Natural History collections contain primary data spanning the history of life on Earth. Much of these data remain understudied and therefore has not been integrated into our current understanding of paleontology. One such collection is the eurypterid collection at the University of Michigan Museum of Paleontology (UMMP). Last summer this material was digitized and preliminary morphometrics work was conducted. Here, we leverage the work we completed to include material from other previously published studies on eurypterid morphometrics. Specifically, we are interested in evaluating landmark placement between studies and comparing results of the two studies separately and combined. 130 specimens from the UMMP possess intact prosoma and were landmarked in the StereoMorph package in R. Four fixed landmarks and two sets of sliding landmarks along curves of the prosoma were employed. The data were analyzed using a Principal Components Analysis(PCA) and results were visualized in R using ggplot2. Previous work utilized more landmarks, which were unobtainable with the UMMP dataset. So for a viable comparison, approximately 115 specimens (those used in Bicknell and Amati 2021) from the New York State Museum and Yale Peabody were landmarked using our smaller landmark set. This allows us to examine the efficacy of different amounts and types of landmarks (fixed versus curves) and the resulting distribution in morphospace. The resulting morphospace shows a broad occupation of the genus Eurypterus, which supports previous studies. Additionally, there is a difference in distance between groups in the combined morphospace compared to previous work. This is likely due to the variation in landmarks used to capture specific aspects of the prosoma. This case study in landmark variation provides evidence that landmark selection, research question, and reproducibility should be carefully considered. Furthermore, targeted digitization of museum collections will increase mobilization of primary datasets.
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WESTERMANN MORPHOSPACE ANALYSIS OF THE CRETACEOUS AMMONOID SUPERFAMILY DESMOCERATOIDEA
Ammonoids of the Cretaceous superfamily Desmoceratoidea are geographically and stratigraphically widespread. However, the group is understudied, with just one prominent Japanese worker, T. Matsumoto, who worked on desmoceratoids extensively in the 1970s-1990s. Since then, few researchers have studied desmoceratoid taxonomy, phylogeny, or ecology. Based on their geographic distributions and typical geologic contexts, desmoceratoids are traditionally interpreted to have been open ocean dwellers. However, details of their paleoecology and mode of life are lacking, limiting our ability to interpret desmoceratoid diversity dynamics through the Cretaceous. The Westermann morphospace method is a way to predict the life mode of coiled (non-heteromorph) ammonoids based on morphological measurements of shell shape. The morphospace has three end-member morphotypes, spherocone, oxycone, and serpenticone, with predicted modes of life for different morphospace regions. Shell shape measurements were made on 112 desmoceratoid specimens from collections at the U.S. National Museum of Natural History and the Natural History Museum in London (UK); these specimens are from every continent except Australia and Antarctica. Westermann parameters were computed and specimens were plotted in Westermann morphospace so that patterns of morphospace occupation could be assessed. Desmoceratoids generally fall towards the oxycone corner of the morphospace, with genera falling into two groups, one more platyconic with predicted good swimming efficiency and one more discoconic with more limited swimming efficiency. Lewesiceras and Desmoceras have specimens in both groups, while Puzosia uniquely occupies a more central position in the morphospace. Temporally and regionally, there were no significant variations in morphology. While often interpreted as uniformly effective open ocean swimmers, these results indicate that desmoceratoid ammonoids had varying modes of life.
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- Award ID(s):
- 2129629
- NSF-PAR ID:
- 10497772
- Publisher / Repository:
- Geological Society of America
- Date Published:
- Journal Name:
- Abstracts with programs Geological Society of America
- Volume:
- 55
- Issue:
- 6
- ISSN:
- 0016-7592
- Subject(s) / Keyword(s):
- Ammonoidea Cretaceous Morphometrics
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1130/abs/2023AM-392985
