Extinction

Begin this procedure by reading the extinction reading supplement that has been printed out for you.
NOTE: Alternatively, you may download the reading supplement at the link below.  Click here to download the extinction reading supplement

Using the information contained in the extinction reading supplements pertaining to the taxa of interest and the Chicxulub impact event, make predictions for each taxon listed in Table 1. Consider whether diversity in each taxon increased, decreased, or stayed the same immediately following the Cretaceous-Paleogene boundary and later on in the Paleogene epoch. Click Here to download Table 1

Then, fill out the reasons for each of your predictions in the Contributing Factors column. HYPOTHESES: The experimental hypothesis is that many of the different taxa will show changes in diversity after the Cretaceous-Paleogene event, and again at the end of the Paleogene, with some increasing in diversity, while others decrease. The null hypothesis is that there will be no changes in diversity between taxa following the Cretaceous-Paleogene event, or at the end of the Paleogene.

Gather diversity data by going to the Paleobiology Database: www.paleobiodb.org.

In the center of the screen, click the yellow box labeled Download Data. Under the italicized heading, “What do you want to download?”, select Diversity over time on the left side and Comma-separated values on the right side.

Scroll down to the heading “Select by taxonomy”.

In the first box labeled 'Taxon or taxa to include', type in the name of the taxon that data is being gathered on. NOTE: Ensure the spelling is correct.

Now, go to the dropdown menu right below that box labeled “Taxonomic resolution”, and select genera.

Under the next heading, Select by time, type Maastrichtian into the first box and Chattian in the box directly below. Make sure the dropdown menu labeled Time rule is set to major and the Temporal resolution is set to stage.

Select “Assume extant taxa range through to present”. Scroll back up to the middle of the page and click download. A save window will open.

Save the .csv file to a safe and accessible place and rename it to make it easy to identify.

Open the file and scroll down to the main dataset under Records. NOTE: The data are arranged in reverse time order by geological stage. The second column, interval_name, gives the accepted name of the stage in question. The next two columns give the appropriate dates of the stage in millions of years before the present. The final column, number of occurrences, gives a total count of the genera extant during that geological stage as determined from occurrence of fossils.

To more easily work with this data, copy and paste each column into a new sheet. Be sure to label this sheet with the taxon in question, the data and time the data were obtained, and the data source.

Repeat this process for each of the taxa in Table 1 (steps 4 – 12). NOTE: Data from multiple taxa can be kept on the same sheet, so long as they are kept distinct and labeled appropriately.

To create line plots for each of the taxa showing the change in diversity over time, select the max_ma column and the number of occurrences column simultaneously.

In Excel, select Insert from the top toolbar and find the section labeled Charts. Select the bottom center icon, Insert Scatter Chart.

Then, select the Scatter with Straight Lines and Markers and a graph should appear. NOTE: Since the axis of this graph is in units of millions of years ago, the axis is in the reverse direction of time when put in numerical order.

To fix this, click on the green plus sign in the top-right corner of the graph and hover over Axes. This should reveal a small black arrow. Click the arrow to open up a small menu and select More Options.

This will open the Axis Options menu. Under Axis Options, click the box next to Values in reverse order. NOTE: It is also possible to change the axis scales from this menu, which can be used to eliminate the excess time that is not being analyzed in this lab. Keep any changes consistent between different graphs.

Double-click on the title at the top of the graph and change it to the taxon being represented.

Make a separate graph for each of the taxa in Table 1. Keep them organized and in one location. A separate sheet for graphs is recommended.

For each graph, identify the location of the Cretaceous-Paleogene boundary and draw a vertical line through the graph at this point.

Using the information from the graphs, fill out Table 2. In some cases, it may be helpful to go back to the original dataset and compare actual values, particularly when they are small. Click Here to download Table 2

Compare these values to the predictions made in Table 1 and discuss if the original contributing factors are still likely candidates.

Using the dataset, calculate the percentage of total taxa that went extinct over the Cretaceous-Paleogene boundary using this equation.

There is an event in the middle of the Paleogene known as the Paleocene-Eocene Thermal Maximum about 55.5 million years ago. This represents a high point in temperature during the Paleogene epoch at approximately 8 °C higher than today's average temperature. Does this point seem to have an effect on diversity for any of the taxa? If yes, then which ones?