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Earliest HomininsHominin Phylogeny

PrimitiveArchaicGenus HomoMosaic EvolutionModern human characteristicsAppeared at different times Evolved at different rates

Extinct hominids show a mosaic of derived and ancestral characteristics

Hominin Evolutionary SequencesLocomotionShift from inefficient to more efficient bipedality ca. 2 mya

DentitionEnamel thickening ca. 4 myaGradual reduction of anterior dentition 4.5 mya to presentGradual reduction of posterior dentition ca. 2.5 mya to present

EncephalizationLimited encephalization from 4 mya to 2.5 myaMarked encephalization from 2.5 mya to ca. 150 kya

Bipedality

Skeletal Indicators of BipedalityPelvis

Distribution of body mass

Relative limb-length

Position of foramen magnum

Lumbar vertebrae

Foot

Primate Taxonomy (DNA-based)

DentitionDentition comparison

Early Hominin Molar Size

Primitive Hominins

Sahelanthropus tchadensisAge estimated to be between 6 and 7 myaFossil remainsNearly complete cranium Several fragmentary mandiblesIsolated teeth Cranial capacity 320-380 ccClassification uncertain several possibilitiesPosition of foramen magnum suggests non-bipedalSahelanthropus tchadensisChimp-sized brainHominin-like brow ridgesCanine wear pattern not ape-likeThick hominin-like mandible

Orrorin tugenensisAge ca. 6myaFossils remains mandibles, femur, humerus, large molars, small caninesFemur suggests bipedalityHumerus suggests tree-climbing skills (but not brachiation)Long bones suggest chimpanzee sizeTeeth resemble later hominidsOrrorin tugenensis Femur

Ardipithecus ramidus

Archaic Hominins

24GRACILE & ROBUST AUSTRALOPITHECINES

Gracile(afarensis)Robust (aethiopicus)24Australopithecus africanusSTS 5

Paranthropus boisei (OH 5)

gracile vs robust archaic homininsAu. africanusP. boisei

Australopithecus ghariAge ca. 2.5 myaLater AustralopithecineLimbs suggest bipedalityIncipient megadontia

Found with stone tools and butchered animal remainsAustralopithecus ghari

The Genus Homo

Homo [?] habilis

Cranial ComparisonsDmanisi Homo erectus

Homo ergaster KNM-ER 3733

Comparison of Later Forms of Homo