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A reconnaissance of skeletal crystallography in rhombiferans, diploporans, and paracrinoids

Brian E. Bodenbender and Erik J. Hiemstra
A reconnaissance of skeletal crystallography in rhombiferans, diploporans, and paracrinoids
Journal of Paleontology (November 2004) 78 (6): 1154-1162


We characterized the skeletal crystallography of representatives of nine rhombiferan, three diploporan, and three paracrinoid species. Crystallographic data from these groups are similar to data from previous studies of crinoids, echinoids, and blastoids in that 1) orientations of c axes are consistent within species and within higher taxonomic groups; 2) c axes typically are oriented subparallel to the medial plane of their respective plates; and 3) the inclination of axes within the medial plane varies between taxa. Rhombiferan c axes are oriented normal to plate surfaces whereas diploporan c axes are tangential to plate surfaces. Paracrinoids more closely resemble diploporans in having irregular patterns of thecal plating but their c axes are approximately perpendicular to plate surfaces as in rhombiferans. In contrast to c axes, a axes in all specimens show little regularity and cannot be distinguished from random orientations. The rhombiferan Caryocrinites ornatus displays minor differences in the inclinations of c axes depending on the location of skeletal elements on the theca. Plates at the base of the theca have slightly aborally inclined axes, whereas distal plates have axes inclined slightly adorally. This pattern matches orientations in some early crinoids, suggesting similarities between rhombiferans and crinoids in development or skeletal construction. Skeletal crystallography in various echinoderms can be compared in light of hypotheses of homology proposed in the Extraxial-Axial Theory (EAT). Skeletal elements homologized under the EAT do not correspond to any particular crystallographic axis orientation, suggesting that the homologies proposed in the EAT encompass significant underlying skeletal variation.

ISSN: 0022-3360
EISSN: 1937-2337
Serial Title: Journal of Paleontology
Serial Volume: 78
Serial Issue: 6
Title: A reconnaissance of skeletal crystallography in rhombiferans, diploporans, and paracrinoids
Affiliation: Hope College, Department of Geological and Environmental Sciences, Holland, MI, United States
Pages: 1154-1162
Published: 200411
Text Language: English
Publisher: Paleontological Society, Lawrence, KS, United States
References: 37
Accession Number: 2005-004633
Categories: Invertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendix
Illustration Description: illus.
Secondary Affiliation: ChevronTexaco, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200502
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