Quantifying the Functional Morphology of Productidine Brachiopods through Performance

• Author / Creator

  Dievert, Rylan V.

• Functional morphology is an important tool for paleoecology. However, functional interpretations which are based on tenuous logic without a proper test or which rely on circular reasoning can be problematic. Biomechanical tests can help to provide structured and absolute assessments of functionality and performance. But by combining multiple measures of performance, performance spaces/landscapes can be constructed. In the same way a morphospace quantifies overall morphology with multiple measurements, a performance space quantifies overall function through multiple measures of performance. By including more than one measure of performance, it becomes possible to evaluate how changes in morphology affect multiple aspects of function and performance. Thus, we can more easily identify evolutionary trade-offs and evaluate whole organism fitness. Additionally, by combining performance with additional taxonomic or environmental context it is possible to look for cases of adaptation, both as a process and as a product. In this thesis, I examine productidine functional morphology using the framework of a performance space.
  The first application of the performance space used in this thesis was to quantify adaptation as a process of evolution. By combining the performance with taxonomic context, performance across lineages can be used to evaluate whether taxonomic, and thus morphological, patterns mirror or correspond to performance patterns. In Chapter 2 I used the performance of the brachiopod superfamily Echinoconchoidea to test for adaptation. Because they are liberosessile suspensions feeders, hydrodynamic performance is expected to exert strong selective pressure on brachiopod morphology. The echinoconchoid performance space I constructed consists of 5 performance axes: 1) stability in mobile substrates, 2) stability of soft substrates, 3) feeding efficiency, 4) respiration/metabolic efficiency 5) defense against predation. This performance space was populated with eight North American genera from two families, one primitive (Sentosiidae) and one derived (Echinoconchidae). The Echinoconchidae contains two disparate subfamilies the Echinoconchinae with bands of short densely spaced spines, and the Juresaniinae with longer and variably spaced spines. I found two patterns in echinoconchoid performance. The first is a trend driven by size (r=0.85, p=0.006), in which larger echinoconchoids had increased passive feeding, proportionally smaller lophophores, and lower cost/benefit ratios for potential predators. This coincides with a general increase in echinoconchoid size through time. The second pattern is the relative spacing of genera in the performance space in which genera are distant from each other essentially “filling out” the space. This spacing suggests niche differentiation based, at least in part, on hydrodynamic performance.
  The second application of the performance space evaluated adaptation as a product of evolution. In this context, it is expected that the performance of a given organism should be at the very least consistent with environmental conditions. Combining performance and paleoenvironment serves as a test of both the functional hypotheses and as an additional test of paleoenvironmental interpretations. I constructed a performance space using genera with well-described environmental distribution patterns from the late Paleozoic of the North American Mid-continent. I chose three performance variables reflecting environmental variables: 1) stability in high velocity flow over mobile substrates, 2) stability on soft muds in calm water 3) respiration potential using lophophore (the brachiopod feeding and respiration apparatus) size as a proxy. This study included genera from all three productidine superfamilies. For this study, I chose eight genera: two associated with nearshore environments, two associated with offshore well oxygenated settings, two associated with dysoxia, and two rare genera with ambiguous distributions and associations. This study produced two broad results. The first result is that Mid-continent productidine generic performance is consistent with paleoenvironmental interpretations and distributions. Nearshore taxa remain stable in high velocity flows and have proportionally smaller lophophores. Rare and well oxygenated setting taxa perform well on muds and mobile substrates and have proportionally smaller lophophores. Dysoxic taxa have high resistance to sinking in soft muds and proportionally larger lophophores. The second result is a demonstration that productidine spine length greatly affects overall hydrodynamic stability; longer spines prevent instability in mobile substrates and increase resistance to sinking better than short spines.
  Overall, productidine spines and morphology display adaptation to multiple functions and environments. This study tests and supports the hypothesized function of spines as a means of maintaining stability without a pedicle.

• Subjects / Keywords

  • brachiopod
  • productidine
  • functional morphology

• Graduation date

  Spring 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-89ag-h083

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.