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Lecture 9

Lecture 9

5 Pages
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Department
Anthropology
Course Code
ANTB14H3
Professor
Michael Schillaci

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Chapter 9: From Tree Shrew to Ape
During Permian and early Triassic periods, much of worlds fauna was dominated by therapsids, a
diverse group of reptiles that possessed traits, such as warm blooded, and covered with hair
One therapsid lineage evolved and diversified to become first true mammals
oProbably mouse sized, nocturnal creatures that fed mainly on seeds and insects
oHad internal fertilization but still laid eggs
By end of Mesozoic era, 65 mya, placental and marsupial mammals that bore live young evolved
Modern humans have many complex adaptations- grasping hands, bipedal locomotion, tool making
abilities, language, and large scale cooperation
Continental drift and climate change
To understand evolution of our species, important to understand geological, climatic, biological
conditions under which these evolutionary changes occurred
World become much colder and drier in last 20 million years
Positions of continents have changed relative to each other and to the poles
One factors that contributed to change of world is movement of continents continental drift
Enormous and relatively light plates of rock that make up continents slowly wander around globe,
floating on denser rock that forms floor of deep ocean
200 mya, all of land making up present-day continents joined together in single, huge landmass
call Pangaea
125 mya, Pangaea began to break apart into separate pieces
oNorthern half, Laurasia, included North America and Eurasia minus India
oSouthern half, Gondwanaland consisted of others
By time dinosaurs became extinct in 65 mya, Gondwanaland broken up into several pieces
oAfrica and India separated, India headed north, crashing into Eurasia, remainder of
Gondwanaland stayed in south
oEventually Gondwanaland separated into South America, Antarctica, Australia
oSouth America did not drift north to join N.A. until about 5mya
Continental drift important to history of human lineage:
oOceans serve as barriers that isolate certain species from others, so position of continents
play important role in evolution of species
oContinental drift is one of engines of climate change, climate change has fundamentally
influenced human evolution
Climate changed substantially during last 65 million years, becoming warmer and less variable
and then cooling, finally fluctuating widely in temperature
Very large continents tend to have severe weather
When continents restrict circulation of water from tropics to poles, world climates seem to become
cooler
The methods of paleontology
Much of knowledge of history of life comes from study of fossils, the mineralized bones of dead
organisms
Palaeontologists scientists who recover, describe, and interpret fossil remains
In order to assign fossil to particular position in phylogeny, must know how old it is
Radiometric methods: provide one of most important ways to date fossils
All atoms of particular element have same number of protons in nucleus
For any particular isotope, radioactive decay occur at constant
Several different radiometric methods:
oPotassium-argon dating
Used to date age of volcanic rocks found in association with fossil material
www.notesolution.com
Molten rock emerges from a volcano at very high temperature, all of argon gas boiled
out of rock
Any argon present in rock must be due to decay of potassium, occurs at known and
constant rate, ratio of potassium to argon can be used to date volcanic rock
If fossil discovered in geological stratum lying under stratum that contains volcanic
rock, can confirm that fossil is older than rock
Argon-argon dating because potassium in sample is converted to isotope of argon
before it is measured, allows more accurate dating of single rock crystals
oCarbon-14 dating (radiocarbon dating)
Based on unstable isotope of carbon that living animals and plants incorporate into
cells
As long as organism is alive, ratio of unstable isotope (carbon-14) to stable isotope
(carbon-12) is same as ratio of 2 isotopes in atmosphere
Once animal dies, carbon-14 starts to decay into carbon-12 at constant rate
By measuring ratio of C 12 to C 14, can estimate amount of time that has passed
since organism died
oThermoluminescence dating
Based on effect of high-energy nuclear particles traveling through rock
Particles come from decay of radioactive material in and around rock and from
cosmic rays that bombard Earth from outer space
Can estimate number of trapped electrons in flints by heating them in laboratory
and measuring amount of flint given off
If density of high energy particles currently flowing through site is also know,
scientists can estimate length of time that has elapsed since flint was burned
oElectron-spin-resonance dating
Used to determine age of apatite crystals, an inorganic component of tooth enamel
Estimate number of trapped electrons by subjecting teeth to variable magnetic field-
electron spin resonance
To estimate number of years since tooth was formed, must measure flow of radiation
at site where tooth was found
Absolute radiometric dating is supplemented by relative dating methods based on magnetic
reversals and comparison with other fossil assemblages
Radiometric dating methods problematic for 2 reasons:
oParticular site may not always contain material that is appropriate for radiometric dating
oRadiometric methods have relatively large margins for error
The evolution of early primates
Evolution of flowering plants created a new set of ecological niches
Primates were among animals that evolved to fill these niches
During fire two-thirds of Mesozoic, forests of world dominated by gymnosperms, trees like
contemporary redwood, pine, fir
With breakup of Pangaea during Cretaceous, revolution in plant world occurred
Flowering plants, angiosperms, appeared and spread
Ancestors of modern primates were small bodied nocturnal quadrupeds much like contemporary
shrews
Plesiadapiforms, group of fossil animals found in what is now Montana, Colorado, New Mexico,
Wyoming give us clues about early primates
oFound in sites date back from Paleocene epoch, 65-54 mya
oTiny, shrew-sized
oQuadrupeds with well developed smell
www.notesolution.com

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Description
Chapter 9: From Tree Shrew to Ape During Permian and early Triassic periods, much of worlds fauna was dominated by therapsids, a diverse group of reptiles that possessed traits, such as warm blooded, and covered with hair One therapsid lineage evolved and diversified to become first true mammals o Probably mouse sized, nocturnal creatures that fed mainly on seeds and insects o Had internal fertilization but still laid eggs By end of Mesozoic era, 65 mya, placental and marsupial mammals that bore live young evolved Modern humans have many complex adaptations- grasping hands, bipedal locomotion, tool making abilities, language, and large scale cooperation Continental drift and climate change To understand evolution of our species, important to understand geological, climatic, biological conditions under which these evolutionary changes occurred World become much colder and drier in last 20 million years Positions of continents have changed relative to each other and to the poles One factors that contributed to change of world is movement of continents continental drift Enormous and relatively light plates of rock that make up continents slowly wander around globe, floating on denser rock that forms floor of deep ocean 200 mya, all of land making up present-day continents joined together in single, huge landmass call Pangaea 125 mya, Pangaea began to break apart into separate pieces o Northern half, Laurasia, included North America and Eurasia minus India o Southern half, Gondwanaland consisted of others By time dinosaurs became extinct in 65 mya, Gondwanaland broken up into several pieces o Africa and India separated, India headed north, crashing into Eurasia, remainder of Gondwanaland stayed in south o Eventually Gondwanaland separated into South America, Antarctica, Australia o South America did not drift north to join N.A. until about 5mya Continental drift important to history of human lineage: o Oceans serve as barriers that isolate certain species from others, so position of continents play important role in evolution of species o Continental drift is one of engines of climate change, climate change has fundamentally influenced human evolution Climate changed substantially during last 65 million years, becoming warmer and less variable and then cooling, finally fluctuating widely in temperature Very large continents tend to have severe weather When continents restrict circulation of water from tropics to poles, world climates seem to become cooler The methods of paleontology Much of knowledge of history of life comes from study of fossils, the mineralized bones of dead organisms Palaeontologists scientists who recover, describe, and interpret fossil remains In order to assign fossil to particular position in phylogeny, must know how old it is Radiometric methods: provide one of most important ways to date fossils All atoms of particular element have same number of protons in nucleus For any particular isotope, radioactive decay occur at constant Several different radiometric methods: o Potassium-argon dating Used to date age of volcanic rocks found in association with fossil material www.notesolution.com
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