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Chapter 10

BIOLOGY 1M03 Chapter 10: Chapter 10-bio 1m03

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Jon Stone

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Chapter 10 From Hominoid to Hominin
- cooling + climate of the Earth led to the evolution of Hominins
- End of Miocene - Cooling, less rain, rain seasonality, woodland and savannah spread
- Appeared approximately six million years ago
What is unique about Hominins?
- Bipedalism ! led to major morphological changes
- Small canines, large molars, thick enamel
- Large brains
- Slow life histories, long juvenile period
- Language, walk, talk, symbolic culture
What does it take to be a Biped?
- Hominoids to Hominins - Many new adaptations
- Human pelvis is different from forest-dwelling apes like the chimp.
- Torque - created by a twisting force from pelvis
- Torso does not tip due to abductor muscles that run from outer side of pelvis to the femur !
Abductors are attached to the ilium.
- Lengthening neck of femur add to leverage that he abductors can exert and make bipedal walking
more efficient
- Knee joint much more complex
- Feet ! non-grasping big toes and arches
First Hominin
- First Hominin discovered between 7 to 5 mya ! Sahelanthropus tchadensis
- Has derived and ancestral traits
- Chimpanzee sized brain, shares many traits with chimpanzees
- Small canines
- Flat face, large browridge
Foramen Magnum
- Hole in the skull through which the spinal cord passes, suggests bipedal locomotion
Orrorin tugenensis
- Dated to 6 mya, found in Kenya
- Also similar to chimps ! incisors, canines, premolar
- But also similar to humans ! Smaller molars, thicker enamel, larger thigh bones
- More human-like than ape-like
- Found in Ethiopia ! dry conditions very nice for fossils
A. ramidus
- 4.4 mya ! fossils in very poor condition
- Lived in a woodland habitat
- Bipedal; climber; small brain and canines
- Smaller incisors than frugivorous chimps
- Non sharpened and non dimorphic canines, similar to chimpanzees
- Thicker tooth enamel than apes, but thinner than humans
- Teeth size of males > teeth size of females
- Hands ! showed bipedalism ! no “knuckle-walking” as shown in chimps
- Feet - grasping toes for climbing and stuff; feet for bipedalism
- Pelvis configured for bipedalism
Ape vs chimpanzee pelvis
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- ilium shorter and broader in humans ! provides more room for attachment of powerful muscles that
make bipedalism possible
A. kadabba
- 5.2-5.8mya
- Primitive and derived dental traits
- Toe bone suggests bipedalism
- Canine sharpens against premolar
Advantages of Bipedalism
- **Evolved among arboreal Miocene apes as a feeding adaptation and was retained within hominins**
- Apes would use feet to grasp multiple small branches to support bodyweight and used hands for
balance and grasping food items ! Although a. ramidus specimen had monkeylike limb proportions
which doesn’t fit with this theory.
-**Allows efficient harvesting of fruit from small trees**
- Studies have shown chimps rarely walk bipedally but stand bipedally to harvest fruit from small trees
! allows for use of both hands
-**Erect posture**
- Allows for hominins to keep cool (see pic)
-**Leaves hands free to carry stuff**
- Quadrpeds have to carry things in their mouths ! bipeds don’t.
- Carry larger portions of food for longer distances
-**Saves energy**
- Reduces heat stress and overall energy usage in many different ways.
Hominin Diversification
- Proliferation of homnins occurred approx.. 4-2mya in Africa
- Au. Anamensis, au. Afarensis, au. Africanus, au. Garhi, au. Sediba
- Small bipeds, teeth, skull and jaws !generalized diet
- P. aethopicus, P. robustus, P. boisei
- Similar to Australopithecus from neck down
- Massive teeth + jaws - heavy chewing of tough plants
- powerful jaw muscles
- K. platyops
- Flattened face, small teeth
- First members of this genus likely coexisted with several other homnin species in East Africa
- Large brains and smaller teeth than hominins
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find more resources at oneclass.com
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