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How Humans Evolved Textbook Notes: Part 3 The History of the Human Lineage Chapter 9, 10, 11, 12, 13

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McGill University
ANTH 203
Michael Bisson

How Humans Evolved Textbook NotesThe History of the Human Lineage Part 3 Chapter 9From Tree Shrew to Ape During the Permian and early Triassic periods worlds fauna dominated by therapsids a diverse group of reptiles that possessed traits such as being warmblooded and covered with hair Linked to the mammals that evolved laterEnd of Triassic period o Most therapsid groups disappeared and the dinosaurs dominated o One therapsid lineage evolved and diversified to become the first true mammalsEnd of Mesozoic era o Placental and marsupial mammals that bore live young have evolved Extinction of the dinosaurs at the beginning of the Cenozoic eraAfter them came the radiation of mammals o All modern descendants include horses bats whales elephants lions and primatesBelieved to have evolved from something like a shrewContinental Drift and Climate Change Remember evolution produces adaptation but what is adaptive in one environment may not be adaptive in anotherContinental drift the movements of the continentsPangaea the joining of all continentsLaurasia northern half on Pangaea once it began to break apart o Includes North America and Eurasia minus IndiaGondwanaland the rest of Pangaea o Had broken up into several smaller pieces once the dinosaurs became extinct o Africa and India separated India crashing into Eurasia and the rest remained in the south o Eventually separated into South America Antarctica and Australia remained separated for millions of yearsContinental drift is important for 2 reasons o Oceans serve as barriers that isolate certain species from otherso One of the engines of climate change The Methods of Paleontology A great deal of what we know about the history of the human lineage comes from the study of fossilsShapes of different bones tell us what early hominins were like o How big they were what they ate where they lived how they moved how they livedThere are several radiometric methods for estimating the age of fossils o Radiometric methods provide one of the most important ways to date fossils o Potassiumargon datingUsed to date the age of volcanic rocks found in associated with fossil materialIf a fossil is discovered in a geological stratum of the rock it can be sure that the fossil is older than the rockStratumstrata layer of rockNew variant called argonargon dating Allows accurate dating of single rock crystals o Carbon14 datingradiocarbon datingBased on an unstable isotope of carbon that living animals and plants incorporate into their cells o Thermoluminescence datingBased on an effect of highenergy nuclear particles traveling through rockThese particles come from the decay of radioactive material in and around the rock from cosmic rays from outer space It is possible to estimated the number of trapped electrons in these flints by heating them in the laboratory and measuring the amount of light given off If the density of highenergy particles currently flowing through the site is also known scientists can estimate the length of time that has elapsed since the flint was burnedo Electronspinresonance datingUsed to determine the age of apatite crystals An inorganic component of tooth enamelForm as teeth grow and initially contain no trapped electronsPreserved in fossil teeth and are bombarded by a flow of highenergy particles that generate trapped electrons in the crystal latticeMust also measure the flow of radiation at the site where the tooth was found o UraniumLead UPb datingUsed to date zirconium crystals found in igneous rocks Radiometric dating methods are problematic for 2 reasons o A particular site may not always contain material that is appropriate for radiometric dating o They have relatively large margins for errorThese drawbacks have led scientists to supplement these absolute methods with relative methodso One relative method based on the earths magnetic field o Another approach is to make use of the fact that sometimes the fossils of interest are found in association with fossils of other organisms that existed for only a limited period of timeThe Evolution of the Early Primates The evolution of flowering plants created a new set of ecological niches o Primates were among the animals that evolved to fill these nichesCretaceous period o Revolution in plant world occurred o Flowering plants called angiosperms appeared and spread which created a new set of ecological niches for animals o Angiosperms depend on animals to pollinate them o Tropical birds bats insects and small rodent like animals probably competed with early primates for the bounty of the angiosperm treesThe ancestors of modern primates were smallbodied nocturnal quadrupeds much like modern shrewsThe plesiadapiforms a group of fossil animals give us some clue about what the earliest primates were likeo They varied from tiny shrewsized creatures to animals as big as marmots o Seemed like they were quadrupeds with a well developed sense of smell o Wide range of dietary specializationso Most had claws on their hands and feet o Did not have binocular visionRecent discovery of a 56 million year old plesiadapiforms provides important clues about primate origins o Named Carpolestes simpsonio Had an opposable big toe with a flat nail but claws on other digits which likely helped it climb large tree trunks o Also able to grasp small supports o Lowcrowned molars which are favourable for eating fruits o Eyes on the side of its head o Field of vision did not overlapThe discovery of C simsponi helps explain why natural selection favoured the basic features of primate morphologyGrasping hands and feel allowed early primates to forage on fruit flowers and nectar in the terminal branches of angiospermsLater the eyes shifted forward to facilitate visually directed predation on insectso These characteristics fit with the evidence from C simpsoni Primates with modern features appeared in the Eocene epochEocene epoch o 5434 mya o Wetter and warmer than the preceding Paleocene o Tropical rain forests covered most of the globe o North America and Europe separated and grew farther apart o Animals on these continents evolved in isolation and became progressively more different o In the Eocene primates we begin to see the beginning of the features that define early primatesGrasping hands and feet with nailsHindlimb dominated postureShorter snoutsEyes moved forward in the headRelatively large brains
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