Early Hominins

Terminology

• Hominoid: All apes and humans, living and extinct.

• Hominin: Modern humans, extinct human species, and immediate ancestors (e.g., Homo, Australopithecus, Paranthropus, Ardipithecus).

Key Evolutionary Trends

• Late Miocene (~6 mya): First hominins appear in Eastern Africa.

• Two defining traits:

  • Non-honing chewing: Smaller canines, no diastema, thicker enamel.

  • Bipedalism: Habitual and obligate; evolved before brain enlargement.

Bipedal Adaptations (8 Traits)

1. Centered foramen magnum

1. Lumbar curve

2. Broad, short pelvis

3. Longer legs

4. Valgus angle (knee)

5. Long femoral neck

6. Foot arches

7. Non-opposable big toe

• Benefits: Visibility, tool use, energy-efficient locomotion.

• Costs: Slower, vulnerable to predators, skeletal strain.

Important Regions

• East African Rift Valley: Rich in hominin fossils due to exposed sediment layers.

Pre-Australopithecines (6–4.4 mya)

General Traits:

• Mixture of ape-like and derived (hominin) features.

• Ancestral: Long arms, divergent big toe, curved fingers.

• Derived: Centered foramen magnum, bowl-shaped pelvis.

Key Genera:

• Sahelanthropus tchadensis (7–6 mya, Chad)

  • Small brain (360cc), flat face, anterior foramen magnum.

• Orrorin tugenensis (6–5.7 mya, Kenya)

  • Bipedal femur, long arms, small teeth.

• Ardipithecus (5.8–4.4 mya, Ethiopia)

  • Grasping big toe, small brain (300–350cc), bipedal pelvis and foramen magnum.

  • Two species: Ar. kadabba (more primitive) and Ar. ramidus.

Australopithecines (4.2–1.2 mya)

General Traits:

• Primitive: Small brains, prognathic faces, large teeth, long arms.

• Derived: Varies by species; bipedalism widespread.

Key Species:

• Australopithecus anamensis (4.2–3.9 mya, Kenya/Ethiopia)

  • V-shaped dental arcade, bipedal knees.

• Australopithecus afarensis (3.9–2.9 mya, East Africa)

  • “Lucy” (3.2 mya, Hadar): 40% complete skeleton, confirmed biped.

  • Laetoli footprints (3.75 mya): Evidence of bipedal gait.

• Australopithecus garhi (2.5 mya, Ethiopia)

  • Transitional features; possible tool use.

• Australopithecus africanus (3.3–2.1 mya, South Africa)

  • Larger brain, smaller canines, curved phalanges.

  • “Taung Child” (first Australopith discovered).

• Australopithecus sediba (<2 mya, South Africa)

  • Mix of primitive and derived traits; frontal lobe reorganization.

Later Australopithecines – Robust Forms (Genus: Paranthropus)

Traits:

• Extremely robust jaws, flared cheekbones, sagittal crest, massive molars.

• Brain size: ~500cc; postcranial anatomy similar to graciles.

Key Species:

• Paranthropus aethiopicus (2.5 mya, East Africa)

  • Link to afarensis, very prognathic.

• Paranthropus boisei (2.4–1.4 mya, East Africa)

  • “Nutcracker Man”; highly specialized diet, mainly C4 plants.

• Paranthropus robustus (1.8–1.2 mya, South Africa)

  • Less robust than boisei; mixed diet including nuts/seeds.

• Debate: Is Paranthropus a true monophyletic group or a convergence of similar traits?

Diet & Microwear

• P. robustus: C3 foods with fallback on hard items (nuts, seeds).

• P. boisei: C4 plants; microwear shows consumption of tough, not hard, items.

Gracile vs. Robust Comparison

• Similarities: Bipedalism, body size, brain size (~450–500cc).

• Differences: Robusts more specialized in cranial/dental traits.

Key Fossil Discoveries

• Lucy (A. afarensis)

• Laetoli footprints

• Taung Child (A. africanus)

• Australopithecus sediba (Malapa cave)

Piltdown Hoax

• Fake “missing link” fossil (England, 1912).

• Combined human skull with orangutan jaw.

• Disproven in 1953; hindered acceptance of African origins for humans.