ANTH151 Lecture Notes - Lecture 4: Taphonomy, Palaeoarchaeology, Anatomical Terms Of Motion
1 Jun 2018
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ANTH151 – Week 4; Early Hominids and Bipedalism
• Pre-adaptation (exaptation) → trait selected for one function may serve later
for a different purpose
o Exaptation is counterintuitive
• ‘Lucy’ – Australopithecus afarensis
o Theorists of human evolution assumed early human-like creatures
would have large brains and ape-like bodies
o ‘Lucy’ discovered in Hadar, Ethiopia by Donald Johanson 1974
o Approximately 40% complete
o 107cm tall and 28kg when alive
o Probably 25-30 years old (a bit of arthritis); most likely female
o Dated to 3.5 million years ago
o Probably around 60% of a modern human (quite a smaller body)
o Joint degeneration
• Human-like traits from Lucy:
o Large grinding molars
o Bipedal
• Ape-like traits:
o Sharp canines (pointed)
o Long arms
o Sexual dimorphic
o Brain size and shape
• Adapted to coarse-food diet (gritty teeth), dependent young and possible
polygyny (multiple wives)
• Lucy and a modern woman’s skeleton
o Size contrast is obvious
o Bone remains in red
o Illustration also shows many of the subtle differences in skeletal
morphology
• Classification issues
o Lumpers (lump everything together) vs. splitters
o How different should a specimen be to justify a new species?
(incentives for naming)
o Relations among extinct species difficult to determine (genetic
evidence not available)
o Species may have been variable at certain points in time (stabilizing
selection over time?)
• Hominid genealogy less a ‘tree’ than a bush, with many branches that died out
• Recall that Miocene was period of great diversity in apes
• Today, we focus on Australopithecus and Paranthropus
• Australopithecus
o Paleoanthropologists disagree about how many species and what they
should be called;
▪ A. afarensis
▪ A. africanus
▪ P. boisei
▪ P. robustus
• Australopithecence and Chimp – key differences:
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o Spine
o Pelvis
o Arms
o Teeth
o Leg
o Feet
• Evidence in skull for bipedalism – location of foramen magnum (the hole)
suggests whether spine was vertical (on a chimp, the hole is back from the
centre of the skull)
• Evidence from the foramen magnum – how vertical was the posture of early
hominins?
o Evidence from very early hominins – computer reconstruction of S.
tchadensis skull showing foramen magnum (still got a lot of snout
sticking out, face is projecting forward yet brain is sitting on neck –
similar to a chimp) → vertical foramen magnum, but not balanced
• Comparison of pelvic bones
o Short, broad ilium compared to a human’s ilium which is long and
narrow
o Changed ilium, hip abductor muscle and walking (chimps cannot hold
their weight on their body – their body wants to fall back down when
picking up a certain muscle/body part)
• Australopithecus compared pelvis bones and feet – looks more like the
human/homosapiens pelvis than chimp
• Australopithecus compared hip joints, knees and ‘kneeing in’
• Australopithecus compared pelvis, legs and feet
• Legs elongated → increasing stride length, improves efficiency
o Stride lengthens when we accelerate to run (more than just increased
cadence)
• Major anatomical changes:
o Skull → position of foramen magnum
o Spine → distinctive double curves
o Hips → bowl-shaped pelvis and ilium is short and broad
o Knees → turn in (adduction) and valgus angle
o Feet → hallux (big toe) also adducted
o At first, arms still long
o Bipedalism is facultative but becomes obligate (obligatory)
• Why is this significant?
o Bipedalism preceded other major innovations of our genus, such as
large brain, tool making or social advances
o Bipedalism may not have been gained by Australopithecenes but
retained from earlier suite of arboreal adaptations
• Why become bipedal?
o Humans are not the only bipedal; dinosaurs, lizards, cockroaches,
penguins etc.
o Being bipedal alone does not mean you are human
• Disadvantages to bipedalism:
o Climbing is more difficult without grasping foot
o Holding children also more difficult without grasping foot, especially
in arboreal settings
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