852 Systematic paleontology
The classification used herein follows the phylogeny-based revision of crinoid higher taxa by Wright et al. (2017). Recent phylogenetic analyses find disparids to be sister to the Cladida, with hybocrinids nested within the Cladida and sister to the porocrinids (Ausich et al., 2015; Wright, 2017). At higher taxonomic scales, both disparids and hybocrinids belong to the infraclass Inadunata, which is placed within the newly resur- rected subclass Pentacrinoidea (Wright et al., 2017). Morpho- logical terminology follows Ubaghs (1978) and Ausich et al. (1999), with modifications from Ausich (1996, 1998) and Ausich et al. (2015). Plate diagrams for the genera treated in this study are given in Supplemental Data. Abbreviations used in designating measurements include: ACH, aboral cup height; ACW, aboral cup width; AH, arm height; ASH, anal sac height; CaH, calyx height; CoH, column height; and CrH, crown height. All measurements are given inmm; an asterisk (*) indicates that a measurement is of a partial or compacted specimen.
Class Crinoidea Miller, 1821 Subclass Pentacrinoidea Jaekel, 1894
Infraclass Inadunata Wachsmuth and Springer, 1885 Parvclass Disparida Moore and Laudon, 1943 Order Eustenocrinida Ausich, 1998 Family Eustenocrinidae Ulrich, 1925
Genus Eustenocrinus Ulrich, 1925
Type species.—Eustenocrinus springeri Ulrich, 1925, by monotypy.
Occurrence.—Ordovician (Katian), Ontario, Canada.
Remarks.—In many ways, Eustenocrinus is an iconic Ordovi- cian crinoid. It has an unusual morphology that defines an order- level taxonomic rank with compound radial plates in all five rays, only four functional arms, and the anal sac seated directly on the C radial plate. However, Eustenocrinus is a monospecific genus, and its only species, E. springeri, is relatively poorly documented. Prior to the present study, we were aware of only a single specimen (the holotype) of this taxon. Ulrich (1925) illustrated his new taxon with only line drawings: one a plate diagram and the other of a partial crown in lateral view. With the exception of Moore and Lane (1978a, fig. 347.1c, d), all sub- sequent authors have illustrated E. springeri with either a reproduction or modification of Ulrich’s original drawings. The exceptions are photographs of two sides of the holotype (USNMS 2148) byMoore and Lane (1978a). The holotype is a partial crown that has been prepared to be
loose from the matrix. The two parts of this specimen include the separated partial aboral cup that includes inferradial plates to the proximal secundibrachials (Fig. 2.1, 2.2). The proximal
Journal of Paleontology 92(5):850–871
column is still embedded in the matrix and includes the attached basal circlet (Fig. 2.3). Thus, the three new specimens documented herein from the Brechin fauna add significantly to our understanding of this important Ordovician crinoid. Two specimens (UMMP 74652 and 74653) are partial crowns with some column attached, and the third specimen (UMMP 74654) is a set of complete or nearly complete arms.
Eustenocrinus springeri Ulrich, 1925 Figures 2, 3
1925 Eustenocrinus springeri Ulrich in Foerste, p. 99, fig. 14. 1938 Eustenocrinus springeri; Bassler, p. 99. 1943 Eustenocrinus springeri; Bassler and Moodey, p. 474. 1953 Eustenocrinus springeri; Ubaghs, p. 744, fig. 18a, b. 1964 Eustenocrinus springeri; Yakovlev, p. 66, fig. 92a. 1973 Eustenocrinus springeri; Webster, p. 129. 1978 Eustenocrinus springeri; Ubaghs, p. T122, fig. 93.1, 93.2.
1978a Eustenocrinus springeri; Moore and Lane, p. T553, fig. 347.1.
1986 Eustenocrinus springeri; Webster, p. 147. 2013 Eustenocrinus springeri; Webster andWebster, p. 1477.
Holotype.—USNM S 2148.
Diagnosis.—Disparid with compound radials in all five rays; four free arms, one each in A, B, D, and E rays; anal series articulated directly above the C superradial plate.
Occurrence.—Eustenocrinus springeri was originally descri- bed from the ‘lower Trenton’ at Kirkfield, Ontario, Canada, which is stratigraphically equivalent to the upper Bobcaygeon Formation. New material is from the Bobcaygeon-Verulam contact zone at the Carden Quarry (UMMP74654) and from an uncertain location but probably the Carden Quarry (UMMP 74652, UMMP 74653) (Ordovician, Katian).
Description.—Crown large, cylindrical when in closed, trauma posture (Fig. 2.1). Aboral cup small, subcylindrical, but constricted at basal circlet-inferradial circlet juncture (Fig. 2.5), approximately of same diameter at proximal column (Fig. 2.6); width to height ratio ~1.0–2.0; plates gently convex, sculpture smooth. Basal circlet ~30% of aboral cup height; basal plates five,
pentagonal, slightly wider than high. Radial circlet ~70%of aboral cup height; radial plates five, all compound. Inferradial plates as high as wide; superradials slightly wider than high. Radial facet plenary with first primibrachial sutured into calyx (Fig. 3.3). Anal X only anal plate in cup, indistinguishable from first
primibrachial, sutured immediately above C radial plate, approximately as wide as high (Fig. 3.4). More distal anal plates above anal X similar to brachials. Arms four, extremely long (Fig. 2.8), branching once isotomously on seventh or eleventh primibrachial (Fig. 2.4, 2.7).
Figure 2. Eustenocrinus springeri Ulrich, 1925: (1–3) holotype, USNM S 2148; (1) AB interray view of partial crown (radial circlet at the bottom to proximal secundibrachials); (2) C ray (note anal sac directly above C superradial plate) view of partial crown (radial circlet at the bottom to proximal secundibrachials); (3) lateral view of partial column with attached basal circlet; (4) UMMP 74653, lateral view of partial crown and column (note indentation at basal circlet- inferradial circlet junction); (5–6) UMMP 74652; (5) enlargement of C ray (note anal sac directly above C superradial plate) lateral view of crown and proximal column; (6) entire preserved specimen; (7–8) nearly complete set of arms assigned to E. springeri, UMMP 74654; (7) enlargement of proximal rays; (8) arms (note long, gracile ramules). Scale bars=2.5mm (1–3, 5, 7); 5.0mm (4, 6, 8).
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