EARLY ORDOVICIAN MITRATES AND A POSSIBLE SOLUTE (ECHINODERMATA) FROM THE WESTERN UNITED STATES COLIN D. SUMRALL, 1 JAMES SPRINKLE, 2 THOMAS E. GUENSBURG, 3 AND BENJAMIN F. DATTILO 4 1 Department of Earth and Planetary Sciences, University of Tennessee, Knoxville 37996-1410, USA, ,csumrall@utk.edu.; 2 Department of Geological Sciences, Jackson School of Geosciences, University of Texas, Austin 78712-0254, USA, ,echino@mail.utexas.edu.; 3 Physical Science Division, Rock Valley College, Rockford, Illinois 61114, USA, ,t.guensburg@rockvalleycollege.edu.; and 4 Department of Geosciences, Indiana University–Purdue University Fort Wayne, Fort Wayne, Indiana 46805, USA, ,dattilob@ipfw.edu. ABSTRACT—Two new kirkocystid mitrate stylophorans (Echinodermata, Homalozoa) and a new possible solute (Echinodermata, Homalozoa) are described from the Early Ordovician of the western United States. The mitrates are among the earliest members of their clade to appear near the beginning of the Ordovician Radiation. Anatifopsis ninemilensis new species comes from the Ninemile Shale in central Nevada and the McKelligon Canyon Formation in west Texas. Anatifopsis fillmorensis new species comes from the middle Fillmore Formation in western Utah and a Ninemile Shale equivalent limestone bed in southern Nevada. The possible solute Drepanocystis dubius new genus new species from the lower Wah Wah Limestone in western Utah, shows unusual morphology with an elongate theca and a long arm shaped like a sickle. INTRODUCTION A LTHOUGH THE kirkocystid mitrate Anatifopsis is among the most common and successful stylophorans in the Ordovician, to date none have been described from the western United States. This genus is known from deposits ranging throughout the Ordovician from the Tremadocian to the Hirnantian with species recorded from various parts of Laurentia, Perigondwanan Europe, North Africa, and Korea (Lee et al., 2004; Lefebvre et al., in press). Presently, none are recorded from Baltica. Here we describe two new species of Anatifopsis and a very unusual possible solute from Early Ordovician faunas from Nevada and Utah, with a few additional mitrate specimens included from the McKelligon Canyon Formation in west Texas. Unlike most of the crinoids, eocrinoids, parablastoids, and edrioasteroids in these faunas, which attached to hard substrates such as hardgrounds and lithified mounds, these homalozoan groups were free-living on soft muddy or micritic sediments. Early Ordovician echinoderm faunas from the Fillmore Formation, Wah Wah Limestone, and Ninemile Shale show previously unexpected levels of diversity. These faunas indicate that the Ordovician echinoderm radiation was well under way earlier than formerly expected including: edrioas- teroids (Guensburg and Sprinkle, 1994), eocrinoids (Sumrall et al., 2001), protocrinoid, camerate, and disparid crinoids (Guensburg and Sprinkle, 2003; Guensburg, 2010), asteroids (Blake and Guensburg, 2005; Blake et al., 2007), and parablastoids (Sprinkle and Sumrall, 2008). Further informa- tion on the depositional environments, collection, distribution, diversity, and evolutionary history of the echinoderms in these faunas can be reviewed in Guensburg and Sprinkle (1992, 2000, 2001, 2003), Sprinkle and Guensburg (1995, 1997) and Sprinkle et al. (2008). PREVIOUS WORK Kirkocystid mitrate stylophorans are the most abundant and diverse clade of peltocystid mitrates found throughout Europe, Korea, North America, and Morocco (for a review see Parsley, 1991; Lee et al., 2004; and Lefebvre, 2007). The general morphology of kirkocystids is congruent with other mitrate stylophorans. The main body comprises a small, globular to flattened theca with distinctly different surfaces. The upper surface is domed and convex, dominated by two large adoral plates. The lower surface is flat to slightly concave with the edges of the adorals and several additional smaller plates. These plates largely overlap and some are not visible from the thecal exterior but can be seen in serial sections and disarticulated material (Jefferies, 1981, 1986; Lefebvre, 1999, 2001, 2003). The aulacophore appendage is tripartite with a highly flexible proximal region, a stylocone interpreted as the position of the mouth, and a distal feeding portion with uniserial ossicles and biserial cover plates. At the opposite end of the theca is a single, small, movable spine. The western U.S. kirkocystid fauna was included in the Lower to Middle Ordovician kirkocystid biofacies by Lefebvre (2007). Localities where these specimens occur, however, vary widely in their depositional environment. The Ninemile Shale was deposited on the outer shelf in deep water below storm wave base. Although echinoderms and echinoderm fragments are generally in low abundance in the Ninemile Shale, kirkocystids are among the most common elements of this fauna. In contrast, the Fillmore Formation was deposited in shallow water environment associated with storm beds. Kirkocystids include isolated specimens buried by obrution events as well as small storm beds made of disarticulated plates in high abundance. Similarly, material from ‘‘Unit O pd ’’ in the Arrow Canyon Range includes numerous specimens preserved in a storm bed that is a 2.5 to 3 cm thick kirkocystid grainstone. The McKelligon Canyon Formation has produced only a few complete specimens and one small slab of plates but appears to be similar to the Fillmore Formation in having a generally shallow depositional environment. GEOGRAPHIC AND STRATIGRAPHIC OCCURRENCE The specimens reported in this paper come from three different geographic areas and four zones in the Early Ordovician. About 20 mitrate specimens along with several slabs of fragments (Sprinkle and Guensburg, 1995, fig. 10) have been collected from seven localities of the Fillmore Formation in the Ibex area of western Utah. These mitrates come from near the middle of the Fillmore Formation in Zones G-1 and G-2 (Hintzeia celsaora and Protopliomerella contracta Zones) which are middle Ibexian (latest Tremado- cian to early Floian or Arenigian) in age. The possible solute was collected in the overlying basal Wah Wah Limestone in Journal of Paleontology, 86(4), 2012, p. 595–604 Copyright ’ 2012, The Paleontological Society 0022-3360/12/0086-0595$03.00 595