Introduction
The Whiterockian Series is the Laurentian expression of the Middle Ordovician Series. Originally described as a stage composed of five faunal zones (Cooper, Reference Cooper1956), the Whiterockian was elevated to the rank of series by Ross (Reference Ross1982). Ross and Ethington (Reference Ross and Ethington1991) selected the section at the Whiterock Canyon Narrows, Nevada, as its stratotype and located the first appearance datum (FAD) of the conodont Tripodus combsi (senior subjective synonym of T. laevis) within the section. The Whiterock Canyon Narrows section was suggested as the global boundary stratotype with the FAD of T. combsi acting as the bioevent to mark the base of the Middle Ordovician (Ross and Ethington, Reference Ross and Ethington1992). Graptolite data, however, demonstrated that the FAD of T. combsi correlated to a younger graptolite interval than previously thought. Further complicating the status of the Whiterockian was the suggestion (Fortey and Droser, Reference Fortey and Droser1999, p. 186) that a faunal break was present, a suggestion borne out in this study, that conflicts with the International Stratigraphic Guide’s (Salvador, Reference Salvador1994) assertion that boundary stratotypes must exhibit “essentially continuous deposition.” Eventually the FAD of the conodont Baltoniodus triangularis in the Huanghuachang section, southern China, was selected as the GSSP (Global Standard Stratotype and Point) for the Middle Ordovician Series and the Dapingian Stage (Wang et al., Reference Wang, Stouge, Chen, Li, Wang, Finney, Zeng, Zhou and Erdtmann2009).
Location and measured sections
The stratotype for the Laurentian Whiterockian Series (Middle Ordovician) is the Whiterock Canyon Narrows section, Nevada (Fig. 1; see Finney and Ethington, Reference Finney and Ethington2000, fig. 2 for detailed location). The section lies on a steep, southeast-facing slope on the north side of Whiterock Canyon within the Monitor Range.
Figure 1 Index map for the Whiterock Canyon Narrows section (WCN) in the Monitor Range, Nevada (inset), and showing access from Copenhagen Canyon on the topographic base. The section is located in the NW ¼, sec. 3, T. 49 N., R. 16 W. on the Horse Heaven Mountain 15’ Quadrangle (UTM grid Zone 11, E 548, 525 m, N 4, 339, 225 m).
Outcrops low on the slope at Whiterock Canyon Narrows are assigned to the Devonian Rabbit Hill Formation (Finney and Ethington, Reference Finney and Ethington2000). The dense, yellow weathering shale and black chert lie in fault contact with the overlying Lower Ordovician Ninemile Formation.
Low within the Ninemile Formation there occurs a laterally persistent, 15cm thick, medium-gray, argillaceous limestone that has yielded trilobites, linguliform brachiopods, moldic gastropods, and conodonts. This bed, known informally as the “0 bed”, has served as the base of the Whiterock Canyon Narrows section for this and previous studies, including Finney and Ethington (Reference Finney and Ethington2000). Estimates of the thickness, originally measured in feet, of the Ninemile Formation above the “0 bed” range from 42.8–52.4 m, with at least an additional 3 m of Ninemile Formation shale below. Individual limestone beds within the Ninemile Formation have been processed for conodonts (Finney and Ethington, Reference Finney and Ethington2000) and collected for trilobites.
Historically, Ethington (Ross and Ethington, Reference Ross and Ethington1991; Finney and Ethington, Reference Finney and Ethington2000) has measured the Ninemile Formation directly up the slope (Fig. 2, east section). The present study followed that line through the lower 24 m of the section, then traversed to the west ~25 m in order to collect trilobites through a 9m thick interval of limestone (west section) that is not represented on the historic, east, line of section. Several limestone beds in the west section were processed for conodonts. The section ends within the Middle Ordovician Antelope Valley Limestone.
Figure 2 Whiterock Canyon Narrows section, Nevada, with the historic east and new west sections highlighted.
Lithostratigraphy
The Ninemile Formation is dominated by fissile, medium-gray shale that weathers to form an extensive talus slope in the Whiterock Canyon Narrow section. Laterally persistent, bedded limestone beds punctuate the talus slope. Uncommon, medium-gray, 3 to 46cm thick, argillaceous, petroliferous, lime mudstone beds are present in the lower 36 m of the section. Laterally discontinuous wackestone and packstone beds that have yielded trilobite, echinoderm, and linguliform brachiopod bioclasts are interbedded with shale in the upper 10 m of the Ninemile Formation. Texturally, these upper limestones are similar to those of the overlying Antelope Valley Limestone. One or more hardgrounds are suggested within these upper Ninemile Formation limestones by the presence of dark-gray bedding surfaces to which echinoderm holdfasts are attached. Additionally, intervals of the lower talus slope are armored by nodular limestone clasts that weather to yellowish gray. The nodular limestones have yielded articulated trilobites and echinoderms along with rare graptolites.
The base of the overlying Antelope Valley Limestone is placed at the base of the lowest, laterally continuous, 1.5m thick bed of wackestone to packstone. This bed forms a prominent bench on the slope. The Antelope Valley Limestone is divisible into an oncolitic middle member and a lower member that includes lime mudstone to grainstone interbedded with minor shales (Ross and Ethington, Reference Ross and Ethington1991).
Biostratigraphy
Brachiopod biostratigraphy
Cooper (Reference Cooper1956) outlined the concept of the Orthidiella brachiopod Zone, based upon the presence of the eponymous genus, as the lowest zone of his Whiterockian Stage. Cooper conjectured that this zone, in part, filled an evolutionary gap between the brachiopod faunas of the former Canadian (Lower Ordovician) and Chazyan (Middle Ordovician) series in eastern Laurentia at the Sauk-Tippecanoe sequence unconformity of Sloss (Reference Sloss1963). Following the practice of the time, however, he did not record specific stratigraphic distribution for his materials or define its zonal boundaries. Subsequently, the Orthidiella Zone was correlated with trilobite Zone L of Ross (Reference Ross1951) and the Orthis subalata brachiopod Zone of Hintze (Reference Hintze1953) of Idaho and Utah (Fig. 3). More recently this interval in Utah has been treated as the Orthidiella Zone (Ross and Ethington, Reference Ross and Ethington1992) and the Paralenorthis-Orthidiella Zone (Ross et al., Reference Ross, Hintze, Ethington, Miller, Taylor and Repetski1997).
Figure 3 Biostratigraphic framework for the Lower-Middle Ordovician boundary in Utah and Nevada. The gray interval in the Whiterock Canyon Narrows columns suggests the extent of the sub-Whiterockian lacuna. Abbreviations: AV—Antelope Valley Limestone; Pr.—Presbynileus; Ps.—Psephosthenaspis. Columns 1, 2, 5, 6, 7 after Ross et al. (Reference Ross, Hintze, Ethington, Miller, Taylor and Repetski1997); column 3 after Ross (Reference Ross1951), Hintze (Reference Hintze1953), and Ross et al. (Reference Ross, Hintze, Ethington, Miller, Taylor and Repetski1997); column 4 after Fortey and Droser (Reference Fortey and Droser1996), Adrain et al. (Reference Adrain, McAdams and Westrop2009), and Adrain et al. (Reference Adrain, McAdams and Karim2012).
Trilobite biostratigraphy
A classic succession of silicified trilobites from Idaho and Utah has served as the basis of the zonation of the Lower and lower Middle Ordovician strata in Laurentia (Fig. 3). These zones were given letter designations (Zones A–M) when developed by Ross (Reference Ross1951) with taxon-based names subsequently provided by Hintze (Reference Hintze1953). Adrain et al. (Reference Adrain, McAdams and Westrop2009) recollected strata assigned to the latest Ibexian Zone J (the Pseudocybele nasuta trilobite Zone) and were able to divide it into three more finely resolved intervals, in ascending order: the Pseudocybele paranasuta Zone, a restricted “P. nasuta” Zone, and an uppermost unstudied interval. Unfortunately, the basal Whiterockian trilobite faunas of the overlying Zone L (the Orthis subalata brachiopod Zone in Utah) are poorly silicified and were understudied until the work of Fortey and Droser (Reference Fortey and Droser1996). In examining calcareous, “crack out” material they were able to establish a succession of 3 trilobite subzones based upon species of the trilobite Psephosthenaspis: the P. microspinosa, P. pseudobathyurus, and P. glabrior subzones (in succession). Adrain et al. (Reference Adrain, McAdams and Karim2012) subsequently elevated these subzones to zones.
The trilobite faunas recovered from the Whiterock Canyon Narrows section in this study (Fig. 4) resolve neatly into two components. The collections from the lower Ninemile Formation include species of the trilobite Lachnostoma, a genus that appears to be restricted to the “Pseudocybele nasuta” Zone (see Adrain et al., Reference Adrain, McAdams and Westrop2009). By definition, trilobites documented by Fortey and Droser (Reference Fortey and Droser1999) from the lower Antelope Valley Limestone are Whiterockian. The present study increases the documented diversity in the Antelope Valley Limestone in this section by five species and extends the ranges of previously identified species downward into the uppermost Ninemile Formation in the collections in the west section. While no specimens of Psephosthenaspis were recovered from Whiterock Canyon, the recovery of Pseudomera arachnopyge (Fortey and Droser, Reference Fortey and Droser1996) allows this Whiterockian fauna to be correlated with the Psephosthenaspis pseudobathyurus Zone from Ibex.
Figure 4 Trilobite species range chart for the Whiterock Canyon Narrows section, Nevada. Collections from WCN-(-10) to WCN-122 were recovered from the eastern sections while collections WCN-132 to WCN-190 were recovered from the western section. Species ranges are connected with solid line, generic ranges are connected with dashed line. Gray shading indicates intervals within which nodular limestone was recovered from float. Abbreviations: AVL—Antelope Valley Limestone; P.—Psephosthenaspis.
Conodont biostratigraphy
Ethington and Clark (Reference Ethington and Clark1971, Reference Ethington and Clark1981) collected conodonts from the entire Lower Ordovician and lower Middle Ordovician succession from Ibex, Utah. They were able to integrate the bases of their thirteen conodont zones and intervals (Ethington and Clark, Reference Ethington and Clark1981) with the boundaries in Hintze’s (Reference Hintze1953) trilobite zonal succession in order to produce an integrated faunal zonation for the region (Ross et al., Reference Ross, Hintze, Ethington, Miller, Taylor and Repetski1997). The latest Ibexian rocks at Ibex, Utah, are assigned to the Reutterodus andinus conodont Zone (Ross et al., Reference Ross, Hintze, Ethington, Miller, Taylor and Repetski1997).
Ross et al. (Reference Ross, Hintze, Ethington, Miller, Taylor and Repetski1997) revised the conodont biozonation for the Ibexian and lower Whiterockian Series at Ibex and introduced the Tripodus laevis conodont Zone to replace the former Microzarkodina flabellum–Tripodus laevis interval of Ethington and Clark (Reference Ethington and Clark1981). The First Appearance Datum (FAD) of T. laevis, a horizon that also served to mark the base of the Middle Ordovician, served to mark the base of this zone. The name of the eponymous species was synonymized with T. combsi (Bradshaw), with the acceptance by Sweet et al. (Reference Sweet, Ethington and Harris2005) of an earlier reconstruction (Stouge, Reference Stouge1984) of the elements in the apparatus of Tripodus Bradshaw. Ross and Ethington (Reference Ross and Ethington1991, Reference Ross and Ethington1992) documented the FAD of T. combsi from the Whiterock Canyon Narrows section at the base of the Antelope Valley Limestone, emplaced a “spike” in the section to indicate the base of the Whiterockian Series, and suggested that it might serve as the GSSP for the middle series of the Ordovician. Subsequent work revised the FAD of T. combsi downward 3 m (10 feet) into the underlying Ninemile Formation (Fig. 3; Finney and Ethington, Reference Finney and Ethington2000). Ultimately, analysis of a small graptolite fauna from the Whiterock Canyon Narrows section indicated that the FAD of T. combsi occurred higher in the graptolite succession than previously understood, which disqualified it to serve as the GSSP.
Tripodus combsi was recovered from the western section at the Whiterock Canyon Narrows (Fig. 5) from a horizon 11.8 m below the top of the Ninemile Formation. Additional collections within the overlying Ninemile Formation yielded a fauna typical of the Tripodus combsi Zone. A subjacent collection from the western section yielded Reutterodus andinus, the eponymous species for the underlying Reutterodus andinus conodont Zone. Three additional collections (8–20 m) that were resampled from the eastern section yielded Juanognathus variabilis and Parapanderodus asymmetricus. These latter taxa are known to be associated with R. andinus in the Ibex region, Utah (Ross et al., Reference Ross, Hintze, Ethington, Miller, Taylor and Repetski1997, p. 26, pl. 1), which suggests that the base of the R. andinus Zone may extend down section to ~8 m above the “0 bed” within the section.
Figure 5 Conodont species range chart for the Whiterock Canyon Narrows, east section (0–20 m) and west section (30–55 m), Nevada. Base of the Reutterodus andinus Zone based upon Finney and Ethington (Reference Finney and Ethington2000). Abbreviations: AVL—Antelope Valley Limestone; B—Bergstroemognathus; D—Drepanoistodus; J—Juanognathus; O. c. – F. m.—Oepikodus communis-Faraeusodus marathonensis conodont Zone; Pa—Parapanderodus; Pr—Protopanderodus.
The presence of a sub-Whiterockian unconformity in the upper Ninemile Formation at Whiterock Canyon Narrows
Continuity of deposition within the Whiterock Canyon Narrows section has been a contentious issue. Adrain and Fortey (Reference Adrain and Fortey1997, p. 80) and Fortey and Droser (Reference Fortey and Droser1999, p. 186) provided trilobite data suggestive of a hiatus. Finney and Ethington (Reference Finney and Ethington2000) and Loch (Reference Loch2002), however, asserted that evolutionary conodont lineages and lack of physical evidence argued for continuous deposition across the base of the Whiterockian Series. Examination of parallel sections provides a final resolution to this question and establishes an approximate position of a cryptic unconformity at the base of the Whiterockian at its stratotype.
In the historic (Figs. 2, 6; east section) ascent of the Whiterock Canyon Narrows section, shale dominates the uppermost 12 m of the Ninemile Formation. The first appearance (FAD) of Tripodus combsi occurs 3 m below the top of the Ninemile Formation (Finney and Ethington, Reference Finney and Ethington2000). This horizon defines the base of the Whiterockian Series (Ross and Ethington, Reference Ross and Ethington1991). Fortey and Droser (Reference Fortey and Droser1999) described a suite of 13 trilobite species from the lower Antelope Valley Limestone above this horizon that must be considered as Whiterockian along with the brachiopod species listed by Cooper (Reference Cooper1956). Fortey and Droser (Reference Fortey and Droser1999) identified the Ibexian trilobite Lachnostoma latucelsum from 6 m below the top of the Ninemile Formation on this ascent.
Figure 6 Distribution of selected taxa to highlight position of cryptic, sub-Whiterockian unconformity (dashed line) in the Ninemile Formation, Whiterock Canyon Narrows section, Nevada. Gray shading indicates limestone within the section. Distribution of trilobites in the eastern section above 25 m is from Fortey and Droser (Reference Fortey and Droser1999). Abbreviation: AVL—Antelope Valley Limestone; T. Tripodus.
The traverse westward to a second ascent (Figs. 2, 6; west section) passes through a nine-meter-thick package of laterally discontinuous wackestone and grainstone that is overlain by shale. Trilobites and conodonts recovered from this west section place the three biostratigraphic horizons discussed above at different positions within the Ninemile Formation. Tripodus combsi has its FAD 9 m lower in the section at 11.8 m below the base of the Antelope Valley Limestone. Whiterockian trilobites extend 11.8 m below the base of the Antelope Valley Limestone. The last appearance (LAD) of Lachnostoma spp. occurs 37.2 m below the base of the Antelope Valley Limestone, 11.2 m lower than on the eastern ascent. These six data points allow the approximate position of a cryptic unconformity to be traced between the two sections (dashed line in Fig. 6) with a relief of 9 m. The presence of this unconformity at the Whiterock Canyon Narrows section, however, should not be used to suggest the presence of a regionally significant unconformity without further data. Instead, an alternative section that includes a more continuous depositional record (Salvador, Reference Salvador1994), as well as the FAD of Tripodus combsi, needs to be identified to serve as a better boundary stratotype for the Whiterockian.
A model can be developed for the formation of this sub-Whiterockian unconformity. The sequence begins with deposition of Ninemile Formation shale with bedded and nodular limestone during the late Ibexian in a ramp or outer continental-slope setting below wave base (Ross et al., Reference Ross, James, Hintze and Poole1989). Regression and a sea-level drop in the late Ibexian to earliest Whiterockian (Nielson, Reference Neilsen1992; Wang et al., Reference Wang, Stouge, Chen, Li, Wang, Finney, Zeng, Zhou and Erdtmann2009; Landing, Reference Landing2012) resulted in the scouring of a localized channel into the Ninemile Formation shale. Transgression and rapid progradation of lower Antelope Valley-type limestone (Ross et al., Reference Ross, James, Hintze and Poole1989) filled the channel through the periodic influx of wackestone and grainstone, with occasions of hardground formation, that interrupted intervals of shale deposition. Transgression and progradation of upper-slope limestone climaxed in the formation of outer continental-shelf oncolite complexes of the middle member of the Antelope Valley Limestone (Ross et al., Reference Ross, James, Hintze and Poole1989).
Repositories and institutional abbreviations
All trilobite types and illustrated specimens are curated at the Carnegie Museum of Natural History (CM) in Pittsburgh, Pennsylvania. Occurrence data are keyed by measured section abbreviation and measured distance (in original feet) above the base of the section (ex. WCN-137). Some trilobite material was collected as float (F) from the slopes in the Ninemile Formation for comparative purposes with their approximate stratigraphic position indicated (e.g., WCN-F25–40). Abundance data are recorded as (cranidia-pygidia-librigenae) for each collection horizon.
Systematic paleontology
Morphologic terms used follow Whittington (Reference Whittington1997). Most taxa are held in open nomenclature due to the small and often fragmentary nature of the specimens recovered. The contrast in preservation when trying to compare mechanically prepared material from Whiterock Canyon and silicified materials from the Ibex region, Utah, exacerbated these problems.
Phylum Arthropoda Latreille, Reference Latreille1829
Class Uncertain
Order Agnostida Salter, Reference Salter1864
Family Metagnostidae Jaekel, Reference Jaekel1909
Genus Arthrorhachis Hawle and Corda, Reference Hawle and Corda1847
Type species
Battus tardus Barrande, Reference Barrande1846, p. 35, from the Kraluv Dvur Formation of the Czech Republic.
Arthrorhachis sp.
Figure 7 Arthrorhachis Hawle and Corda, Reference Hawle and Corda1847 and Lachnostoma Ross, Reference Ross1951. (1, 2) Arthrorhachis sp., (1) dorsal view (×15.0) testate cephalon, Antelope Valley Limestone, WCN-178, CM 59000; (2) dorsal view (×15.0) testate cephalon, Ninemile Formation, WCN-F25, CM 59001. (3–13) Lachnostoma sp. 1, all from Ninemile Formation, (3, 4, 7) palpebral (×6.4), lateral (×4.7), and anterior (×6.5) views, testate carapace, WCN-F40, CM 59002; (5, 8) lateral oblique (×2.8) and palpebral (×2.4) views of testate, partially disarticulated cephalon, WCN-F25–40, CM 59003; (6) palpebral view (×3.0) of partially exfoliated cranidium, WCN-F25–40, CM 59004; (9, 10) lateral (×4.9) and dorsal (×4.1) views of testate librigena, WCN-F40–70, CM 59005; (11, 12) dorsal (×1.8) and lateral oblique (×2.6) views of testate, enrolled, thoraco-pygidium, WCN-F25–40, CM 59006; (13) dorsal view (×4.5) of testate pygidium, WCN-F25–40, CM 59007. (14–20) Lachnostoma sp. 2, all from Ninemile Formation, (14, 15, 17, 18) palpebral (×2.9), anterior (×1.8), left lateral (×2.2), and dorsal pygidial (×1.8) views of testate, slightly compacted, enrolled carapace, WCN-F40–70, CM 59008; (16, 19, 20) palpebral view (×2.5) of cephalon, view dorsal (×2.5) of pygidium, and palpebral (×6.8) enlargement of testate, fragmentary, enrolled carapace, WCN-F40–70, CM 59009.
Remarks
Three poorly preserved cranidia from WCN-F25–40, WCN-174, and WCN-178 appear similar to Trinodus sp. 1 of Ross (Reference Ross1967, p. D9, pl. 3, fig. 19, 1972, p. 28, pl. 11, fig. 15) from the Antelope Valley Limestone in Nevada. The specimens from the Whiterock Canyon Narrows share the broad border and border furrow, the weak F2 furrow, and ovate glabella illustrated by Ross. Fortey (Reference Fortey1980, p. 27), however, restricted Trinodus McCoy, Reference McCoy1846, to type and asserted that Arthrorhachis can accommodate species formerly assigned to Trinodus.
Class Trilobita Walch, Reference Walch1771
Order Asaphida Fortey and Chatterton, Reference Fortey and Chatterton1988
Family Asaphidae Burmeister, Reference Burmeister1843
Genus Lachnostoma Ross, Reference Ross1951
Type species
Lachnostoma latucelsum Ross, Reference Ross1951, p. 95, by original designation, from the Ibexian Garden City Formation of northern Utah.
Lachnostoma species 1
cf. 1989 Lachnostoma latucelsum Ross; Reference DeanDean, p. 39, pl. 32, figs. 10–15, pl. 33, figs. 1–16.
cf.1996Lachnostoma latucelsum; Reference Fortey and DroserFortey and Droser, fig. 7.12, 7.13.
Material and occurrence
Total of 28 cranidia, 67 pygidia, 29 librigenae, and seven articulated individuals. Present in the Ibexian Ninemile Formation in WCN-(-10) (3-0-0), WCN-0 (1-0-0), WCN-2 (0-1-0), WCN-25 (1-1-0), WCN-F25-40 (11-41-15 and seven articulated individuals), WCN-39 (0-0-1), WCN-F40–70 (0-3-2), WCN-41 (0-1-1), WCN-64 (7-6-4), WCN-67 (5-10-6), WCN-111 (0-3-0), WCN-116 (0-1-0), and WCN-122 (0-1-0).
Remarks
Specimens of Lachnostoma sp. 1 examined from the Ninemile Formation are united in their smooth prosopon. Lachnostoma sp. 1 differ from the type material (Lachnostoma latucelsum Ross, Reference Ross1951, p. 95–97, pl. 21, figs. 13–25, pl. 22, figs. 3, 6–8, pl. 23, figs. 5, 6; Adrain et al., Reference Adrain, McAdams and Westrop2009, figs. 21Q, 21U) and contemporaneous material from Utah (Hintze, Reference Hintze1953, p. 187, pl. 18, figs. 4–16), however, in that the glabella appears more constricted between the palpebral lobes. The anterior course of the facial sutures in L. sp. 1 forms a more even, broad curve than in L. latucelsum. The maximum width of the cranidium (tr.) of L. sp. 1 is approximately 90% the total cranidial length, whereas in the type the maximum width and length are nearly equivalent. The pygidia of L. sp. 1 differs from the type material in having axial furrows that are recurved distally, rather than straight, which results in the distal end of the axis being more convex and pronounced. In these aspects, L. sp. 1 compares more closely to the specimen previously illustrated as L. latucelsum by Fortey and Droser (Reference Fortey and Droser1996) from the Ninemile Formation and those identified by Dean (Reference Dean1989) from the Outram and Skoki formations of Alberta, Canada.
Lachnostoma species 2
Material and occurrence
Present in the Ibexian Ninemile Formation in WCN-(-10) (1-0-0), WCN-F25–40 (0-0-1 and one articulated carapace), and WCN-F40–70 (0-1-0 and one articulated carapace).
Remarks
The presence of the granulose prosopon on Lachnostoma sp. 2 was used to distinguish it from similar sized specimens of Lachnostoma sp. 1. Additionally, two pairs of broad depressions along the weakly impressed axial furrows and steeply inclined palpebral lobes serve to further distinguish L. sp. 2.
Dean (Reference Dean1988, p. 5, pl. 1.3, figs. 4, 6–9, 11) illustrated Lachnostoma n. sp. from the McKay Group of British Columbia. Lachnostoma n. sp. compares with Lachnostoma sp. 2 in the presence of two broad depressions along the axial furrow. These depressions in L. n. sp., however, lie at the posterior end of the palpebral lobes and behind the glabellar tubercle. Further, L. n. sp. lacks a granular prosopon and the glabella is not as well defined between the palpebral lobes.
Genus Presbynileus Hintze, Reference Hintze1954
1953Paranileus Hintze. [Junior homonym of Paranileus Kobayashi, Reference Kobayashi1951]
Type species
Paranileus ibexensis Hintze, Reference Hintze1953, p. 199–200, by original designation, from the Ibexian Fillmore Limestone of the Ibex region of Utah.
Diagnosis
See Jaanusson in Moore, Reference Moore1959, p. O343.
Remarks
Hintze (Reference Hintze1953) erected the genera Pseudonileus and Paranileus from the Ibex region of Utah for two generally effaced, slightly to moderately convex asaphids. Hintze separated the genera on the basis of their hypostomal shape, degree of convexity (sag.), curvature of the anterior facial suture, and relative proportions and position of the palpebral lobes. Both names were preoccupied and Hintze (Reference Hintze1954) proposed replacement names for both (Protopresbynileus and Presbynileus, respectively). Jaanusson (in Moore, Reference Moore1959) moved both taxa to the rank of subgenus within Presbynileus, a practice followed by Fortey (Reference Fortey1975) and Dean (Reference Dean1989). We prefer, however, to follow Hintze (Reference Hintze1953, Reference Hintze1954) and, subsequently, Fortey and Droser (Reference Fortey and Droser1999) in retaining these two taxa at the rank of genus.
Dean (Reference Dean1989) erected the species Presbynileus (Presbynileus) latifrons, although without benefit of an associated hypostome. Presbynileus latifrons, however, exhibits axial furrows on both the cranidium and pygidium that are moderately impressed, moderately inclined palpebral areas, a steeply declined frontal lobe of the glabella, and a moderately convex pygidial axis. Further, there is a pronounced set of terrace lines limited to the frontal lobe of the glabella. These stand in contrast to the type species for both Protopresbynileus and Presbynileus.
The cranidium illustrated by Fortey and Droser (Reference Fortey and Droser1999, fig. 7.16) from the basal Antelope Valley Limestone as Protopresbynileus cf. glaber exhibits moderately impressed axial furrows, a steeply declined frontal glabellar lobe, and terrace lines on the frontal lobe. These characters conform more closely to P. latifrons than to P.? glaber Fortey (Reference Fortey1975, p. 19–21, pl. 9, figs. 1, 2, 4) in their convexity, the impression of the axial furrows, and the width (tr.) between the axial furrows at the palpebral lobes. Additional cranidia recovered from the Ninemile Formation (Fig. 8.8–8.10) exhibit the same inclination to the frontal lobe, terrace lines, and moderately impressed axial furrows. Were further specimens exhibiting these characters and additional sclerites available, these Nevada materials (in conjunction with P. latifrons and P. glaber) may represent a new genus.
Figure 8 Presbynileus (Hintze, Reference Hintze1954). (1–3, 11, 14, 15) Presbynileus cf. P. latifrons Dean, Reference Dean1989, all from Ninemile Formation, (1–3) palpebral (×4.5), anterior (×4.4), and anterior oblique (×4.4) views of largely testate cranidium, WCN-F25-40, CM 59010; (11, 14) dorsal (×2.8) and lateral (×3.0) views of testate librigena, WCN-64, CM 59011; (15) dorsal view (×4.0) of fragmentary pygidium with doublure exposed on right side, WCN-64, CM 590012. (4–10, 12, 13) Presbynileus spp., all from Ninemile Formation, (4, 6) anterior and palpebral views (×2.5) of large, largely exfoliated cranidium, WCN-111, CM 59013; (5, 7) palpebral (×2.3) and anterior oblique (×1.6) views of exfoliated cranidium, Ninemile Formation, WCN-64, CM 59014; (8–10) palpebral (×4.8), anterior oblique, (×4.4) and anterior view showing prosopon (×7.2) of testate cranidium, WCN-F25–40, CM 59015; (12) palpebral view (×2.0) of fragmentary, testate cranidium, WCN-132, CM 59016; (13) dorsal view (×4.0) testate pygidium, WCN-(-10), CM 59017.
Presbynileus cf. P. latifrons Dean, Reference Dean1989
Figure 8.1–8.3, 8.11, 8.14, 8.15
cf. 1989Presbynileus (Presbynileus) latifrons Reference DeanDean, p. 40, pl. 34, figs. 1–4, 6, 7, 9–13, pl. 35, figs. 1–11.
Material and occurrence
Total of one cranidium, four pygidia, and two librigenae from the Ninemile Formation in WCN-(-10) (0-1-1), WCN-F12 (0-3-0), WCN-F25–40 (0-2-0), WCN-64 (0-2-1), and WCN-111 (1-0-0). Also known from the Pseudocybele nasuta Zone (Zone J) of the Outram Formation of Alberta, Canada, (Dean, Reference Dean1989).
Remarks
The cranidium illustrated from the Ninemile Formation conforms in shape and convexity of the glabella (both sag. and tr.), orientation of the palpebral lobes, orientation and impression of the axial furrows, and the prosopon of coarse terrace lines to the specimens of Presbynileus latifrons illustrated by Dean (Reference Dean1989). The fragmentary nature of both the Nevada and original material makes confident assignment of the cranidia problematic. The assigned librigenae exhibit a corresponding cord-like border, broad genal angle, and downward flexure of the posterior margin seen in P. latifrons. The pygidia from Nevada exhibit the long, evenly tapered axis, “panderian protuberance”, and evenly convex pleural region seen from Alberta. The broad (tr.) pygidia with a long, clearly defined axis are consistent with those assigned to Presbynileus latifrons (Dean, Reference Dean1989, pl. 34, figs. 10, 13, pl. 35, figs. 1–11). The Nevada pygidia (Figure 8.13), however, possess a more convex (tr.) axis (closer to Dean, Reference Dean1989, pl. 35, figs. 7, 8).
Presbynileus spp.
Remarks
Three cranidia were recovered singularly from the Ninemile Formation from WCN-F25–40 (Fig. 10.11–10.14), WCN-F40–70, and WCN-111 (Fig. 8.4, 8.6). These cranidia each exhibit the steeply declined frontal glabellar lobe bearing the terrace lines seen in Presbynileus latifrons Dean (Reference Dean1989). They each differ, however, in their width between the palpebral lobes relative to their total length and in the impression of the axial furrows.
Four additional smooth cranidia recovered singularly from the Ninemile Formation in WCN-F25-40, WCN-64, WCN-111, and WCN-132 are assigned to Presbynileus sp. in exhibiting a moderately declined frontal glabellar lobe, weakly impressed axial furrows, and a slight inclination of the palpebral areas. The palpebral lobes for the exfoliated cranidia from WCN-64 (Fig. 8.5, 8.7) and WCN-111 (Fig. 8.4, 8.6) are large and relatively close together, which results in a shape that is more elongate (sag.) than the specimens illustrated for Presbynileus ibexensis (Hintze, Reference Hintze1953, p. 199–200, pl. 12, figs. 6–12) or for Presbynileus utahensis (Hintze, Reference Hintze1953, p. 200–201, pl. 13, figs. 1–4).
Four pygidia from the Ninemile Formation were recovered from WCN-(-10) (0-1-0) and WCN-F12 (0-3-0) and assigned to Presbynileus based upon their greater overall convexity (tr., sag.) than seen in Protopresbynileus. The pygidia of Presbynileus ibexensis (Hintze, Reference Hintze1953, p. 199–200, pl. 12, figs. 10a, 10b, 12a, 12b) and of Presbynileus utahensis (Hintze, Reference Hintze1953, p. 200–201, pl. 13, fig. 3a–3d), in contrast to those from the Ninemile Formation, are nearly effaced.
Genus Ptyocephalus Whittington, Reference Whittington1948
Type species
Ptyocephalus vigilans Whittington, Reference Whittington1948, p. 567–572, by original designation, from the Pogonip Group, Antelope Range, Nevada.
Remarks
We follow Hu (Reference Hu1963), Dean (Reference Dean1989), and Adrain et al. (Reference Adrain, McAdams and Westrop2009) in the pragmatic use of Ptyocephalus Whittington, a taxon that is based upon the articulated carapace of Ptyocephalus vigilans. Although Kirkella Kobayashi (Reference Kobayashi1942) is the senior subjective synonym of Ptyocephalus (Whittington, Reference Whittington1948; Dean, Reference Dean1989), it is based on an isolated pygidia and is itself a homonym (Kirkella Gunnell, Reference Gunnell1933).
Ptyocephalus cf. P. declevitus (Ross, Reference Ross1951)
Figure 9 Ptyocephalus Whittington, Reference Whittington1948, and Nileidae Angelin, 1854. (1–5) Ptyocephalus cf. P. declevitus (Ross, Reference Ross1951), all from Ninemile Formation, (1, 2) dorsal (×1.3) and lateral oblique showing prosopon (×2.9) views of testate, partially crushed pygidium, WCN-0, CM 59018; (3, 4) lateral and dorsal views (×3.8) of testate, fragmentary librigena, WCN-0, CM 59019; (5) dorsal view (×2.8) of testate, fragmentary pygidium, WCN-64, CM 59020. (6–11) Nileus cf. N. hesperaffinis Ross, Reference Ross1967, (6, 7) palpebral (×8.2) and lateral oblique (×11.0) views of testate, fragmentary cephalon, Ninemile Formation, WCN-159, CM 59021; (8) palpebral view (×8.1) of testate cranidium, Ninemile Formation, WCN-159, CM 59022; (9) palpebral view (×6.0) of exfoliated, fragmentary cranidium, Antelope Valley Limestone, WCN-174, CM 59023; (10) dorsal view (×5.3) of testate, pygidium, Ninemile Formation, WCN-132, CM 59024; (11) dorsal view (×7.3) of exfoliated pygidium, Antelope Valley Limestone, WCN-174, CM 59025. (12) Nileus? sp., dorsal view (×1.5) of testate pygidium, Antelope Valley Limestone, WC-190, CM 59026. (13–15) Nileus cf. N. svalbardensis Fortey, Reference Fortey1975, n. comb., all from Ninemile Formation, (13) palpebral view (×5.4) of testate cranidium, WCN-132, CM 59027; (14) palpebral view (×5.7) of testate, fragmentary cranidium, WCN-146, CM 59028; (15) anterior view (×6.7) of testate cranidium showing punctate prosopon, WCN-146, CM 5929. (16, 17) Nileidae indet., from the Ninemile Formation, WCN-0, (16) dorsal view (×3.4) of testate pygidium, CM 59030; (17) dorsal view (×1.5) of exfoliated pygidium, CM 59031.
cf. 1951Kirkella declevita Reference RossRoss, p. 91, pl. 21, figs. 1–12, pl. 37, figs. 6, 11, 12.
cf. 1953Kirkella declivata (sic); Reference HintzeHintze, p. 183, pl. 15, figs. 3, 4, 9–12.
cf. 1963Ptyocephalus declevitus; Reference HuHu, p. 88, pl. 13, figs. 10–14.
cf. 1989Ptyocephalus declevitus; Reference DeanDean, p. 41, pl. 35, figs. 12–15, pl. 36, 1–4, 6–13, pl. 37, figs. 6, 11, 12.
cf. 2009Ptyocephalus declevitus; Reference Adrain, McAdams and WestropAdrain et al., fig. 21R, 21V.
Material and occurrence
Two pygidia and one librigena were recovered from the Ibexian Ninemile Formation in WCN-0 (0-1-1) and WCN-64 (0-1-0).
Remarks
The pentagonal pygidial outline with an axis poorly defined by faintly impressed axial furrows conforms to the generic concept of Ptyocephalus. The long pygidia, approximately equal to their width, conform more in dimension to the younger species Ptyocephalus declevitus and P. acclivus (Hintze, Reference Hintze1953). The Ninemile Formation specimens differ from Ross’ (Reference Ross1951), however, in having axial and ring furrows that are less well impressed. The posteriolateral pygidial corners of the Nevada material are more angular than the rounded corners in P. acclivus (Hintze, Reference Hintze1953, 185–186, pl. 14, figs. 16–17, pl. 15, figs 1–2; Young, Reference Young1973, p. 110, 112, pl. 2, figs. 23, 24; Dean, Reference Dean1989, p. 41, pl. 36, fig. 5). Ross (Reference Ross1951, p. 92) noted that the pygidial length of Ptyocephalus vigilans Whittington (Reference Whittington1948, p. 567–572, pl. 82, figs. 1–5 for the holotype), the type species, is slightly less than the pygidial width in distinguishing it from P. declevitus. Adrain et al. (Reference Adrain, McAdams and Westrop2009, figs. 16X, 17F, 17G, 20 F) illustrated four older Ptyocephalus species in open nomenclature. The pygidia of these species, however, are uniformly shorter relative to their width than the Ninemile Formation pygidia.
Family Nileidae Angelin, Reference Angelin1854
Genus Nileus Dalman, Reference Dalman1827
Type species
Asaphus (Nileus) armadillo Dalman, Reference Dalman1827, by monotypy, from the Holen Limestone of Sweden.
Nileus cf. N. hesperaffinis Ross, Reference Ross1967
cf. 1967Nileus hesperaffinis Reference RossRoss, p. D13, pl. 4, figs. 18–25.
cf.1999Nileus hesperaffinis; Reference Fortey and DroserFortey and Droser, p. 193, fig. 7.1–7.7.
Material and occurrence
Total of 27 cranidia, 36 pygidia, and three librigenae. Present in the Ninemile Formation in WCN-132 (0-4-0), WCN-140 (1-0-0), WCN-145 (0-4-0), WCN-146 (1-2-0), WCN-159 (11-10-2), WCN-163.5 (3-2-0), and WCN-166 (0-1-1). Present in the Antelope Valley Limestone in WCN-172 (2-2-0), WCN-174 (9-8-0), WCN-176 (0-1-0), and WCN-178 (0-2-0). This extends the known range for this taxon at the Whiterock Canyon Narrows, Nevada (Fortey and Droser, Reference Fortey and Droser1999) from the Antelope Valley downward into the Ninemile.
Remarks
The cranidia and pygidia of Nileus cf. N. hesperaffinis from the Ninemile Formation conform completely to those illustrated previously from the Antelope Valley Limestone (Fortey and Droser, Reference Fortey and Droser1999). Ontogenetic variation is evident in the development of the genal spine. The spine is most pronounced in the smallest specimen (Fig. 10.2, 10.3) and is reduced as the specimen size increases (Ross, Reference Ross1967, pl. 4, fig. 19; Fortey and Droser, Reference Fortey and Droser1999, fig. 7.4) until lost in the largest illustrated specimen (Fortey and Droser, Reference Fortey and Droser1999, fig. 7.1).
Figure 10 Raphiophoridae Angelin, 1854. (1–8) Ampyx cf. A. compactus Ross, Reference Ross1967, all from the Ninemile Formation, (1–2) palpebral (×3.9) and anterior oblique (×6.2) views of testate cranidium, WCN-67, CM 59032; (3) palpebral view (×6.1) of partially exfoliated cranidium, WCN-67, CM 59033; (4) oblique view (×4.7) of 2 corroded cranidia that shows the extent of the glabellar spine, WCN-F25–40, CM 59034; (5, 6) palpebral and anterior oblique views (×5.8) of testate cranidium, WCN-F25–40, CM 59035; (7, 8) dorsal (×8.9) and posterior (×8.4) views of testate pygidium, WCN-67, CM 59036. (9–14) Ampyxoides cf. A. occipitalis Dean, Reference Dean1973, from Ninemile Formation; (9–10) dorsal, dorsal oblique views (×6.3) of partially exfoliated, fragmentary cranidium, WCN-159, CM 59040; (11–14) anterior (×6.3), dorsal (×4.5), dorsal oblique (×4.8), and lateral (×5.5) views of largely exfoliated cranidium, WCN-159, CM 59039. (15–20) Ampyxoides? sp. 1, from Antelope Valley Limestone, WCN-177, (15–18) lateral (×7.2), anterior (×6.2), dorsal (×4.6), and dorsal oblique (×5.3) views of partially exfoliated cranidium, CM 59037; (19, 20) dorsal and dorsal oblique views (×6.4) of exfoliated cranidium, Antelope Valley Limestone, CM 59038.
Nileus cf. N. hesperaffinis differs in minor manners from N. hesperaffinis Ross (Reference Ross1967) in having a cranidium that appears longer than wide, in a slightly narrower pygidial border, and in the presence of a very faintly defined pygidial axis. These differences, however, may be of preservational or ontogenetic in origin.
Nileus cf. N. svalbardensis Fortey, Reference Fortey1975, new combination
cf. 1975Nileus orbiculatoides svalbardensis Reference ForteyFortey, p. 43, pl. 11, figs. 1–13.
Material and occurrence
Total of eight cranidia and one hypostome from the Whiterockian Ninemile Formation in WCN-132 (4-0-0) and WCN-146 (4-0-0 + one hypostome).
Remarks
Several small, punctate cranidia were recovered that lacked evidence of axial furrows or an inflection passing laterally (tr.) from the axis to the palpebral lobes. The palpebral lobes of these individuals were relatively large and set posteriorly, which resulted in short (exsag.) posterior areas. Poronileus Fortey (Reference Fortey1975, p. 51) exhibits pronounced punctae, but has palpebral lobes that are smaller and set more anteriorly along with faintly impressed axial furrows.
The proportions of the palpebral lobes, the short (exsag.) posterior areas, and the lack of glabellar furrows seen in these specimens conform to Nileus Dahlman (1827). Within Nileus, Fortey (Reference Fortey1975) described two punctate species: Nileus porosus and Nileus orbiculatoides svalbardensis. Nileus porosus Fortey (Reference Fortey1975, p. 44–46, pl. 12, figs. 1–14) exhibits faintly impressed axial furrows, slightly inclined palpebral lobes that are set medially, and long (exsag.) posterior areas. These characters are not seen in the cranidia from Nevada. Fortey (Reference Fortey1975) erected Nileus orbiculatoides svalbardensis as a subspecies of N. orbiculatoides Schrank, Reference Schrank1972. Nielsen (Reference Neilsen1995, p. 239), however, excluded N. svalbardensis as a subspecies of N. orbiculatoides. While Nielsen (Reference Neilsen1995) suggested that N. svalbardensis may be related to a “Nileus depressus group,” he did not formally reassign it as a subspecies within that group. We elevate this subspecies to species rank and treat it as N. svalbardensis, pending further discussion. The short posterior areas and larger, medially positioned, declined palpebral lobes seen in the Nevada material are consistent with N. svalbardensis Fortey (Reference Fortey1975). Nileus cf. N. svalbardensis from Nevada, however, appears to exhibit an anterior course of the facial suture that diverges at less of an angle to the axis than N. svalbardensis and that passes into broad, rather than tight, curve as the facial suture approaches the axis.
Whittington (Reference Whittington1965, p. 362–363, pl. 36, figs. 1–10, pl. 32, figs. 8, 11) described the punctate Nileus? lacunosa from the younger Table Head Group of Newfoundland, Canada. This species differs from the Nevada material in having a more quadrate cranidial outline resulting from a shorter (sag.) frontal lobe.
Nileus? sp.
Figure 9.12
Remarks
A single pygidium from WCN-190 from the Antelope Valley Limestone is tentatively assigned to Nileus based upon its transverse outline and effaced axis, which are characters highlighted by Fortey (Reference Fortey1975, p. 40) in his diagnosis of the genus. This pygidium differs from that of Nileus cf. N. hesperaffinis (Fig. 9.10) in its larger size, the possession of a shorter (sag.) and narrower (tr.) border, and a moderate pygidial convexity (sag.). Ross (Reference Ross1967, p. D13, pl. 4, fig. 15) illustrated an additional Nileus pygidium in open nomenclature from the Antelope Valley Limestone. Ross’s pygidium is more elongate and with a broader border than that illustrated here.
Nileidae indet.
Remarks
Two distinctive pygidia from the Ninemile Formation, WCN-0, are comparable to species of Poronileus Fortey (Reference Fortey1975) in the rapidly tapering, long axis, the faintly impressed axial furrows, faintly impressed anteriormost ring furrow, and concave border. The Nevada specimens, however, appear relatively shorter (sag.) and have a border furrow that is better impressed post-axially. The assignment of these pygidia to Poronileus is tentative in the absence of punctate prosopon. They differ from each other in the width (tr.) of the axis relative to the pygidial width, the axial length (sag.) relative to the pygidial length, and the rate of taper of the axis.
Family Raphiophoridae Angelin, Reference Angelin1854
Genus Ampyx Dalman, Reference Dalman1827
Type species
Asaphus (Ampyx) nasuta Dalman, Reference Dalman1827, p. 252, by monotypy, from Sweden.
Ampyx cf. A. compactus Ross, Reference Ross1967
cf. 1967Ampyx compactus Reference RossRoss, p. D21, pl. 7, figs. 8–16.
Material and occurrence
Total of 18 cranidia and two pygidia from the Ibexian Ninemile Formation in WCN-F25-40 (13-1-0, plus two articulated carapaces) and WCN-67 (5-1-0).
Remarks
The material recovered from the Ninemile Formation compares with Ampyx compactus Ross (Reference Ross1967) in the shape of the glabella, the S1 lateral glabellar furrows, and the inclined posterior border of the cranidium. The occipital ring and posterior of the glabella, however, are wider (tr.) than in the specimens illustrated by Ross. Further, while the overall shape of the pygidium and the convexity of the pygidial margin are consistent, the Ninemile Formation pygidia are somewhat more elongate and have axial and ring furrows that are more well impressed.
Genus Ampyxoides Whittington, Reference Whittington1965
Type species
Ampyx semicostatus Billings, Reference Billings1865, by original designation, from the Table Head Group of Newfoundland, Canada.
Remarks
Two moderately common species from the upper Ninemile Formation and lower Antelope Valley Limestone are questionably assigned to Ampyxoides following Fortey and Droser (Reference Fortey and Droser1999, p. 195). The diagnosis of Ampyxoides (Whittington, Reference Whittington1965, p. 319), however, notes the presence of a glabellar spine that the Nevada specimens lack. Additionally, the Nevada taxa achieve their maximum glabellar width at or posterior to the glabellar mid-length. Both conditions appear uncommon among the Raphiophoridae and these species may better represent a new genus. In the absence of an assigned pygidium, however, they are retained with uncertainty within Ampyxoides.
Ampyxoides? cf. A. occipitalis Fortey and Droser, Reference Fortey and Droser1999
1999Ampyxoides cf. occipitalis Dean, Reference Dean1973; Reference Fortey and DroserFortey and Droser, p. 195, fig. 8.1–8.5.
Material and occurrence
Total of 10 cranidia. Present in the Ninemile Formation in WCN-159 (6-0-0) and WCN-163.5 (1-0-0), and in the Antelope Valley Limestone in WCN-174 (2-0-0) and WCN-177 (1-0-0). This material extends the range of the species, previously known from the lower Antelope Valley Limestone (Fortey and Droser, Reference Fortey and Droser1999), downward into the upper Ninemile Formation.
Remarks
Fortey and Droser (Reference Fortey and Droser1999) first illustrated this species from the basal Antelope Valley Limestone at the Whiterock Canyon Narrows and compared it to known species of Ampyxoides. The Ninemile Formation specimens appear conspecific with those illustrated by Fortey and Droser (Reference Fortey and Droser1999) in lacking a glabellar spine, exhibiting a weakly keeled glabella that is widest slightly posterior to its mid-length, the posterior width (tr.) of the glabella at the occipital furrow is slightly less than half the maximum pygidial width, axial furrows that are slightly adaxially convex posteriorly, and very faint S1, S2 furrows, and a pit-like S3 furrow present anterior to the glabellar mid-length.
The cranidium of Ampyxoides cf. occipitalis compares broadly to that of Ampyxoides occipitalis Dean (Reference Dean1973, p. 4–6, pl. 1, figs. 7–9, 15, 16) in having a glabella that is constricted posteriorly. The glabella of A. occipitalis, however, bears a glabellar spine, is more angular anteriorly, stands well above the occipital lobe in lateral view, and is proportionately narrower medially (tr.) compared to its length. Further, the fixigenae are larger (exsag., tr.) in A. occipitalis. Were additional sclerites of the Nevada material available, the introduction of a new species name would appear appropriate.
Ampyxoides? species 1
Material and occurrence
Total of eight cranidia. Present in the Whiterockian Antelope Valley Limestone in WCN-176 (2-0-0), WCN-177 (3-0-0), and WCN-178 (3-0-0).
Remarks
A species of Ampyxoides? with a faintly keeled glabella that is broad and ovate in outline and with elongate S1 glabellar furrows that extend anteriorly on exfoliated specimens. Ampyxoides? sp. 1 differs from Ampyxoides cf. A. occipitalis (Fortey and Droser, Reference Fortey and Droser1999, p. 195, figs. 8.1–8.5) in the outline of the glabella that is broader posteriorly, the less well-developed keel, and the elongate S1 furrow. Ampyxoides? sp. 1 differs from the type species, Ampyxoides semicostatus (Billings, Reference Billings1865; Whittington, Reference Whittington1965, p. 319–321, pl. 12, figs. 13–20, pl. 13, figs. 1–10, 12) in lacking a glabellar spine, in the more ovate shape of the glabella, and elongate 1S furrows. Ampyxoides inermis Fortey (Reference Fortey1975, p. 74–76, pl. 30, figs. 10–15, 1980, pl. 17, fig. 9) exhibits a small glabellar spine, fixigenae that are more broad (tr.), posterior border furrows that are only faintly impressed, and has axial furrows that are curved abaxially rather than adaxially from the occipital furrow to the glabellar mid-length. Ampyxoides occipitalis Dean (Reference Dean1973, p. 4–6, pl. 1, figs. 7–9, 13, 15, 16) possesses a glabellar spine, lacks a preglabellar area, and has a glabella that is inflated posteriorly to stand above the occipital ring in lateral view.
Order Corynexochida Kobayashi, Reference Kobayashi1935
Family Illaenidae Hawle and Corda, Reference Hawle and Corda1847
Genus Illaenus Dalman, Reference Dalman1827
Type species
Entomostracites crassicauda Wahlenberg, Reference Wahlenberg1821, subsequent designation by Miller (Reference Miller1889), from the Crassicauda Limestone of Sweden.
Illaenus welchi new species
Figure 11 Illaenus Dalman, Reference Dalman1827. (1–11) Illaenus welchi n. sp., all from Ninemile Formation, (1–5) palpebral (×1.9), anterior cranidial (×1.7), dorsal pygidial (×1.9), lateral (×1.7), and posterior pygidial (×1.9) views of partially exfoliated, holotype carapace, WCN-145, CM 59041; (6) palpebral view (×2.2) of testate, fragmentary paratype cranidium, WCN-132, CM 59042; (7) palpebral view (×1.9) of exfoliated, paratype cranidium, WCN-145, CM 59043; (8, 9) palpebral and anterior views (×2.7) of testate, paratype cranidium, WCN-146, CM 59044; (10) dorsal view (×1.8) of largely exfoliated, paratype pygidium, WCN-145, CM 59045; (11) dorsal view (×2.0) of partially exfoliated, paratype pygidium exhibiting doublure, WCN-145, CM 59046. (12–15) Illaenus cf. I. auriculatus Ross, Reference Ross1972, all from Antelope Valley Limestone, (12) palpebral view (×3.2) of testate cranidium, WCN-176, CM 59047; (13) palpebral view (×1.7) of fragmentary, testate cranidium, WCN-178, CM 59048; (14) dorsal view (×4.8) of exfoliated pygidium, WCN-190, CM 59049; (15) dorsal view (×4.6) of fragmentary, exfoliated pygidium, WCN-176, CM 59050.
1972Illaenus sp. b Reference RossRoss, p. 32, pl. 13, figs. 14–19, pl. 14, figs. 1–6.
1972Illaenus sp. d Reference RossRoss, p. 33, pl. 14, figs. 13–15.
Type specimens
Holotype, enrolled carapace, CM 59041, Ibexian Ninemile Formation at the Whiterock Canyon Narrows, Nevada. Paratypes, CM 59042-46.
Diagnosis
Illaenus with angular axial furrows, narrow, cord-like anterior border, and anterior branch of the facial sutures that are subparallel or weakly convergent to anterior margin. Pygidium semi-elliptical in outline, pygidial width equal to twice pygidial length measured dorsally, triangular axis with length equal to maximum axial width.
Description
Cranidium large, up to 1.5 cm in palpebral view, tall, up to 1.5 cm in anterior view, subrectangular in outline; strongly convex (sag.) to overhang anterior margin, passes through ~270° of arc in lateral view. Axial furrows broad, moderately impressed, subparallel at posterior margin; bent adaxially at 15° angle opposite posterior end of palpebral lobes; bent at anterior end of palpebral lobes back to subparallel orientation, shallowed until obsolete before overhang in anterior area. Glabella broad posteriorly, greater than half cranidial width (tr.), narrowed to 9/10 of basal glabellar width at anterior end of palpebral lobes. Preglabellar furrow not defined. Anterior border cord-like, mildly elevated above preglabellar area; anterior border furrow slightly impressed, of uniform depth laterally. Palpebral lobes simple, slightly declined from axial furrows. Anterior branch of facial suture subparallel to slightly convergent to anterior border; posterior branch of facial suture subperpendicular to posterior margin. Prosopon on testate specimens of fine terrace lines across entire cranidium except for smooth spot in the axial furrows at the anterior end of the palpebral lobes, lines more densely packed on anterior area, most densely packed on anterior border, scattered fine pits present on glabella, posterior and palpebral areas. Exfoliated surfaces with gentle rugae reflecting terrace lines, pits aligned in recesses of rugae, smooth spot in axial furrows present, faint occipital node present.
Pygidium large, up to 2.0 cm in length measured dorsally; semi-elliptical in outline, twice as broad as long measured in dorsal view; moderately convex (tr., sag.) with distal margin slightly overturned. Axis long, 6/10 pygidial length measured in dorsal view, triangular in outline on exfoliated surfaces with axial length equal to maximum axial width, poorly defined posteriorly on testate specimens; slightly convex (tr.). Axial furrows broad, faintly impressed, incomplete posteriorly on testate surfaces; weakly impressed, meet along axis on exfoliated surfaces. Articulating furrow moderately impressed. Pleural fields undivided except for single intrapleural furrow defining short anterior band; slightly convex (exsag.), strongly declined becoming overturned marginally. Long (sag.), slightly concave doublure, longer axially than laterally, with broad fold axially.
Etymology
In honor of James R. Welch, in recognition of the support for this research by the American Association of Paleontological Suppliers under their James R. Welch Scholarship.
Material and occurrence
Total of 14 cranidia, six pygidia, one fragmentary librigena, and one enrolled carapace. Present in the Whiterockian Ninemile Formation in WCN-132 (5-2-0), WCN-134 (4-2-0), WCN-145 (1-1-0, plus one enrolled carapace), WCN-146 (2-1-1), and WCN-159 (2-0-0). Previously reported from the Antelope Valley Limestone at Meiklejohn Peak, Nevada (Ross, Reference Ross1972).
Remarks
Illaenus welchi n. sp. is based upon an enrolled carapace that allowed for the certain association of cranidia and librigenae illustrated by Ross (Reference Ross1972) as Illaenus sp. b with pygidia illustrated as Illaenus sp. d.
Ross (Reference Ross1972, p. 32) suggested that Illaenus sp. ind. 2 of Whittington (Reference Whittington1963, p. 73–74, pl. 19, figs. 5, 6, 8, 9) bore a close resemblance to Illaenus sp. b (=Illaenus welchi n. sp.). Illaenus sp. ind. 2, however, has divergent axial furrows adjacent to the posterior cranidial margin and it is excluded from I. welchi.
Illaenus oscitatus Fortey (Reference Fortey1980, p. 60–62, pl. 10, figs. 1–13) is similar to Illaenus welchi n. sp. in the angular course of its cranidial axial furrows, raised anterior border, and subparallel anterior facial sutures. Illaenus oscitatus, however, has prominent pits and a more greatly overhung frontal area on the cranidium. The pygidium of I. oscitatus also is proportionally longer in dorsal view with concave, rather than straight, axial furrows.
Illaenus cf. I. auriculatus Ross, Reference Ross1972
1972Illaenus cf. I. auriculatus Reference RossRoss, p. 32, pl. 12, figs. 19–26, pl. 13, figs. 1–13, pl. 14, figs. 23–25.
1999Illaenus cf. I. auriculatus; Reference Fortey and DroserFortey and Droser, p. 192, fig. 6.1–6.11.
Material and occurrence
Total of five cranidia, five pygidia, and one librigena. Present in the Antelope Valley Limestone in WCN-176 (4-2-0), WCN-177 (1-0-0), WCN-178 (1-1-1), and WCN-190 (0-2-0). Previously documented from the Antelope Valley Limestone by Ross (Reference Ross1972) and Fortey and Droser (Reference Fortey and Droser1999).
Remarks
Illaenus auriculatus Ross (Reference Ross1972) was based upon a silicified collection of small specimens from the Antelope Valley Limestone at Pyramid Peak, California. Ross later (Reference Ross1972) considered “crack out” material from Meiklejohn Peak, Nevada, as comparable to I. auriculatus. The evenly curved, weakly impressed axial furrows on the cranidium that terminate at the anterior end of the palpebral lobes are consistent with these latter specimens. Fortey and Droser (Reference Fortey and Droser1999) provided a good discussion of larger Illaenus cf. I. auriculatus specimens from mechanically prepared specimens and comparisons to other Illaenus species.
Family Styginidae Vodges, Reference Vodges1890
Genus Perischoclonus Raymond, Reference Raymond1925
Type species
Perischoclonus capitalis Raymond, Reference Raymond1925, by original designation, from the Shallow Bay Formation of Newfoundland, Canada.
Perischoclonus sp.
Figure 12 Styginidae Vodges, Reference Vodges1890. (1–7) Raymondaspis cf. R. vespertina Ross, Reference Ross1967, (1, 3) palpebral (×6.7) and anterior (×7.5) views of testate cranidium, Antelope Valley Limestone, WCN-174, CM 59051; (2) palpebral view (×8.1) of testate cranidium, Ninemile Formation, WCN-159, CM 59052; (4) dorsal view (×6.9) of testate pygidium, Ninemile Formation, WCN-159, CM 59053; (5) dorsal view (×6.9) of testate pygidium, Ninemile Formation, WCN-159, CM 59054; (6, 7) lateral (×9.5) and dorsal (×13.2) views of testate librigena, Ninemile Formation, WCN-159, CM 59055. (8) Perischoclonus sp., dorsal view (×15.0) of testate pygidium, Ninemile Formation, WCN-146, CM 59056.
Remarks
A single transverse pygidium from the Ninemile Formation, WCN-146, is assigned to the genus Perischoclonus. This pygidium exhibits a long axis of 6+ rings, moderately impressed pleural furrows that extend onto the border, a slightly concave border defined by a weakly impressed border furrow, and granulose prosopon. In these characters, the pygidium is consistent with the type species, Perischoclonus capitalis Raymond, Reference Raymond1925 (see Whittington, Reference Whittington1963, p. 80–84, pl. 22, figs. 1–13, pl. 35, figs. 10, 11, pl. 36, figs. 5, 7, 8). The Nevada pygidium differs from the type in being more transverse, having a more distinct border furrow, and pleural furrows that are better impressed adaxially. Granules appear in two lines on the anterior three pleural ribs, suggesting the presence of faintly impressed interpleural furrows anteriorly. Ross (Reference Ross1970, p. 89, pl. 17, fig. 20) assigned a poorly preserved cranidium from the Antelope Valley Limestone at Ikes Canyon to Perischoclonus, noting the presence of a Bertillion pattern on the glabella rather than granules.
Genus Raymondaspis Pribyl in Prantl and Pribyl, Reference Prantl and Pribyl1948
Type species
Holometopus limbatus Angelin, Reference Angelin1854, by original designation, from the Komstad Limestone of Sweden.
Remarks
Neilsen (Reference Neilsen1995) chose to treat Turgicephalus Fortey (Reference Fortey1980) as a subgenus of Raymondaspis. We prefer retain the two taxa as separate at the generic rank.
Raymondaspis cf. R. vespertina Ross, Reference Ross1967
non1967Raymondaspis vespertinus Reference RossRoss, p. D15, pl. 4, figs. 16–20.
non1980Raymondaspis vespertina; Reference ForteyFortey, p. 50, pl. 6, figs. 1–8, 11.
cf. 1999Raymondaspis vespertina; Reference Fortey and DroserFortey and Droser, p. 193, fig. 5.9–5.11.
Material and occurrence
Total of 29 cranidia, 17 pygidia, and seven librigenae. Present in the Whiterockian Ninemile Formation in WCN-132 (2-1-0), WCN-145 (7-0-0), WCN-146 (3-2-0), WCN-159 (6-8-7), and WCN-163.5 (5-0-0). Present in the Antelope Valley Limestone in collections WCN-172 (0-1-0) and WCN-174 (6-5-1). These collections extend the range of the species previously documented from the Antelope Valley Limestone (Fortey and Droser, Reference Fortey and Droser1999) downward into the Ninemile Formation.
Remarks
The testate specimens recovered and illustrated from the Ninemile Formation conform to those previously illustrated from the Antelope Valley Limestone at Whiterock Canyon (Fortey and Droser, Reference Fortey and Droser1999) in their prosopon of fine terrace lines, the small occipital node, the small fossula in the axial furrows, and moderately long (exsag.) preocular portion of the anterior border. The pygidia in each case exhibit axial furrows that are slightly curved so that the axis tapers markedly. The recovery of conspecific specimens from the Ninemile Formation extends the documented range of Raymondaspis cf. R. vespertina at the Whiterock Canyon Narrows.
Raymondaspis cf. R. vespertina differs in its cranidia from the silicified type material from Pyramid Peak, California, (Ross, Reference Ross1967) by possessing a glabella that is proportionately narrower at its maximum width and in having a more clearly defined anterior border, particularly at the anterolateral corner. The Nevada pygidia differ from the type material in having an evenly curved posterior margin, whereas the type material has a slight angulation axially, and a proportionately longer axis.
Cranidia from Spitzbergen assigned to Raymondaspis vespertina by Fortey (Reference Fortey1980) have better impressed lateral glabellar furrows than in R. cf. R. vespertina, although this may reflect the larger size of the illustrated Spitzbergen cranidia. Further, the length of the anterior border (exsag.) at the anterolateral corner appears longer in the Spitzbergen material. The Spitzbergen pygidia possess axes that are slightly more than half the pygidial length while those from Nevada approach three-quarters of the pygidial length. The Spitzbergen pygidia are weakly furrowed on the pleural fields while the Nevada specimens appear unfurrowed. Finally, although the librigena illustrated from Nevada (Fig. 12.6, 12.7) is fragmentary, the genal spine appears less rapidly tapering and longer than those from Spitzbergen.
Order Phacopida Salter, Reference Salter1864
Family Calymenidae Burmeister, Reference Burmeister1843
Genus Protocalymene Ross, Reference Ross1967
Type species
Protocalymene mcallisteri Ross, Reference Ross1967, p. D27, by original designation, from the Antelope Valley Limestone of Nevada and California.
Protocalymene sp.
Figure 13 Order Phacopida Salter, Reference Salter1864. (1–5) Pseudocybele sp., palpebral (×4.5), anterior oblique (×4.5), dorsal (×1.7), lateral oblique (×2.4), and anterior (×2.4), views of testate carapace, Ninemile Formation, WCN-F25–40, CM 59057. (6) Protocalymene sp., dorsal view (×10.5) of small, fragmentary, testate pygidium, Ninemile Formation, WCN-169, CM 59058. (7) Cybelurus sp., palpebral view (×7.0) of fragmentary, testate cranidium, Ninemile Formation, WCN-146, CM 59059. (8) Pseudomera arachnopyge Fortey and Droser, Reference Fortey and Droser1996, palpebral view (×1.8) of large, fragmentary, partially exfoliated cranidium, Antelope Valley Limestone, WCN-190, CM 59060. (9, 10) Cheiruridae indet., palpebral and lateral views (×3.4) of fragmentary, testate cranidium, Antelope Valley Limestone, WCN-190, CM 59061. (11–14) Ectenonotus spp., from Ninemile Formation, (11) palpebral view (×8.3) of fragmentary, exfoliated cranidium, WCN-159, CM 59062; (12) palpebral view (×1.8) of fragmentary, exfoliated cranidium, WCN-149, CM 59063; (13, 14) dorsal and lateral oblique views (×2.5) of largely exfoliated pygidium, WCN-145, CM 59064.
Remarks
A single fragmentary pygidium from WCN-169 in the uppermost Ninemile Formation is assigned to Protocalymene sp. This pygidium exhibits a slightly convex (tr.) axis of four rings with an inflated terminal axial piece (sag), ring furrows that are deeply incised laterally, interpleural and pleural furrows that cross to a poorly defined border furrow, a distinct arch in posterior view, and a granulose prosopon that is more dense on the distal pleural fields than proximally. While these characters are reminiscent of Protocalymene mcallisteri Ross (Reference Ross1967, p. D27–D28, pl. 9, figs. 1–28), the specimen is too fragmentary to permit definitive assignment.
Family Cheiruridae Salter, Reference Salter1864
Cheiruridae indet.
Remarks
A single fragmentary cranidium was recovered from the Antelope Valley Limestone, WCN-190. It is a finely granulose glabella, bearing three pairs of faint lateral glabellar furrows, that is strongly convex (sag.) to appear overhung in lateral view. The glabella is reminiscent of specimens of Kawina ? unicornica Hintze (Reference Hintze1953, pl. 28, p. 179) in the finely granulose prosopon, lateral glabellar furrows, and prominent size of the glabella. Although there is insufficient material to assign the specimen to genus, it does seem to conform to aspects of other cheirurids.
Family Encrinuridae Angelin, Reference Angelin1854
Genus Cybelurus Levitsky, Reference Levitsky1962
Type species
Cybelurus planus Levitsky, Reference Levitsky1962, by original designation, from the Bugryshikhinsk Beds, Sayan Altay, Russia.
Cybelurus sp.
Material and occurrence
A total of three cranidia from the Whiterockian Ninemile Formation in WCN-134 (1-0-0) and WCN-146 (2-0-0).
Remarks
These cranidia are assigned to Cybelurus on the basis of their anteriorly expanding glabella, median glabellar furrow, and well impressed lateral glabellar furrows. The fragmentary specimens recovered from the Ninemile Formation are broadly similar to Cybelurus halo Fortey (Reference Fortey1980, p. 95–98, pl. 22, figs. 1–15, pl. 25, fig. 12) from Spitzbergen, although preservation prevents a definitive identification. The Nevada material possesses a glabella that is moderately broad (tr.) posteriorly and is broadly rounded in the anteriolateral corners; further the S3 and S4 lateral glabellar furrows intersect at a discrete distance from the axial furrows. While Fortey and Droser (Reference Fortey and Droser1999) have identified C. halo from the Antelope Valley Limestone from Little Rawhide Mountain, Nevada, this is the first recovery of Cybelurus from the Whiterock Canyon Narrows. Cybelurus brutoni Fortey (Reference Fortey1980, p. 95, 98, pl. 23, figs. 1–6) exhibits a more posteriorly constricted glabella with S3 and S4 that intersect at the axial furrrow. The Ninemile Formation specimens lack the separate S4 lateral glabellar furrow seen on Cybelurus occidentalis Dean (Reference Dean1973, p. 10–13, pl. 2, figs. 2, 3, 5–10, pl. 3, figs. 1, 2, 4).
Family Pliomeridae Raymond, Reference Raymond1913
Genus Ectenonotus Raymond, Reference Raymond1920
Type species
Amphion westoni Billings, Reference Billings1865, p. 321–322, by original designation, from the Mystic Conglomerate of Quebec, Canada.
Remarks
Raymond (Reference Raymond1920) erected Ectenonotus to include those pliomerids with 12–15 axial rings on the pygidium. Whittington (Reference Whittington1961, p. 915–916, pl. 99, text-fig. 4, figs. 1–4, 6–9) selected a lectotype, described and reillustrated the type species, Ectenonotus westoni. Whittington (Reference Whittington1961, p. 916–917, pl. 99, figs. 5, 10–15), and illustrated specimens that he recovered from the Whiterock Canyon Narrows, referring them to Ectenonotus cf. westoni. He separated E. cf. westoni from the type species without diagnosing specific differences. Subsequently, Ross (Reference Ross1967, p. D24–D25) erected Ectenonotus whittingtoni based upon specimens recovered from the Antelope Valley Limestone and included Whittington’s Ectenonotus cf. westoni within it.
Ectenonotus spp.
Material and occurrence
A total of two cranidia, three pygidia, and two librigenae from the Whiterockian Ninemile Formation shale in WCN-146 (1-1-0),WCN-159 (1-1-1), and WCN-163.5 (1-0-0), and from the Antelope Valley Limestone in WCN-172 (0-1-0) and WCN-174 (0-1-1) are treated as Ectenonotus spp.
Remarks
The incomplete cranidia (Fig. 13.11, 13.12) from the Ninemile Formation exhibit long and curving 3S lateral glabellar furrows, anteriorly rounded frontal glabellar lobes, and elongate glabella. They differ from the species Ectenonotus whittingtoni Ross (Reference Ross1967, p. D24–D25, pl. 7, figs. 33, 34, pl. 8, figs. 1–22) that exhibit short, straight 3S lateral glabellar furrows and glabellas that are proportionately wider.
The illustrated pygidium (Fig. 13.13, 13.14) conforms in relative proportions, general shape, and composition of the axis, and the shape and orientation of the interpleural furrow to Ectenonotus whittingtoni. The post-axial portion of the pygidium, however, is longer in dorsal view, more steeply declined, and more rounded in posterior view than seen in E. whittingtoni.
Genus Pseudocybele Ross, Reference Ross1951
Type species
Pseudocybele nasuta Ross, Reference Ross1951, p. 137–138, by original designation, from the Garden City Formation of Utah.
Pseudocybele sp.
Remarks
Two articulated individuals and an articulated thorax were recovered from the Ibexian Ninemile Formation from WCN-F40. The individual illustrated here conforms in its cranidial details to Pseudocybele in the shape of the anterior border and the anterior position of the palpebral lobes. The glabella in this specimen is markedly parallel-sided and bluntly rounded anteriorly. Anteriorly, the axial furrows on Pseudocybele nasuta Ross (Reference Ross1951, p. 138–140, pl. 33, figs. 1–14, pl. 34, figs. 13–17, 21–27; = “Pseudocybele nasuta” in Adrain et al., Reference Adrain, McAdams and Westrop2009, fig. 21A, 21D) and P. paranasuta McAdams and Adrain (Reference McAdams and Adrain2010, p. 25–37, figs. 3–8) converge so that the anterior lobe to the glabella appears more tapered. Pseudocybele altinasuta Hintze (Reference Hintze1953, p. 216, pl. 24, figs. 1, 2) also exhibits a parallel-sided glabella, which, however, is markedly more narrow.
Genus Pseudomera Holliday, Reference Holliday1942
Type species
Amphion barrandei Billings, Reference Billings1865, p. 288–289, by original designation, from Newfoundland, Canada.
Pseudomera arachnopyge Fortey and Droser, Reference Fortey and Droser1996
1996Pseudomera arachnopyge Reference Fortey and DroserFortey and Droser, p. 96, fig. 18.1–18.8.
Holotype
Pygidium, United States National Museum (USNM) 481385, Whiterockian Juab Formation from Ibex, Nevada, section J of Hintze (Reference Hintze1953).
Occurrence
A single cranidium from the Antelope Valley Limestone was recovered from WCN-190. Pseudomera arachnopyge has been reported from the Psephosthenaspis pseudobathyurus Zone of Fortey and Droser, Reference Fortey and Droser1996 (=Orthis subalata Zone [Zone L] of Hintze, Reference Hintze1953, or the Paralenorthis-Orthidiella Zone of Ross et al., Reference Ross, Hintze, Ethington, Miller, Taylor and Repetski1997) from the uppermost Wah Wah Limestone Formation and lower Juab Formation of the Ibex region and the Garden City Formation of Utah, (Fortey and Droser, Reference Fortey and Droser1996), as well as, without illustration, from the Antelope Valley Limestone at the Whiterock Canyon Narrows (Fortey and Droser, Reference Fortey and Droser1999, fig. 2).
Remarks
The fragmentary cranidium compares well with Pseudomera arachnopyge Fortey and Droser (Reference Fortey and Droser1996) in the subrectangular and bluntly truncate outline of the glabella, the position of the palpebral lobes, and the position and orientation of the S3 lateral glabellar furrows.
Order Proetida Fortey and Owens, Reference Fortey and Owens1975
Family Bathyuridae Walcott, Reference Walcott1886
Genus Acidiphorus Raymond, Reference Raymond1925
Type species
Acidiphorus spinifer Raymond, Reference Raymond1925, p. 131, by original designation, from the Head Group, Newfoundland, Canada.
Acidiphorus cf. A.? lineotuberculatus Fortey and Droser, Reference Fortey and Droser1999
Figure 14 Orders Proetida Fortey and Owens, Reference Fortey and Owens1975, and Ptychopariida Swinnerton, Reference Swinnerton1915. (1, 2) Acidiphorus? cf. A.? lineotuberculatus Fortey and Droser, Reference Fortey and Droser1999, from Ninemile Formation, (1) palpebral view (×7.0) of partially exfoliated cranidium, WCN-132, CM 59065; (2) dorsal view (×5.8) of testate librigena, collection WCN-132, CM 59066. (3, 4) Benthamaspis sera Fortey and Droser, Reference Fortey and Droser1999, palpebral and anterior oblique views (×5.3) of testate cranidium, Ninemile Formation, WCN-144, CM 59067. (5, 6) Uromystrum sp. 3 (Ross, Reference Ross1972), palpebral and lateral views (×3.1) of corroded cranidium, Ninemile Formation, collected from float, CM 59068. (7–9) Ischyrotoma cf. I. caudanodosa Ross (Reference Ross1951), from Ninemile Formation, (7) palpebral view (×18.0) of small, corroded cranidium, WCN-F25-40, CM 59069; (8, 9) dorsal and posterior view (×15.0) of small, testate pygidium, WCN-F25-40, CM 59070. (10) Oopsites sp. (Reed in Gardiner and Reynolds, Reference Gardiner and Reynolds1909), palpebral view (×7.8), crushed cranidium, Ninemile Formation, WCN-113, CM 59071. (11–14) Carolinites sibiricus Chugaeva, Reference Chugaeva1964, (11, 12) palpebral and anterior oblique views (×15.0) of fragmentary, testate cranidium, Antelope Valley Limestone, WCN-177, CM 59072; (13, 14) dorsal and posterior oblique views (×7.8) of largely exfoliated pygidium, Ninemile Formation, WCN-143, CM 59073. (15) Harpetidae indet., dorsal view (×2.5) of fragmentary cephalon, Ninemile Formation, WCN-64, CM 59074.
cf. 1999Acidiphorus? lineotuberculatus Reference Fortey and DroserFortey and Droser, p. 189, fig. 4.14–4.19.
non1999Acidiphorus? lineotuberculatus Reference Fortey and DroserFortey and Droser, fig. 4.20 (=Pseudoolenoides pogonipensis Adrain, McAdams, and Karim, Reference Adrain, McAdams and Karim2012).
Holotype
Cranidium, United States National Museum (USNM) 495715, Whiterockian Antelope Valley Limestone at Whiterock Canyon, Nevada.
Material and occurrence
Total of 15 cranidia and two librigenae. Present in the Whiterockian Ninemile Formation in WCN-132 (2-0-1), WCN-145 (1-0-0), WCN-146 (1-0-0), WCN-159 (1-0-0), and WCN-163.5 (2-0-0). Present in the Antelope Valley Limestone in WCN-172 (3-0-0), WCN-174 (3-0-1), and WCN-178 (2-0-0). This report extends the known range (Fortey and Droser, Reference Fortey and Droser1999) of the taxon downward into the Ninemile Formation.
Remarks
The small specimens of Acidiphorus cf. A.? lineotuberculatus recovered from the Ninemile Formation conform to the specimens from the overlying Antelope Valley Limestone described by Fortey and Droser (Reference Fortey and Droser1999) in their prosopon of mixed lines and tubercles. The present cranidia, however, exhibit axial furrows that diverge anteriorly to form a glabella that is markedly more broad and rapidly expanding anteriorly than in the type cranidia. Additionally, the fragmentary librigenae recovered exhibit a pronounced swelling at the proximal end of the genal spine greater than that seen in A.? lineotuberculatus itself.
Genus Benthamaspis Poulsen, Reference Poulsen1946
Oculomagnus Lochman, Reference Lochman1966, p. 541. [Junior subjective synonym; see Fortey, Reference Fortey1979, p. 100]
Type species
Benthamaspis problematica Poulsen, Reference Poulsen1946, p. 325–326, by monotypy, from the Nunatami Formation at Cape Stevens, Ellesmere Island.
Benthamaspis sera Fortey and Droser, Reference Fortey and Droser1999
1997Benthamaspis sp. Reference Adrain and ForteyAdrain and Fortey, p. 101, pl. 1, figs. 7–9.
1999Benthamaspis sera Reference Fortey and DroserFortey and Droser, p. 189, fig. 4.1–4.13.
Holotype
Cranidium, United States National Museum (USNM) 495705; Whiterockian Antelope Valley Limestone from Meiklejohn Peak, Nevada.
Material and occurrence
One cranidium from the Whiterockian Ninemile Formation, WCN-144. Previously recovered from Meiklejohn Peak, Nevada (Fortey and Droser, Reference Fortey and Droser1999) and the Tourmakeady Beds of Ireland (Adrain and Fortey, Reference Adrain and Fortey1997).
Remarks
The impression of the axial furrows, shape of the preocular area, proportions of the palpebral lobes, and glabellar convexity of the small specimen illustrated from the Whiterock Canyon Narrows conform well to the specimens from Meiklejohn Peak, Nevada (Fortey and Droser, Reference Fortey and Droser1999). Benthamaspis diminutiva Hintze (Reference Hintze1953, p. 142–143, pl. 13, figs. 9–12; Dean, Reference Dean1989, p. 28–29, pl. 20, figs. 9–13; Fortey and Droser, Reference Fortey and Droser1999, fig. 21O, 21S), known from Zone J (=the “Pseudocybele nasuta” Zone of Adrain et al., Reference Adrain, McAdams and Westrop2009), differs in the breadth of the glabella and the abaxially curved axial furrows.
Genus Uromystrum Whittington, Reference Whittington1953
Type species
Bathyurellus validus Billings, Reference Billings1865, p. 268, by original designation, from the Table Head Group of Newfoundland, Canada.
Uromystrum sp. 3 (Ross, Reference Ross1972)
1972 Bathyurellus sp. 3 Reference RossRoss, p. 35, pl. 15, figs. 17–19.
Material and occurrence
A single cranidium recovered from an unrecorded position within the Antelope Valley Limestone. Also known from the Antelope Valley Limestone at Meiklejohn Peak, Nevada (Ross, Reference Ross1972).
Remarks
This fragmentary cranidium conforms to the description of Bathyurellus sp. 3 of Ross (Reference Ross1972) in the length (sag.) and shape of the glabella, the declined and posteriorly set palpebral lobes, the moderately rounded anterior glabella lobe, and the lack of an occipital furrow. Ross (Reference Ross1972) noted the similarity between this species and Uromystrum pogonipensis (Hintze, Reference Hintze1953, p. 138, pl. 10, figs. 11–19) from the Pseudoolenoides dilectus Zone (Zone M) at Ibex. Uromystrum pogonipensis, however, appears to have a longer anterior border, subhorizontal palpebral lobes, axial furrows that were better impressed posteriorly and weaker anteriorly, and a glabella that was less constricted at the palpebral lobes than seen in the Nevada specimens.
Fortey (Reference Fortey1979, p. 90) restricted the generic concept of Bathyurellus and reillustrated material of the type species, Bathyurellus abruptus Billings (Reference Billings1865). The cranidia associated with the lectotype pygidium of B. abruptus possess subparallel axial furrows that result in a rectangular outline for the glabella. Uromystrum (see Whittington, Reference Whittington1953, p. 658–660, pl. 67, figs. 1, 2), however, exhibits sinuous axial furrows and a glabella that is constricted at the palpebral lobes. Further, the occipital furrow of the type species is weakly impressed axially and seems to have become more faint laterally. Bathyurellus sp. 3, therefore, conforms more closely to the generic concept of Uromystrum and is reassigned. This parallels the reassignment of Bathyurellus pogonipensis to Uromystrum (Ross, Reference Ross1972, p. 34).
Uromystrum sp. 3 (Ross) is illustrated from float to provide a more complete assessment of faunal diversity in the Antelope Valley Limestone at the Whiterock Canyon Narrows.
Family Dimeropygidae Hupé, Reference Hupé1953
Genus Dimeropygiella Ross, Reference Ross1951
Type species
Dimeropygiella caudanodosa Ross, Reference Ross1951, by original designation, from the Ibexian Garden City Formation of Utah.
Dimeropygiella cf. D. caudanodosa Ross, Reference Ross1951
cf. 1951Dimeropygiella caudanodosa Reference RossRoss, p. 124, pl. 35, figs. 18, 22–28.
cf. 1953Dimeropygiella caudanodosa; Reference HintzeHintze, p. 154, pl. 19, figs. 5, 10.
cf. 1963Ischyrotoma caudanodosa; Reference WhittingtonWhittington, p. 47.
cf. 1979Ischyrotoma caudanodosa; Reference ForteyFortey, p. 106.
cf. 1989Ischyrotoma cf. I. caudanodosa; Reference DeanDean, p. 36, pl. 28, figs. 7, 9, 10, 13, 15–17.
cf. 1994Ischyrotoma caudinodosa [sic]; Reference ChattertonChatterton, p. 543, fig. 1, table 1.
cf. 2001Dimeropygiella caudanodosa; Reference Adrain, Westrop, Landing and ForteyAdrain et al., p. 964, figs. 7.24–7.50, 8, 9.
Holotype
Cranidium, Yale Peabody Museum (YPM) 18217, Ibexian Garden City Formation, Utah.
Remarks
A single, small, corroded cranidium was recovered from float (WCN F25–40) in the Ninemile Formation that exhibits an elongate, ovate glabella, and a narrow (tr.) anterior border that is not overhung by the anterior lobe of the glabella. While this is consistent with Dimeropygiella caudanodosa, the size and corroded nature of the specimen dictates that it be treated with a degree of uncertainty. A small pygidium, recovered from the same interval (WCN F25–40), is broadly similar to the pygidia illustrated for D. caudanodosa in the number of axial rings and the development of the post-axial nodes and is treated in a like manner.
Dimeropygiella blanda (Hintze, Reference Hintze1953, p. 155–156, pl. 19, figs. 6–8; Adrain et al., Reference Adrain, Westrop, Landing and Fortey2001, p. 967, figs. 13, 14, 15.1–15.11) has a distinct preglabellar field, a broad (tr.) anterior border, and a glabella that is more broadly ovate than in D. caudanodosa. Dimeropygiella ovata (Hintze, Reference Hintze1953, p. 155, pl. 19, figs. 1–4; Adrain et al., Reference Adrain, Westrop, Landing and Fortey2001, p. 965, figs. 10, 11.1–11.8, 11.10–11.12) has a wide (tr.) anterior border and a glabella that is more broadly ovate in outline. Dimeropygiella fillmorensis Adrain et al. (Reference Adrain, Westrop, Landing and Fortey2001, p. 965–967, figs. 11.9, 12), similarly, has a broad (tr.) anterior border and a glabella that is more broadly ovate in outline.
Family Telephinidae Marek, Reference Marek1952
Genus Carolinites Kobayashi, Reference Kobayashi1940
Type species
Carolinites bulbosus Kobayashi, Reference Kobayashi1940, by original designation, from the Caroline Creek Sandstone of Tasmania.
Carolinites sibiricus Chugaeva, Reference Chugaeva1964
1964Carolinites sibiricus Reference ChugaevaChugaeva, p. 45, pl. 1, figs. 4, 5.
1967Carolinites angustagena Reference RossRoss, p. D10, pl. 3, figs. 29–39.
1974Carolinites angustagena; Reference ShawShaw, p. 10, pl. 1, figs. 29–34, pl. 2, figs. 1–4, 7, 8.
1975Carolinites sibiricus; Reference ForteyFortey, p. 111, pl. 40, figs. 1–10, 12, 13.
1999Carolinites sibiricus; Reference Fortey and DroserFortey and Droser, p. 187, fig. 3.11–3.13.
1999Carolinites sibiricus; Reference McCormick and ForteyMcCormick and Fortey, fig. 3.22, 3.23, 3.27–3.29.
Diagnosis
See Fortey, Reference Fortey1975, p. 111.
Occurrence
Previously known from Siberia (Chugaeva, Reference Chugaeva1964), the Profilbekken Member of the Valhallfonna Formation of Spitzbergen (Fortey, Reference Fortey1975), the Joins Formation of Oklahoma (Shaw, Reference Shaw1974), and the Antelope Valley Limestone of California (Ross, Reference Ross1967) and Nevada (Fortey and Droser, Reference Fortey and Droser1999). This report extends the known range of the species downward from the Antelope Valley Limestone into the Ninemile Formation.
Material and occurrence
Total of 10 cranidia and four pygidia from the Ninemile Formation from WCN-143 (1-0-0), WCN-146 (1-1-0), WCN-159 (3-2-0), and WCN-160 (1-0-0), and the Antelope Valley Limestone from WCN-177 (1-0-0), WCN-178 (2-0-0), and WCN-190 (0-1-0).
Remarks
We have accepted the synonymy of Carolinites angustagena Ross with C. sibiricus Chugaeva outlined by Fortey (Reference Fortey1975). Specimens recovered from the Ninemile Formation at the Whiterock Canyon Narrows conform to those illustrated from the overlying Antelope Valley Limestone (Fortey and Droser, Reference Fortey and Droser1999) in the shape and proportions of the glabella, the width of the palpebral areas, the width of the posterior area, and the relative size of the bacculae.
Genus Oopsites Fortey, Reference Fortey1975
Type species
Telephus hibernicus Reed in Gardiner and Reynolds, Reference Gardiner and Reynolds1909, by original designation, from the Tourmakeady Limestone of Ireland.
Oopsites sp.
Remarks
Although crushed, the cranidium recovered from the Ninemile Formation collection WCN-113 conforms to the genus Oopsites in the large, anteriorly placed palpebral lobes and anteriorly rounded glabella. The presence of the scattered granulose prosopon and single pair of lateral glabellar furrows are reminiscent of Oopsites hibernicus (Reed in Gardiner and Reynolds, Reference Gardiner and Reynolds1909) (see Adrain and Fortey, Reference Adrain and Fortey1997, p. 101, pl. 11, figs. 10–12, 15, pl. 13, figs. 1–3, pl. 16, fig. 24).
Order Ptychopariida Swinnerton, Reference Swinnerton1915
Family Harpetidae Hawle and Corda, Reference Hawle and Corda1847
Harpetidae indet.
Remarks
A single fragmentary cephalon from collection WCN-64 is assigned to the family Harpetidae on the basis of a pitted cephalic fringe. This fragment is reminiscent of Selenoharpes sp. (Ross, Reference Ross1972, p. 36, pl. 16, figs. 7, 8) from the Antelope Valley Limestone at the Meiklejohn Peak bioherm in the arcuate nature of the fringe in dorsal view and its slight convexity (sag.).
Conclusions
Moderately diverse trilobite faunas characteristic of the uppermost Ibexian Series (Zone J, the “Pseudocybele nasuta” Zone) and the lowermost Whiterockian Series (Zone L, the Psephosthenaspis pseudobathyurus Zone, the Orthidiella Zone) are present in the Whiterock Canyon Narrows section, Nevada. A cryptic unconformity separates these two faunas as demonstrated by approximately 10 m of paleobathymetric relief along a channel scoured into shale and interbedded limestone in the upper Ninemile Formation. An alternative section that lacks evidence of an unconformity should be sought to serve as the type section across the base of the Whiterockian Stage.
Acknowledgments
JDL received support through a University Research Grant and sabbatical leave from the University of Central Missouri and a Jim Welsh Scholarship from the American Association of Paleontological Suppliers; R. Burkhalter and S.R. Westrop provided photographic assistance; J. Adrain and E. Landing provided valued constructive reviews.
