A field guide to the Silurian Echinodermata of the British Isles: Part 2 - Crinoidea, minor groups and discussion

摘要

Crinoids are the most common and diverse group of echinoderms in the Silurian of the British Isles. Ibis guide describes examples of all nominal crinoid groups recognized from this interval and region (48 genera, about 100 species). In contrast, coronate, edrioasteroid, mitrate and cyclocystoid echinoderms are rare, the first three higher taxonomic groups being represented by a single species each, and the last by two species. Of 145 species of echinoderms in the Silurian of the British Isles, 74 are known from the Much Wenlock Limestone Formation of Wenlock age at Dudley in the West Midlands. For comparison, the most diverse faunas from the Llandovery Series (North Esk Inlier, Pentland Hills, Scotland) and Ludlow Series (Lower Leintwardine Formation, Leintwardine, Herefordshire) consist of only 16 and 17 species, respectively. If the echinoderm-rich succession at Dudley was unknown, the three older series of the Silurian, the Llandovery, Wenlock and Ludlow, would each include about 30 known species of echinoderm. It is the extreme diversity of the Much Wenlock Limestone Formation at Dudley that makes the echinoderm diversities of the Llandovery and Ludlow appear depauperate.