Morphometric approaches to systematics and microevolution: Applications from paleozoic bryozoa
Hageman, Steven James
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Permalink
https://hdl.handle.net/2142/23314
Description
Title
Morphometric approaches to systematics and microevolution: Applications from paleozoic bryozoa
Author(s)
Hageman, Steven James
Issue Date
1992
Doctoral Committee Chair(s)
Blake, Daniel B.
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Biostatistics
Paleontology
Language
eng
Abstract
Documentation of microevolution through geologic time is a significant paleontologic contribution to evolutionary biology. Paleomicroevolutionary studies require accurate stratigraphic resolution over a large geographic area, through changing environments, over a sustained period of time, with an abundant, complex, eurytopic fossil group. The combination of cryptostome bryozoans, revised taxonomic procedures, multivariate morphometric methods, and advances in microcomputer technology allows for research of this nature.
Multivariate analysis of a large morphometric data set demonstrates that discrete fenestrate bryozoan morphs can be recognized objectively at three hierarchical levels: species, genera and families. Recent studies of hard-part versus electrophoretic species recognition in cheilostome bryozoans and scleractinian corals support the interpretation that fenestrate species represent true biological species rather than morphotaxa. Morphometric analysis demonstrates that some characters are taxonomically more important than others, but use of all available characters yields the most reliable results.
Worthenopora is a Mississippian cryptostome bryozoan tentatively assigned to the order Cheilostomata (Jurassic and younger) but some early workers. This alignment raises the question of affinities between cryptostomes (class Stenolaemata) and cheilostomes (class Gymnolaemata). Based on wall structure, growth sequence, zooecial shape, and secondary structures such as stylets, Worthenopora is here shown to be a stenolaemate, assignable to the suborder Ptilodictyina with other bifoliate cryptostomes, with no special affinities with cheilostomes.
Paleontologic data frequently do not satisfy assumptions of normality and homoscedasticity of many parametric statistical tests. Normal scores tests, which employ normal order deviates (rankits), provide an attractive alternative for treatment of such data. Computer programs Rankit and Mathematica provide a practical method of calculating rankits and converting raw data, making normal scores tests more accessible.
Three-dimensional shapes of cryptostome bryozoan autozooecial chambers are important for systematics and paleoecologic interpretations, however, computer automation of three-dimensional reconstruction from serial sections is not yet practical.
Based on morphometric analysis of the rhabdomesoid Streblotrypa prisca, ecophenotypic and geographic variation are significant factors for microevolutionary studies. Apparently non-astogenetic morphologic growth gradients are demonstrated with colonies of S. prisca. A morphologic cline distributed over a 300 km transect is demonstrated; control is unclear, but it may be associated with a depth gradient.
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