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Chapter 9

Chapter 9 From Tree Shrew to Ape

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McMaster University
Jon Stone

Chapter 9 From Tree Shrew to Ape I) Continental Drift and Climate Change a. The world having become colder and drier in the last 20 myrs and particularly variable in the last 800kys is the reason that natural selection made us, if remained warm we would still monkey like b. Continental Drift – The movement of the continents i. Pangaea- all landmass together ~ 200 mya ii. Laurasia – NA and Eurasia + Gondwanaland – SA, SAf, Antarctica, Australia, India ~ 150 mya iii. By 65.5 mya, supercontinents had broken off into pieces iv. Oceans act as barriers preventing gene flow, allowing speciation c. Climate changed dramatically in last 65 my first becoming warmer and less variable and then cooling and finally fluctuating d. Deeps see cores can help reconstruct climate by looking at ration of O16 to O18 O18 H2O is heavier and more prevalent in warmer climates II) The Methods of Paleontology a. Paleontologists look primarily at fossils to gain knowledge b. Several Types of radiometric dating – it is based on the fact that certain isotopes of elements are radioactive/unstable and can use the rate of decay and ratios to calculate the age of fossils. Different techniques work for different periods. i. Potassium-Argon Dating – used to figure out age of volcanic rock near fossils, as lava comes out all the argon escapes as gas, so any argon in the material must have come from the decay of potassium after lava cooled. (another more precise method is Ar-Ar dating) >500000 y ii. Carbon 14 dating – As long as animal is alive, ratio of C12 to C14 will be same as in atmosphere. Soon as animal dies C14 will convert to N14 at constant rate <40000 y iii. Thermo-luminescence dating- high-energy particles dislodge electrons from orbit and trap them elsewhere in rock lattice. Heating a rock relaxes the bonds holding the e- and they are recaptured by the atoms giving off light. Using data of density of high-energy particles, can estimate length of time since rock ex. flint was burned. iv. Electron-Spin-Resonance dating- used to determine age of apatite crystals (inorganic component of tooth enamel that forms as teeth grow). Electrons are trapped in it, and subjecting to a variable magnetic field can allow estimating number of electrons trapped in the teeth. Then using radiation data from the site, age can be determined. v. Uranium-Lead dating- used to measure age of zirconium crystals by using the rate of decay of uranium to stable isotope of lead c. Radiometric dating has large error margin material may not always be appropriate for it and so is supplemented by relative dating methods based on magnetic pole reversal and comparison with other fossil assemblages i. Pole change is recoded creates pattern in rock formation, so can use pattern at sight to compare with well sequenced pattern elsewhere to date sites ii. Some known species existed only for limited time so if they are found with fossils of interest, the fossil of interest must have existed between their age parameters III) The Evolution of Early Primates a. Evolution of Angiosperms (evolved after Gymnosperms) created a new set of ecological niches. Primates were one of animals to fill these niches. Angiosperms entice animals to disperse their seeds by providing nutritious and easily digestible food. Arboreal animals that could find, manipulate, chew and digest these fruit exploited these niches. Primates, birds, insects etc. b. The ancestor of modern primates were small-bodied nocturnal quadrupeds much like contemporary shrews i. Plesiadapiforms 65 -64 mya 1. Shrew to marmot in size 2. Solitary , well developed smell sense 3. Teeth variable  variety of dietary specializations some arboreal quadrupeds, some terrestrial, some gliders ii. C. simpsoni 56 mya, type of plesidapiform that had opposable thumbs but lacked many traits that characterize modern primates c. Discovery of C. simpsoni helps explain why natural selection favoured basic features of primate morphology. Possible theories: i. Forward facing binocular eyes, grasping hands and feet, and nails all evolved together to enhance visually directed predation on insects ii. Grasping hands and feet + flat nails = easier leaping locomotion iii. Enhance ability to exploit new areas of plant resources iv. ***Grasping hands and feet allowed early primates to forage on fruits flower and nectar on terminal branches. Later eyes were shifted forward to facilitate visually directed insect predation d. Primates with modern features appeared in the Eocene Epoch (54-34 mya) i. Weather warm and wet- tropical forests. Most continents had some contact accept for SA which was isolated 200 fossils have been identified of strepsirrhines ii. Eocene primates were highly successful and diverse iii. They had grasping hands and feet with nails instead of claws, hind limb dominated posture, shorter snouts frontal vision and relatively large brains iv. 2 families: 1. Omomyidae a. large orbitals so prob nocturnal b. Variable dentition frugivory-insectivory c. Elongated calcaneus bones – leap from branch to branch 2. Adapidae a. Smaller eye o
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