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Bio 1M03 ch 1

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Ben Evans

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Chapter 10: From Tree Shrew to Ape
Bernard Ho
February 13, 2011
During the Permian and early Triassic periods, much of the world’s fauna was
dominated by therapsids, a diverse group of reptiles that possessed traits such as being
warm-blooded and covered with hair that linked them to mammals that evolved later
At the end of the Triassic, most therapsid groups disappeared and dinosaurs radiated to
fill all of the niches for large, terrestrial animals
One therapsid lineage evolved and diversified
These early mammals were probably mouse-sized, nocturnal creatures that fed mainly
on seeds and insects
They had internal fertilization, but still laid eggs
By the end of the Mesozoic era, placental and marsupial mammals that bore live young
had evolved
With extinction of dinosaurs at the beginning of the next era (Cenozoic) came the
radiation of mammals
According to Darwin’s theory, complex adaptations are assembled gradually, each step
favoured by natural selection
Modern humans have many complex adaptations, like grasping hands, bipedal
locomotion, toolmaking abilities, language and large-scale cooperation
Continental Drift and Climate Change
To understand the evolution of our species, it is important to understand the geological,
climatic and biological conditions under which these evolutionary changes occurred
Evolution produces adaptation, but what is adaptive in one environment may not be
adaptive in another environment
o If the environment remained the same over the course of human evolution, then
the kinds of evolutionary changes observed in the hominin fossil record would
have to be seen as steady improvements in perfection of human adaptations
o But if environment varied through time, evolution would have to track a moving
One factor that contributed to change in the world is the movement of continents or
continental drift
About 200mya, all of the land making up the present-day continents was joined
together in a single, huge landmass called Pangaea
About 125 mya, Pangaea began to break apart into separate pieces
o The northern half, called Laurasia, included what is now North American and
Eurasia minus India
o The southern half, Gondwanaland, consisted of the rest
o Eventually, Gondwanaland separated into South America, Antarctica and
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