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Evolution Notes

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Biology 3466B
Yolanda Morbey

Evolution NotesOct 2011 Animals living in shallow marine environments are more likely to fossilize Fossilization is more likely to happen to molluscs because they live in marine environments and they have hard shells Describing macroevolution 1 PaleontologyThere are many types of fossils and these fossils can be dated in two ways Relative is the sequence in which organisms were present on earth Absolute is how many mya the animal lived and can be determined using radiometric dating and looking at layering in rock strata There are some sampling biases geographic animals must die in certain environments in order to fossilize taxonomic certain species with hard shells are more likely to fossilize than animals with soft bodies temporal cant find fossils from every period in earths history earths crust is changing can only go so far back Transitional forms which are links between animals may be missing and this can obscure patterns because not everything is going to fossilize The fossil record should show evidence of transformations in progress Transitional species should show a mix of features including traits typical of ancestral populations and novel traits seen later in descendants Transitional fossils document the past existence of species displaying mixtures of traits typical of what are today distinct groups of organisms They are evidence for macroevolutionWhat is the missing link between dinosaurs and birds The first link was the fossil archaeopteryxTransitional formsexample 1 Archaeopteryx was found in 1859 a year after Darwin wrote Origin of the Species It is crowsized and lived 145150 mya It had birdlike feathers and a reptilianlike skeleton characteristics of both dinosaurs and birds It is a transition between dinosaurs and birds Finding missing links creates new missing links One missing links creates two new missing links This is a problem with missing linksyou will always create new ones when you find one Transitional formsexample 2 Sinosauropteryx was a chickensized therapod with simple downlike feathers This is seen as a link between dinosaurs and archaeopteryx Transitional formsexample 3 Caudipteryx was a turkeysized therapod dinosaur with elongated feathers on hands and tails Transitional formsexample 4 Microraptor gui was a dromaeosaur dinosaur with modern flight feathers on all 4 limbs These transitional forms support an evolutionary link between dinosaurs and birds Radiometric dating is used for absolute dating It involves the radioactive decay process of isotopes Different elements have different halflives A halflife is the amount of time it takes for half of the parent isotope to degrade or decay into its daughter isotope One halflife occurs when there is 50 of parent isotope remaining Radioactive isotopes function as natural clocks because decay rates are not affected by temperature moisture or other environmental factorsIn order to do radiometric dating you need to know how much parent isotope was present when the rock was formed and you need to look at the ratio of the two isotopes present Methods such as rubidiumstrontium uraniumlead thoriumlead and potassiumargon are used to date rocks within which fossils or minerals embedded while the rock formed date rock strata These methods have long halflives and can date rocks that formed a long time ago C14 can only be used for carbonbearing material like bones and wood not rocks It has a short halflife and is used to date younger things things of recent origin100100000 years Describing macroevolution2 PhylogeneticsCan date origin of species using relative timing more recent branching is more recent origin and absolute timing Some problems with it are Sampling bias taxonomicmay know more about certain animals or taxa than others Statistical biasmethods to find trees
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