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The Effects of Scale, Community Structure, and Environment on Ordovician through Early Silurian Laurentian Crinoid Disparity

Deline, Bradley
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1258392774

Abstract Details

2009, PhD, University of Cincinnati, Arts and Sciences : Geology.
The quantification of morphological disparity is an important tool in the study of macroevolution. Estimating disparity is difficult and is therefore relatively understudied in relation to taxonomic diversity. The current study aims to reexamine and explore the disparity of Early Paleozoic crinoids across geographic and taxonomic scales. Disparity is calculated based on the coding of discrete morphological characters. Regional crinoid disparity was examined using greater stratigraphic resolution and taxonomic coverage in order to test the patterns and interpretation of previous studies. At the local level (i.e. biofacies) the effects of different communities on measures of disparity as well as the meaning of rarity in regard to morphological uniqueness was examined. In agreement with previous studies, Ordovician through Early Silurian crinoid disparity rapidly expanded than stabilized during the Ordovician. However, the current study shows a major rise in disparity during the Silurian recovery following the Ordovician Mass Extinction. This rise is mostly because of the proliferation of the myelodactylids that were well suited to the soft substrate environments that expanded late in the Ordovician. Examination of both the Late Ordovician and Permian extinctions indicate that there is no evidence of an increased rigidness of morphology during recoveries and if genetic canalization played a large role in crinoid morphologic history, it likely occurred during the Early Ordovician. Biofacies level disparity shows a very different pattern from the regional patterns. On average biofacies have equitable disparity through time and individual biofacies do not show strong differences in disparity with regard to environment, time, or geography. Contrary to previous studies the choice of taxonomic level can affect the results in two ways. First, the number of species per genera can change through time such that the disparity of time bins with a higher ratio will be underestimated. Secondly, combining aberrant species into a single genus can drastically reduce disparity values as is seen in myelodactylids in the Early Silurian. Local disparity was also examined in regard to community structure. Even though many disparity metrics are not sample-size dependant biases can result from rare taxa being outliers or merely segregated in morphospace from common taxa. In Early Paleozoic crinoids rare species do not contribute more to local disparity than common species, however, in some biofacies rare crinoids occupy separate areas of morphospace. Weighting local disparity by abundance is a less biased metric that includes elements of morphology, evenness, and subgroup occupation. Localities that have a low weighted to unweighted disparity ratio often are strongly structured following aerosol filtration theory. Localities that have equitable values for the two metrics often are at intermediate depths, occur early in crinoid history, or are environmentally or ecologically disturbed. Examining the ratio of these metrics for crinoid biofacies through time it appears that structured community based on aerosol filtration theory appeared no later than the Late Middle Ordovician.
Carlton Brett (Advisor)
Michael Foote (Other)
David Meyer (Other)
Arnold Miller (Other)
Colin Sumrall (Other)
Geology
Crinoid; Cupulocrinus

Recommended Citations

Citations

  • Deline, B. (2009). The Effects of Scale, Community Structure, and Environment on Ordovician through Early Silurian Laurentian Crinoid Disparity [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1258392774

    APA Style (7th edition)

  • Deline, Bradley. The Effects of Scale, Community Structure, and Environment on Ordovician through Early Silurian Laurentian Crinoid Disparity. 2009. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1258392774.

    MLA Style (8th edition)

  • Deline, Bradley. "The Effects of Scale, Community Structure, and Environment on Ordovician through Early Silurian Laurentian Crinoid Disparity." Doctoral dissertation, University of Cincinnati, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1258392774

    Chicago Manual of Style (17th edition)

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© 2009, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.