Download - Earliest Hominins
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
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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