Actinocrinitidae from the Lower Mississippian Fort Payne Formation of Kentucky, Tennessee, and Alabama (Crinoidea, Viséan) Elizabeth C. Rhenberg, 1 William I. Ausich, 2 and David L. Meyer 3 1 Department of Geology, Earlham College, 801 National Road West, Richmond, IN 47374-4095, USA 〈rhenbel@earlham.edu〉 2 School of Earth Sciences, 155 South Oval Mall, The Ohio State University, Columbus, OH 43210, USA 〈ausich.1@osu.edu〉 3 Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA 〈david.meyer@uc.edu〉 Abstract.—The Actinocrinitidae were among the most abundant crinoids worldwide during the Lower Mississippian. Recent systematic revisions of the family allow a revised genus- and species-level understanding of these crinoids globally and a more precise means by which to understand the temporal and facies distribution of genera and species in this important Mississippian family. Two genera with a total of five species of Actinocrinitidae (and five additional forms left in open nomenclature) are recognized from the Fort Payne Formation, including Actinocrinites jugosus (Hall, 1859), Actinocrinites spp. indeterminate, Thinocrinus gibsoni (Miller and Gurley, 1893), Thinocrinus lowei (Hall, 1858), Thinocrinus probolos (Ausich and Kammer, 1991), Thinocrinus akanthos new species, Thinocrinus sp. aff. T. gibsoni, Thinocrinus spp. indeterminate, and two taxa recognized as only Actinocrinitidae genus and species indeterminate. Actinocrinites tripus Ehlers and Kesling, 1963 is recognized as a junior synonym of Thinocrinus gibsoni. Thinocrinus, rather than Actinocrinites as previously thought, is the dominant Fort Payne Formation actinocrinitid. Fort Payne Formation carbonate buildup facies (wackestone buildups and crinoidal packstone buildups) each have characteristic species of Thinocrinus. Actinocrinites is relatively rare in the Fort Payne Formation, but occurs preferentially in crinoidal packstone buildups. Introduction The Mississippian was the ‘Age of Crinoids’ (Kammer and Ausich, 2006), and the Fort Payne Formation has been a model setting for understanding the composition, facies distribution, taphonomy, and paleoecology of Mississippian crinoid faunas (early Viséan; late Osagean). The first descriptions of Fort Payne Formation crinoids were in the pioneering works of Gerard Troost (1849, 1850a, 1850b; see Ausich, 2009) and James Hall (1858, 1859). With the exception of Ehlers and Kesling (1963), little further research was completed on crinoids from the Fort Payne Formation until the 1980s when two of the present authors began a long-term study of the Fort Payne Formation. Ausich and Meyer (1990) delineated sedimentary facies in the Fort Payne Formation and recognized autochthonous and allochthonous facies in this mixed carbonate-siliciclastic, toe-of-slope setting. Fort Payne Formation background sedimentation was siltstone punctuated by carbonate turbidites, which eventually buried autochthonous carbonate buildups. Well-preserved crinoid fossils are especially abundant in autochthonous facies, including packstone buildups, wackestone buildups, and green shale facies (Ausich and Meyer, 1990). As demonstrated by Krivicich et al. (2014) and despite close spatial proximity, each autochthonous facies supported a distinct crinoid-blastoid assemblage. Further, despite the allochthonous sedimentary fill of incised channels, this channel-form packstone facies also contained a separate, distinct crinoid assemblage. These contemporaneous depositional settings also provided contrasting conditions that allowed for an understanding of the comparative taphonomy of different echinoderm clades (Meyer et al., 1989). In addition, Thompson and Ausich (2016) recently examined the distribution of echinoids in the Fort Payne Formation, which like many crinoids were concentrated in the two autochthonous buildup facies. To date, comprehensive systematic treatment of Fort Payne Formation blastoids (Ausich and Meyer, 1988), flexible crinoids (Ausich and Meyer, 1992), disparid crinoids (Ausich et al., 1997), and the camerate Agaricocrinus (Meyer and Ausich, 1997) have been published. In this contribution, the systematics of Fort Payne Formation Actinocrinitidae is presented, which is now possible because of a revised understanding of actinocrinitids (Ausich and Sevastopulo, 2001) and a comprehensive review of the North American Actinocrinitidae by Rhenberg et al. (2015). Actinocrinitids are especially important elements of the carbonate buildup facies in the Fort Payne Formation. Thinocrinus, with its exaggerated arm lobes, is a characteristic taxon of the wackestone buildups (Krivicich et al., 2014). Herein, five nominal species assigned to two genera (and five additional taxa left in open nomenclature) of actinocrinitids are recognized from the Fort Payne Formation, including Actinocrinites jugosus (Hall, 1859), Actinocrinites spp. indeterminate, Thinocrinus gibsoni (Miller and Gurley, 1893), Thinocrinus lowei (Hall, 1858), Thinocrinus probolos (Ausich and Kammer, 1991), Thinocrinus akanthos n. sp., Thinocrinus sp. aff. T. gibsoni, and Thinocrinus spp. indeterminate. Two taxa only identified as Actinocrinitidae Journal of Paleontology, page 1 of 12 Copyright © 2016, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2016.85 1 http://dx.doi.org/10.1017/jpa.2016.85 Downloaded from http:/www.cambridge.org/core. 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