  • http//www.pbs.org/wgbh/evolution/library/07/1/l_0
    71_03.html

31
Australopithecus afarensis
  • Skull
  • Cranium low
  • Forehead sloped backwards
  • Pronounced brow ridge
  • Flat nose
  • Chinless with large jaws relative to skull size
  • Saggital crest and temporo-nuchal crest across
    lower back of skull
  • Apelike face

32
Australopithecus afarensis
  • Cranial capacity about 310-500 cc
  • Height 3.5 to 5 ft.
  • Weight 29-45 kg
  • Locomotion Bipedal and climbing,
  • Sexual dimorphism
  • Extreme. This is seen in size of body and in
    dentition where males tend to have a more molar
    like, two cusped 1st premolar while females do
    not have this.
  • May be due to female eating better quality food
    in trees.

33
Australopithecus afarensis
  • Dentition
  • Generally show features reminiscent of late
    Miocene sivapithecines
  • Incisors and canines larger than in A. africanus
    and canine protrudes more
  • First lower molars are less like molars
  • Dental arch less rounded than in A Africanus
  • Evidence of grinding plant food

34
AustralopithecusAfricanus
  • 3-2.3 mya during the Pliocene Epoch
  • Later than A afarensis
  • Southern Africa
  • Includes Taung Child and Mrs Ples
  • Numerous fossils found

35
AustralopithecusAfricanus
  • Taung Child
  • Found in 1925 by Raymond Dart
  • Taung Cave at edge of Kalahari Desert
  • Skull of a child, probably 3 to 4 years old
  • http//www.mnh.si.edu/anthro/humanorigins/ha/taung
    1.html
  • Doubt about the fossil came from beleief that
    hominids originated in Asia

36
AustralopithecusAfricanus
  • Mrs Ples
  • 2.6 mya
  • Found in 1947 in Transvaal region of southern
    Africa
  • Validated the Taung child skull
  • http//www.mnh.si.edu/anthro/humanorigins/ha/sts5.
    html

37
AustralopithecusAfricanus
  • Skull
  • chinless jaw
  • rounded brain case with well-developed forehead
    sloping backward
  • Moderate brow ridges

38
AustralopithecusAfricanus
  • Cranial capacity 428-510 cc (size of large chimp
    brain and 1/3 size of modern human brain)
  • Brain organization more like an ape than like a
    human

39
AustralopithecusAfricanus
  • Height 3.5-4.5 ft.
  • Dentition
  • Broad incisors and short canines (like modern
    humans)
  • Larger premolars and molars than modern humans
    but similar in shape.
  • Jaw is increasingly parabolic in shape

40
AustralopithecusAfricanus
  • Skeletal features and locomotion
  • Similar pelvis to modern humans and therefore
    probably bipedal
  • Similar S-shaped spine, hip joints a femurs to
    modern humans suggesting that they walked in a
    similar fashion.

41
Australopithecus boisei
  • Called Paranthropus boisei by some
    anthropologists who think this hominid is a
    different species from Australopithecus because
    it is so robust
  • 2.2-1.3 mya
  • Found in East Africa
  • Omo Basin, Ethiopia
  • Lake Turkana, Kenya
  • Olduvai Gorge, Tanzania

42
Australopithecus boisei
  • First specimen was the OH 5 skull (Zinj) found
    at Olduvai Gorge (Tanzania) in 1959 by Mary
    Leakey and named Zinjanthropus boisei
  • http//www.mnh.si.edu/anthro/humanorigins/ha/oh5.h
    tml

43
Australopithecus boisei
  • Skull known as KNM ER 406
  • Adult male
  • Cranial capacity of 510 cc
  • Dates to 1.7 mya
  • Found by Richard Leaky at Koobi Fora, Kenya in
    1969
  • http//www.mnh.si.edu/anthro/humanorigins/ha/er406
    .html

44
Australopithecus boisei
  • Dentition
  • Enormous molars and premolars and palate like A.
    robustus but bigger
  • Skull
  • More massive than A. robustus with enormous
    sagittal crest
  • Prominent brow ridgeslarger than A. robustus
  • Efficient chewing machine

45
Australopithecus boisei
  • Cranial capacity 500-530 cc
  • Weight 34-49 kg
  • Skeletal features Heavy bones. Larger than A.
    robustus
  • Geneaology
  • Probably evolved from A. afarensis ancestor
    rather than A. africanus ancestor
  • Not an ancestor or modern humans. Evolutionary
    deadend
  • Co-existed in East Africa with Homo habilis

46
Australopithecus robustus
  • Like Australopithecus boisei, this hominid is
    also sometimes called Paranthropus.
  • This is because it is thought to be a different
    genus than the gracile Australopithecines

47
Australopithecus robustus
  • 2-1.5 mya ((1.8 to 1 mya in your text Ember et
    al.)
  • Found beginning in the 1930s in South African
    caves
  • Kromdraai
  • Swartkrans
  • http//www.mnh.si.edu/anthro/humanorigins/ha/rob.h
    tm

48
Australopithecus robustus
  • Skeletal features
  • Similar to A. africanus in size but thick bones
    with markings where strong muscles were attached.
  • Body would have been bigger and more muscular
    than that of A africanus
  • Skull
  • Sagittal crest running from front to back along
    top to hold jaw muscles needed for eating
  • Efficient chewing machine

49
Australopithecus robustus
  • Cranial capacity 490-530 cc
  • Weight 32-40 kg.
  • Dentition
  • Larger molars and premolars but smaller incisors
    than A. africanus
  • Geneaology
  • May have been descended from A. africanus
  • NOT an ancestor of modern humans. Evolutionary
    dead end

50
Comparison of A. boisei, A. robustus and other
Australopithecines
  • A boisei had larger molars, expanded pre-molars,
    thicker jaw and cheekbones and a larger sagittal
    crest than A robustus.
  • This is probably evidence of great chewing
    capability

51
Comparison of A. boisei, A. robustus and other
Australopithecines
  • Robust forms were of similar body size to gracile
    forms, but skulls were more robust
  • Was robust form a vegetarian while gracile forms
    were omniverous? Recent evidence makes us
    question this assumption.
  • Both A robustus and A boisei died out about 1.2
    to 1 mya so could not have been our ancestors

52
Early Homo species habilis and rudolfensis
  • 2.5-1.5 mya
  • Mostly in east Africa (Kenya and Tanzania) but
    have also been found in southern Africa
  • Some anthropologists place both in the same
    species, H habilis
  • Homo habilis is thought to be in direct ancestral
    line to modern humans
  • Lived in the same places and at the same time as
    the robust australopithecines (A robustus and A
    boisei)

53
Homo habilis
  • Earlier than A rudolfensis beginning 2.3 mya
  • OH 7 was the first fossil evidence of Homo
    habilis at Olduvai Gorge
  • http//www.mnh.si.edu/anthro/humanorigins/ha/oh7.h
    tml
  • OH 24 Twiggy was the oldest H habilis fossil
    skull found at Olduvai Gorge
  • http//www.mnh.si.edu/anthro/humanorigins/ha/oh24.
    html

54
Homo habilis
  • Larger brain than australopithecies at 630-640 cc
  • Reduced molars and premolars
  • Body similar to australopithecines
  • Long arms may indicate that they were still
    partly arboreal

55
Homo rudolfensis
  • Contemporary with H habilis
  • Many anthropologists place them in the same
    species (H habilis)
  • Brain the same size as H habilis and larger than
    the australopithecines
  • Modern limb proportions
  • Cheek teeth thickly enamelled
  • Flat, Broad face
  • KNM ER 1470
  • http//www.mnh.si.edu/anthro/humanorigins/ha/er147
    0.html

56
Homo habilis, the first tool maker?
  • Stone tools first found at Olduvai Gorge in the
    1930s with no associated fossil bones
  • Stone tools found from sites in East Africa date
    to 2.5 mya and on, about the same time as H
    habilis
  • Assumption has been made that H habilis was the
    first tool maker
  • Tools found at Olduvai Gorge and from other sites
    date from 2.5 to 1.5 mya and are referred to as
    Oldowan.

57
Oldowan Tools
  • Flakes and cobble or core tools
  • Percussion flaking
  • Choppers at Olduvai Gorge were core tools that
    had been partially flaked and may have been used
    for chopping
  • Scrapers are core tools flaked on one side
  • Most Oldowan tools were unifacial rather than
    bifacial

58
Oldowan tools
  • After 2 mya hominids were cutting up animal
    carcasses
  • They were probably scavengers rather than hunters
  • These hominids were mobile, with the Olduvai
    Gorge site used only in the dry season
  • Hominids used many kinds of animalsfrom wild
    pigs to elephants

59
Homo habilis
  • Homo habilis had culture
  • Culture is learned and shared
  • Culture is adaptive
  • Culture is always changing
  • Home bases?
  • Sharing food
  • Making tools
  • H habilis was a social being with culture
  • Language?

60
Sources
  • Ember, Carol, Melvin Ember, Peter Peregrine and
    Robert Hoppa (2006) Physical Anthropology and
    Archaeology, 2nd Canadian Edition. Toronto
    Pearson/Prentice Hall.
  • Haviland, William A. (1997) Anthropology, 8th
    edition. Fort Worth Harcourt Brace.
  • http//www.talkorigins.org/faqs/homs/
  • http//www.mnh.si.edu/anthro/humanorigins/ha/ances
    _start.html
  • http//www.pbs.org/wgbh/evolution/library/07/1/l_0
    71_03.html
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