Investigations in blastoid phylogenetics, speciation, and the sedimentology of an echinoderm-defined stratotype.
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Morgan, Ryan Fitzgerald.
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This dissertation addresses questions on blastoid (Deltoblastus) speciation and phylogeny, as well as investigation the sedimentology of an echinoderm-defined (Marsupites) stratotype. Deltoblastus is a genus of Permian blastoid comprised of 15 species which differ based on thecal morphology. Investigation into described species revealed three new species, which are described within based on characteristics that distinguish individuals from established morphotypes. Enhancing understanding of the genus is the construction of a character matrix containing all known species. Differences in characters provide evidence for unique thecal morphologies. In addition, Deltoblastus is characterized using phylogenetic and clustering methods. Parsimony analysis allows construction of a phylogeny of the genus, with Schizoblastus sayi serving as the primary outgroup. Neighbor joining cluster analysis together with Principal Components Analysis support clade associations, and demonstrate the unique morphologies of Deltoblastus species. Despite demonstrating distinct separation of Deltoblastus from possible sister genera, parsimony analysis fails to completely discern Deltoblastus species relationships. Supporting analyses aid in differentiation, and suggest separation of D. molengraaffi and D. sebotensis into a new genus. Whereas it has been put forward that Schizoblastus, among others, is the sister genus of Deltoblastus, this study fails to discern among the many genera which is the true sister group. While investigating an echinoderm-defined stratotype exposure outside of Waco, Texas, a new species of Gyrolithes was discovered. This helical marine trace fossil occurs in beds of the Austin Chalk. The new ichnospecies Gyrolithes texanus is characterized by unique morphology and wall construction. This discovery expands the current geographic and environmental range of Gyrolithes, extending this ichnogenus into the chalk-dominated beds of the Cretaceous of Texas. Irregular bedding features from the Gyrolithes locality indicate this section of the Austin Chalk was deposited within a storm-dominated depositional regime, interspersed with periods of quiescence which allowed for firm ground formation and colonization by the trace maker. Gyrolithes is associated with marginal marine settings but is not with storm deposits; therefore, this discovery constitutes an expansion of environment for this ichnogenus. Although seemingly disparate, these studies prove insightful to the development of echinoderm paleontology. These investigations are described in detail within.