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Article: STEM STRUCTURE AND EVOLUTION IN THE EARLIEST PELMATOZOAN ECHINODERMS
- Article from:
- Journal of Paleontology
- Article date:
- July 1, 2008
- Author:
CopyrightCopyright Paleontological Society Jul 2008. Provided by ProQuest LLC. (Hide copyright information)
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ABSTRACT-
Echinoderm skeletal debris from the Early-Middle Cambrian boundary Micmacca Breccia of Morocco includes the oldest known holomeric columnals. The original calcite of these ossicles is coated and replaced by iron oxides, occasionally overlain by a late coating of silica, and preserves with high fidelity fine details of their three-dimensional microstructure. Irrespective of their external morphology, columnals can be divided into three groups based on the distribution of stereom microfabrics, which we suggest indicates the presence of at least three different holomeric stemmed taxa. One of these columnal types has well-developed galleried stereom perpendicular to its articulation ...