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---------------------------------------------------------------------------------------------------------------------Counting Critters: Using the PBDB to track fossil diversity and extinction through geologic timeIntroductionOne of the most fundamental questions we can ask in geology is how the diversity of life has changed over time. Data on the diversity of organisms in the fossil record make it possible to identify intervals of mass extinction and origination, determine how climate change has affected diversity in the past, and gain perspective on the loss of biodiversity in modern ecosystems.To do this, paleontologists track the occurrence of fossil organisms, in other words where a species occurs in space (geographically) and when a species occurs in time (stratigraphically). The Paleobiology Database (PBDB, ) is a huge online database that seeks to catalogue all fossil occurrences, across all geologic time, and across the whole tree of life. It’s the standard tool used by paleobiologists to create diversity curves—which are visual plots of the diversity of life over time.Delving into the DatabaseOpen the PBDB Navigator and spend some time getting comfortable with how it works: Navigator consists of three parts:Map (CENTER) showing continents with dots representing fossil occurrences. The color of these dots represents their geologic age. If you click on the dots, you can see all of the information on each site and the fossil species that occur there.Geologic time scale (BOTTOM) showing the major eras, periods, and stages. If you click on the timescale, the map will show you the location of all fossil occurrences from that time interval.Tool bar (LEFT) showing the tools you can use to explore the database. These include:zoom in/out on the mapreconstruct plate tectonic configurations for time interval (era or smaller) you are exploring narrow down which taxonomic group is plotted on mapcreate a diversity curve for the occurrences currently plotted on mapdownload the data (lat/long, geologic age, etc.) for the occurrences plotted on mapNeed help? Here’s a Youtube video to help you get started: TO STUDENTS: Several of the questions asked in this activity are open-ended and do not have explicitly right or wrong answers. These questions give you the freedom to explore this material and think about it creatively. ---------------------------------------------------------------------------------------------------------------------Part 1: Constructing a Diversity CurveGiven what you know about the early history of life on Earth, predict how the number of organisms would change over the past 500 million years. 259242034957Would it increase, decrease, or stay the same? (b) If you predicted it would change, would it change linearly (i.e., increasing or decreasing in a straight line) or exponentially (i.e., increasing or decreasing rapidly towards today) or in another pattern? (c) Sketch the pattern you expect to see on the graph to the RIGHT. Now, use the PBDB Navigator to develop a diversity curve—for all organisms, globally, throughout the past 500 million years. To do this, Make sure that the PBDB map is as zoomed out as far as possible1647825200025Click on the icon on the toolbar on the left side of the screenFor taxonomic level, choose “genus” For temporal resolution, choose “Age” Then click on “Use advanced diversity curve generator” buttonWAIT. Please be patient, it can take 5-10 minutes to calculate all of life’s diversity through time!When a graph appears on the screen, check the box “Rangethrough diversity”UNCHECK the boxes “Sampled-in-bin diversity” and “Include singletons”(a) Does the general pattern (i.e., increasing, decreasing, staying the same, linear, exponential) match your predicted diversity curve from Question 1? (b) If no, how is it different (in detail)?Insert your diversity curve (using the “Save this image” button, then the Insert Pictures tool in Word) and make it as large as possible below. This curve displays “Rangethrough diversity”-- which assumes that each genus as present in the fossil record from its oldest occurrence to its youngest occurrence, regardless of whether or not it was actually found in the intervening intervals. Singletons are fossil genera that have only been found in one time interval. Your diversity curve does not include singletons.4. (a) Do you see any evidence for rapid increases in diversity on your graph? If so, circle these on your graph above. (b) How many did you circle?(a) Do you see any evidence for rapid decreases in diversity on your graph? If so, mark these with a star on your graph above. (b) How many did you mark with a star?Examine the earliest increase in diversity that occurs on this diversity curve. In which geologic (i.e., time) period does it occur? (b) Given this time interval, do you think this increase in diversity occurred in the ocean or on land or both? (c) Why? This sudden increase in diversity is called the “Cambrian Explosion.” Use internet sources to learn more about this particular event.(d) Do you think this increase in diversity is due to an increase in origination rates or a decrease in extinction rates or both? (e) Describe (in detail) two possible causes for this event.7. Compare the decreases in diversity that occur throughout the Phanerozoic. Examine diversity from 400 to 0 million years ago. Find the interval of time in which diversity is at its lowest from 400 to 0 million years ago. (a) Between which two geological time intervals does it occur? Need help figuring out geological periods? See the following link: event is called the end-Permian mass extinction. Use internet sources to learn more about this particular event. (b) When (approximately) did this extinction occur in millions of years?(c) What percentage of species went extinct?(d) Describe (in detail) one possible causal mechanism for this extinction.---------------------------------------------------------------------------------------------------------------------Part 2: Sampling and Preservational BiasFiguring out how biodiversity has changed over time is complicated by a number of sampling and preservational issues. Sampling issues occur when paleontologists study one time interval (or site or organism) more thoroughly than another. Poor sampling can artificially decrease estimates of diversity for a particular time interval (or site or organism). Given what you already know about the fossil record, can you identify two intervals of time that have been particularly well sampled? Why are these two well sampled?Preservational issues occur because the likelihood that an organism gets preserved in the fossil record may vary occur to time interval, site, or organism. Preservation can artificially decrease estimates of diversity for a particular time interval (or site or organism). Given what you know about fossil preservation, identify at least two groups of organisms that are likely to have a well-preserved fossil record.Why did you choose these?3. Several paleontologists have suggested that the number of singletons in a time interval should increase when sampling and preservational quality decrease. Experiment with the effects of singletons on your diversity curve by checking and unchecking the box labeled “Include singletons.” Does including singletons change the overall shape of your diversity curve? If so, how?Does including singletons change the increase in diversity at the Cambrian Explosion? If so, how?Does including singletons change the decrease in diversity at the end-Permian extinction? If so, how?4. The term “Pull of the Recent” refers to the hypothesis that biodiversity estimates are artificially inflated during more recent time intervals because: (A) older fossils are more likely to have been destroyed by taphonomic processes and (B) younger strata and organisms are easier to sample. Re-examine the diversity curve you produced in Part 1. Do you think “Pull of the Recent” has affected this curve? Why or why not?5. How could you control for “Pull of the Recent” when you develop diversity curves? Describe at least one solution that would allow you to solve this problem—either mathematically or otherwise. ................
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