Two species of disparid Eomyelodactylus, E. sparteus Eckert and E. uniformis Eckert, and one unusual camerate Stipatocrinus hulveri Eckert and Brett, have been previously described from the Reynales Limestone.
Author: James D. Eckert
Category: Crinoidea, Fossil
Early Silurian (Llandovery) crinoids have been poorly known. The present paper describes 26 species and six unassigned columnal taxa of Early Silurian crinoids on the basis of new and well preserved fossils from the lower Clinton Group of western New York. The new material, comprising eighteen genera, and unclassified skeletal material, spans the late middle Llandovery to the latest Llandovery and has been derived from several lithostratigraphic units. The Reynales Formation (Acronian) contains the following new genera: Dynamocrinus, Thaerocrinus, Haptocrinus, and Prolixocrinus: new species include Dynamocrinus robusts, Thaerocrinus crenatus, Haptocrinus calvatus, Prolixocrinus nodocaudis and Macrostylocrinus sp. Two species of disparid Eomyelodactylus, E. sparteus Eckert and E. uniformis Eckert, and one unusual camerate Stipatocrinus hulveri Eckert and Brett, have been previously described from the Reynales Limestone. Compsocrinus relictus, Dendrocrinus ursae, and an unidentified camerate occur in the laterally equivalent Bear Creek Shale. New taxa from the Wolcott Limestone (lower Telychian) include the Atalocrinacea, new superfamily: Atalocrinidae, Callistocrinidae, and Anisocrinidae, new families: Callistocrinus, Tormosocrinus, Atalocrinus, Aclistocrinus, Kyphosocrinus, and Scapanocrinus, all new genera: and the species Callistocrinus tesselatus, Tormosocrinus furberi, Atalocrinus arctus, Aclistocrinus capistratus, Kyphosocrinus tetreaulti, Scapanocrinus muricatus, Myelodactylus linae, Euspirocrinus wolcottense, Dendrocrinus aphelos, D. bactronodosus, Haptocrinus sp., ?anisocrinid sp., and an unidentified flexible crinoid. Protaxocrinus anellus n. sp., and five unidentifed columnal types occur in the upper Telychian Willowvale Shale. Taxonomic revisions also necessitate reassignments of three previously described taxa. The disparid Macnamaratylus Bolton is synonymized with Eumelodactylus, the flexible crinoid Clidochirus americanus Springer is reassigned to Prolixocrinus n. gen. and the cladid genus Quinquecaudex Brower and Veinus, 1981, is synonymized with Dendrocrinus. The erroneous species, Glyptocrinus plumosus Hall is reviewed: the cotype specimens in part represent the cirral column of a myelodactylid disparid crionid, here tentatively assigned to Eomeyelodatylus (E. ? plumosus (Hall)); the remaining material consists of columnals and pluricolumnals probably belonging to Haptocrinus. Physically stressed, uncrowed environments of the Early Silurian in western New York were characterized by low diversity crinoid assemblages and provided a refuge for relictual Ordovician taxa that became extinct in the late Llandovery. Diverse assemblages of crinoids dominated by Wenlock precursors inhabited mixed carbonate-siliciclastic regimes distal to shoals. Early silurian crinoids of the Clinton Group are highly endemic in marked contrast to the generally low provincialism of other taxa (e.g., brachiopods) during this interval.