Community relations of Silurian crinoids at Dudley, England

Abstract

Silurian crinoids reached maximum abundance on shallow shelf bottoms of skeletal-rich carbonate. In-place crinoid preservation in the Wenlock Limestone of Dudley, England, provides a community model for these occurrences, showing a pattern among crinoids of high taxonomic diversity, conspecific clustering, relatively robust morphology, and numerical dominance of other invertebrates. Densities of about 40 crinoid individuals per m2 occupied a feeding level between 10 cm and 1 m above the bottom and may have effected trophic control over other fauna. Beneath the crinoids lived a second level of bryozoa, a third level of tabulates, and a sparse fauna of brachiopods and other solitary organisms. Crinoids also exercised significant biologic control of substrate. In contrast to the Dudley assemblage, Silurian communities of terrigenous, soft-bottom environments contained crinoids of low abundance, low taxonomic diversity, and small size. In the terrigenous communities, crinoids appear to have had no major effect on either trophic structure or substrate. High sedimentation rates limited the role of crinoids in such communities, and the dominant organisms were deposit feeders and solitary, low-level suspension feeders.