Earliest Hominins Flashcards
What are the anatomical adaptations for bipedalism?
- Wide, flared pelvis for hip abductor muscles
- Femur angled so knee joints are close together under the body
- Big toe is not opposable
- Arched foot (shock absorption and spring)
- Foramen Magnum positioned at bottom of skull
- Long neck of femur cortical bone indicates weight bearing in upright position
- Stiff ankle with limited to side movement
Discuss the human pelvis in relation to hominins.
- Most altered bony anatomy in humans
- Trade-offs between walking and need for birthing large brained babies (wide birth canal)
Discuss the hip abductor muscles in relation to hominins.
- Attach to the iliac crest on the pelvis
- Wide, short ilium with distinctive sciatic notch present in humans and hominins
- Keep pelvis from slanting downwards with each step
- Minimize movement of centre of gravity got efficient walking
What other anatomical features can be discussed in relation to hominins?
- Extended knee and hip
- Lumbar curve
- Ventral foramen magnum
- Places centre of gravity with major joints
- Stable, not much muscle activity needed for bipedalism (other primates are the opposite)
Why is bipedalism beneficial?
- Less energy expenditure
- Thermoregulation
- Carrying stuff or infants
- Hunting (posture for seeing further)
- Endurance running
- Low hanging fruit
- Making tools (need both hands)
When did fossil apes start declining?
Late miocene about 9 million years ago in Africa. There was a lot of drying and cooling (very few rocks at this age, very few fossils), and there is a poor fossil record of this time
What is Sahelanthropus tchadensis?
- Oldest fossil hominin
- Found in Chad and dated to 6-7 million years ago using relative dating with fauna
- Woodland environment
- Near complete cranium and mandible
- Primitive brain size to chimps
- Derived flat face, thick enamel on molars, and small canines
- Location of foramen magnum and placement of neck muscle attachment suggest bipedalism
What is Orrorin tugenensis?
- Second oldest fossil hominin
- Found in Tugen Hills, Kenya and dated to about 6 million years ago
- Teeth and postcranial bones
- Primitive curved proximal phalanx (finger/toe bones)
- Derived teeth with thick enamel, femoral neck length/shape and distribution of bone suggest bipedalism
What is Ardipithecus kadabba?
- third oldest hominin
- Found in Middle Awash, Ethiopia and dated to 5.2 - 5.8 million years ago
- Limited material (dental remains, toe bone)
- Primitive upper canine hones
- Derived toe bone similar to toe bones of later hominins (maybe bipedalism??)
What is Ardipithecus ramidus?
- Fourth oldest hominin
- Found in Middle Awash, Ethiopia and dated to 4.4 million years ago
- Very complete skeleton (hands, feet, pelvis, skull, teeth)
- Woodland environment
- Primitive opposable big toe, long fingers/short thumb, thin enamel, small brain
- Derived anterior foramen magnum, bipedal adaptations on pelvis, small canines
Discuss locomotion in relation to Ardipithecus ramidus.
Argument is that A.ramidus was bipedal on the ground but spent significant time in trees (arboreal)
- Also no evidence for knuckle walking, so LCA wasn’t likely a knuckle walker
What are some issues with Ardipithecus ramidus?
- Skull seems hominin like but postcranium looks very chimp like
- Pelvis is very poorly preserved
What do the first hominins tell us?
- They were more widespread than just east and south Africa
- Bipedalism, thicker tooth enamel, and reduced canines are the first key derived features (not brain size or tool use)
- Environment was likely a woodland
