Ch 8 Primate and Hominin Origins Flashcards Preview

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Flashcards in Ch 8 Primate and Hominin Origins Deck (13)
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Dating Methods:
Relative Dating

"Tell if something is older or younger than something else, but doesn’t give exact dates"


Dating Methods:
Relative Dating
- Stratigraphy
- Biostratigraphy
- Paleomagnetism

- The lower layer (stratum) is older than the higher layer. Superimposition can be disturbed: volcanic activity, earthquakes/faulting, rivers & lakes
- Different layers can accumulate at vastly different rates

- Use fossils with known dates from other nearby areas to date your layer (index fossils)

- Based on known shifts in the earth’s geomagnetic pole
- Examine magnetically charged particles in rock as an ancient compass


Dating Methods:
Chronometric (Absolute) Dating (2)

*Potassium (K)-Argon (Ar) dating
- Half-life of radioactive K-40 is 1.25 billion years after which half of its will have decayed into stable Ar-40

*Carbon-14 dating
- Half-life of 5,730 years
- Can only be used going back about 75 thousand years


Hominid vs. Hominin

- Hominid reflects morphological/anatomical classification
• Historically used term
- In this course use the term hominin


What makes a hominin a hominin?

Three major changes
1. Obligate biped
2. Larger brain
3. Reduced and generalized teeth/jaws
Today most reliance put upon bipedalism
Large brains once considered preeminent hominin feature
- Now know they did not appear until 2-3 mya


Why do we not fall over when we walk?

- Change in pelvis shape
- Shorter & broader, stabilize weight transmission
- Change in muscles
- Positions centre of mass over legs


Anatomical features of bipedalism

- Foramen magnum position
- Shape of spine
- Shape/orientation of pelvis
- Angle of thigh bone (femur)
- Loss of opposability of big toe


Facultative vs. obligate bipedalism

Facultative- can stand on two legs whenever you want

Obligate- is our normal and natural way to move


Pros of Bipedalism:

- Especially in grassland, low shrub, open savanna


Pros of Bipedalism:
Carrying objects

‘freeing of the hands’
- Food, sticks, stones, babies

• Scientists propose this idea claiming that they may use three legs to walk, and the other to carry young


Pros of Bipedalism:

- Upright posture (and hairlessness) beneficial in hot climates
- Less exposed surface area, convective/evaporative cooling
- Bipedal primates could walk farther from shade for longer periods of time to look for food


Pros of Bipedalism:
Energetic Efficiency

- Bipedalism more efficient than quadrupedalism at slower speeds?
- Only with long legs, early hominins did not have long legs

- Studied humans and bipedal primates on a treadmill
- Human bipedalism was about 75% less costly in terms of energy use
- Due to the length of the legs- the longer they are the more efficient energy use


Cons of Bipedalism:

Harder to pump blood to heart
- Greater likelihood of heart attack, stroke

Musculoskeletal problems
- ‘Fallen arches’ (feet)
- Prolapse of intervertebral discs
- Inguinal hernia

- Large brain and inflexible shoulder joint of infant
- Human infants must rotate 90° through midplane of birth canal