Lab Exercise from Last Week

							3N03 – Early Hominids

Lab Exercise from Last Week

Similarities to hominoids:
Dental formula 2.1.2.3
Sectorial premolar
Molars w/ large cusps & arrangement of cusps
Monkey-like features:
Mandible is still long & slender (long snout)
Narrow nasal openingNarratives in Human Evolution

Miocene Apes - 'Dental Apes'
Lower molars – Y-5 molar pattern
Large canines
Large front teeth
Molars square
Rel. large orbits

Sivapithecus - similarities to modern orangutans
Narrow snout
Prognathism
Broad zygomatic arches
Tall, narrow nasal opening
High orbits

Gigantopithecus
Morphology of teeth:
Lower incisors small
Canines thick & short
Thick enamel
Broad premolars and molars
Low flat cusps

Early Hominid Evolution

Most scientific theories are essentially narratives
Organize a plausible sequence of events
Which element came first have always been debated
BUT there is a common narrative structure in all reconstructions

Goals of these Narratives
Explain biological and behavioral evolution
Explain origins of hominids & later development
Explain origins of human traits (bipedalism, tool use, etc…)
Explain origins of social systems



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Examples
1960’s – Social Carnivore Model – early hominids evolved social structure due to ‘the
hunting way of life’
Baboon Model – as hominids moved onto the savannah, they adopted a social structure
like that of baboons (male hierarchy, group structure, etc…)
Late 1970’s – Gathering & Hominid Adaptation – gathering of plant foods was the basic
hominid adaptation

Pliocene Epoch
~5 mya
Separation between apes and humans – between 10-5mya
Early definite hominids 4.4-4mya
Two major events:
Spread of OWM throughout the Old World
First appearance of hominids

Hominid Characteristics
Small front teeth and large molars relative to other primates
Bipedalism & associated anatomical adaptations (e.g., anatomy of pelvis, knee, femur &
foot)
Increased dexterity of hands
Increased brain size
Reduction of face, teeth, and jaws
Tool making behavior
Problem – not all occurred at the same time

Hominids: The Early Years

Earliest Possible Ancestor
Sahelanthropos tchadensis
Dated to 6-7 m.y.a.
Chad
Last common ancestor with Pongidae
Mix of ‘primitive’ and ‘derived’ anatomical features
Cranial capacity – 350 cm3

Orrorin tugenensis
Tugen Hills, Kenya
13 fossils; 5 individuals
Upper limbs adapted for trees
Femur adapted for bipedalism
Teeth - frugivorous




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Ardipithecus ramidus
4.4mya in Ethiopia
>50 individuals recovered from site
Cranial, postcranial, and (mainly) dental remains
Primitive skeletal morphology
Not clear if it was bipedal

The Australopithecine Years (plus a few others)

Australopithecus anamensis
3.9-4.2mya in northern Kenya
Dental remains and some postcranial bones
Mosaic of primitive and derived features
Considerable sexual dimorphism in teeth
Probably bipedal

Australopithecus afarensis
3.0-4.2mya from East Africa
Big teeth; small brains; short stature; sexually dimorphic
Cranium is more ape-like
Extremely large molars and large anterior teeth
Probably frugivorous
Definitely bipedal features to pelvis and lower limbs
Traveled bipedally, but still had arboreal capabilities

A. africanus
Taung child was the first specimen described
From sites in South Africa (Sterkfontein and Makapansgat)
2.3-3.0mya
Similar to A. afarensis in many ways
Some see it as a regional variant of A. afarensis, others view it as a separate species

A. garhi
(garhi = ‘surprise’)
Found in 1997, reported in Science 1999
2.5mya from Ethiopia
Ape-like face, small braincase
Teeth are much larger than A. afarensis
Some see this is an ancestor of early Homo

Robust Australopithecines
Fleagle calls them Paranthropus; others still refer to them as Australopithecus
1.0-2.5mya from East and South Africa
Larger molars and premolars
Smaller canines and incisors
Broader, flatter faces



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Sexually dimorphic
Bipedal

P. aethiopicus - The Black Skull
Oldest; most primitive
Few specimens attributed to this species
Important link between ‘robust’ and ‘gracile’ australopithecines
2.3-2.7mya from southern Ethiopia
Massive face; long snout
Extr. Large sagittal and nuchal crests
Small cranial capacity (410 cc)

P. robustus
Known from South Africa; 1-2mya
Smaller anterior teeth
Larger cheek teeth; thicker enamel; thicker mandible
Tooth wear studies indicate a different diet than other australopithecines
Tooth wear studies indicate an herbivorous diet consisting of harder, smaller food
Short, broad face; sagittal crest
Sexual dimorphism

P. bosei (hyper-robust forms)
East Africa; 1.2-2.2mya
Smaller anterior teeth than P. robustus and massive cheek teeth
Broad, short face; flaring zygomatics; small brain; pronounced sagittal and nuchal crests
in males
First identified as Zinjanthropus bosei by the Leakeys
Considered a highly specialized form
Adaptations to high masticatory stress
Reduced sexual dimorphism
May have made and used tools

Hominid Origins
Australopithecus and Paranthropus show that the unique ‘hominid’ features did not
evolve all at once
Early hominids were bipedal before brain size started to increase
Habitual bipedalism seems to be the feature that clearly distinguishes early hominids
from other primates
Still to be resolved – the relationship of australopithecines to the genus Homo

Narratives about origins of bipedalism – see Fleagle (pp. 525-528)
Examples:
Tool use (Darwin) - use of tools led to bipedalism
Pedator avoidance - standing on two feet to look over savannah grasses for predators
Long distance travel - more efficient (not faster) to walk bipedally




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Gathering hypothesis (Zihlman and Tanner) – bipedalism allowed females to carry
infants, carry surplus food, and use tools
Male provisioning (Lovejoy) – bipedalism freed the hands of males to bring food back to
the family
Thermoregulation (Wheeler) – bipedalism limited direct exposure to sunlight and
facilitated heat loss
Preadaptation to terrestrial life - they lived in trees but traveled between them bipedally




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