Earliest Hominins

Hominin Phylogeny

Primitive

Archaic

Genus Homo

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

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

Bipedality

Skeletal Indicators of Bipedality Pelvis

Distribution of body mass

Relative limb-length

Position of foramen magnum

Lumbar vertebrae

Foot

Primate Taxonomy (DNA-based)

Dentition

Dentition comparison

Early Hominin Molar Size

Primitive Hominins

Sahelanthropus tchadensis

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 tchadensis Chimp-sized brain Hominin-like brow

ridges Canine wear

pattern not ape-like

Thick hominin-like mandible

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

Orrorin tugenensis Femur

Ardipithecus ramidus

Archaic Hominins

24

GRACILE & ROBUST AUSTRALOPITHECINES

“Gracile”(afarensis)

“Robust” (aethiopicus)

Australopithecus africanus

STS 5

Paranthropus boisei (OH 5)

“gracile” vs “robust” archaic hominins

Au. africanus P. boisei

Australopithecus ghari

Age ca. 2.5 mya› Later Australopithecine

Limbs suggest bipedality Incipient megadontia

Found with stone tools and butchered animal remains

Australopithecus ghari

The Genus Homo

Homo [?] habilis

Cranial Comparisons

Dmanisi Homo erectus

Homo ergaster KNM-ER 3733

Comparison of Later Forms of Homo