TAPHONOMY OF AN ORDOVICIAN CRINOID LAGERSTÄTTE FROM KENTUCKY
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Abstract:
A Lagerstatte of Glyptocrinus decadactylus collected from the Upper Fairview Formation at Maysville, Kentucky, USA, yields new insights into the paleoautecology of camerate crinoids of the Late Ordovician. The Lagerstatte represents an autochthonous community composed of a single siltstone bed representing an obrution event and containing over 400 individual glyptocrinids that had colonized a slight topographic rise of relatively high energy within the deep subtidal zone. The high density of the crinoid community was accommodated by tiering, in which the crinoids presumably employed macroalgae (not preserved), occasionally bryozoans, and the columns of earlier-settled specimens as attachment sites; differing column lengths positioned the crinoids at various levels within the community. A further strategy for crowded conditions may have been small body size. Storm-induced turbidity flows led to the suspension of silts by a lofting plume that smothered the crinoids in their habitat. The densely packed crinoid-macroalgae assemblage may have baffled the sediment plume and induced deposition, facilitating burial. Some specimens apparently died shortly prior to burial, suggesting more than one earlier killing event, likely related to the storm that ultimately caused the obrution. Other specimens were killed by the obrution event and subjected to little or no subsequent scavenging or decay after burial, leading to excellent preservation.Keywords:
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The Fezouata Lagerstätte, discovered in the Lower Ordovician rocks of Morocco, is a Konservat-Lagerstätte of prime scientific importance. It provides access not only to the 'shelly' (skeletonized) part of its fossil assemblages, but also to non-biomineralized to lightly sclerotized organisms and to exceptionally preserved soft tissues of a complex ecosystem, mixing elements of both the 'Cambrian Explosion' and the 'Great Ordovician Biodiversification Event' (GOBE). The Fezouata Lagerstätte occurs at different intervals in the Fezouata Shale, a formation ranging from the lower Tremadocian to the upper Floian (Lower Ordovician). In spite of recent major advances in the detailed biostratigraphy of the Fezouata Shale, there is currently no consensus on the precise age of the fossiliferous levels yielding exceptionally preserved assemblages. Consequently, all available biostratigraphical evidence based on several fossil groups is here critically reviewed and discussed. It can be concluded that exceptional preservation is restricted to a few thin, discontinuous, lens-shaped horizons occurring in two distinct parts of the Fezouata Shale: a lower interval (260–330 m above the base of the formation) and an upper interval (570–620 m). Integrated biostratigraphical studies, essentially based on investigations of graptolites, acritarchs and conodonts, indicate that the lower interval can be correlated with the upper Tremadocian, whereas the upper interval corresponds to the middle Floian.
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The Tremadocian-to-Floian siliciclastic deposits of the Shirgesht Formation in the Kalmard Block of central Iran show abundant occurrences of the mid-tier Trichophycus venosus, a common ichnotaxon in the archetypical Cruziana ichnofacies. This trace fossil records a considerable increase in exploitation of offshore infaunal ecospace in comparison with older formations. Here, Trichophycus is relatively long and wide, with numerous and deep successively stacked causative burrows, which form dense burrow systems building the Crowded Trichophycus ichnofabric (CTI). Such development of CTI and the increase in depth of bioturbation had a negative effect on preservation of shallow-tier traces, for example arthropod burrows and trackways. This resulted in decreasing abundance of trilobite-produced trace fossils towards the top of the succession. The palaeobiological and palaeoecological interpretation of CTI points to stable habitats in muddy substrates above the storm wave base with high content of food and oxygen in pore waters, low-energy hydrodynamic regimes and a long colonization window. Moreover, the architecture and the morphological features of Trichophycus suggest a combined dwelling-feeding activity of the resident fair-weather producer showing the K-selected/climax strategy. The ethology of the producer, palaeoecological interpretations and taphonomic signatures revealed that it preferred dewatered, compacted muddy substrates (firmgrounds) in offshore settings, which might be related to minor hiatuses or short-lived discontinuities. Although the appearance of Trichophycus is concomitant to the earliest Cambrian agronomic revolution, it was uncommon until the early Ordovician, when locally it records infaunalization related to the Great Ordovician Biodiversification Event.
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Abstract A new species of cladid(?) crinoid, Segmentocolumnus (col.) clarksoni , based on distinctive, disarticulated stem material, is described from the Upper Llandovery Kilbride Formation. Hitherto, this unit has yielded two taxa based on single, nearly complete crinoids. In contrast, S . (col.) clarksoni is known from numerous specimens, including common long pentagonal, pentameric, heteromorphic pluricolumnals with symplectial articulations, broad pentagonal lumina and narrow claustra. A related morphospecies is known from the Ashgill (Upper Ordovician) of Ireland. The fossil echinoderms of the Llandovery (Lower Silurian) are poorly known globally. Where present in this interval, echinoderms are more commonly preserved as disarticulated ossicles and rarely as complete specimens. Complete crinoids have now been identified from nine horizons in the Llandovery of the British Isles, making this one of the better known pelmatozoan faunas from this time interval. However, only two of these occurrences have yielded as many as five or more identifiable taxa. Seven of the nine occurrences are Upper Llandovery (Telychian). Genera are typical of the Silurian or (Upper Ordovician + Silurian); the only remnant Ashgill taxon that did not survive the Llandovery was the morphogenus Segmentocolumnus (col.) Donovan, an ‘extinction’ that probably owes more to taxonomic method than any evolutionary pattern. Copyright © 2003 John Wiley & Sons, Ltd.
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Crinoids (Phylum Echinodermata) represent major components of fossil assemblages in the type Cincinnatian (Upper Ordovician: Katian) of the greater Cincinnati Arch region. However, certain shallow marine lithofacies are characterized by a nonexistent to depauperate crinoid fauna, being instead dominated by trilobites, bryozoans, mollusks, and in some layers solenoporid algae? and stromatoporoids. One such setting is represented by the Grant Lake Formation, equivalent to the upper Corryville and Mount Auburn members of the McMillan Formation of Ohio, as exposed south of Flemingsburg, Fleming County, northern Kentucky. Described herein is an articulated crinoid crown (Anomalocrinus?) from this otherwise crinoid-poor interval. This occurrence may reflect either (1) a brief interval where conditions were more amenable to occupation by crinoids, possibly corresponding to a minor flooding surface, or (2) transportation of skeletal remains from nearby, deeper offshore areas that contained crinoids in greater abundance. The second interpretation seems more likely given the absence of in situ attachment structures and rarity of disarticulated column material at the study site. This study illustrates the value of echinoderm remains in paleoenvironmental analysis, the significance of crinoidal material in taphonomic interpretation of Paleozoic argillaceous carbonate deposits, and the sensitivity of crinoid fossils as indicators of allochthony or autochthony.
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Abstract Ohiocrinus byeongseoni n. sp. from the Middle Ordovician (Darriwilian) Jigunsan Formation of South Korea in the Sino-Korean (North China) block is the oldest species of Ohiocrinus of the Cincinnaticrinidae and the first record outside Laurentia. O . byeongseoni is characterized by a loosely clockwise-coiled anal sac, isotomous branching throughout arms, long, slender xenomorphic column, and small lichenocrinid-type holdfast. The new species occurs in association with a deep-water siliciclastic environment, unlike the Laurentian species with a shallow-water carbonate environment. The monospecific crinoid assemblage is interpreted as parautochthonous, considering that the crinoids were reworked by relatively weak down-current probably caused by storm but preserved within the environment where they lived. The occurrence of O . byeongseoni presents a considerable spatiotemporal gap and ecologic disparity in evolution of Ohiocrinus and the Cincinnaticrinidae. UUID: http://zoobank.org/240417a4-8d33-4f45-aedb-afcc07f1ecbb
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A deep-water Konservat Lagerstätte from the lower Caradoc (Sandbian) at Girvan is dominated by the trilobite Diacanthaspis trippi, the carpoids Anatifopsis n. sp.? and a new genus of ctenocystoid together with the polyplacophoran Solenocaris solenoides and the brachiopod Onniella williamsi. Most of these are multi-element organisms, with many specimens preserved in an articulated state in finely laminated rocks, indicating minimal disturbance and suggesting that the fauna is largely an in situ association. It contains few of the species known from other deep-water sites of similar age at Girvan which contain diverse assemblages of trilobites and brachiopods absent from the Lagerstätte. The taphonomy of the site indicates preservation by rapid burial followed by early diagenesis under dysaerobic conditions. It provides a 'taphonomic window' on otherwise unknown faunas from distal shelf facies on the Ordovician Laurentian margin, and, moreover, is an important reminder of the hidden biodiversity that resided in thin-shelled, multi-element organisms.
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A Lagerstatte of Glyptocrinus decadactylus collected from the Upper Fairview Formation at Maysville, Kentucky, USA, yields new insights into the paleoautecology of camerate crinoids of the Late Ordovician. The Lagerstatte represents an autochthonous community composed of a single siltstone bed representing an obrution event and containing over 400 individual glyptocrinids that had colonized a slight topographic rise of relatively high energy within the deep subtidal zone. The high density of the crinoid community was accommodated by tiering, in which the crinoids presumably employed macroalgae (not preserved), occasionally bryozoans, and the columns of earlier-settled specimens as attachment sites; differing column lengths positioned the crinoids at various levels within the community. A further strategy for crowded conditions may have been small body size. Storm-induced turbidity flows led to the suspension of silts by a lofting plume that smothered the crinoids in their habitat. The densely packed crinoid-macroalgae assemblage may have baffled the sediment plume and induced deposition, facilitating burial. Some specimens apparently died shortly prior to burial, suggesting more than one earlier killing event, likely related to the storm that ultimately caused the obrution. Other specimens were killed by the obrution event and subjected to little or no subsequent scavenging or decay after burial, leading to excellent preservation.
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