A re-evaluation of crinoid morphology and proposed relationship of crown groups, with insights from biogeography


A re-evaluation of crinoid morphology and proposed relationship of crown groups, with insights from biogeography

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dc.contributor.advisor Sprinkle, James, 1943-
dc.creator Womack, Kyle Richard
dc.date.accessioned 2011-10-04T20:53:39Z
dc.date.available 2011-10-04T20:53:39Z
dc.date.created 2011-08
dc.date.issued 2011-10-04
dc.date.submitted August 2011
dc.identifier.uri http://hdl.handle.net/2152/ETD-UT-2011-08-4243
dc.description.abstract Crinoids 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.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subject Crinoid
dc.subject Morphology
dc.subject Cladistic analysis
dc.subject Phylogenetics
dc.subject Biogeography
dc.subject Echinodermata
dc.subject Crown groups
dc.subject Column
dc.subject Caly
dc.subject Plate homology
dc.subject Two-circlet
dc.subject Three-circlet
dc.title A re-evaluation of crinoid morphology and proposed relationship of crown groups, with insights from biogeography
dc.date.updated 2011-10-04T20:53:59Z
dc.identifier.slug 2152/ETD-UT-2011-08-4243
dc.contributor.committeeMember Molineux, Ann
dc.contributor.committeeMember Rowe, Timothy
dc.description.department Geological Sciences
dc.type.genre thesis
dc.type.material text
thesis.degree.department Geological Sciences
thesis.degree.discipline Geological Sciences
thesis.degree.grantor University of Texas at Austin
thesis.degree.level Masters
thesis.degree.name Master of Science in Geological Sciences

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