Middle Ordovician Crinoids from Southwestern Virginia and Eastern Tennessee PDF Download

Author: James C. Brower
Publisher:
ISBN: 9780877102212
Category : Crinoidea, Fossil
Languages : en
Pages : 125

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Book Description
This paper describes the crinoid fauna of the Benbolt and allied formations of eastern Tennessee and southwestern Virginia. One new genus and 14 new species are proposed. These are Ectenocrinus punctalus, n. sp., anulocrinus latus, n. sp., Ristnacrinus ? altobasalis, n. sp., Hybocrinus punctatocristatus, n. sp., H. perperamnominatus, n. sp., Palaeocrinus planobasalis, n. sp., P. avondalensis, n. sp., Carabocrinus stellifer, n. sp., C. micropunctatus, n. sp., Pararchaeocrinus convexus, n., sp., Paradiabolocrinus irregularis, n. gen., n. sp., P. sinuorugosus, n. gen., n. sp., Rhaphanocrinus simplex, n. sp., and Wilsonicrinus culmensiuosus, n. sp. Due to poorly preserved material, two new species are not formally described but are referred to Isotomocrinus and Diabolocrinus. Two previously described species, Archaeocrinus peculiaris Miller and Gurley and Geraocrinus sculptus Ulrich, are treated here. The crinoid proposed by Miller and Gurley as Indianocrinus punctatus is a broken hybocrinid with some plates missing; consequently, Indianocrinus is placed in synonymy with Hybocrinus and the species retained as H. punctatus (Miller and Gurley). The pores of the Tennessee and Virgina palaeocrinids are shown to be respiratory; in addition, the ontogeny of the pores is discussed. Diabolocrinus vesperalis (White) is considered a highly variable form which includes six previously erected "species". As indicated in the above tabulation, the fauna is dominated by archaeocrinids, hybocrinids, and peculiar dicyclic cyathocrinid inadunates. The greatest faunal affinities are with the Chazyan crinoids of New York and adjacent areas and with the presumably specialized crinoids (e.g., Ristnacrinus, Hybocrinus, Carabocrinus, and Palaeocrinus) suggests that Late Chazyan and Black River time was an epoch of evolutionary experimentation for crinoids. Three of the peculiar genera survived the Black River, and persisted into the Trenton of North America, but they all became extinct prior to the Upper Ordovician. Most of the Benbolt and allied formation genera which failed to survive after the Black River epoch in North America are "normal" crinoids such as Anulocrinus, Pararchaeocrinus, Paradiabolocrinus, and Diabolocrinus. Reconstruction of the environment of the crinoids suggests that they were rooted in a relatively soft substrate and lived in shallow water of normal marine salinity and high oxygen content which was alternatingly agitated and calm. Agitated conditions probably prevailed as most species show structures which are best interpreted as adaptations to rough water conditions. The only crinoids which do not exhibit such adaptations are Geraocrinus sculptus Ulrich, two Palaeocrinus species, and Rhaphanocrinus simplex, n. sp.