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| Sahelanthropus cranium traits |
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Definition
• Supraorbital torus (browridge)
• Brain size estimated at 320-380 (350) cc
• Small canine
• Postorbital constriction |
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| Orrorin tugenensis year and location |
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Definition
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| Orrorin tugenensis a biped? |
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Definition
• Proximal femora: heads large relative to necks
upper femur, showing evidence of bone buildup typical of a biped |
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Term
| Ape-like features of Sahelanthropus |
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Definition
| Apelike features included a small brain (even slightly smaller than a chimpanzee’s), sloping face, very prominent brow ridges, and elongated skull |
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| Human-like features of Sahelanthropus |
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Definition
| Humanlike features included small canine teeth, a short middle part of the face, and a spinal cord opening underneath the skull instead of towards the back as seen in non-bipedal apes. |
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| 6 indicators of bipedalism |
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Definition
vertebral column curvature
foramen magnum position
inner ear balance
shape of pelvis
lower limb anatomny
upper limb anatomy |
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Term
| Vertebral Column Curvature |
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Definition
• Mostly compressive stress, though some tension.
• Human spinal column-> vertebral bodies get larger and larger as you go down the spine
• Chimp-> some increase in vertebral body size, but not as much as humans because there is a greater distribution of weight (walk on all fours generally)
• Humans-> curvy spine (1 convex and 2 concave).
o Concave 1: Serves to bring head in line with shoulders and helps bring weight of the head in the center mass of the body. These both lessen the amount of work that neck muscles have to do.
o Convex-> puts chest cavity over the pelvis. Shifts the center of mass over our supports (legs). Chimps tend to fall forward |
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Definition
| • The more quadrapedal an animal is, the farther back the foramen magnum will be |
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Definition
• Semi-circular canals
• The labyrinth helps detect whether or not we are falling. The more sensitive, the better balanced.
• Human-> larger
• Chimp-> smaller |
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Definition
• Humans are more bowl-shaped
• Our illium shape allows for greater function of hip muscles (keeps body in line as we are walking and fatigues muscles less)
• Expanded illium allows for more space to attach the muscles. |
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Term
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Definition
• Valgus femur
o Human femurs are angled in. (Bicondylar angle)
o Human condyles are bigger than chimps
• Human knees have more of an oval surface for more surface areas
• Neck of the Femur
o Under a lot of stress
• Feet
o Shorter toes, larger calcaneus, two arches, no divergent big toe, enlarged big toes
o Plantar flexors, helps us keep our weight over our heels
o Large arch (chimps are flatfooted)
o Chimp feet still have grasping ability while human feet are solely focused on bipedal locomotion |
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Definition
• Arms are relatively short compared to legs
• Our scapula and shoulder joint points straight out to side
• Thorax-> more barrel shaped
• Lost things to climb trees to gain finer manipulatory systems |
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Definition
• Frees hands
• Increases visual range
• Efficient at low speeds (in modern humans)
• Thermoregulation |
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Term
| disadvantages of bipedalism |
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Definition
• Less stable – high center of gravity
• Head further from the ground: challenge in forest-> must duck down…don’t want to waste energy |
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Term
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Definition
• Chimp vs. human walking: humans win
• Human running is less efficient
• Slower running speeds: most humans=20mph, some are really fast=28mph in a short distance
• Cats can run about 30, cheetahs about 70
• Cant outrun predators, cant outrun prey |
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| 5 Hypotheses Regarding the Origins of Bipedalism |
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Definition
• Energy efficiency
• Female provisioning
• Feeding hypotheses
• Carrying
• Protection/Predator Defense |
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Definition
• Advantage: freeing of hands
• Darwin: carry tools, weapons, etc. (after large brains evolved)
Problem for this is that tools were probably wayyy after bipedalism
• Carry meat or other food
• Hasn’t affected any other primate |
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| Protection/Predator Avoidance Hypotheses |
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Definition
• Dart, others: Vigilance – see over tall grass, locate predators.
• Problem: bipedal all the time? Also assumes that in an open environment. Also, makes you visible to predator
• Throwing: Hominids could throw stones, etc. at enemies.
• Threat: Standing up makes a better threat. |
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| Energy Efficiency 1: Long Distance Travel (Shipman, et al.) (fairly supported) |
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Definition
• Dry habitat, trees further apart.
• More time walking between trees.
• Humans more efficient than chimps in such settings.
• Maybe needs to come in later, also relies on our environmental predictions. Some of the earliest bipeds did live in heavily forested places. |
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Term
| Efficiency 2: Heat Stress (Wheeler) |
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Definition
• Heat is very dangerous to brains.
• Bipeds expose much less surface area to direct sunlight, and raise brains into cooler air above ground. (take better advantage of convection cooling-sweat evaporates)
• Less heat that has to be dissipated
• Feel better in warm environments
• Problems-> more thought given to advantage to moving around at noon in the hottest part of the day. Also, humans may not have lived in such open environment |
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Term
| Female Provisioning (Lovejoy) |
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Definition
• Loss of estrus, possible decrease in birth spacing monogamy
• If you have two parents helping to raise the offspring, less stress on female and more ability to decrease interbirth interval (increase estrus times for female)
• Monogamy encouraged by provisioning female
• Bipedalism helps in carrying food |
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Term
Feeding Hypothesis 1:
Seed Eating (Clifford Jolly) |
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Definition
• Analogy: Gelada baboon (eats grass seeds)
• Reduced canines, retracted face-> brings grinding teeth back under, more efficient jaw muscle movement
• Thick enamel also selected for
• Dexterity, erect trunk – efficient seed collection |
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Term
Feeding Hypothesis 2:
Postural Feeding (Kevin Hunt) |
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Definition
• Analogy: Chimpanzee (small fruits, drier habitats)
• Postural, not locomotor
• 75% chimp bipedalism: feeding from small trees
• Arm hanging for support
• Hominids: stay upright for travel
• Could explain some ape-like features of early hominids |
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Term
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Definition
| Endurance running (Bramble and Lieberman) may have encouraged further bipedalism when it was already established. To travel long distances, refinements were made to our anatomy. We have a relatively stable energy endurance run. |
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Definition
– Molars not large; shape ape-like
– Dental proportions
– Thin enamel (only a tiny bit thicker than chimp) |
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Definition
– Small, blunt canines (smaller in ramidus; larger in kadabba)
– Incisors intermediate between australopiths and chimps
– Lower molars broader than comparable ape
– Foramen magnum position: bipedality |
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Term
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Definition
| Geological desposites from which fossils come from span about 10km (lots of space). There were a range of habitats. Stable isotope date (helps determine types of food eaten) points to a more wooded or forested environment. Eating woodland type fruits and plants, nuts and tubers, some insects, and some meat. |
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| Ardis dental/cranial traits |
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Definition
-Brain size seems to be small
-300-350 ccs (about the size of a modern chimp)
-face is fairly small
-forward projection of lower part of the face (prognathism)
=a little less than a chimp
-Smaller overall size of incisors and canines than a chimp…less social aggression?
-Ardi was eating less fruit than a chimp because of smaller incisors?
-Orientation of occipitals shows that Ardi has a flexed cranial base |
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Term
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Definition
-Super long arms compared to legs. Huge hands.
-Implications to whether we think our ancestors were quadrupeds or knuckle walkers.
-Ardi would’ve been able to support her weight on her palms rather than knuckle walking. Less stiff wrist joint than knuckle walkers |
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Term
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Definition
-Ardi is more primitive than Lucy but is not chimp like
-Broad illium like humans
-Has an anterior inferior iliac spine (chimps don’t have this, but Lucy and humans do)
-Has a greater sciatic notch
-Hamstring muscles are oriented in a way that supports bipedality
-Effective biped, but not so much as Lucy
-Divergent big toe |
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Term
| Ardi phylogeny and implications |
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Definition
-Last common ancestor from chimps and humans may not have been a knuckle walker, but could have walked on its palms
-Ardi might have been a falcultative biped and may have done lots of tree climbing |
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Term
| Australopithecus anamensis suggestion of bipedality |
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Definition
| • Proximal and distal surfaces of tibia |
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Term
| Why might A. anamensis not be a viable species |
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Definition
| ? Teeth and jaws resembles anamensis, but also fits afarensis |
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Term
| A. afarensis Cranial Anatomy |
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Definition
• Brain avg. 400 cc
• Browridge
• Cheekbones robust and flared
• Teeth: canine larger than later homs’, smaller than chimps’ and honed; incisors smaller than chimps but still large. Molars large, thick enamel.
• Compound temporonuchal crest (important for attaching chewing muscles)
• Sharp nuchal plane
• More robusticity in face, more flared zygomatics
• Subnasal prognathism and no chin |
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Term
| A. afarensis postcranial anatomy |
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Definition
Flexor sheath ridges.
May not be as adapted to carrying things
Lucy’s spine suggests that she may have had some orthopedic problems
Bicondylar (or valgus) angle
2-3 individuals walking across the ash. 1 small, 1 big, 1 walking in the tracks of the other?
Human like locomotion?
60-150 lbs
Above waist-> chimplike
Below waist-> humanlike
Short legs, long curved toes, very wide hips
Synapomorphies-> overall configuration of head and neck of femur, arches in feet, larger heel bone (shared, derived features from later humans) |
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Term
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Definition
• Definitely sexual dimorphism
• Dimorphism: males fight alone (male-male competition)
• Social system: female choice?
• Concealed estrus?
• Nomadic; siblings may be basis for larger groups. Sleep in trees. Perhaps scavenge meat. Stealing from others? |
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