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ANTA01H3 Lecture Notes - Foramen Magnum, Pelvis

Course Code
Emma Humphrey

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Week 8 – Early Hominid Evolutions - The First Bipeds
June 22, 2010
**non-cumulative final exam- but know the dating technique, the skeleton, it is impt for the
second part of the course
2 general models
1) large brain -predominant model
2) more correct model bc of fossil records
8mya – genetic split, but only shows in fossil record 5mya
Major climatic changes in late Miocene:
1) drying up of mediterranean sea
movement of Africa northward has closed up the water and thus drying of mediterranean
India pushing up to South West Asia created the Himalayas
South America going northward, closed the sea currents, cooling the temp, created an
environment with ice caps forming in polar regions ie glacier possibilities
thus, dryer environment, increased size of Sahara desert in Africa
2) breaking up forests
creating of the East Valley in Africa
3) these two (aforementioned changes) created mosaic environment
moving out of the treed environment
so not entirely terrestrial or arboreal (treed environ)
Possible models to explain:
Carrying Model -gather and transport of food;
males bringing supplies to females
-the more bipedal, the most successful they'll be reproductively
2. Vigilance Model –see over barriers to find food, see danger.
-could just require an upright posture,
3. Heat Dissipation Model -To cope with heat stress out in the open
-upright stance, helps cool the body faster so only top of head etc only affected by sun
if quadrapedal, whole back etc will be affected by sun
Energy Efficient Model -Bipedalism is far more economical
than quadrupedal locomotion at walking speed.
-long steady walking bipedally vs chimps walking bipedally for short periods
Foraging/Harvesting Model –standing upright to reach food
in branches
-ties closely with carrying model
-allows us to do two activities at once
-reaching seeds from tall grasses
-get food from tall bushes

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Display Model –standing up to display dominance
-standing taller shows dominance
-Bipedalism- risky and efficient method
Anatomical features associated w/ Bipedalism
Skull: Anterior foramen magnum, shortened basicranium (skull base area)
Spine: Curved lumbar (lower back) region
Hip: Pelvis- short, broad, flared blades; deep, spherical acetabulum; Sacrum- short, broad,
curved inward
Leg: Longer than arm; elongated femoral neck; large, spherical femoral head, rotated
anteriorly (toward front); lengthened tibia with concave facets; increased valgus angle at
Foot: -Big toe aligned with rest of foot (rigid platform)
Longitundinal and transverse arches (arch of the foot to create spring)
Flattened foot bones (metatarsals/phalanges)
Diagram- shape, position, function of bones
in apes, center gravity is outside the body
in humans, center gravity inside body
Humans standing erect
larger pelvis in apes, so it allows them to swing their legs more than we can
we have larger behinds and bigger muscles to swing legs forward when walking also to
keep us stable structure
we (humans) have an S curve,
concave depressions [1] in slide 11 figure 30
2 twinned depressions on the top for humans (ie where rounded bottoms of femurs rest)
-twinned depressions is expected in bipedal primates
Austrapithecus anamensis
5mya- 1.6 mya- Pilocene
Brow ridge
Frontal bone
Zygomatic bone
Temporal bone
Foramen magnum
Occipital bone
Nuchal crest
Parietal bone
Sagittal crest

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- biostratigraphy method (ref back to defn)
-“Toumai” is the ape on this slide
-U-shaped dental archade- apelike
-we're more side to side (like more looser U.)
-(humans have thick enamels)
-less ape-like but generalized diet
-humans straight phalanges
-apes curved phalange
-Orrorin tugenesis is in between this, somewhat curved
omit the info abt Ard. ramidus in textbook, its not up to date.
Ardi nickname for Ardipithecus r. ramidus
-apes stiff wrist joints, we have more flexible wrist joints
so Ardi is more like us in terms of wrist joints because not stiff wrist joints
big toe- ie still arboreal
-arm bones much longer than legs
Everyone thought early hominids it is just in Rift Valley
early hominids more widespread than we thought
Michele Brune went outside of Rift Valley
West Africa- mostly Potassium argon dating
South Africa- mostly biostratigraphy
slide 19 – pilocenes
radio-carbon dating
humerus—upper arm bone
still not fully bipedal at this point
slide 21 -LUCY the skeletal diagram
central foramen magnum therefore bipedal -(central like humans)
bit of safittal crest, nuchal crest, receding chin- apelike features
Bipedal angle- not straight angle
Quadrapedal angle- vertical straight
Laetoli footprint- bipedal, big toe not as divergent as apes
New as of today!!1
-New afarensis skeleton *this weeks issue of PNAS- Kadanuumu “Big Man”
-3.58 mya, Afar Ethiopia
-Large bodied-almost 2 metres tall (Lucy only ~1 m)
-designed for walking- arms short rel. to legs (shorter than lucy); clavicle & shoulder
blade not strictly weight-bearing
-old theory (afarensis is transitional to bipedalism) out
new theory is afarensis is fully bipedal
A. gahri- interesting part of this species- tool use
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