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Earliest Hominins. Hominin Phylogeny. Genus Homo. Archaic. Primitive. Mosaic Evolution. Modern human characteristics Appeared at different times Evolved at different rates Extinct hominids show a mosaic of derived and ancestral characteristics. Hominin Evolutionary Sequences.

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hominin phylogeny
Hominin Phylogeny

Genus Homo

Archaic

Primitive

mosaic evolution
Mosaic Evolution
  • Modern human characteristics
    • Appeared at different times
    • Evolved at different rates
  • Extinct hominids show a mosaic of derived and ancestral characteristics
hominin evolutionary sequences
Hominin Evolutionary Sequences
  • Locomotion
    • Shift from inefficient to more efficient bipedality ca. 2 mya
  • Dentition
    • Enamel thickening ca. 4 mya
    • Gradual reduction of anterior dentition 4.5 mya to present
    • Gradual reduction of posterior dentition ca. 2.5 mya to present
  • Encephalization
    • Limited encephalization from 4 mya to 2.5 mya
    • Marked encephalization from 2.5 mya to ca. 150 kya
skeletal indicators of bipedality
Skeletal Indicators of Bipedality
  • Pelvis
  • Distribution of body mass
  • Relative limb-length
  • Position of foramen magnum
  • Lumbar vertebrae
  • Foot
sahelanthropus tchadensis
Sahelanthropustchadensis
  • Age – estimated to be between 6 and 7 mya
  • Fossil remains
    • Nearly complete cranium
    • Several fragmentary mandibles
    • Isolated teeth
  • Cranial capacity – 320-380 cc
  • Classification uncertain – several possibilities
  • Position of foramen magnum suggests non-bipedal
sahelanthropus tchadensis1
Sahelanthropus tchadensis
  • Chimp-sized brain
  • Hominin-like brow ridges
  • Canine wear pattern not ape-like
  • Thick hominin-like mandible
orrorin tugenensis
Orrorin tugenensis
  • Age ca. 6mya
  • Fossils remains – mandibles, femur, humerus, large molars, small canines
    • Femur suggests bipedality
    • Humerus suggests tree-climbing skills (but not brachiation)
    • Long bones suggest chimpanzee size
    • Teeth resemble later hominids
gracile robust australopithecines
GRACILE & ROBUST AUSTRALOPITHECINES

“Robust” (aethiopicus)

“Gracile”

(afarensis)

australopithecus ghari
Australopithecus ghari
  • Age ca. 2.5 mya
    • Later Australopithecine
  • Limbs suggest bipedality
  • Incipient megadontia
  • Found with stone tools and butchered animal remains