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dc.contributor.advisorSprinkle, James, 1943-en
dc.creatorWomack, Kyle Richarden
dc.date.accessioned2011-10-04T20:53:39Zen
dc.date.available2011-10-04T20:53:39Zen
dc.date.created2011-08en
dc.date.issued2011-10-04en
dc.date.submittedAugust 2011en
dc.identifier.urihttp://hdl.handle.net/2152/ETD-UT-2011-08-4243en
dc.descriptiontexten
dc.description.abstractCrinoids are the most primitive living members of the Phylum Echinodermata. Though still present in reduced numbers today, crinoids were the dominant echinoderms from the Ordovician to the Permian. The crinoid body plan consists of three major regions, the column, the calyx, and the arms. Each region serves important functions in crinoids. The column raises the rest of the body into the water column for more efficient feeding. The calyx contains the visceral mass and mouth. Arms extend out from the top of the calyx to trap microorgansisms and suspended organic particles in the water column. A re-evaluation of these functional units is undertaken to understand the importance of various structures and to obtain discrete characters for use in a cladistic analysis. The relationship of crinoid crown groups has been an active area of research for the past couple of decades. With each proposed phylogenetic relationship, a new interpretation of thecal plate homology has been proposed. Here each study is re-examined in the light of new data. A review of functional morphology indicates a dual-reference system to be the most supported interpretation of plate homology. The two reference points in this system are the stem-cup and the cup-arm junctions, at the top and bottom of the calyx. The difference between a two-circlet and three-circlet crinoid is the presence or absence of the middle (basal) circlet. A new cladistic analysis is presented, with the topology of trees obtained giving support for the retention of Paleozoic crinoid stem and crown groups. Crinoids appear abruptly in the fossil record. Questions pertaining to origins and ancestral stock abound. A biogeography study is employed to look at the distribution of crinoids from the Early to Middle Ordovician. Locality information, combined with an understanding of the movement of major plates, paleoclimate data, an understanding of larval distribution, and a review of similar studies carried out on different taxa, gives insight into possible radiation and dispersal patterns of crinoids from the first half of the Ordovician.en
dc.format.mimetypeapplication/pdfen
dc.language.isoengen
dc.subjectCrinoiden
dc.subjectMorphologyen
dc.subjectCladistic analysisen
dc.subjectPhylogeneticsen
dc.subjectBiogeographyen
dc.subjectEchinodermataen
dc.subjectCrown groupsen
dc.subjectColumnen
dc.subjectCalyen
dc.subjectPlate homologyen
dc.subjectTwo-circleten
dc.subjectThree-circleten
dc.titleA re-evaluation of crinoid morphology and proposed relationship of crown groups, with insights from biogeographyen
dc.date.updated2011-10-04T20:53:59Zen
dc.identifier.slug2152/ETD-UT-2011-08-4243en
dc.contributor.committeeMemberMolineux, Annen
dc.contributor.committeeMemberRowe, Timothyen
dc.description.departmentGeological Sciencesen
dc.type.genrethesisen
thesis.degree.departmentGeological Sciencesen
thesis.degree.disciplineGeological Sciencesen
thesis.degree.grantorUniversity of Texas at Austinen
thesis.degree.levelMastersen
thesis.degree.nameMaster of Science in Geological Sciencesen


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