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Quantifying morphological variability through the latest ontogeny of Hoploscaphites (Jeletzkytes) from the Late Cretaceous Western Interior using geographic information systems as a morphometric tool

Knauss, Mathew J.
http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1370375799

Abstract Details

2013, Master of Science (MS), Bowling Green State University, Geology.
Ammonoids are known for their intraspecific and interspecific morphological variation through ontogeny, particularly in shell shape and ornamentation. Many shell features covary and individual shell elements (e.g., tubercles, ribs, etc.) are difficult to homologize, which make qualitative descriptions and widely-used morphometric tools inappropriate for quantifying these complex morphologies. However, spatial analyses such as those applied in geographic information systems (GIS) allow for quantification and visualization of global shell form. Here, I present a GIS-based methodology in which the variability of complex shell features is assessed in order to evaluate evolutionary patterns in a Cretaceous ammonoid clade. I applied GIS-based techniques to sister species from the Late Cretaceous Western Interior Seaway: the ancestral and more variable Hoploscaphites spedeni, and descendant and less variable H. nebrascensis. I created digital models exhibiting the shells’ lateral surfaces using photogrammetric software and imported the reconstructions into a GIS environment. I used the number of discrete aspect patches and the 3D to 2D area ratios of the lateral surface as terrain roughness indices. These 3D analyses exposed the overlapping morphological ranges of H. spedeni and H. nebrascensis, with H. nebrascensis specimens exhibiting similar ornamentation to the most ornate H. spedeni. In order to assess more specific shell characters, I digitized the tubercles (points), ribs (polylines) and shell shape (polygons) of select specimens from photographs for 2D analyses. These 2D analyses revealed that the distribution of ribs and the shape of the body chambers are fairly constrained in at least H. spedeni, and the distribution of tubercles is the most variable feature through ontogeny between both Hoploscaphites species. The results of the GIS-based spatial analyses demonstrated that the target for evolutionary change in this clade resides in the macroconch body chamber. Additionally, the results support the hypothesis that H. nebrascensis is a paedomorphic descendant of H. spedeni, derived by means of prolonged tubercle expression through later ontogenetic stages. H. nebrascensis microconchs retain developmental flexibility, and the macroconchs are more constrained. These geospatial analyses not only successfully quantified variability in complex morphologies, but also demonstrated the versatility of this method to address questions related to ontogeny and phylogeny.
Margaret Yacobucci (Advisor)
Enrique Gomezdelcampo (Committee Member)
Sheila Roberts (Committee Member)
159 p.
Biology; Geographic Information Science; Geology; Paleontology
Ammonoid; GIS; Ontogeny; Intraspecific Variation

Recommended Citations

Citations

  • Knauss, M. J. (2013). Quantifying morphological variability through the latest ontogeny of Hoploscaphites (Jeletzkytes) from the Late Cretaceous Western Interior using geographic information systems as a morphometric tool [Master's thesis, Bowling Green State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1370375799

    APA Style (7th edition)

  • Knauss, Mathew. Quantifying morphological variability through the latest ontogeny of Hoploscaphites (Jeletzkytes) from the Late Cretaceous Western Interior using geographic information systems as a morphometric tool. 2013. Bowling Green State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1370375799.

    MLA Style (8th edition)

  • Knauss, Mathew. "Quantifying morphological variability through the latest ontogeny of Hoploscaphites (Jeletzkytes) from the Late Cretaceous Western Interior using geographic information systems as a morphometric tool." Master's thesis, Bowling Green State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1370375799

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Bowling Green State University and OhioLINK.