Trends in Ammonite Shell Shape Over Time
Lindsey Howard
Author
08/03/2021
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Description
Study of change in Ammonite shell shape over time.
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- [00:00:00.810]Hello. My name is Lindsey Howard.
- [00:00:02.790]I'm a senior studying animal biotechnology and biology at UNL. This summer,
- [00:00:07.620]I took part in the UCARE research program,
- [00:00:10.170]studying the trend in ammonite shell shape over time.
- [00:00:15.930]Ammonites are an extinct cephalopod species related to octopuses and squids.
- [00:00:20.850]Ammonites lived in a wide variety of environments for a long period of time. As
- [00:00:25.380]seen in the photo to the right,
- [00:00:27.000]these animals also had dramatic and intricate shell designs,
- [00:00:30.240]which help with the identification of the specimen.
- [00:00:33.180]These are all reasons why ammonite are a great zonal specimen so that all
- [00:00:37.110]groups are used to date beds and fossils in a noninvasive way.
- [00:00:44.160]My goals for this project were to examine the collections for species diversity
- [00:00:49.020]and collect basic data on invertebrate fossil specimens,
- [00:00:53.400]to quantify the trends in shell shape of Ammonites in the collections over
- [00:00:57.120]different areas and to assess which intervals of time are better sampled than
- [00:01:01.230]others. Some more goals were to develop Excel knowledge, learn to use R code,
- [00:01:06.180]to process large amounts of data in a timely manner,
- [00:01:09.240]and to develop a hands-on skill to measure and examine specimens.
- [00:01:16.840]Different shell shape types were better evolved for different areas of the water
- [00:01:20.440]column. Ammonites had three overall shell shape types. The first,
- [00:01:25.120]serpenticone, was very narrow and floated near the top.
- [00:01:28.510]The second, sphereocone, was very bulbous with an overinflated shell.
- [00:01:32.890]This type tended to be lower in the water column. The final shape was oxycone,
- [00:01:37.390]which stayed primarily in the shallower, more shelf like,
- [00:01:40.450]part of the water column. On the right is a ternary plot,
- [00:01:45.520]which I use to plot my data.
- [00:01:47.230]These graphs were used when comparing three different data types. On the top left
- [00:01:51.610]it's the serpenticone shell type. These Ammonites have an exposed umbilicus,
- [00:01:56.590]which is the hole in the center of the shell.
- [00:01:58.990]This shell type had difficulty swimming. So it used a plankton hunting style.
- [00:02:03.250]This is a passive swimming style that uses currents to move. The top right
- [00:02:07.660]is the bulbous spherocone.
- [00:02:09.340]This shell had a covered in umbilicus and relied on a vertical migrant
- [00:02:13.090]swimming style to hunt.
- [00:02:14.890]The bottom shell shape is the oxycone. Oxycone had a covered umbilicus like
- [00:02:19.840]the sphereocone but was much more compressed.
- [00:02:22.570]This shell shape was great for an active or nektonic hunting and swimming
- [00:02:27.100]style.
- [00:02:29.500]I use the Westerman Morphospace method to measure the shells.
- [00:02:33.040]This included measuring the length and width of the whorls,
- [00:02:35.890]and then applying simple equations to stabilize the data.
- [00:02:41.290]For my UCARE project,
- [00:02:43.060]I first combed through the invertebrate paleontology collections for proper
- [00:02:47.650]Ammonite specimens.
- [00:02:49.180]I then measured and collected data from a wide variety of the specimens. In total,
- [00:02:53.650]163. Finally,
- [00:02:56.050]I used Excel equations in R code to transfer data to an
- [00:03:00.700]understandable graph.
- [00:03:06.110]As you can see on this slide,
- [00:03:07.550]there was a large range in the amount of data I was able to collect over the
- [00:03:11.840]different periods.
- [00:03:13.190]The most was Cretaceous at 74 and the smallest was Jurassic at only
- [00:03:17.870]six.
- [00:03:20.330]I expected to find a trend in overall shell shape change over time.
- [00:03:25.220]I also expected to find clear data trends in eras that have a larger number of
- [00:03:29.690]specimens collected versus eras that have a smaller number of
- [00:03:34.340]collected specimens.
- [00:03:39.110]So first off is the Carboniferous. The Carboniferous data trended towards
- [00:03:43.310]oxycoone with one outlier near the serpenticone. On the right is a
- [00:03:48.020]map of the world during the Carboniferous as shown with the yellow circle, the
- [00:03:52.580]specimens used were from the shallower waters off of Laurentia.
- [00:03:59.090]The Permian data also trended towards Oxycone.
- [00:04:02.000]These were also drawn from shallow waters,
- [00:04:04.310]this time off of the supercontinent Gondwana
- [00:04:08.870]Triassic had more data points,
- [00:04:10.910]so the trend towards Oxicone was even more obvious.
- [00:04:14.180]These specimens were also from a shallower ocean system off of Pangea.
- [00:04:21.200]There weren't many points found for Jurassic,
- [00:04:23.450]but those that I did collect pointed once again for oxycone.
- [00:04:27.230]These specimens were from a central sea in Laurasia.
- [00:04:34.520]The Cretaceous period had the most data points and was pretty central with some
- [00:04:38.870]points. The trend, however, was still for oxycone.
- [00:04:42.290]These were from the Midwestern Seaway,
- [00:04:45.080]which is now Nebraska and the surrounding states
- [00:04:51.080]As shown on the right, the trends for all of the eras was for oxycone.
- [00:04:55.280]This is not what I was expecting.
- [00:04:57.050]I was expecting a change in the trends over time as the ocean and prey type
- [00:05:01.520]changed. On the left is my graph.
- [00:05:06.380]And on the right is a Ritterbush outcome. As you can see,
- [00:05:09.950]Ritterbush had a more even trend style while
- [00:05:12.410]mine was much more heavily oxycone.
- [00:05:16.880]I believe this is because most of our specimens came from shallow marine
- [00:05:20.660]environments. Nektonic may be the best swimming style for these environments
- [00:05:24.710]no matter the time or temperature.
- [00:05:29.390]What will I do next?
- [00:05:31.010]I want to apply my data to the University of Nebraska State Museums collections
- [00:05:35.540]digitization effort.
- [00:05:37.340]I want to continue developing understanding of coding to help process large
- [00:05:41.240]amounts of data in the paleontological field.
- [00:05:44.480]I also would like to continue the study of Ammonite shell shape change over
- [00:05:48.470]time, using a wider variety of collections,
- [00:05:51.680]including those that include a larger number of Jurassic and Devonian specimens.
- [00:05:57.860]Finally, I would like to acknowledge and thank Dr.
- [00:06:00.800]Peter Wagner for giving me the guidance I needed to develop and work through
- [00:06:04.610]this project. Along with his assistance in the R code aspect of the work,
- [00:06:08.930]I would also like to thank Dr.
- [00:06:10.460]Robert Diffindal for his assistance and knowledge of the collections.
- [00:06:14.510]I would finally like to thank Miss Justina Clark and the UCARE team for their
- [00:06:18.800]advice over the summer and for giving me the opportunity to work on this project.
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