|2011 GSA Annual Meeting in Minneapolis (9–12 October 2011)|
|Paper No. 27-17|
|Presentation Time: 9:00 AM-6:00 PM|
RECOGNITION OF UNIVERSAL ELEMENTAL HOMOLOGIES IN CRINOIDS AND BLASTOZOANS
KAMMER, Thomas W., Department of Geology and Geography, West Virginia University, 330 Brooks Hall, Morgantown, WV 26506-6300, email@example.com, SUMRALL, Colin D., Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, AUSICH, William I., School of Earth Sciences, The Ohio State University, 275 Mendenhall Lab, 125 S. Oval Mall, Columbus, OH 43210, and DELINE, Bradley, Department of Geosciences, University of West Georgia, 1601 Maple St, Carrollton, GA 30118|
To investigate the phylogenetic relationships between crinoids and other Paleozoic stemmed echinoderms, it is necessary to recognize homologies across groups. Echinoderm skeletal plates with shared evolutionary origins are termed universal elemental homologies (UEH). Often, such plates have different names between groups, preventing easy recognition of homology.
Earlier work (Sumrall and Waters, 2011) on the axial systems of the ambulacra and mouth demonstrated examples of UEH between various blastozoans including glyptocystitoids, diploporans, hemicosmitoids, coronoids, and blastoids. Analysis of the axial systems on crinoid oral surfaces recognizes many of these same UEH. Using Ordovician glyptocystitoids as a general model, the following homologies are recognized in crinoids: interradial oral plates forming a mouth frame bearing proximal food grooves along adjacent sutures; peristomial cover plates over the mouth; a 2-1-2 symmetry of the ambulacra; ambulacral cover plates; hydropore within Oral 1; and a periproct posterior to Oral 1. Apomorphies found in Middle Ordovician and younger Paleozoic crinoids include coelomic canals that penetrate the ring of oral plates and extend up the arms, loss of ambulacral floor plates, and apparent fusion of Orals 1, 6, and 7. Crinoid arms contain coelomic extensions and may branch, unlike the non-branching brachioles of blastozoans that lack coelomic extensions.
Hybocrinid crinoids exhibit oral surfaces most similar to blastozoans, but lack the floor plates from which brachioles arose in blastozoans. The ranking of homologous similarities in oral surfaces of Paleozoic crinoids with blastozoans appears to be: hybocrinids, cladids, flexibles, and camerates. The position of disparids within this ranking is unclear, although many appear paedomorphic with only five tegmen plates, which may be the peristomial cover plates. Hybocrinids, cladids, and flexibles had movable ambulacral and peristomial cover plates. Camerates had fixed ambulacral and peristomial cover plates, which along with interambulacrals, were used to form a rigid tegmen over a covered mouth. In general, true orals are not visible on the camerate tegmen.
2011 GSA Annual Meeting in Minneapolis (9–12 October 2011)
General Information for this Meeting
|Session No. 27--Booth# 58|
Paleontology (Posters) I: Ecology and Phylogeny
Minneapolis Convention Center: Hall C
9:00 AM-6:00 PM, Sunday, 9 October 2011
Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 84
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