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GFF Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/sgff20 First report of Silurian crinoid columnals with tetralobate and hexalobate lumen structures James R. Thomkaa & Gary J. Motza a Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA; , Published online: 10 Jan 2014.

To cite this article: James R. Thomka & Gary J. Motz (2014) First report of Silurian crinoid columnals with tetralobate and hexalobate lumen structures, GFF, 136:1, 266-269, DOI: 10.1080/11035897.2013.854271 To link to this article: http://dx.doi.org/10.1080/11035897.2013.854271

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First report of Silurian crinoid columnals with tetralobate and hexalobate lumen structures

JAMES R. THOMKA and GARY J. MOTZ

Thomka, J.R. & Motz, G.J., 2014: First report of Silurian crinoid columnals with tetralobate and hexalobate lumen structures. GFF, Vol. 136 (Pt. 1, March), pp. 266–269. q Geologiska Fo¨reningen. doi: http://dx.doi.org/10.1080/11035897.2013.854271. Abstract: Two specimens of crinoid columnals with previously undocumented lumen morphologies are described from Silurian (Wenlock) strata of the Cincinnati Arch region, eastern-midcontinent North America. An attachment structure with a prominent tetralobate lumen, the first tetralobate lumen in a columnal reported from the Silurian, was recovered from a microbioherm in the Massie Formation of southeastern Indiana. An isolated columnal ossicle with a large hexalobate lumen, the first hexalobate lumen-bearing columnal documented, was recovered from a skeletal dolowackestone in the Lilley Formation of southwestern Ohio. These discoveries significantly increase the disparity of the otherwise morphologically conservative Silurian crinoid-columnal fauna. Keywords: Crinoidea; Echinodermata; Eucalyptocrinites; Wenlock; holdfast.

Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA; [email protected], [email protected] Manuscript received 9 May 2013. Revised manuscript accepted 8 October 2013.

Introduction Deviation from the five-part symmetry characteristic of columnal morphological disparity and fill a fairly large gap in echinoderms is rare within Crinoidea. Nevertheless, develop- the record of unusual crinoid stem morphologies. mental abnormalities have been observed in several pelma- tozoan groups (e.g., Macurda 1980) and evolutionary modifications of crown morphology, including reduction in Localities and stratigraphy ray number and/or fusion of calyx plates, have been All materials studied here were recovered from middle Silurian occasionally documented in crinoid lineages (e.g., Foote (Wenlock: Sheinwoodian) carbonate units from the eastern 1994; Ciampaglio 2002;Liow2004). Particularly rare, midcontinent of the USA. Lithostratigraphic nomenclature in however, is the development of columnal symmetry that is this region has undergone a recent and long-needed revision, not radial or pentaradial. Tetrameral symmetry in crinoid resulting in formation-scale terminology that is more consist- columnals has been documented in several Paleozoic groups, ently applied across state and county boundaries, but differing manifest in overall columnal shape (rectangular or square from historically used terms (e.g., Foerste 1897, 1906; Frest outline) and/or development of a tetralobate lumen (Moore & Downloaded by [University of Cincinnati Libraries] at 07:23 09 May 2014 et al. 1999; Slucher et al. 2006; McLaughlin et al. 2008). Jeffords 1968). Hexameral symmetry can potentially be Stratigraphic terminology here follows Brett et al. (2012) and expressed in the same manner, but no such morphologies the reader is directed there for detailed explanations of have been previously documented. nomenclatorial revisions. Survey of the literature reveals that tetrameral symmetry in The tetralobate lumen-bearing attachment structure was crinoid column morphology has been documented primarily in recovered from a fistuliporoid bryozoan-dominated microbio- Devonian taxa, notably within the cladid genus Ancyrocrinus herm (sensu Archer & Feldman 1986) in the Massie Formation (e.g., McIntosh & Schreiber 1971) and family Cupressocrini- exposed at the New Point Stone quarry near Napoleon, tidae (e.g., Głuchowski 1993; Ures et al. 1999; Bohaty´ 2009) and southeastern Indiana (N39812031.3900,W85818053.7400). The the flexible genus Ammonicrinus (Bohaty´ 2011), as well as a hardground horizon from which the microbioherms and variety of Ordovician cladid and camerate taxa (e.g., Sprinkle & associated pelmatozoan fauna emanate separates the basal Kolata 1982; Donovan 1983, 1984, 1990; Cope 1988; Donovan carbonate lithofacies of the Massie Formation from the & Veltkamp 1993; Ausich et al. 2002). The Silurian, in contrast, overlying mudstone lithofacies (see Brett et al. 2012, figure 8) represents an interval of conservatism in crinoid columnal and represents a major flooding surface, associated with an morphologies (Donovan 2012). Herein, we report the occurrence episode of rapid sea-level rise, that is widely traceable of crinoid columnal ossicles with tetralobate and hexalobate throughout the Cincinnati Arch region (Brett & Ray 2005; lumina from the middle Silurian of eastern Laurentia. These McLaughlin et al. 2008; Brett et al. 2012). Recent studies have discoveries contribute significantly to the record of Silurian revealed that this surface is densely encrusted by pelmatozoan GFF 136 (2014) Thomka and Motz: Unusual Silurian crinoid columnals 267

attachment structures attributable to both crinoids and blastozoans (Thomka & Brett in press); this suspension feeder- dominated biofacies is commonly found at this stratigraphic position in other Paleozoic sequences, seemingly resulting primarily from the availability of hard substrates and the decreased turbidity of bottom water (Brett 1995). The hexalobate lumen-bearing columnal was recovered in a float block from a thick dolomitic carbonate succession in the middle portion of the Lilley Formation at a roadcut on OH-32 near Peebles, southwestern Ohio (N38856010.7400, W83826048.3800; see McLaughlin et al. 2008, pp. 142–149; Cramer et al. 2012). Although the entire Lilley Formation represents carbonate deposition in shallow upramp to midramp environments during an interval of tectonic quiescence and overall transgression, the undifferentiated middle portion is distinctly thinner-bedded, suggesting the onset of highstand sedimentation at some scale. The slab containing the columnal displays a wackestone to packstone fabric on one side and is barren on the other, which we interpret as representing a graded bed generated through storm activity.

Tetralobate lumen-bearing columnal This specimen (CMC IP 70230) comprises a distal column and radicular attachment structure encrusting and cemented to a portion of a microbioherm (Fig. 1). Columnals are circular in plan view, holomeric and are approximately eight times as wide as they are high. Articulations between columnals are symplectial. The preserved portion of the column is home- omorphic, displays no tapering and terminates in a dendritic radix (sensu Brett 1981). Component radicles taper distally and branch dichotomously to irregularly. The lumen is centrally located, is relatively large, comprising approximately one-third the diameter of the columnal, and consists of four lobes, set at 908 from each other, each of which expands slightly before terminating in rounded lobes. The margin of the lumen is somewhat obscured by pyrite mineralization, but there is no evidence for a distinct areola. There is also no evidence for an epifacet. Crenulae radiate outward from the edge of the lumen and extend to the margin of the column, so that the crenularium comprises the zygum; culmina are sharp and straight. Fig. 1. Crinoid columnal and associated attachment structure with tetralobate lumen (CMC IP 70230). A. View of specimen embedded in Hexalobate lumen-bearing columnal fistuliporoid bryozoan-dominated microbioherm. Scale bar ¼ 1 cm. B. This specimen comprises an isolated columnal ossicle on the Close-up of columnal showing perfect tetra-radial symmetry. Scale bar ¼ 0.25 cm.

Downloaded by [University of Cincinnati Libraries] at 07:23 09 May 2014 base of a graded skeletal dolopackstone bed (CMC IP 70231) recovered as float from the lower portion of the Lilley Formation. Dolomitization has partially obscured the fine details of sedimentary fabric and fossil texture and microstructure; and/or erosion of the margin, rather than an exceptionally large however, large fossils are relatively well preserved, and a fairly amount of viscera in the lumen (cf. e.g., Fearnhead & Donovan diverse associated pelmatozoan fauna can be identified based on 2007). The lumen is centrally located and hexalobate to individual ossicles. Thecal and columnal plates belonging to the hexastellate, comprising six equally sized lobes spaced evenly camerate crinoid Eucalyptocrinites and the rhombiferan around the center of the axial canal. Each lobe displays strong Caryocrinites are identifiable, as are thecal plates tentatively tapering toward the columnal margin, terminating in relatively attributed to (gomphocystitid?) diploporites (Fig. 2A). sharp points. Imperfect preservation prevents description of As the studied material consists of a single ossicle, column details of the articular surface, but the columnal lacks a fulcral homeomorphy cannot be determined, nor can the nature of ridge and contains no obvious evidence for an epifacet or areola. articulations between adjacent columnals. The columnal (Fig. 2B) is circular in plan view and holomeric. Since it is embedded firmly in matrix sediment, the exact height cannot be Discussion determined. The lumen is relatively large, comprising over half As neither of the specimens described here is definitively of the diameter of the columnal; this almost certainly reflects associated with identifiable calyx plates, erection of new crinoid weathering of the material, resulting in widening of the lumen taxa is inappropriate at this time. Several authors have 268 Thomka and Motz: Unusual Silurian crinoid columnals GFF 136 (2014)

perfect. Reports of teratological Eucalyptocrinites specimens are absent from published literature, and, in spite of the widespread geographic distribution and long temporal range of this genus, these crinoids were apparently not prone to mutation. Further, attachment structures belonging to Eucalyptocrinites that are encrusting microbioherms of the Napoleon hardground are typically severely swollen by secondary stereomic over- growths. Although the exact reasons for this unusual skeletal growth are currently unknown (see Thomka & Brett 2013), the lack of secondary stereom secretion on the tetralobate lumen- bearing holdfast may indicate taxonomic differentiation from Eucalyptocrinites. Further collection at these localities is necessary to provide additional material that can definitively resolve whether these columnals represent new crinoids or aberrant representatives of known taxa. Acknowledgements – Funding for this study was provided by a Dry Dredgers Paul Sanders Grant awarded to JRT. The owners and management of the New Point Stone quarry at Napoleon graciously allowed access to the tetralobate lumen-bearing holdfast locality. Earlier drafts of this article were improved by discussions with Carlton E. Brett (University of Cincinnati) and the constructive reviews provided by William I. Ausich (Ohio State University) and Fiona E. Fearnhead (Birkbeck College, University of London). This is a contribution to the International Geoscience Programme (IGCP) Project No. 591 – The Early to Middle Paleozoic Revolution.

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