Chapter 9Hominin Origins

Plio-PleistocenePertaining to the Pliocene and first half of the Pleistocene, a time range of 5 - 1 mya. For this time period, numerous fossil hominins have been found in Africa.

Miocene HominoidsAfrican forms (2314 mya) Especially from western Kenya, these include quite generalized and primitive hominoids.European forms (1611 mya) Known from widely scattered localities in France, Spain, Italy, Greece, Austria, Germany, and Hungary, most of these forms are quite derived.Asian forms (167 mya) The largest and most varied group of Miocene hominoids, they are dispersed from Turkey through India and Pakistan to southern China.

PostcranialIn a quadruped, referring to that portion of the body behind the head.In a biped, referring to all parts of the body beneath the head.

Traditional Hominoid Classification

Revised Hominoid Classification

Bipedal AdaptationBipedal locomotion freed the hands for carrying objects and for making and using tools.Bipedal walking is an efficient means of covering long distances, and when large game hunting came into play, further refinements in the locomotor complex may have been favored.

Ossa Coxae (pelvis)(a) Homo sapiens.(b) Early hominin (Australopithecus) from South Africa. (c) Great ape.

Habitual BipedalismBipedal locomotion as the form of locomotion shown by hominins most of the time.

Obligate BipedalismBipedalism as the only form of hominin terrestrial locomotion.Since major anatomical changes in the spine, pelvis, and lower limb are required for bipedal locomotion, once hominins adapted it, other forms of locomotion on the ground became impossible.

Major Features of Hominin BipedalismThe foramen magnum (shown in red) is repositioned farther underneath the skull, so the head is more or less balanced on the spine (and requires less robust neck muscles to hold the head upright).

Major Features of Hominin BipedalismThe spine has two distinctive curvesa backward (thoracic) one and a forward (lumbar) onethat keep the trunk (and weight) centered above the pelvis.

Major Features of Hominin BipedalismThe pelvis is shaped in the form of a basin to support internal organs; the ossa coxae are shorter and broader, thus stabilizing weight transmission.

Major Features of Hominin BipedalismLower limbs are elongated, as shown by the proportional lengths of various body segments.

Major Features of Hominin BipedalismThe femur is angled inward, keeping the legs more directly under the body; modified knee anatomy also permits full extension of this joint.

Major Features of Hominin BipedalismThe big toe is enlarged and brought in line with the other toes; in addition, a distinctive longitudinal arch forms, helping absorb shock and adding propulsive spring.

Position of the Foramen MagnumNote the more forward position of the foramen magnum in the human cranium.HumanChimpanzee

3 Major Early Hominins from AfricaPre-australopiths the earliest and most primitive hominins (7.04.4 mya)Australopithsdiverse forms, some more primitive, others highly derived (4.21.0 mya)Early Homo the first members of our genus (2.41.4 mya)

Pre-Australopiths (7.0 4.4 mya)Cranium usually only bone foundCranial slope, braincase size, crest, browridgesMuscle attachments are rear of skull (neck/jaw)Teeth/dentition, thin enamel on molarsForamen magnum position/orientationAre they apes or hominins?Post-cranial elements lacking, cannot determine locomotion behaviorDating techniques only enable provisional assignment to genus

Key Pre-Australopith Discoveries

Estimated Body Weights in Plio-Pleistocene Hominins

MaleFemaleA. afarensis45 kg (99 lb)29 kg (64 lb)A. africanus41 kg (90 lb)30 kg (65 lb)South African robust40 kg (88 lb)32 kg (70 lb)East African robust49 kg (108 lb)34 kg (75 lb)H. habilis52 kg (114 lb)32 kg (70 lb)

Estimated Stature in Plio-Pleistocene Hominins

MaleFemaleA. afarensis151 cm (59 in.)105 cm (41 in.)A. Africanus138 cm (54 in.)115 cm (45 in.)South African robust132 cm (52 in.) 110 cm (43 in.)East African robust137 cm (54 in.)124 cm (49 in.)H. Habilis157 cm (62 in.)125 cm (49 in.)

Earlier More Primitive Australopiths (4.23.0 mya)Australopiths diverse and very successful group of hominins made up of two closely related genera:Australopithecus.Paranthropus.Longest enduring hominin yet documented.Most widely distributed early homininMost studied

Major features that all Australopiths shareAre clearly bipedal (although not necessarily identical to Homo in this regard).Have relatively small brains (at least compared to Homo).Have large teeth, particularly the back teeth, with thick to very thick enamel on the molars.

AustralopithecusAn early hominin genus, known from the Plio-Pleistocene of Africa, characterized by bipedal locomotion, a relatively small brain, and large back teeth.Australopithecine The colloquial name for members of the genus Australopithecus.

Australopithecus afarensisSeveral hundred specimens, representing a minimum of 60 individuals have been excavated at Laetoli and Hadar. A. afarensis is less evolved than later-occurring hominin species and shares more primitive features with early hominoids and living great apes than do later hominins.A. afarensis were obligate bipeds, which would have hampered their climbing but would not have kept them out of the trees.

Later More Derived Australopiths (2.51.0 mya)Following 2.5 mya, hominins became more diverse in Africa. Adapted to various niches and are more derived.3 separate lineages of hominins

Paranthropus A hominin genus characterized by very large back teeth and jaws (highly derived, 3 species, sagittal crest, rough vegetable foods)Australopithecus africanus A late Australopith found at sites in southernmost Africa (big toothed, small brained)Homo at least two coexisting

Early Homo (2.41.4 m ya)Homo habilis A species of early Homo, well known from East Africa but possibly also found in other regions. Refers to those found at OlduvaiKnown as handy man

Cranial Capacity of Early Hominins and Contemporary Hominoids

Lower Paleolithic PeriodBegins with the oldest identifiable stone tools around 2.6 mya and end about 200,000 ya.Two major stone tool industries:Oldowan: oldest identified toolsAcheulian: begins around 1.4 mya

Oldowan (2.6 1.4 MYA)Oldest recognized hominin tools.Tool-assisted gatherers and meat scavengersNamed for Olduvai Gorge, Tanzania.Tools made by hard hammer percussion (also called direct percussion).Assemblages consist mostly of:Core forms: Choppers & cores.FlakesHammerstonesExpedient tools

Hard Hammer Percussion

Oldowan Tool Assemblage

A Tentative Early Hominin Phylogeny

Steps in Interpreting Evolutionary EventsSelecting and surveying sites.Excavating sites and recovering fossil hominins.Designating individual finds with specimen numbers for clear reference.Cleaning, preparing, studying, and describing fossils.Comparing with other fossil material.Comparing fossil variation with ranges of variation in related groups of living primates.Assigning taxonomic names to fossil material.