Earliest Hominins

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Earliest Hominins

description

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. - PowerPoint PPT Presentation

Transcript of Earliest Hominins

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Earliest Hominins

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Hominin Phylogeny

Primitive

Archaic

Genus Homo

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Mosaic Evolution Modern human characteristics

› Appeared at different times › Evolved at different rates

Extinct hominids show a mosaic of derived and ancestral characteristics

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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

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Bipedality

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Skeletal Indicators of Bipedality Pelvis

Distribution of body mass

Relative limb-length

Position of foramen magnum

Lumbar vertebrae

Foot

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Primate Taxonomy (DNA-based)

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Dentition

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Dentition comparison

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Early Hominin Molar Size

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Primitive Hominins

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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

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Sahelanthropus tchadensis Chimp-sized brain Hominin-like brow

ridges Canine wear

pattern not ape-like

Thick hominin-like mandible

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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

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Orrorin tugenensis Femur

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Ardipithecus ramidus

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Archaic Hominins

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GRACILE & ROBUST AUSTRALOPITHECINES

“Gracile”(afarensis)

“Robust” (aethiopicus)

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Australopithecus africanus

STS 5

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Paranthropus boisei (OH 5)

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“gracile” vs “robust” archaic hominins

Au. africanus P. boisei

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Australopithecus ghari

Age ca. 2.5 mya› Later Australopithecine

Limbs suggest bipedality Incipient megadontia

Found with stone tools and butchered animal remains

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Australopithecus ghari

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The Genus Homo

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Homo [?] habilis

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Cranial Comparisons

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Dmanisi Homo erectus

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Homo ergaster KNM-ER 3733

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Comparison of Later Forms of Homo