Bipedalism involves walking upright on two feet instead of four. Key anatomical changes that enabled effective bipedal movement include a cone-shaped rib cage, basin-shaped pelvis, inward-angled lower limbs, and lumbar curve in the spine. The foramen magnum also shifted below the skull to balance the head. Various hominin species such as Ardipithecus, Australopithecus, and Homo evolved increasingly specialized anatomies over millions of years that enhanced efficient bipedal locomotion.

1. BIPEDALISM
PAIGE WISE

2. BIPEDAL MOVEMENT
walk on 2, instead of 4
upright bipedal walking is a habitual and obligatory
form of transportation
Ardipithecus and Australopithecus

3. PARTS OF THE BODY
Neck, Skull, Rib Cage, Pelvis, and Limbs
Rib Cage - cone-like shape
Pelvis - basin-like shape
Lower Limbs - lengthen and angle inward
Major structures are all stack on top of each other,
supporting the next feature up

4. HOW DOES IT WORK?
Each step shifts body wait from one foot to the other
Both feet are on the ground only 25% of the time
Knees bend to keep balance
Upper body weight must remain stable over pelvis

5. FORAMEN MAGNUM
Apes - angled backward
Humans - located beneath the skull to balance head
and hold upright

6. SPINE
Apes - have no lumbar curve to pull upper body back
over pelvis
Humans - Additional lumbar curve that positions
body inward, over pelvis

7. FEMUR
Apes - straight, rotate pelvis to side with every step
Humans - angles inward so that weight is supported
at the midline
long, increasing stride length for efficient walking

8. KNEE
Apes - more mobile knee (climbing)
more rotation
Humans - stable during walking, reduction of
rotation

9. FOOT
Ape - big toe is divergent (grasp branches)
transverse arch
Humans - big toe is enlarged, lined up with other
toes, giving balance
two arches

10. HOMINIDS

11. ARDIPITHECUS
RAMIDUS
4.4 million years
East Africa, Woodland forest
Foramen magnum positioned forward under skull
Arms - ape features
Long, curved finger bones

12. AUSTRALOPITECUS
BOISEI
2.3 - 1.2 million years
East Africa, Savanna Woodland
Brain Size (410 - 530 cm sq.)
Robust chewing forces, including teeth and jaw
Femur angles in placing knee over foot

13. HOMO SAPIENS
100,000 years - present
Large brain size (1000-1700 cm 3)
Small, generalized teeth
Modern body proportions
Fully bipedal anatomy