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Palaeoanthropology > Bipedalism > Flashcards

Bipedalism Flashcards

1
Q

Types of relative dating of fossils

A
  1. Stratigraphy - layers of sediment
  2. Biostratigraphy - changes in animal communities e.g. presence/absence of species, changes in morphology of teeth in rodents
  3. Palaeomagnetism - evidence of the Earth’s magnetic field in rocks
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2
Q

Types of absolute dating of fossils

A
  1. Dating the sediment surrounding fossils e.g. K-Ar, 40Ar-10-Ar, uranium series, fission track, thermoluminescence, electron spin resonance
  2. Dating fossil bone e.g. 14C, uranium series, amino acid racemisation, electron spin resonance
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3
Q

Types of bipedalism

A
  1. Optional - extant apes
  2. Habitual - Ardipithecus
  3. Obligate non-modern - Australopithecus
  4. Obligate modern - Homo
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4
Q

Anatomical modifications of an obligate biped

A
  1. Body plan and body proportions
  2. Position of the foramen magnum
  3. Basicranial flexion
  4. Vertebral column shape and flexibility
  5. Pelvis shape
  6. Femoral neck morphology
  7. Knee/distal femur shape
  8. Foot morphology
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5
Q

Basicranial flexion

A

Brings the foramen magnum forward

Correlated with a reduction in facial size and increase in brain size

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6
Q

Striding gait

A

Type of locomotion that allows to walk with long strides

High mechanical efficiency

Far more efficient than bent-hip bent-knee bipedalism seen in chimps

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7
Q

Chimpanzee brain size

A

~350cc

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8
Q

Human brain size

A

~1300cc

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9
Q

Candidates for ape-human LCA

A

Morotopithecus and Proconsul, 20mya, east and south Africa.

Quadrupedal, lacked derived features for suspensory locomotion

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10
Q

Decline of Miocene apes

A

Climate changes in the late Miocene and slow generation time/developmental period to deal with climate changes

Same climatic conditions favoured the evolution of the earliest ancestors of the human lineage

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11
Q

Sahelanthropus tchadensis

A

6-7mya, Chad (central Africa)

Primitve features: ape-shaped brain, U-shaped palate

Derived traits: reduced prognathism, more anterior foramen magnum, small canines, no diastema, intermediate enamel thickness

Basicranium indicades that S. tchadensis may have been a biped - this is controversial

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12
Q

Orrorin tugenensis

A

6.2-5.65mya, Tugen Hills, Kenya

Woodland/lake environment.

Primitive traits: ape-like teeth in size and morphology, curved proximal phalanges

Derived traits: thicker enamel than chimps, derived aspects of the femur (elongated femoral neck, linea aspera, increased bone density in femoral neck)

Derived traits suggest bipedalism, but ipper limb morphology suggest arboreality

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13
Q

Ardipithecus kadabba

A

5.2-5.8mya, Ethiopia

Intermediate canine size between apes and later hominins
Curved foot phalanx - weak evidence for bipedalism, based on single bone

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14
Q

Ardipithecus ramidus

A

4.4mya, Ethiopia

Combination of primitive and derived traits:
Relatively small brain
Prognathism as in apes
More anterior foramen magnum - consisten with bipedalism
Reduced canine size
Minimal sexual dimorphism
Short and broad ilium
Divergent hallux
Lacked other features for suspension, vertical climbing, and knuckle walking seen in apes

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15
Q

ARA-VP-6/500

A

“Ardi”

Ardipithecus ramidus

Exceptionally complete skeleton for a hominin of this age
Probably female based on canine size

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16
Q

Phylogenetic placement of Ardipithecus ramidus

A

Hypothesis 1: all known evidence represents a species lineage evolving phyletically across its entire range.

Hypothesis 2: an Ardipithecus-to-Australopithecus transition occurring between 4.5mya and 4.2mya in a local group.

Hypothesis 3: an earlier allopatric speciation event with Ar. ramidus representing the end point of the lineage.

17
Q

Models for the origins of bipedalism

A
  1. Savannah hypothesis
  2. Postural feeding model
  3. Travel efficiency
  4. Thermoregulation
  5. Carrying hypothesis/male provisioning model
  6. Complex topography
18
Q

Savannah hypothesis

A

Raymond Dart

Environmentally driven

Shift to grasslands as forests receded - lack of trees forced hominins to adapt to terrestriality, freed hands

Make and use tools to scavenge - eventually leads to hunting

HOWEVER hominins known to be bipedal evolved in non-savannah conditions

19
Q

Postural feeding model

A

Based on the feeding ecology of chimpanzees and other primates

Hominins spending much time feeding while standing

Preadaption to obligate bipedalism seen in later hominins

20
Q

Travel efficiency model

A

Climate driven model

Patchy food resources with forest fragmentation

Need to travel long distances

Walking bipedally consumes less energy

21
Q

Thermoregulatory model

A

Reduced heat gain and better heat dissipation

BUT earliest bipeds evolved in closed wooded environments

22
Q

Carrying hypothesis/male provisioning model

A

Various iterations since the 1960s - food, infants

Owen Lovejoy - linked to monogamy, allows for a reduction in interbirth interval and increases infant survivorship - linked to infant dependence on mother

Evidence against male provisioning:
body size dimorphism is high in most Au. species; more likely that early hominins lived in polygynous groups

23
Q

Complex typography model

A

Rough terrain provided an ecological niche that afforded protection from predators and access to food resources

Explains retention of climbing anatomy in Pliocene hominins

Difficult to test

24
Q

Australopithecus anamensis

A

4.1-3.9mya, Kenya and Ethiopia

25
Q

Australopithecus afarensis

A

3.9-3.0mya, Ethiopia and Tanzania

26
Q

Australopithecus africanus

A

3.0-2.3mya, South Africa

27
Q

Paranthropus aethiopicus

A

2.6-2.4mya, Ethiopia and Kenya

28
Q

Paranthropus robustus

A

1.9.-1.0mya, South Africa

29
Q

Paranthropus boisei

A

2.3-1.4mya, East Africa

30
Q

AL 288-1

A

“Lucy”

Australopithecus afarensis

31
Q

STS 14

A

Australopithecus africanus

32
Q

Axial skeleton

A

Head and trunk

33
Q

Appendicular skeleton

A

Limbs

34
Q

MH1 and MH2

A

Two partial skeletons of Australopithecus sediba

Palaeoanthropology (9 decks)

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