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Chap 10

Course Code
Michael Schillaci

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Chapter 10: From Hominoid to
At the beginning Sahelanthropus tchadensis
Orrorin tugenensis
The Hominin Community DiversifiesAustralopithecus
Homo habilis/rudolfensis
Hominin Phylogensies
The evolution of early hominin morphology
and behavior
The evolution of bipedalism
Early hominin subsistence
Early hominin social organization
Miocene, earths temperature began to fall, caused two important changes in the
climate of the African tropics
oTotal amount of rain that fell each year declined
oRainfall became more seasonal, there were several months each year when no
rain fell
Africa became drier, moist tropical forests shrank and drier woodlands and
fresslands expanded
Ape lineage of period failed to adapt, became extinct
Natural selection allowed a few species to move down from the trees, earliest
hominins, were among these pioneering species
The spread of woodland and savanna led to the evolution of the first hominins about 6mya
Ranged through eastern and southern Africa
Different in two ways:

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oWalked upright, major morphological changes in their bodies
oNew savanna and woodland habitats, new kinds of food became available,
chewing apparatus, features of the teeth, jaw and skull changed
A number of shared derived characters distinguish modern humans from other living
hominoids: bipedal locomotion, larger brain, slower development, several features of dental
morphology and cultural adaptation
Hominins: are classified with humans in the tribe hominini, taxonomic unit between
the family and the genus
Humans belong to family hominidae, includes all great apes and genus Homo
Five categories of derived traits distinguish modern humans from contemporary
oWalk bipedally
oDentition and jaw musculature are different from those of apes in a number
of ways. Ex. We have a wide parabolic dental arcade, thick enamel, reduced
canine teeth, and larger molars in relation to the other teeth
oHave much larger brains in relation to body size
oDevelop slowler, long juvenile period
oDepend on elaborate, symbolic cultrs, transmitted in part of language
Early hominins were bipedal, shared dental features with modern humans, classified
in subfamily
At the beginning
Saleanthropus tchadensis
The earliest known hominin, has a surprising mix of derived and primitive features
Rift Valley of East Africa
Nearly completed cranium, skull minus the lower jawbone, four partial mandibles,
four teeth
Sahel, vast dry region south of the sahara, tchadensis comes from chad, the country
where the fossil was found

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Chad, discovery implies that hominins had a much larger range than expected
Fossil is surprisingly old, is the oldest cranium
Genetic data tell us that the hominin lineage diverged from the chimpanzee lineage
during this period of time
It possesses a very surprising mix of anatomical features
oForamen magnum, is located under the skull, rather than at the back,
associated with bipedal locomotion
oBrains no bigger than the brains of chimpanzees (320-350cc)
oTeeth different than chimpanzees; canines are smaller, upper canine is not
sharpened against the lower premolar as it is, enamel thicker
oFlat face, mossive brow ridge over eyes
These are features associated with hominins who date to later than 2mya, not with
chimpanzees or with australopiths, doubt that its a human ancestor
Orrorin tugenensis original man
Is a second early fossil with similarities to humans?
12 hominin fossils in the Tugen Hills in the highlands of Kenya
Included parts of thigh, arm bones, finger bone, two partial mandibles, several teeth,
securely dated to 6mya
Like sahelanthropusare similar to chimps in some ways and to humans
oIncisors, canines and one of the premolars are more like the teeth of chimps
than hominins
oMolars are smaller than those of A. ramidus and later apelike hominins
oThick enamel like human molars
oArm and giner bones have features that are believed to be adaptations fior
oFemur more similar to those of later bipedal hominins
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