Chapter 9: From Tree Shrew to Ape
●In early Permian and Triassic, world’s fauna was mostly therapsids: diverse group of reptiles w/ traits that linked them to later mammals
●End of Triassic: most therapsids disappeared, dinosaurs radiated to fill large terrestrial animal niches
○One therapsid lineage evolved and diversified to become first mammals
●Early mammals: small, nocturnal, feeding on seeds and insects
○Internal fertilization but laid eggs
■Placental and marsupial mammals evolved by 65Mya
●Extinction of dinos at beginning of the Cenozoic → mammal adaptive radiation
○All contemporary mammals evolved from something similar to a shrew
●Modern humans have many complex adaptations
○Bipedal locomotion
○Grasping hands
○Language and toolmaking
○Cooperation
Continental Drift and Climate Change
●Important to understand geologic, climatic, and biological conditions under which evolution of humans occurred
●Changing enviro changes our interpretation of fossil record
○What is adaptive in one enviro may not be adaptive in another
●The position of the continents have changed in relation to one another and to the poles
○Continental Drift: movement of continents over time
○~300mya all land on Earth was Pangaea
■Pangaea broke apart ~180mya into northern half Laurasia and southern half Gondwanaland
●Continental drift is important to human history because:
○Oceans serve as barriers that isolate species from others
○Continental drift → climate change → influences human evolution
●Size + orientation of comtinents effect climate
○Large continents tend to have more extreme weather
Methods of Paleontology
●Bones of dead organisms may be preserved long enough for organic material to be replaced by minerals ( mineralization) from the surrounding rock
○These natural copies of bones are called fossils
●Most of what we know about history of human lineage comes from fossils ○Can tell us what we ate, how big we were, where we lived, how we moved, and how we lived
●Radiometric Methods: important method of dating fossils
○All atoms of a particular element have same number of protons in their nucleus
○Different isotopes of an element have diff numbers of neutrons in nucleus
○Radiometric methods use the fact that isotopes are unstable
■Spontaneous changes ( radioactive decay ) occurs at constant, clocklike rate that can be measured with precision
●Kinds of radiometric methods:
○Potassium-Argon Dating: used to date age of volcanic rocks found in association with fossils
■Molten rock is at a temperature at which argon gas gets boiled out → any argon left in the rock afterward must be due to decay of potassium
■Decay occurs at known and constant rate → can use ratio of potassium and argon to date the rock
○Argon-Argon Dating: newer method of Potassium-Argon dating where potassium is converted to argon isotope first for more accurate dating
○Carbon 14 Dating (Radiocarbon Dating): based on unstable isotope of carbon that living organisms 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 the 2 isotopes in the atmosphere
■Once animal dies, carbon-14 decays into nitrogen-14 at constant rate
■Can measure ratio of carbon-12 to carbon-14 to estimate amount of time that has passed since organism’s death
○Thermoluminescence Dating: based on effect of high-energy nuclear particles traveling through rock that come from decay of radioactive material in the rock and cosmic rays from space
■When nuclear particles pass thru rock, they dislodge electrons from atoms so electrons get trapped elsewhere in rock
■Heating a rock relaxes the bonds holding it together and the trapped electrons get recaptured + give off light
■Can estimate number of trapped elections in flint from archaeological sites by heating them and measuring light given off
○Electron-Spin-Resonance Dating: used to determine age of apatite crystals, inorganic component of tooth enamel
■Apatite crystals form as teeth grow and have no trapped electrons
■Like burned flints, get bombarded with particles that generate trapped electrons during fossilization
■Scientists subject the teeth to variable magnetic field and measure flow of
radiation to estimate years since tooth was formed
○Uranium-Lead Dating: used to date zirconium crystals found in igneous rocks ■Uranium decay produces series of unstable elements but eventually gives
stable isotope of lead
■Measure ratio of uranium to lead to date the crystal
●Stratum: geologic layer
●Some methods work well for fossils from distant past
○Many isotopes decay very slowly → does not work for recent fossils
○Potassium-argon dating used for samples more than 500,000 years old
●Carbon-14 isotopes decay quickly and are used for recent fossils
●Thermoluminescence and electron-spin resonance used for sites that are too old for carbon-14 but too young for potassium-argon
●Radiometric dating issues:
○Particular site may not always contain material appropriate for radiometric dating
○Relatively large margins of error
●Use other relative methods for dating fossils to supplement radiometric dating
○Every once in a while, Earth’s magnetic field reverses itself
■When certain rocks are formed, they record direction of Earth’s magnetic field at that time
■Can match pattern of magnetic reversal at particular sites with well-dated sequences from other parts of the world to date sites
○Sometimes fossils are found in association w/ other fossils that only existed for a limited period of time
Evolution of Early Primates
●During early Mesozoic, forests were dominated by gymnosperms (trees similar to redwood/pine that produces seeds but no flowers/fruit)
○During cretaceous, flowering plants ( angiosperms) appeared + spread
■→ new ecological niches
●Angiosperms depend on animals to pollinate them or entice animals to disperse seeds by surrounding them with nutritious fruits
●Primates were one group that evolved to take advantage of new opportunities from angiosperms
●Plesiadapiforms: group of fossil animals found in what is now MT/CO/NM/WY that indicate what early primate ancestors were like
○Varied in size from shrew-like to marmot-sized
○Likely solitary quadrupeds with well-developed sense of smell and varied diets
○Claws, no stereoscopic vision
○Possess some but not all of traits associated w/ modern primates → NOT classified as primates but are considered a direct ancestor
●Theory that forward-facing eyes/binocular stereoscopic vision, grasping hands/feet, and nails all evolved together to enhance visually directed predation
○Supported by fact that many arboreal predators today have front facing eyes
○However grasping hands and feet evolved in a different species before eyes shifted forward
●In early Permian and Triassic, world’s fauna was mostly therapsids: diverse group of reptiles w/ traits that linked them to later mammals
●End of Triassic: most therapsids disappeared, dinosaurs radiated to fill large terrestrial animal niches
○One therapsid lineage evolved and diversified to become first mammals
●Early mammals: small, nocturnal, feeding on seeds and insects
○Internal fertilization but laid eggs
■Placental and marsupial mammals evolved by 65Mya
●Extinction of dinos at beginning of the Cenozoic → mammal adaptive radiation
○All contemporary mammals evolved from something similar to a shrew
●Modern humans have many complex adaptations
○Bipedal locomotion
○Grasping hands
○Language and toolmaking
○Cooperation
Continental Drift and Climate Change
●Important to understand geologic, climatic, and biological conditions under which evolution of humans occurred
●Changing enviro changes our interpretation of fossil record
○What is adaptive in one enviro may not be adaptive in another
●The position of the continents have changed in relation to one another and to the poles
○Continental Drift: movement of continents over time
○~300mya all land on Earth was Pangaea
■Pangaea broke apart ~180mya into northern half Laurasia and southern half Gondwanaland
●Continental drift is important to human history because:
○Oceans serve as barriers that isolate species from others
○Continental drift → climate change → influences human evolution
●Size + orientation of comtinents effect climate
○Large continents tend to have more extreme weather
Methods of Paleontology
●Bones of dead organisms may be preserved long enough for organic material to be replaced by minerals ( mineralization) from the surrounding rock
○These natural copies of bones are called fossils
●Most of what we know about history of human lineage comes from fossils ○Can tell us what we ate, how big we were, where we lived, how we moved, and how we lived
●Radiometric Methods: important method of dating fossils
○All atoms of a particular element have same number of protons in their nucleus
○Different isotopes of an element have diff numbers of neutrons in nucleus
○Radiometric methods use the fact that isotopes are unstable
■Spontaneous changes ( radioactive decay ) occurs at constant, clocklike rate that can be measured with precision
●Kinds of radiometric methods:
○Potassium-Argon Dating: used to date age of volcanic rocks found in association with fossils
■Molten rock is at a temperature at which argon gas gets boiled out → any argon left in the rock afterward must be due to decay of potassium
■Decay occurs at known and constant rate → can use ratio of potassium and argon to date the rock
○Argon-Argon Dating: newer method of Potassium-Argon dating where potassium is converted to argon isotope first for more accurate dating
○Carbon 14 Dating (Radiocarbon Dating): based on unstable isotope of carbon that living organisms 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 the 2 isotopes in the atmosphere
■Once animal dies, carbon-14 decays into nitrogen-14 at constant rate
■Can measure ratio of carbon-12 to carbon-14 to estimate amount of time that has passed since organism’s death
○Thermoluminescence Dating: based on effect of high-energy nuclear particles traveling through rock that come from decay of radioactive material in the rock and cosmic rays from space
■When nuclear particles pass thru rock, they dislodge electrons from atoms so electrons get trapped elsewhere in rock
■Heating a rock relaxes the bonds holding it together and the trapped electrons get recaptured + give off light
■Can estimate number of trapped elections in flint from archaeological sites by heating them and measuring light given off
○Electron-Spin-Resonance Dating: used to determine age of apatite crystals, inorganic component of tooth enamel
■Apatite crystals form as teeth grow and have no trapped electrons
■Like burned flints, get bombarded with particles that generate trapped electrons during fossilization
■Scientists subject the teeth to variable magnetic field and measure flow of
radiation to estimate years since tooth was formed
○Uranium-Lead Dating: used to date zirconium crystals found in igneous rocks ■Uranium decay produces series of unstable elements but eventually gives
stable isotope of lead
■Measure ratio of uranium to lead to date the crystal
●Stratum: geologic layer
●Some methods work well for fossils from distant past
○Many isotopes decay very slowly → does not work for recent fossils
○Potassium-argon dating used for samples more than 500,000 years old
●Carbon-14 isotopes decay quickly and are used for recent fossils
●Thermoluminescence and electron-spin resonance used for sites that are too old for carbon-14 but too young for potassium-argon
●Radiometric dating issues:
○Particular site may not always contain material appropriate for radiometric dating
○Relatively large margins of error
●Use other relative methods for dating fossils to supplement radiometric dating
○Every once in a while, Earth’s magnetic field reverses itself
■When certain rocks are formed, they record direction of Earth’s magnetic field at that time
■Can match pattern of magnetic reversal at particular sites with well-dated sequences from other parts of the world to date sites
○Sometimes fossils are found in association w/ other fossils that only existed for a limited period of time
Evolution of Early Primates
●During early Mesozoic, forests were dominated by gymnosperms (trees similar to redwood/pine that produces seeds but no flowers/fruit)
○During cretaceous, flowering plants ( angiosperms) appeared + spread
■→ new ecological niches
●Angiosperms depend on animals to pollinate them or entice animals to disperse seeds by surrounding them with nutritious fruits
●Primates were one group that evolved to take advantage of new opportunities from angiosperms
●Plesiadapiforms: group of fossil animals found in what is now MT/CO/NM/WY that indicate what early primate ancestors were like
○Varied in size from shrew-like to marmot-sized
○Likely solitary quadrupeds with well-developed sense of smell and varied diets
○Claws, no stereoscopic vision
○Possess some but not all of traits associated w/ modern primates → NOT classified as primates but are considered a direct ancestor
●Theory that forward-facing eyes/binocular stereoscopic vision, grasping hands/feet, and nails all evolved together to enhance visually directed predation
○Supported by fact that many arboreal predators today have front facing eyes
○However grasping hands and feet evolved in a different species before eyes shifted forward
