Exploring Molluscs II: Nautiloids, Belemnites, & Gastropods

Exercise 7 – Molluscs II: Cephalopoda and Gastropoda Subclass: Nautiloidea Nautilus : https://skfb.ly/6AJID . This genus includes the only living cephalopods with external shells. (See Clarkson figure 8.21) A. On the image label : a. body cavity (living chamber) b. septal neck c. septum d. siphonal tube e. non-living chambers

B. Examine the straight-shelled nautiloids ( https://skfb.ly/6AFst and https://skfb.ly/6RsRE ) . Long, straight-shelled nautiloids are especially common in the Ordovician. Look for the siphuncle, siphuncular opening, septa, and camerae. Describe the characteristics that allow you to identify this specimen as a nautiloid (as opposed to some other chambered mollusc). - Banded chambers - Larger siphuncle opening - Long septa Sublcass: Coleoidea C. Examine the belemnites ( https://skfb.ly/6AvTC and https://skfb.ly/6AwGV ) and locate the following features: rostrum (or guard), phragmocone, siphuncle, septa. D. Which morphological features will you use to differentiate an orthocone nautiloid and a belemnite? Be certain that these are features you can observe. - - Belemnite has an elongated rostrum - - Belemnite septa are larger You can find images and descriptions of living members of coleoidea here: https://www.uwlax.edu/biology/zoo-lab/lab-6--molluscs/ Subclass Ammonoidea Suture patterns are useful for identification at the species level. The average complexity of sutures also increased over the evolutionary history of the Ammonoidea. For each of the specimens, identify the type of suture pattern. See Clarkson Figure 8.26. Specimen Suture type (goniatitic, ceratitic, ammonitic) https://skfb.ly/6AyI8 Oxynoticeras oxynotum https://skfb.ly/6RoIo Neoglyphioceras https://skfb.ly/6zZMr Meekoceras

H. This pyritized specimen preserves the siphuncle (circled in green), which is visible due to a gap in the exterior of the fossil. Describe the position of the siphuncle with respect to the rest of the shell. - Straight through the center to the opening I. Which morphological features will you use to differentiate a nautiloid and an ammonoid? - The siphuncle runs through the center of the septa and camerae

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Class Gastropod Anatomy Examine the gastropods at your station and find the following features on each. a. Aperture b. Apex c. Youngest Whorl d. Oldest Whorl If you have broken or sectioned gastropods, you should also be able to see the internal columella. J. Label the images on the right with the aperture, apex, youngest whorl, oldest whorl and columella. K. The specimen below (and this one here: https://skfb.ly/6ABqF ) has its operculum in place. What is the function of the operculum? - To protect the organisms form the exposed soft parts of it’s body. Acts as a lid

http://www.thefossilforum.com/uploads/monthly_2019_05/G169a.1.jpg.0ba1548f75fdfd7511ee42633ed08266.jpg Gastropod Shell Shapes L. For gastropod specimen below, label the shell shape and the direction of coiling. See Clarkson figure 8.18 for the types of shell shapes. Specimen Number Coiling direction (sinistral, dextral) Shell shape (ie. trochiform, patellate…) https://skfb.ly/6ADPn Sinistral Acteonella https://skfb.ly/6A7Vu Dextral Euomphalus https://skfb.ly/6AGoJ Dextral Tibia https://skfb.ly/6QXrn Dextral Athleta Pteropod (images below) Sinistral Euomphalus

M. Examine the scaphopods below and list the characteristics you will use to differentiate a scaphopod from gastropods and cephalopods. - Scaphopods are bilaterally symmetrical - Long and tubular shells

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Exercise 7 – Outside-of-Laboratory: Diversity Dynamics and Extinction Risk Mass extinctions are often selective and some taxa are heavily affected by mass extinctions while others are not. In this lab, we will compare the effects mass extinctions had on gastropods and cephalopods. We will compare their diversity histories as well as the dynamics of their origination and extinction patterns. To do so, we will consult the Paleobiology Database (PBDB), which is freely available online. This database is an effort among the paleontological community to create a permanent digital repository for paleontological data that allows paleontologists (and, frankly, anyone with internet access) to analyze the data. The data is “collections-based,” which means that each record consists of a number of co-occurring taxa (taxa found in the same collection) and often also has information on the geologic context in which the fossil taxa occur. Step 1: Select the data. Go to fossilworks.org/?a=home. Click download on the home page. This will take you to the “download request form.” - Where it says “your name,” enter your name or a pseudonym. This is the name of the file that will be created on the server. - Select “ species ” - Under “taxa to include” type in “gastropoda” to get the gastropod data - Under “research group or project”, select “is restricted to” and “marine invertebrate” - Click “Create data set” (This may take some time.) - Accept the terms of use. - Step 2: Download the diversity data. 1. After the page “Download results” appears, select “Generate diversity curve” at the bottom of the page and this will take you to the “Diversity curve request form.” 2. Enter the name you put in as “your name” during step one. 3. Time bins: 10 m.y. bins 4. Taxonomic level: species 5. If family or order name is missing…click yes. 6. Click on “Raw data columns” along the top of page. Select: “Midpoint Ma”, “occurrences”, “collections”, and “sampled taxa”. Deselect anything else that was pre-selected. 7. Click submit and wait for the next page to load. Scroll to the bottom and click “raw_curve_data.csv” and save a copy with the name “RawGastropodDiversity.csv.” Step 3: Check for sampling biases. Open the .csv file in Excel or another spreadsheet program. Plot the number of species against the midpoint age of the time bin as a scatter plot with connecting lines. A. In which time bin did gastropods first appear in the database? - 4 B. Which time bin has the highest diversity? - 49 Plot the number of collections against the midpoint age of the time bin. C. Which time bin has the most collections? - 49

D. Describe any similarities you see between species diversity and the number of collections. - The more number of collections, the more species diversity Make a scatter plot of collections vs. occurrences. E. What is the relationship between the number of collections and the number of fossil occurrences? - higher the number of collections, the higher the number of fossil occurrences Make a scatter plot of number of occurrences and the number of species. F. What is the relationship between number of occurrences and number of species? - more collections = more species We see these relationships because some time periods have received more attention from workers and thus more collections from those time periods have been input into the database – this is researcher bias. There may also be more collections from some time periods due to rock availability. Either way, the more fossil collections there are in the database for a given time period, the more fossil occurrences there will be and the more likely it is that a species will be added to that time period. This can drive up diversity just because collections were input for that time period and not because there were actually more species of gastropods in the world. Step 4: Correct the data for number of occurrences. A method that is commonly used by paleontologists is called rarefaction . This is a statistical procedure that allows prediction of how many genera would probably have been found if fewer occurrences had been sampled. It allows us to compare the diversity in different time bins after controlling for sample size so all time bins are judged on equal footing. Click on “Analyze” at the top of the page and select “Generate Diversity Curve Data” to get back to the diversity request form. 1. Enter your name or pseudonym from above. 2. Then click on the bar that says “subsampling options.” 3. Under “sampling method” select “classical rarefaction.” 4. For “sampling quorum” type in 40 – this is the number of specimens you will subsample for each time bin. 5. For “number of subsampling trials,” select 100 – this is the number of times you will subsample the same time bin to get an average diversity. 6. Click on the “subsampling columns” bar. Select what information will be derived from your data set. We will need: “Midpoint (Ma)”, “Items Sampled”, “Mean Sampled Diversity”. Make sure only what you want is selected. 7. Hit submit and wait for the page to load. Click on the bar that says “Subsampled data.” Scroll to the bottom and click “subsampled diversity curve” and save a copy of the data with the name “SubsampledGastropodDiversity.csv”

Step 5: Plot your rarefied diversity curve. Open your subsampled diversity data in Excel (or another spreadsheet program) and plot mean sampled diversity against midpoint age. H. Focusing on the shapes of the raw diversity curve and the subsampled diversity curve (not the absolute values of the number of genera), describe the major differences between the two curves. What could explain these differences? - Extinction events I. Describe the major diversity changes in the Gastropoda over the Phanerozoic that you observe in the rarefied diversity data. Step 6: Repeat steps 1-5, replacing “Gastropoda” with “Cephalopoda.” ( Only answer the questions above for the Gastropoda data set. ) J. Describe the major diversity changes in the Cephalopoda over the Phanerozoic you observe in the rarefied diversity data. Compare and contrast these changes to those you observed in the Gastropoda data set. K. Examine your subsampled data spreadsheets for both Gastropoda and Cephalopoda. Note that range-through diversity is always higher than sampled diversity. Why would this be?

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The diversity of a taxonomic group is a result of the combination of origination and extinction. For example, diversity could decline because extinction rates intensified or because there were fewer new species originated during a time of background extinction rates. The number of species present affects the number of extinctions and originations that occur. If we want to compare the intensity of extinction or origination between time bins, we need to standardize for the number of species present. Step 7. Range through gives us the number of taxa that must have existed during that time bin somewhere in the world even if that taxon was not sampled by actual collections in that time bin. Thus, to give the rates of origination and extinction, we will divide the number of first appearances and last appearances, respectively, by the number of range though taxa. Create two new columns titled “origination rate” and “extinction rate” and calculate those rates. Step 8. On a single chart, plot the range through diversity, per taxon origination rate, and per taxon extinction rate against time (“midpoint Ma”) for one data set. Use the scatterplot with connecting lines option. Scale the x-axis from 600 to 0 Ma. Do not include the first and last time bins, or time bins with “NA” calculations, on your plots. Step 9. Repeat steps 7-8 for your other data set. You should now have two plots telling you about the diversity dynamics of gastropods and cephalopods through the Phanerozoic. Using that information, answer the following questions. L. What is the range of extinction rates in each group? M. What is the range of origination rates in each group? N. Which group has greater variation in their diversity through time? O. Based on your answers above, which group do you think would be more vulnerable to going completely extinct? Why?

P. Find the Permo-Triassic extinction. Compare the changes in diversity, extinction rates and origination rates in gastropods and cephalopods during this extinction. Q. Given what you know about the ecology of gastropods and cephalopods, pose a reasoned hypothesis for why each were affected differently by the Permo-Triassic extinction. Explain what evidence would support and/or refute this hypothesis. R. Find the Cretaceous-Paleogene extinction. Compare the changes in diversity, extinction rates and origination rates in gastropods and cephalopods during this extinction. S. According to your data, the diversity of cephalopods has been declining since the K-Pg. Based on your data on origination and extinction rates, why is this occurring? - End-Cretaceous extinction event T. Given what you know about the morphology of modern cephalopods verses Mesozoic cephalopods, pose a reasoned alternative hypothesis for this decline.

Exercise 7_Molluscs II_Remote.docx

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