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13 December 2024 Smithian-Aged (Early Triassic, Early Olenekian) Crinoid Ossicles from Exotic Limestone Blocks in the Lower Part of the Thaynes Formation at Crittenden Springs, Elko County, Nevada
Takumi Maekawa, James F. Jenks
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Abstract

We document the occurrence of Early Triassic (Olenekian) crinoid ossicles in exotic blocks contained within the black limestone unit of the Thaynes Formation, which overlies the Dinwoody Formation at the classic Crittenden Springs Smithian ammonoid locality. Crinoid ossicles include two species, i.e., Holocrinus sp. and Articulata ord., fam., gen. et sp. indet. Furthermore, two co-occurring, age diagnostic conodonts, i.e., Neospathodus pakistanensis and Ns. posterolongatus, constrain the age of the crinoids from the early Smithian to the earliest middle Smithian. This discovery represents the third report of Smithian Holocrinidae in the Panthalassan area and it provides important data for the study of crinoid recovery during the Early Triassic.

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Introduction

Lower Triassic marine and terrestrial deposits are widely distributed in the Great Basin area of the western USA (Clark, 1957; Clark and Carr, 1984). The geological structure, age, and paleoenvironments of these deposits have been studied by many researchers (e.g. Kummel, 1954; Clark, 1957, 1959; Paull, 1980; Carr, 1981; Clark and Carr, 1984; Mullen, 1985; Jenks, 2007; Lucas and Orchard, 2007; Lucas et al., 2007a, b; Jenks et al., 2010, 2013, 2021; Brayard et al., 2013, 2017; Jenks and Brayard, 2018; Maekawa and Jenks, 2021) and subsequently, several formations were established for differing lithological units in different areas (e.g. Thomas and Krueger, 1946). Recently, Lucas et al. (2007b) combined these formations into two large groups, i.e., the Thaynes and Moenkopi groups. According to Lucas et al. (2007b), the Thaynes Formation was elevated to group rank to encompass the limestone-dominated sections of Lower Triassic strata recognized across much of Utah, western Wyoming, eastern Idaho and eastern Nevada. The Thaynes Group of Lucas et al. (2007b) includes all Lower Triassic marine deposits in the Great Basin area, including the Dinwoody Formation (Goodspeed and Lucas, 2007; Brayard, personal communication). We acknowledge the validity of the Thaynes Group in this area, however, for practical reasons we choose to refer to the studied portion of the eponymous group and its components by its original name (= Thaynes Formation), as defined by Clark (1957) and Mullen (1985).

The Thaynes Formation of northeastern Nevada, which consists of various sedimentary rocks such as limestone, mudstone, shale and sandstone beds, contains abundant marine fossils, i.e., ammonoids, gastropods, bivalves, conodonts and echinoderms (Goodspeed and Lucas, 2007; Lucas et al., 2007a, b). These sediments were traditionally divided into the Dinwoody and Thaynes formations and their geological ages were generally defined by age-diagnostic ammonoids and conodonts (Clark, 1957, 1959; Kummel and Steel, 1962; Sweet et al., 1971; Solien, 1979; Paull, 1980; Carr, 1981; Clark and Carr, 1984; Mullen, 1985; Jenks, 2007; Jenks et al., 2010, 2013, 2021; Jenks and Brayard, 2018; Maekawa and Jenks, 2021). Considerable biostratigraphical research has been conducted on the ammonoids and conodonts contained within the discontinuous ammonoid-bearing blocks in recent years, but taxonomic work on other groups, e.g. crinoids, has mostly been neglected.

Figure 1.

Index maps of study area. A, geographic map of part of the North American Continent with states of Nevada and Utah; B, locality map of northeastern Nevada and northwestern Utah; C, Geologic map of the area north of the Long Canyon road, modified from fig. 30 of Paull (1980).

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Crinoid development was severely affected by the mass extinction event at the Permian–Triassic boundary along with other major taxonomic groups, but the stem Articulata, phylesis of recent crinoids probably appeared in the earliest Early Triassic and diversified during the Mesozoic (Twitchett and Oji, 2005; Hess and Messing, 2011). However, the fossil record of Early Triassic crinoids is still very sparse and some taxa lack fundamental descriptions. In this study, we report new crinoid fossils together with age-diagnostic conodonts from the Thaynes Formation at the classic fossil locality at Crittenden Springs, Nevada. In addition, we briefly review the recovery, distribution, and diversification of Articulata during the Early Triassic.

Location and geological setting

The study area (original classic ammonoid collecting site) is located about 31 km north of Montello in Elko County, Nevada, on two S-SE facing hillsides immediately north of the Long Canyon road in the E1/2SE1/4 Sec. 4, T42N, R69E (7-1/2' Dairy Valley Quadrangle) (Figure 1). Also considered part of the classic site is a 160 m-long ridge that trends N-NE from the above mentioned two hillsides (Figure 2A).

At Crittenden Springs, the Thaynes Formation was originally described as including four lithological units, i.e., the Meekoceras limestone, the black limestone, the calcareous siltstone and limestone, and the Pentacrinus limestone (Clark, 1957; Mullen, 1985). According to Mullen (1985), the Meekoceras limestone unit generally occurs as large, discontinuous blocks consisting of ammonoid-bearing light gray massive bedded crystalline limestone of varying thickness, or as a single massive bed in a few localities that are not within our study area. Mullen (1985) also reported that the black limestone unit, consisting of dark gray to black limestone with intercalating grey calcareous siltstones, lies directly over the Meekoceras limestone unit. Indeed, the black limestone unit does appear to overlie two of the Meekoceras limestone blocks at one of the more prominent classic outcrops in the study area (route D of Figure 2), but in route A of our study, the black limestone unit actually overlies the alternations of mudstone and limestone of the Dinwoody Formation. Outcrops of the black limestone unit and underlying Dinwoody Formation generally strike in a N-NE direction and dip at varying angles to the W-NW (Mullen, 1985; Jenks et al., 2010; Jenks and Brayard, 2018; Maekawa and Jenks, 2021). Even though the contact between the black limestone unit and the Dinwoody Formation is usually covered by weathered scree, the contact appears to be conformable in the few places where it is visible, but there is a chronological gap between the unit and the formation (Figure 2).

Figure 2.

Route map (A) and columnar sections (B) of study area. A, route map; B, columnar sections. The black limestone unit of the Thaynes Formation unconformably overlies the Dinwoody Formation and contains exotic limestone blocks. Studied crinoid-bearing limestone samples were collected from routes B and D. A few of the ammonoid sample localities on the route map and columns were correlated with those of Jenks and Brayard (2018) and Jenks et al. (2021).

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In the study area, much of the + 20 m thick black limestone unit consists of dark gray calcareous mudstone, which generally exhibits parallel laminations and rarely seen slump structures. It also contains numerous poorly preserved bivalve shells and rare flattened ammonoids as well as calcareous nodules (Figure 2). This study's dark gray calcareous mudstone is similar to the dark gray to black limestone of Mullen (1985) and the dark gray marl of Maekawa and Jenks (2021). Mullen (1985, fig. 28) indirectly suggests that the age of the black limestone unit is Spathian according to her correlation of this unit with the lower to upper black limestone interval of Kummel's (1957) Fort Hall, Idaho section, which contains the Columbites and Prohungarites ammonoid assemblages. In addition to the discontinuous Smithian ammonoid-bearing blocks and crinoid-bearing blocks, innumerable fragments of chert, sandstone and mudstone together with mostly unfossiliferous limestone boulders, whose size range from pebble to block size (∼ 2 m thick), are also contained within the dark gray calcareous mudstone of the black limestone unit (Figure 2). Especially notable is the fact that the strike and dip of most of the large blocks are in general agreement, but nearly all of the discontinuous ammonoid-bearing blocks have been overturned as confirmed by the “upside down” occurrence of their contained Smithian ammonoid faunas (see Jenks, 2007; Jenks and Brayard, 2018; Maekawa and Jenks, 2021). These ammonoid-bearing blocks are similar to the ammonoid-bearing bed of the Meekoceras limestone unit of Mullen (1985). Thus, the Meekoceras limestone unit exists as rootless limestone blocks within the younger dark gray calcareous mudstone matrix in the study area. This chaotic occurrence of various sized, dissimilar rocks within the dark gray calcareous mudstone is a distinguishing characteristic of an olistostrome or tectonic mélange (e.g. Abbate et al., 1970). Our current observations have not yet detected any geological structures, which would indicate the presence of a major fault or fold caused by a tectonic event in the black limestone unit. Thus, we tentatively recognize that this chaotic interval was caused by a mass debris flow such as a submarine gravity slide or slump. This premise is further supported by the presence of the overturned ammonoid-bearing blocks, most of which have not been sheared. However, considerably more field work would be required in order to logically speculate about the tectonic processes that caused this chaotic sedimentary interval, and this type of study is far beyond the scope of the present work.

Material and method

Although the Smithian ammonoid-bearing blocks have been studied by many ammonoid and conodont workers (e.g. Müller, 1956; Kummel and Steel, 1962; Jenks, 2007; Orchard and Zonneveld, 2009; Jenks et al., 2010; Jenks and Brayard, 2018; Maekawa and Jenks, 2021), other blocks within the dark gray calcareous mudstone, i.e., the crinoid-bearing blocks, have received no attention from paleontologists. Subsequently, two crinoid-bearing limestone samples [localities JJ9-23 (NMMNH L-13408) and 0614-A (NMMNH L-13409)] were collected during the 2015, 2019 and 2023 field seasons from the classic Smithian ammonoid locality (Figures 2, 3). GPS data for the localities are as follows: JJ9-23: N41°33'07.7”, W114°08'47.0”; 0614-A: N41°33'09.7”, W114°08'40.5”. We only use samples collected from these localities for observation and microfossil analysis. Portions of sample JJ9-23 were set aside for vertical cross-sectioning (Figure 4A). Samples of limestone from 0614-A (0.5 kg) and JJ9-23 (3 kg) were crushed to 2–5 cm and then immersed in a 5–6% solution of acetic acid for 2–4 days to remove carbonates. The subsequent residues were collected using 2.0 and 0.075 mm mesh screens. This procedure was repeated until all carbonates had been completely removed. Abundant microfossils recovered from the limestone include: linguloid brachiopods, gastropods, bivalves, crinoid ossicles, conodont elements, fish teeth and scales.

Microfossils were picked by brushes from the residues using stereomicroscopes Olympus SZX7 (Olympus Co., Ltd., Tokyo) and Nikon SMZ745T (Nikon Solutions Co., Ltd., Tokyo). Photo images of crinoid samples were captured using a digital microscope VHX-1000 (KEYENCE CORPORATION, Osaka). A quick auto coater JEC-3000FC (JEOL Ltd., Tokyo) and a magnetron sputter MSP-1S (Vacuum Device, Co., Ltd., Ibaraki) were utilized to coat conodont and crinoid samples with platinum for the purpose of capturing images with a scanning electron microscope VE-7800 (KEYENCE CORPORATION, Osaka).

Lithology of the crinoid-bearing limestone samples

The studied crinoid-bearing limestone sample from JJ9-23 consists of two distinct but contiguous beds (Figure 4A). The lower bed is a mudstone or wackestone of Dunham (1962) containing numerous burrows, which are filled by bioclasts (bivalve shells and crinoid ossicles) from the upper bed. The upper bed, which contains abundant bivalve shells (≧1 cm) and crinoid ossicles, probably also corresponds to the rudstone of Dunham (1962). It is generally massive and poorly sorted, but part of it exhibits a concordant bivalve shell arrangement with a geopetal structure. Thus, the crinoid-bearing limestone retains its original sedimentary structure, but it is difficult to determine the exact depositional environment of these limestone beds. A concordant bivalve shell arrangement with a geopetal structure is also contained within the limestone block represented by 0614-A (Figure 4B).

Figure 3.

Outcrops with crinoid-bearing limestones. A, JJ9-23 (NMMNH L-13408); B, C, 0614-A (NMMNH L-13409).

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There are no articulated bivalve shells in the rudstone, and crinoid fossils in the studied limestone samples generally consist of completely disarticulated columnals and cirri. This evidence clearly indicates that these shells and crinoid fossils were transported from their original habitat after death.

Figure 4.

Vertical sections of crinoid-bearing limestone samples. A, Polished vertical section of JJ9-23, which consists of mudstone/ wackestone bed and an overlying rudstone bed. Thin bivalve shells (≧1 cm) and crinoid ossicles are abundant in the rudstone. Concordant bivalve shells with geopetal structure probably indicate the upright direction of the layer. Mudstone/wackestone bed was disturbed by burrows, which were then filled by bivalve shells and crinoid ossicles. White arrows indicate recognizable boundaries between mudstone/wackestone and rudstone, and arrow heads indicate the inside of burrows which are infilled by bioclasts. B, Picture of vertical surface of 0614-A with abundant bivalve shells and crinoid ossicles. A part shows 2 cm thick shell bed consisting of concordant bivalve shells (2–3 cm) with geopetal structure. White arrow head indicates some convex-up disarticulated bivalve shells. Coin indicates scale, 2 cm in diameter.

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Geological age and probable origin of the crinoid-bearing limestone blocks

Two conodont species, i.e., Neospathodus pakistanensis Sweet, 1970, and N. posterolongatus Zhao and Orchard in Zhao et al., 2007, were recovered from the two studied crinoid-bearing limestone samples. Neospathodus pakistanensis generally ranges in age from the late Dienerian to middle Smithian (Sweet, 1970; Sweet et al., 1971; Orchard, 2007a, b; Orchard and Zonneveld, 2009; Hounslow et al., 2017; Krystyn et al., 2017a, b; Han et al., 2022). Han et al. (2022) concluded that N. novaehollandiae McTavish, 1973 is a synonym of N. pakistanensis and considers the former species to be a mature individual of the latter species. Thus, the range of N. pakistanensis is late Dienerian to middle or late Smithian (Bondarenko et al., 2013; Han et al., 2022). On the other hand, the range of N. posterolongatus is limited to the Smithian (e.g. Orchard, 2007a; Zhao et al., 2007; Orchard and Zonneveld, 2009; Maekawa et al., 2018; Maekawa and Jenks, 2021). Therefore, the conodont assemblage is almost certainly of Smithian age.

These two species were previously reported from the middle Smithian Guangxidella bransoni conodont Range Zone of the studied ammonoid-bearing limestone blocks at Crittenden Springs, Nevada (Maekawa and Jenks, 2021). According to these authors, the conodont fauna of the G. bransoni Range Zone is dominated by the subfamily Mullelinae, i.e., Conservatella conservativa (Müller, 1956), Discretella discreta (Müller, 1956), D. robusta (Wang and Wang, 1976), G. bransoni (Müller, 1956) and Paullella meeki (Paull, 1983). Thus, the conodont assemblages of these two limestones are clearly different. Guangxidella bransoni is an important index fossil in the Panthalassa and eastern Tethys and is generally indicative of a middle Smithian age (Shigeta et al., 2014; Maekawa et al., 2018; Maekawa and Jenks, 2021). In northeastern Vietnam, the species occurs in various carbonate rocks, which were deposited in a shallow carbonate platform to slope facies (Komatsu et al., 2014; Shigeta et al., 2014). Hence, the crinoid-bearing limestone was probably deposited before the appearance of G. bransoni. These results suggest that the geological age of the crinoid-bearing limestone is probably slightly older than the ammonoid-bearing limestone blocks.

The conodont assemblage containing the two Neospathodus species has been reported from the lower Smithian Clypeoceras timorense ammonoid Zone of the Zhitokov Formation, South Primorye, Russia (Shigeta et al., 2009) as well as the Rohillites rohilla and Flemingites-Euflemingites ammonoid zones of the Mikin Formation, Spiti, India (Orchard, 2007b; Orchard and Krystyn, 2007). Interestingly, the Clypeoceras timorense Zone also contains ossicles of Holocrinus sp. (Shigeta et al., 2009). These Neospathodus species also co-occur in the lower to lowest middle Smithian Eurygnathodus costatus Subzone of the Tahogawa Member, Taho Formation, Southwest Japan (Maekawa et al., 2018), but Eurygnathodus costatus has never been known to co-occur with G. bransoni. Thus, the conodont assemblage of this study probably ranges in age from early Smithian to earliest middle Smithian. This result is consistent with the above discussion. And because these conodonts came from the crinoid-bearing limestone samples, it follows then that the crinoid fossils are also of early Smithian to earliest middle Smithian in age.

Although the crinoid-bearing limestone is an exotic block within the Spathian black limestone unit of the Thaynes Formation, its Smithian age aligns it more with the Thaynes Formation than the Dinwoody Formation. Therefore, for the purposes of the present study, we assume that the crinoid-bearing limestone was originally derived from a bed of the Thaynes Formation (Figure 5). However, Smithian crinoids have never been reported from the Thaynes Group. Thus, additional fieldwork is needed to locate equivalent crinoid-containing limestones in the Great Basin area. In addition, these limestone beds may be instrumental for locating the Induan/Olenekian boundary in this area.

Distribution and diversification of Early Triassic crinoids

According to Hess and Messing (2011), the family Holocrinidae, a stem group of the Articulata, appeared just after the Permian-Triassic boundary. Induan fossil records of the genus, together with clear fossil images, have only been reported from Spitsbergen, Svalbard (Salamon et al., 2015), Oman (Oji and Twitchett, 2015; Brosse et al., 2019) and South China (Foster et al., 2019). During the Early Triassic, Svalbard, Oman and South China were situated in the middle latitude area of eastern Panthalassa, the tropical area of the central Tethys and the eastern Tethys, respectively. A Panthalassan example was reported from the Kamura Limestone, Southwest Japan (Sano and Nakashima, 1997), but it lacks fossil illustration. Although tentatively recorded from the Salt Range, Pakistan by Kaim et al. (2013), confirmed Smithian (lower Olenekian) records with figures of the Holocrinidae have only been reported from Panthalassan areas such as Svalbard (Holocrinus sp., Salamon et al., 2015), South Primorye, Russia (Holocrinus sp., Shigeta et al., 2009), and South Kitakami, Japan (Holocrinus sp., Kashiyama and Oji, 2004). However, the geological age of the South Kitakami site was shown to be Spathian by the newly reported occurrence of the early Spathian ammonoid Tirolites cf. ussuricus Zharnikova in Buryi and Zharnikova, 1981 from a horizon slightly lower than the Holocrinus bed in the same area (Shigeta and Nakajima, 2017). Thus, the present study represents the third reported Smithian occurrence of the Holocrinidae and its age is also confirmed by age diagnostic conodonts. On the other hand, reports of Spathian Holocrinidae have notably increased and exhibit a wider paleogeographical range, e.g. Svalbard (Salamon et al., 2015), Primorye (Shigeta and Nakajima, 2017), South Kitakami (Kashiyama and Oji, 2004), Iran (Baud et al., 1991), Hungary (Foster et al., 2015), Idaho/Utah (Brayard et al., 2017) and Nevada (Schubert et al., 1992). Moreover, articulated crinoid stems and concentrated beds of crinoid fossils have been reported from a few Spathian localities (e.g. Schubert et al., 1992; Brayard et al., 2017; Gorzelak et al., 2020). These fossil records probably reflect bias due to the small number of sample localities, but they also probably indicate a limited distribution of the Holocrinidae during the Induan and Smithian in contrast with the wider distribution and radiation of Holocrinidae during the Spathian.

Figure 5.

Presumed geological ages of crinoid- and ammonoid-bearing limestones in the study area.

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It is difficult to assess the diversification of Early Triassic crinoids, mainly due to the relatively few reports of confirmed occurrences. Salamon et al. (2015) reported a disarticulated nodal of Isocrinus sp. of the family Isocrinidae from the Induan of Svalbard, which exhibits a ridged interradius and a developed cirrus socket in the radius, features that are more typical of Isocrinus than Holocrinus. However, the identification of the Svalbard specimen is questioned by Stiller (2024). The occurrences of Encrinidae, Ainigmacrinidae and Roveacrinidae during the Early Triassic as reported by Salamon et al. (2015) are also questioned by Brosse et al. (2019). Oji and Twitchett (2015) erected a new taxon, i.e., Baudicrinus krystyni of the family Dadocrinidae, based on disarticulated cylindrical columnals, which were recovered from the Griesbachian (lower Induan) part of a limestone block in Oman. Brosse et al. (2019) reported disarticulated crinoid ossicles, which consist of columnals and cirri, from another Griesbachian limestone block in Oman. Brosse et al. (2019) recognized that these ossicles are the same as B. krystyni and reassigned the species to the Holocrinidae, based on evidence of nodals bearing cirral scars. Saucéde et al. (2023) erected a new taxon, i.e., a completely articulated specimen of Dadocrinus montellonis of the family Dadocrinidae, from a middle to late Spathian-aged bed of the Thaynes Group in Montello Canyon, Elko County, Nevada. Thus, a few species belonging to the family Holocrinidae were in existence during the Early Triassic, and species of the family Dadocrinidae also occurred in the Spathian.

Conclusions and remarks

At Crittenden Springs, crinoid-bearing limestone blocks occur as exotic blocks in the dark gray calcareous mudstone of the black limestone unit of the Thaynes Formation. These crinoid-bearing blocks also contain two age-diagnostic conodont species, i.e., Neospathodus pakistanensis and N. posterolongatus, which unquestionably correlate the crinoid-bearing exotic blocks with the lower Smithian to lowest middle Smithian ammonoid and conodont zones from the Tethyan and Panthalassan realms. The crinoid fossils probably consist of at least two species of Articulata, i.e., Holocrinus sp. and Articulata ord., fam., gen. et sp. indet. Furthermore, this study represents the third confirmed discovery of the Smithian crinoid taxon Holocrinus. Fossil records of Early Triassic Holocrinida are sparse during the Griesbachian, Dienerian and Smithian, but increased significantly during the Spathian. According to current reports, only the Holocrinida and Dadocrinida existed in the Early Triassic.

Additionally, the present study provides new insights for better understanding the depositional process of the dark gray calcareous mudstone, because our knowledge of the process by which pelitic rocks containing rock masses with different geological ages are formed, is limited.

Systematic paleontology

Described specimens are reposited at the New Mexico Museum of Natural History and Science (NMMNH).

Crinoids

The systematic descriptions of crinoid fossils below basically follow the classification by Hess and Messing (2011). All specimens described herein are disarticulated ossicles of internodal, nodal and cirrus; hence, the orientation terms proposed by Hess and Messing (2011) have also been adopted.

Class Crinoidea Miller, 1821
Subclass Articulata von Zittel, 1879
Order Holocrinida Jaekel, 1918
Family Holocrinidae Jaekel, 1918
Genus Holocrinus Wachsmuth and Springer, 1887

  • Type species.—Encrinus beyrichi Picard, 1883.

  • Remarks.—Holocrinus, the stem genus of Articulata, is characterized by the dicyclic cup, which consists of two basals (B1, B2) and radials (R), primibrachial consisting of two ossicles, petaroidal pattern of an articular facet of columnals (Hess and Messing, 2011). The genus appeared during the Early Triassic, but completely articulated specimens containing the cup have only been reported from the Middle Triassic (e.g. Picard, 1883; Hagdorn, 2011). Although Early Triassic holocrinids have generally been reported as disarticulated columnals, ossicles, and cirri (e.g. Oji, 2009; Salamon et al., 2015), only partly articulated stems have been reported from the Great Basin area, USA (Schubert et al., 1992; Brayard et al., 2017), Japan (Kashiyama and Oji, 2004) and Oman (Brosse et al., 2019).

  • Induan specimens have been reported from the Induan Vardebukta Formation, Svalbard (Salamon et al., 2015), limestone blocks from Oman (Oji and Twitchett, 2015; Brosse et al., 2019) and the Daye Formation, Guizhou, South China (Foster et al., 2019) (Figure 6A). Olenekian records have mainly been reported from the trans-Panthalassa areas, i.e., the Great Basin, USA (Schubert et al., 1992; Hofmann et al., 2013; Brayard et al., 2017; Gorzelak et al., 2020), Miyagi Prefecture, Japan (Kashiyama and Oji, 2004), South Primorye, Russia (Shigeta et al., 2009), and Svalbard (Salamon et al., 2015). Tethyan Olenekian records have been reported from Iran (Baud et al., 1991), South China (Galfetti et al., 2008), Salt Range, Pakistan (Kaim et al., 2013) and Hungary (Foster et al., 2015), but reports with illustrations are limited to Iran and Hungary (Figure 6B, 6C).

  • Holocrinus sp.
    Figures 7, 8, 9A–9D, 9G, 9H, 10, 11

  • Isocrinus sp. Kobayashi and Ichikawa, 1951, p. 6; Tamura, 1982, p. 23, pl. 1, figs. 20 and 21.

  • Holocrinus sp. Oji in Kashiyama and Oji, 2004, p. 215, fig. 9; Oji, 2009, p. 180, fig. 150; Salamon et al., 2015, fig. 4A.

  • Figured specimens.—One external mold of columnal, three nodals, eighteen internodals, and nine cirri, NMMNH P-96417–96447, from JJ9-23, one nodal, seven internodals, and three cirri, NMMNH P-96448–96450, 96662–96669, from 0614-A.

  • Description.—Twenty five internodals, varying from 0.60–2.32 mm in diameter, 0.40–1.28 mm in height. Cross section forms circular, pentagonal or stellate outline. In lateral view, both proximal and distal facets show smooth surface or weakly ornamented by symplexial articulation. The suture is straight or convex. Four nodals, varying from 1.11–1.73 mm in diameter, 0.56–1.01 mm in height. Cross section forms stellate form with five well-developed cirral scars. Proximal facet smooth or ornamented by symplexy and shows straight or convex up-lateral outline. Distal facet smooth and shows straight lateral outline. Twelve cirri, varying from 0.38–0.73 mm in diameter, 0.23–0.72 mm in height. Axial section forms circular or elliptical outline and shows central canal near center of the cirrus. In thicker cirri, an axial surface straight but another surface oblique 25–45 degrees to axis, and it generally forms trapezoidal lateral outline. In thinner cirri, axial surfaces show straight, concave or undulated lateral outlines.

  • Remarks.—The diagnosis of Holocrinus is generally determined by the form of the calyx, which clearly differs from Isocrinus. Thus, the assignment of described stems and cirri to the genus Holocrinus in this study is tentative. However, internodals show form variations in height and cross section. These variations have been reported in the other Smithian and Spathian holocrinids (Schubert et al., 1992; Kashiyama and Oji, 2004; Oji, 2009). In addition, the nodal with concave cirral scars of the species clearly differ from nodals with cirrus sockets of species of Encrinida and Isocrinida (Hess and Messing, 2011; Salamon et al., 2015). Thus, we treat the described specimens as a species of Holocrinus.

  • Almost all specimens probably suffered attrition during the sedimentary process and/or dissolution by acetic acid treatment. The smooth axial surfaces of nodals and internodals were also affected by attrition and dissolution. However, the articular surface of an external mold of columnal (NMMNH P-96417) shows symplexial articulation, which is similar to that of Holocrinus sp. of Kashiyama and Oji (2004).

  • According to Oji (2009), the diameter of ossicles of columnals and cirri of Holocrinus sp. from South Primorye vary from 0.6 to 0.8 mm. The size of columnals of Holocrinus? smithi (Clark, 1915) from the Virgin Limestone, Moenkopi Group vary from 1.0 to 5.3 mm (Schubert et al., 1992). According to this size variation, we tentatively treat the former species as the same species, but the latter species is a different species. The different articular ornamentation of columnals between the studied specimen and H.? smithi supports this result.

  • Brosse et al. (2019) reported ossicles of Holocrinidae from Oman. Columnals of these specimens show a cylindrical or pentagonal outline with straight and/or bifurcated radial ridges from near the axial canal to the margin of the columnal on the axial surface, and cirri show a thick column form with two distinctive radial ridges on the axial surface. These features of the Omani specimens are different from those of the Nevada specimens of this study. Thus, in this study, we do not recognize the former specimens as a similar species.

  • Occurrence.—Ossicles of Holocrinus sp. have been reported from Japan (Kashiyama and Oji, 2004), South Primorye, Russia (Oji, 2009), Svalbard (Salamon et al., 2015), Nevada, USA (Schubert et al., 1992; Hofmann et al., 2013; this study) and Idaho, USA (Brayard et al., 2017). Kashiyama and Oji (2004) reported the species from the Smithian Hiraiso Formation, Japan, but Shigeta and Nakajima (2017) recently reported the occurrence of the lower Spathian ammonoid Tirolites cf. ussuriensis from the Formation. Thus, the Japanese specimen is a Spathian example.

  • Figure 6.

    Paleogeographic distribution of crinoid fossils during the Early Triassic based on Baud et al. (1991), Schubert et al. (1992), Sano and Nakashima (1997), Kashiyama and Oji (2004), Galfetti et al. (2008), Kaim et al. (2013), Foster et al. (2015, 2019), Salamon et al. (2015), Brayard et al. (2017), Shigeta and Nakajima (2017) and this study. A, Induan; B, Smithian; C, Spathian. Paleomaps modified after Péron et al. (2005), Brayard et al. (2006, 2009) and Shigeta et al. (2009).

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    Incertae sedis
    Articulata ord., fam., gen. et sp. indet.
    Figure 9E, 9F

  • Figured specimens.—Two nodals, NMMNH P-96670, 96671, from JJ9-23.

  • Description.—Nodal, varying from 0.86 and 1.35 mm in diameter, 0.35 and 0.54 mm in height. Cross section forms stellate shape, which consists of five ridged interradii and five radii with cirrus sockets. Both proximal and distal facets smooth and show straight lateral outlines.

  • Remarks.—The described specimens show ridged interradii and developed cirrus sockets in the radii. This feature is more typical of Isocrinus than Holocrinus. Salamon et al. (2015) has already reported a nodal with cirrus sockets from the Induan part of the Vardebukta Formation, Svalbard. However, the identification of the Svalbard specimen is questioned by Stiller (2024). Both specimens of this study lack a well-developed proximal facet, which was probably worn away during the deposition process and/or dissolved by acetic acid treatment. Thus, in this study, we do not attribute these specimens to the Isocrinidae with certainty.

  • Occurrence.—This indeterminable specimen has only been reported from Nevada, USA (this study).

  • Conodonts

    Locational notation of conodont elements has largely been modified by intensive analysis of multi-element reconstruction of conodont apparatuses (e.g. Purnell et al., 2000). All specimens described herein are discrete P1 elements; hence, the orientation terms proposed by Sweet (1988), Purnell et al. (2000) and Orchard (2005) have also been adopted. The color of all studied specimens ranges from light to dark gray, which likely corresponds to CAI 3–4 of Epstein et al. (1977).

    Figure 7.

    Photo images of crinoid columnals of Holocrinus sp. from JJ9-23. A, outer mold of articular facet of columnal, NMMNH P-96417; B–F, facet of internodals; B, NMMNH P-96418; C, NMMNH P-96419; D, NMMNH P-96420; E, NMMNH P-96421; F, NMMNH P-96422. Scale bars = 0.5 mm.

    img-z11-1_01.jpg

    Class Conodonta Eichenberg, 1930
    Order Ozarkodina Dzik, 1976
    Superfamily Gondolelloidea (Lindström, 1970)
    Subfamily Neogondolellinae Hirsch, 1994
    Genus Neospathodus Mosher, 1968

  • Type species.—Spathognathodus cristagalli Huckriede, 1958.

  • Neospathodus pakistanensis Sweet, 1970
    Figures 12, 13A–13F

  • Neospathodus pakistanensis Sweet, 1970, p. 254, pl. 1, figs. 16, 17; McTavish, 1973, p. 295, pl. 1, figs. 1, 2; Buryi, 1979, p. 57, pl. 9, fig. 2; Wang and Cao, 1981, p. 367, pl. 2, fig. 27; Matsuda, 1983, p. 87, pl. 1, figs. 1–5; Tian et al., 1983, p. 379, pl. 81, fig. 3; Dagis, 1984, p. 26, pl. 5, figs. 9–11; Hatleberg and Clark, 1984, pl. 1, fig. 5; Beyers and Orchard, 1991, pl. 5, fig. 2; Cao and Wang, 1993, pl. 56, fig. 14; Orchard, 2007b, figs. 19, 20, 23–26; Orchard and Krystyn, 2007, figs. 19, 20; Orchard, 2008, p. 407, figs. 8.11, 8.12; Igo, 2009, p. 190, figs. 151.18–151.26, 152.1–152.7, 152.10–152.13, 152.20, 152.21, 153.1–153.7, 154.1–154.6; Orchard and Zonneveld, 2009, p. 784, fig. 13, parts 18–21, 26; Beranek et al., 2010, figs. 6.31–6.33; Metcalfe et al., 2012, figs. 6.2–6.5, 6.8; Maekawa and Igo, 2014, p. 228, figs. 165.4–165.24; Maekawa et al., 2015, p. 315, fig. 5.3; Maekawa in Maekawa et al., 2018, p. 27, figs. 16.5–16.15; Han et al., 2022, p. 15, figs. 11.8–11.10.

  • Neospathodus novaehollandiae McTavish, 1973, p. 294, pl. 1, figs. 4, 5, 14, 16–23; Goel, 1977, p. 1091, pl. 1, figs. 1, 2; Beyers and Orchard, 1991, pl. 5, fig. 7; Orchard, 2007b, figs. 15–18, 27, 28; Igo, 2009, p. 188, figs. 153.8–153.14, 154.7–154.11, 155.1–155.11; Metcalfe et al., 2012, fig. 5; Bondarenko et al., 2013, fig. 7.3; Maekawa and Igo, 2014, p. 228, figs. 164.7–164.24, 165.1–165.3; Maekawa in Maekawa et al., 2018, p. 27, figs. 15.35, 15.36, 16.1–16.4; Maekawa and Jenks, 2021, p. 230, fig. 16.10.

  • Neospathodus homeri (Bender). Bui, 1989, p. 402, pl. 31, fig. 16.

  • Neospathodus concavus Zhao and Orchard in Zhao et al., 2007. Igo, 2009, p. 184, fig. 154.13.

  • Materials.—Fourteen specimens, NMMNH P-96396–96409, from JJ9-23, two specimens, NMMNH P-96410, 96411 from 0614-A.

  • Description.—Laterally compressed blade-like segminate P1 elements. Straight upper edge bears fused and posteriorly reclined denticles, up to 16 in number, which contain one or two posterior small denticles. Highest point generally situated above the basal cavity. Basal margin straight or slightly undulated anteriorly and up-arched with distinctively downturned posterior part beneath basal cavity. Sub-rounded or elliptical basal cavity shows rounded posterior margin. Groove runs from the basal pit to anterior end. One specimen (NMMNH P-96406, Figure 13A) shows arched unit.

  • Remarks.—Neospathodus pakistanensis was originally described by Sweet (1970) from the Salt Range, Pakistan. According to this report, the species is generally characterized by a blade-like P1 element with a distinctly downturned posterior basal margin. The described specimens show the diagnostic character. Han et al. (2022) treated N. novaehollandiae as a junior synonym of N. pakistanensis based on the ontogenetic relationship and similar geological range of these two species. We follow the recommendation of Han et al. (2022).

  • An element (NMMNH P-96406, Figure 13A) shows an arched unit, but the other features well correspond to N. pakistanensis. Thus, it is an aberrant variant of the species. A strongly arched P1 element, which is probably an end member of N. pakistanensis was reported from South Primorye, Russia (N. concavus of Igo, 2009, p. 184, fig. 154.13).

  • Occurrence.—The species, which generally indicates Zone 6 of the Lower Triassic in the Salt Range, Pakistan (Sweet, 1970), has also been reported from the Tethyan, Panthalassan, and Boreal regions (e.g. McTavish, 1973; Beyers and Orchard, 1991; Orchard, 2007b, 2008; Igo, 2009; Orchard and Zonneveld, 2009; Metcalfe et al., 2012; Maekawa et al., 2015, 2018; Han et al., 2022).

  • According to recent research, the first appearance (FA) of the species generally occurs at the same horizon or slightly below the FA of Novispathodus waageni or Novispathodus waageni eowaageni (Zhao and Orchard in Zhao et al., 2007) (e.g. Goudemand, 2014; Hounslow et al., 2017; Krystyn et al., 2017a, b; Maekawa et al., 2018; Han et al., 2022). The range of the species generally continues up to the lowest middle Smithian Flemingites fleminganus ammonoid Zone (e.g. Krystyn et al., 2017a, b). On the other hand, Bondarenko et al. (2013) reported the species from the late Smithian Anasibirites nevolini ammonoid Zone. Thus, the species probably ranges from the late Dienerian to late Smithian.

  • Figure 8.

    SEM images of internodals of Holocrinus sp. from JJ9-23. A, NMMNH P-96423; B, NMMNH P-96424; C, NMMNH P-96425; D, NMMNH P-96426; E, NMMNH P-96427; F, NMMNH P-96428; G, NMMNH P-96429; H, NMMNH P-96430; I, NMMNH P-96421; J, NMMNH P-96431; K, NMMNH P-96432. For A–K: a, c, axial views; b, lateral view.

    img-z12-1_01.jpg

    Figure 9.

    SEM images of crinoid columnals from JJ9-23. A–D, G, H, Holocrinus sp.; A, NMMNH P-96433, internodal; B, NMMNH P-96434, internodal; C, NMMNH P-96435, internodal; D, NMMNH P-96436, nodal; G, NMMNH P-96437, nodal; H, NMMNH P-96438, nodal; E, F, Articulata ord., fam., gen. et sp. indet.; E, NMMNH P-96670, nodal; F, NMMNH P-96671, nodal. For A–H: a, c, axial views; b, lateral view; d, distal view; p, proximal view.

    img-z13-1_01.jpg

    Figure 10.

    SEM images of cirri of Holocrinus sp. from JJ9-23. A, NMMNH P-96439; B, NMMNH P-96440; C, NMMNH P-96441; D, NMMNH P-96442; E, NMMNH P-96443; F, NMMNH P-96444; G, NMMNH P-96445; H, NMMNH P-96446; I, NMMNH P-96447. For A–I: a, c, axial views; b, lateral view.

    img-z14-1_01.jpg

    Figure 11.

    SEM images of columnals and cirri of Holocrinus sp. from 0614-A. A, NMMNH P-96448, internodal; B, NMMNH P-96449, internodal; C, NMMNH P-96450, internodal; D, NMMNH P-96662, nodal; E, NMMNH P-96663, internodal; F, NMMNH P-96664, internodal; G, NMMNH P-96665, internodal; H, NMMNH P-96666, internodal; I, NMMNH P-96667, cirrus; J, NMMNH P-96668, cirrus; K, NMMNH P-96669, cirrus. For A–K: a, c, axial views; b, lateral view; d, distal view; p, proximal view.

    img-z15-1_01.jpg

    Neospathodus posterolongatus Zhao and Orchard in Zhao et al., 2007
    Figure 13G–13K

  • Neospathodus waageni subsp. B Zhao et al., 2004, p. 42, fig. 2.

  • Neospathodus posterolongatus Zhao and Orchard in Zhao et al., 2007, p. 36, pl. 1, fig. 2A–C; Orchard, 2007b, figs. 1–6; Orchard, 2008, p. 407, figs. 8.3, 8.4; Orchard and Zonneveld, 2009, p. 784, fig. 14, parts 7, 8, 16, 17, 21, 22; Beranek et al., 2010, figs. 6.24, 6.25; Maekawa and Igo, 2014, p. 230, figs. 165.25–165.33, 166.1–166.18; Maekawa in Maekawa et al., 2018, p. 29, figs. 16.16–16.20, 17.1, Maekawa and Jenks, 2021, p. 230, figs. 15.21–15.23.

  • Materials.—Four specimens, NMMNH P-96412–96415, from JJ9-23, one specimen NMMNH P-96416, from 0614-A.

  • Description.—Four segminate elements 0.50–0.96 mm in length; 0.40–0.53 mm in height; length to height ratio 1.8–2.1. Arched upper edge gradually increases in height to posterior one-fourth and bears denticles varying in number from 12–14. Basal margin straight or slightly upward in anterior and slightly concaved and upturned beneath basal cavity. Lateral view of the element shows sub-triangular outline. Basal cavity shows elliptical or rhomboidal outline with pointed posterior margin. Groove runs from the basal pit to anterior end.

  • Remarks.—Neospathodus posterolongatus is characterized by its segminate P1 element with a posteriorly elongated basal cavity. The described specimens show this diagnostic feature. The species is distinguished from N. pakistanensis by its much more discrete denticulation and the weaker development of its lateral flange.

  • Occurrence.—The species was originally reported from Anhui Province, South China, and its range probably extends from the lower to middle Smithian (e.g. Orchard, 2007a; Zhao et al., 2007). The species has also been reported from Spiti, India (Orchard, 2007b; Orchard and Krystyn, 2007), Ellesmere Island, Canada (Orchard, 2008), British Columbia, Canada (Orchard and Zonneveld, 2009), northeastern Vietnam (Shigeta et al., 2014), Southwest Japan (Maekawa et al., 2018), and Nevada, USA (Maekawa and Jenks, 2021; this study).

  • Figure 12.

    SEM images of P1 elements of Neospathodus pakistanensis Sweet, 1970 from JJ9-23. A, NMMNH P-96396; B, NMMNH P-96397; C, NMMNH P-96398; D, NMMNH P-96399; E, NMMNH P-96400; F, NMMNH P-96401; G, NMMNH P-96402; H, NMMNH P-96403; I, NMMNH P-96404; J, NMMNH P-96405. For A–J: a, d, lateral views; b, upper view; c, lower view.

    img-z16-1_01.jpg

    Figure 13.

    SEM images of conodont P1 elements from JJ9-23 (A–D, G–J) and 0614-A (E, F, K). A–F, Neospathodus pakistanensis Sweet, 1970; A, NMMNH P-96406; B, NMMNH P-96407; C, NMMNH P-96408; D, NMMNH P-96409; E, NMMNH P-96410; F, NMMNH P-96411; G–K, Neospathodus posterolongatus Zhao and Orchard in Zhao et al., 2007; G, NMMNH P-96412; H, NMMNH P-96413; I, NMMNH P-96414; J, NMMNH P-96415; K, NMMNH P-96416. For A–K: a, lateral view; b, upper view; c, lower view.

    img-z17-1_01.jpg

    Table 1.

    Measurements of crinoid ossicles. Parenthesis shows measurement of broken specimen.

    img-z18-2_01.gif

    Table 2.

    Measurements of conodont elements. Parenthesis shows measurement of broken specimen. “+” shows and incomplete number of denticles. Abbreviations: L, length; H, height.

    img-z19-2_01.gif

    Acknowledgements

    Both authors acknowledge the kind support, encouragement and patience of Ruby Jenks (West Jordan, Utah) during this investigation. We thank Kevin G. Bylund (Spanish Fork, Utah), Daniel A. Stephen (Utah Valley University, Orem, Utah) and Noreen Kittrick (Salt Lake City, Utah) for their support on field trips. We are also grateful to Tatsuo Oji (Nagoya City Science Museum) and Frank Stiller (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China) and Atsushi Yabe (Editor-in-Chief of Paleontological Research) for their advanced comments on the draft. This research was financially supported by the 2015 annual research grant of the Tokyo Geographical Society, the 2019 annual research grant of the Fukada Geological Institute (Fukada Grant-in-Aid), the 2020 Nakatsuji Foresight Foundation Research Grant, and Grant-in-Aids for Young Research (KAKENHI) from the Japan Society for the promotion of Science (21K14036) to T. Maekawa. Fossil localities pertinent to this study at the classic Crittenden Springs site lie on US public land (Department of the Interior, Bureau of Land Management). This study was conducted under the auspices of BLM Paleontological Resources Use Permit N-97816. We thank the BLM for allowing access to the fossil sites.

    This article is licensed under a Creative Commons [Attribution 4.0 International] license.

    © 2024 The Authors.

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    Author contributions

    T. M. and J. F. J. investigated outcrops of the Thaynes Formation at the classic Crittenden Springs site in Long Canyon and wrote this manuscript. T. M. collected conodont and crinoid samples. Both authors contributed to the writing of the paper.

    Takumi Maekawa and James F. Jenks "Smithian-Aged (Early Triassic, Early Olenekian) Crinoid Ossicles from Exotic Limestone Blocks in the Lower Part of the Thaynes Formation at Crittenden Springs, Elko County, Nevada," Paleontological Research 29(1), 1-23, (13 December 2024). https://doi.org/10.2517/prpsj.2400141
    Received: 19 June 2024; Accepted: 2 September 2024; Published: 13 December 2024
    KEYWORDS
    conodont
    Crinoid ossicles
    Crittenden Springs
    Smithian
    Thaynes Formation
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