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A Geometric Morphometric Study of Two Groups of Pteridinium from the Latest Neoproterozoic

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A Geometric Morphometric Study of Two Groups of Pteridinium from the Latest Neoproterozoic University of South Florida Scholar Commons Graduate Theses and Dissertations Graduate School 8-13-2009 How Plastic is Vendobionta Morphology? A Geometric Morphometric Study of Two Groups of Pteridinium From the Latest Neoproterozoic Michael B. Meyer University of South Florida Follow this and additional works at: https://scholarcommons.usf.edu/etd Part of the American Studies Commons Scholar Commons Citation Meyer, Michael B., "How Plastic is Vendobionta Morphology? A Geometric Morphometric Study of Two Groups of Pteridinium From the Latest Neoproterozoic" (2009). Graduate Theses and Dissertations. https://scholarcommons.usf.edu/etd/1713 This Thesis is brought to you for free and open access by the Graduate School at Scholar Commons. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. How Plastic is Vendobionta Morphology? A Geometric Morphometric Study of Two Groups of Pteridinium From the Latest Neoproterozoic by Michael B. Meyer A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology College of Arts and Sciences University of South Florida Major Professor: Peter Harries, Ph.D. Gregory Herbert, Ph.D. Jonathan Wynn, Ph.D. Date of Approval: August 13, 2009 Keywords: Ediacaran, Nama, Namibia, North Carolina, Terrane © Copyright 2010, Michael B. Meyer Acknowledgements I would like to thank all of my committee members, especially my advisor Peter Harries for helping me put together this thesis. I would also like to thank Jennifer Sliko for being patient in the making and editing of this presentation and its associated thesis, I couldn’t have done it without you; also to my parents for always supporting me, whatever my goal. Finally, the following individuals have helped me significantly (in no particular order): Gregory Herbert, Jonathan Wynn, Dolf Seilacher, Gail Gibson, Steve Teeter, Chris Tacker, Patricia Weaver, Patricia Vickers-Rich, The Erni’s (of Namibia), Roger Portell, the entire administrative staff in the department, and my gregarious Lab Mates. Table of Contents List of Tables ii List of Figures iii Abstract v Introduction 1 Geology and History of the Ediacaran 2 Geology of the Ediacaran 2 Previous work on Pteridinium 8 Description of Pteridinium morphology 8 Pteridinium Species 9 Pteridinium habitat and life habit 12 Geologic setting and Pteridinium Preservation 14 Namibia 14 North Carolina 16 Geometric Morphometrics 18 Landmarks 19 Methods 21 Image and Data Acquisition 22 Statistical Tests 25 Analysis 27 Results of Statistical Tests 29 Discussion 34 Conclusion 39 References 40 i List of Tables Table 1 Specimen Information 21 Table 2a Pteridinium Eigenvalues 29 Table 2b Piranha Eigenvalues 29 ii List of Figures Figure 1a. Composite Neoproterozoic carbon isotope record 3 Figure 1b. Correlation of global Neoproterozoic successions 4 Figure 2. Mat ecology during the Precambrian 5 Figure 3a. Cyanobacterial mat types 5 Figure 3b. Ediacaran “Death Mask” Preservation 7 Figure 4. Quilted Ediacaran fossils 8 Figure 5. Pteridinium simplex 9 Figure 6a. Two different inferred growth paths for Pteridinium 10 Figure 6b. Linear regression of Seilacher’s original data 11 Figure 6c. Two leading hypothesized Pteridinium life position 13 Figure 7. Map of Namibia 14 Figure 8. Seilacher Slab 15 Figure 9a. North Carolina Map 16 Figure 9b. Column and Map of Stanly County 17 Figure 10. Traditional Morphometric measurements on a Trilobite 18 Figure 11. Non-homologous width measurements on two Arthropods 19 Figure 12. Landmark Types 20 Figure 13. Photo setup 23 Figure 14a. Photo setup, position A 24 iii Figure 14b. Photo setup, position B 24 Figure 15a. Procrustes deformation vectors for Namibian samples 26 Figure 15b. Procrustes deformation vectors for North Carolina samples 27 Figure 16. Landmark placement on Pteridinium 27 Figure 17a. General Procrustes centroid of all samples 30 Figure 17b. Mean Procrustes centroids of the two groups 30 Figure 17c. North Carolina landmarks 31 Figure 17d. Namibian landmarks 31 Figure 18a. Locality PCA results by specimen 32 Figure 18b. Preservational PCA results 32 Figure 18c. Taphonomic PCA results 33 Figure 19a. Landmarks from two different species of Piranha 35 Figure 19b. Mean Procrustes centroids of two species of Piranha 35 Figure 19c. PCA plot for two different species of Piranha 36 Figure 20a. PCA plot with 95% ellipse for two different localities 36 Figure 20b. PCA plot with 95% ellipse for two different taphonomic factors 37 Figure 20c. PCA plot with 95% ellipse for two different preservational factors 37 Figure 20d. PCA plot with 95% ellipse for two different Piranha species 38 iv How Plastic is Vendobionta Morphology? A Geometric Morphometric Study of Two Groups of Pteridinium From the Latest Neoproterozoic Michael B. Meyer ABSTRACT The analysis and interpretation of Vendobionta morphology is critical to elucidating a range of issues about their ontogeny and evolution, as well as life habits. These analyses, however, are complicated because these organisms are often morphologically enigmatic and defy ready categorization within modern taxonomic schemes. This study delves into the morphology of one of these problematic groups: Pteridinium. Specimens were investigated from two localities, Namibia and North Carolina, using geometric morphometrics. The landmark data, which was analyzed to compare specimens based on locality, taphonomy, and preservation, were subjected to three statistical tests: Principle Components Analysis, Procrustes shape analyses, and Foote’s disparity test. All tests revealed no distinct clustering within or by either group due to any of the variables. All variables plotted within the same 95% confidence ellipses, displaying a lack of statistical support for the distinctness of these groups. Therefore, the most parsimonious reason for the lack of differences observed by these two groups stem from them being part of the same morphological group, a conclusion that places into question the validity of the inclusion of two separate species in the genus Pteridinium. v Introduction Ediacaran fossils allow us the opportunity to investigate how the earliest preserved metazoans lived, interacted, and diversified. Such interpretations are complex as these organisms are often morphologically enigmatic and defy ready categorization within modern taxonomic schemes (Jensen et al, 1998). Therefore, researchers have an incomplete view of their biological affinities. Pteridinium (Family Petalonamae) (Gürich, 1930) has been the focus of taxonomic studies due to its unique quilted, triple-bladed morphology (Fedonkin, 1992; Ivantsov and Grazhdankin, 1997; Gehling, 1999; Seilacher and Grazhdankin, 2002). While currently there are only two formally recognized species within the genus, P. simplex and P. carolinaensis (Gürich 1930, 1933; Richter 1955; Glaessner 1963, Seilacher, 1999), in the past decade discoveries of new quilted/multi- bladed Neoproterozoic organisms have initiated a debate as to what characteristics differentiate Pteridinium from other Ediacaran genera, such as Onegia nenoxa or Swartpuntia. The primary features that have been used in past research to differentiate these specimens are: wall size, the mode of attachment between blades, individual quilt size, outline shape, and hypothesized life position (Seilacher and Grazhdankin, 2002; Grazhdankin, 2004). Some authors speculate that Pteridinium, as classically defined, only exists in Namibia (Grazhdankin, 2004), whereas others contend that all triple-bladed forms, regardless of location, are morphologically identical and simply represent specimens deformed during preservation or ecophenotypy reflecting variable environmental factors (Droser, 2002; McCall, 2006) In this study, material will be examined from two localities, Namibia and North Carolina, as the fossils are thought to represent two distinct species and, hence, display pronounced morphological differences between them. The morphology of Pteridinium will be investigated using geometric morphometrics. This analytical technique allows for the statistical quantification of the differences in various attributes present in these two groups utilizing a process that allows a fuller understanding of the nature of the differences and what process(es) may underlie them, including such factors as ecology, taphonomy, and metamorphism. By using geometric morphometric analysis to statistically examine the nature of the morphological variability displayed by two groups of Pteridinium, morphology unknown in extant taxa, a greater understanding can be reached as to how disparate populations of Pteridinium were related to each other. More so, a study of these two species differences, within the larger genus of Pteridinium, might help us better understand how Ediacaran organisms diversified, and how that differs from later, during the Phanerozoic. 1 Geology and History of the Ediacaran Geology of the Ediacaran The Ediacaran Period spans from the end of the Marinoan glaciation (~635 mya) to the Precambrian-Cambrian boundary, currently placed at ~542 mya. The beginning of the Ediacaran is marked by rapid global warming following the Marinoan glaciation (Fig. 1a, Halverson et al, 2005). This deglaciation is thought to be expressed by the synchronous appearance of global “cap” carbonates (Halverson et al, 2005, McCall, 2006), which overlie glacial diamictites found below them, and is believed
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