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A Glyptagnostus reticulatus trilobite faunule from the Cambrian of the Northern Qilian Mountains, northwest China, and its paleogeographical implications

Published online by Cambridge University Press:  15 March 2022

Xuejian Zhu Open the ORCID record for Xuejian Zhu [Opens in a new window] ,
Nigel C. Hughes Open the ORCID record for Nigel C. Hughes [Opens in a new window]  and
Zhiqiang Zhou
Xuejian Zhu*
Affiliation:
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
Nigel C. Hughes
Affiliation:
Department of Earth and Planetary Sciences, University of California, Riverside, California 92521, USA
Zhiqiang Zhou
Affiliation:
Xi'an Institute of Geology and Mineral Resources, 438 East You Yi Road, Xi'an 710054, China
*
*Corresponding author.
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Abstract

A Glyptagnostus reticulatus (Angelin, 1851)–bearing trilobite assemblage has been found from an unnamed Cambrian formation in the Northern Qilian Mountains area, of which geographical placement in the Cambrian is contested. Glyptagnostus reticulatus is a biostratigraphic indicator of the Furongian Series and Paibian Stage, and three agnostoid and six polymerid taxa from the Changgou section, Daliang area are described herein, along with conspecific forms from the nearby Chuancigou section. This well-preserved assemblage shows strong taxonomic affinity with northwestern Queensland, Australia, and western Hunan–eastern Guizhou, China, and likely comes from deep outer-shelf to slope setting associated with the Northern Qilian arc. It is consistent with other arguments that during the Cambrian, the Northern Qilian arc, along with the Hexi Corridor of the Alxa terrane, were more closely allied to South China than to North China.

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Journal of Paleontology , Volume 96 , Issue 4 , July 2022 , pp. 875 - 885
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Copyright © The Author(s), 2022. Published by Cambridge University Press on behalf of The Paleontological Society

Introduction

Fossils can be of unique significance in areas with complex geological histories for the information they provide on age and geographical associations. The northwestern part of Tibet is one of Earth's most complex areas geologically, and its early Paleozoic history is particularly difficult to decipher. During the Cambrian, the Qilian Mountains comprised a series of island arc complexes that were later juxtaposed between the converging Qaidam and Alxa blocks (e.g., Xiao et al., Reference Xiao, Windley, Yong, Yan, Yuan and Liu2009; Pan et al., Reference Pan, Wang, Li, Yuan, Ji, Yin, Zhang and Wang2012; Song et al., Reference Song, Niu, Su and Xia2013; Yu et al., Reference Yu2021). The region contains a Neoproterozoic to early Paleozoic ophiolite sequence, belts of high-pressure metamorphic rock, island-arc volcanic rocks and granitoid plutons, and a series of Silurian–Carboniferous sedimentary cover sequences (Song et al., Reference Song, Niu, Su and Xia2013) that finally accreted to the North China block at the end of the early Paleozoic or possibly later (Zhang et al., Reference Zhang, Zhang, Xiao, Wang and Zhang2015). In the Northern Qilian Mountains area, the Cambrian outcrops sporadically and is characterized by the development of a thick series of marine volcanic rocks that are commonly strongly tectonically deformed. The specimens in this study have not been strongly deformed and are preserved in limestone, offering the unique opportunity for more confident identification.

Traditionally, the Qilian Mountains area is divided into five tectonically defined regions: the Hexi Corridor area (assigned to the Alxa Block), the Northern, Central, and Southern Qilian Mountains areas, and the Lajishan Range area (Zhou et al., Reference Zhou, Cao, Hu and Zhao1996) (Fig. 1.1). Terreneuvian–Series 2 trilobites have never been found in these areas, but Miaolingian–Furongian trilobites are quite frequently preserved. They are all from deep shelf to basinal environments. Miaolingian–Furongian trilobites of the Hexi Corridor area have been studied by Zhu et al. (Reference Zhu, Lin and Zhang1979) and Zhou et al. (Reference Zhou, Li and Qu1982). Lin et al. (Reference Lin, Peng, Zhou and Yang2013, Reference Lin, Peng and Zhou2015) have respectively studied Miaolingian–Furongian agnostoid and polymerid trilobites collected from the Lajishan Range area. Before that, in the Central Qilian Mountains area, Miaolingian–Furongian Cambrian trilobites were studied by Zhu (Reference Zhu1960a, Reference Zhu1965), Zhu et al. (Reference Zhu, Lin and Zhang1979), and Zhou et al. (Reference Zhou, Cao, Hu and Zhao1996). In the North Qilian Mountains area, some Miaolingian trilobites have been reported from Tianzhu, Gansu Province (Zhu, Reference Zhu1960b), and a Furongian trilobite fauna has been discovered from Chuancigou, Qilian County, Qinghai Province (Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979). Later, a similar Furongian trilobite faunule was discovered by Zhou and his colleagues from the Changgou section, Daliang area, Menyuan County, Qinghai Province, 170 km southeast of Chuancigou (Fig. 1.2), when they studied the early Paleozoic stratigraphy and sedimentary–tectonic evolution of the eastern Qilian Mountains. These authors listed some trilobite names along with some plates illustrating fossils (Zhou et al., Reference Zhou, Cao, Hu and Zhao1996). Here the collections from the Changgou section, Daliang area, are formally described for the first time, Glyptagnostus reticulatus (Angelin, Reference Angelin1851) is recognized in the Qilian Mountains area for the first time, and some of the original identifications are revised. Glyptagnostus reticulatus is cosmopolitan and defines the conterminous base of the Furongian Series and Paibian Stage (Peng et al., Reference Peng, Babcock, Robison, Lin, Rees and Saltzman2004b). Its occurrence can help pinpoint the base of the Furongian Series in this region. Other regional Cambrian trilobites collected by Zhou and his colleagues (1996) will be the subject of forthcoming papers.

Figure 1. (1) Schematic map showing major tectonic units of China (modified from Song et al., Reference Song, Niu, Su and Xia2013). (2) Geological sketch of Qilian Mountain area, northwest China (modified from Lin et al., Reference Lin, Peng, Zhou and Yang2013). (3) Geological map of Changgou section, Daliang area (modified from unpublished data, Qinghai Geological Bureau, 1969). C3 - Miaolingian, C4 - Furongian, O2 - Middle Ordovician, O3 - Late Ordovician, S1 - Llandovery, P - Permian, T - Triassic, Q - Quaternary.

Stratigraphy, age, and affinity

This trilobite faunule has been collected from Changgou, Daliang, Menyuan County, Qinghai Province (Fig. 1.3). The Cambrian strata of this area are traditionally ascribed to the Heicigou Group (Zhou et al., Reference Zhou, Cao, Hu and Zhao1996) because their lithological features are similar to those of the eponymous section of the group, which lies in Heicigou, Tianzhu County, Gansu Province. The Heicigou Group in the type section belongs to the Wuliuan to Drumian Stages, Miaolingian Series, but the so-called Heicigou Group in the Changgou section is within the Furongian Series, and thus these two groups are not chronostratigraphically congruent. Therefore, the Cambrian strata of Changgou section likely merits a new lithostratigraphic unit name. Full discussion of the lithostratigraphy is beyond the scope of this paper, and in this paper the rocks from which our specimens were collected are referred to simply as an unnamed formation. It comprises thick spilitic basalts extruded subaqueously with one limestone interval (Fig. 2). Underlying rocks are not exposed, and the formation is overlain by the limestone of the Late Ordovician Koumenzi Formation. The contact between these two formations is mapped as a normal fault (unpublished data, Qinghai Geological Bureau, 1969).

Figure 2. Stratigraphic column of the unnamed formation at Changgou section, Daliang area, Menyuan County, Qinghai Province, showing fossiliferous limestone layer occurring within a thick sequence of spilitic basalts and other volcanogenic rocks.

Trilobites were collected from the limestone interval near the base of this unnamed formation (Fig. 2). The occurrence of Glyptagnostus reticulatus indicates this faunule is from the lower part of the Paibian Stage. Other agnostoid trilobites include Pseudagnostus idalis Öpik, Reference Öpik1967 and Innitagnostus inexpectans (Kobayashi, Reference Kobayashi1938). The polymerid trilobites include Baikadamaspis sinensis (Yang in Zhou et al., Reference Zhou, Liu, Meng and Sun1977), Aphelaspis granulata Kuo in Egorova et al., Reference Egorova, Xiang, Li, Nan and Kuo1963, Eugonocare (Olenaspella) transversa Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979, Paraacidaspis hunanica Egorova in Poletaeva, Reference Poletaeva1960, Shengia shergoldi Peng, Babcock, and Lin, Reference Peng, Babcock and Lin2004c, and Corynexochus plumula Whitehouse, Reference Whitehouse1939.

The Changgou fauna is similar to that of Chuancigou. The latter comprises Pseudagnostus communis (Hall and Whitfield, Reference Hall and Whitfield1877), Corynexochus plumula, Aphelaspis qilianensis Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979, Eugonocare (Olenaspella) transversa, Shengia shergoldi, Dunderbergia elongata Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979, Proceratopyge chuancigouensis Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979, and Baikadamaspis sinensis. These two faunas share four species, Baikadamaspis sinensis, Shengia shergoldi, Corynexochus plumula, and Eugonocare (Olenaspella) transversa, and two genera, Pseudagnostus and Aphelaspis. They are almost coeval, although Glyptagnostus reticulatus is not found in the Chuancigou section.

This trilobite association reveals strong affinities with western Hunan–eastern Guizhou, China, as described by Peng (Reference Peng1992), with all the genera and most of the species being found in both areas. Affinities with northwestern Queensland, Australia, are shown by the presence of all the agnostid species, Corynexochus plumula, and Eugonocare (Öpik, Reference Öpik1967). These associations are of interest considering the markedly different paleogeographic positions and associations proposed for North Qilian and associated regions during the early Paleozoic (e.g., compare Gehrels et al., Reference Gehrels, Kapp, DeCelles, Pullen, Blakey, Weislogel, Ding, Guynn, Martin, McQuarrie and Yin2011, fig. 10; Pan et al., Reference Pan, Wang, Li, Yuan, Ji, Yin, Zhang and Wang2012, fig. 5; Hu et al., Reference Hu, Zhai, Jahn, Wang, Li, Lee and Tang2015, fig. 12a; Zhang et al., Reference Zhang, Zhang, Xiao, Wang and Zhang2015, fig. 12; Han et al., Reference Han, Zhao, Cawood, Sun, Eizenhöfer, Hou, Zhang and Liu2016, fig. 4; Li et al., Reference Li, Zhao, Liu, Cao, Yu, Li, Somerville, Yu and Suo2018, fig. 20B; Yu et al., Reference Yu2021, fig. 11). Given the slope setting that these forms inhabited, high endemism for the fauna is unlikely. Nevertheless, the presence of species shared with South China and Australia supports a low-latitude peri-Gondwanan affinity for this fauna and is thus consistent with locating North Qilian in that region at the time.

The paleogeographical implications of this result are consistent with recent results based on integrated geological data that suggest that during the Cambrian, the Qaidam–Qilian–Alxa region was in the process of amalgamation (Xiao et al., Reference Xiao, Windley, Yong, Yan, Yuan and Liu2009, fig. 12; Pan et al., Reference Pan, Wang, Li, Yuan, Ji, Yin, Zhang and Wang2012, fig. 5; Song et al., Reference Song, Niu, Su and Xia2013, fig. 22) and sufficiently close to share fauna and sediment sources common to the South Chinese and Indian sectors of the Gondwana margin. Our results are thus in accord with those of Zhang et al. (Reference Zhang, Zhang, Xiao, Wang and Zhang2015), who pointed out that during the early Paleozoic provenance, data support a closer association of the Alxa block with South China than with North China. Accordingly, if recent reconstructions that link South China to western India in the Cambrian are correct (e.g., Burrett et al., Reference Burrett, Zaw, Meffre, Lai, Khositanont, Chaodumrong, Udchachon, Ekins and Halpin2014; Xu et al., Reference Xu, Cawood, Du, Zhong and Hughes2014; Yao et al., Reference Yao, Li, Li and Yang2014; Hughes, Reference Hughes2016; Zhou et al., Reference Zhou, Zheng, Li, Griffin, Qing, Hadi Shafaii and O'Reilly2019), the Qaidam–Qilian–Alxa regions were likely associated with it. Although some authors (Li et al., Reference Li, Zhao, Liu, Cao, Yu, Li, Somerville, Yu and Suo2018, fig. 20B; Zhao et al., Reference Zhao, Zhang, Zhu, Ding, Li, Yang and Wu2021, fig. 3) isolate North China from equatorial Gondwana during the Cambrian, detrital zircon and faunal evidence for its continuity with Gondwana at the time remains strong (McKenzie et al., Reference McKenzie, Hughes, Myrow, Choi and Park2011; Wernette et al., Reference Wernette, Hughes, Myrow and Aung2021). Our results need not suggest great geographic distance between the Northern Qilian Mountains area and the North China block during the Furongian, but rather highlight the paleoenvironmental contrast between the platform environment of the North Chinese late Cambrian deposits and the deeper water setting of the fauna described herein.

Repository and institutional abbreviation

Illustrated materials are housed in the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences (NIGP). We appreciate ongoing debates about the taxonomic affinity of Agnostina (e.g., Legg et al., Reference Legg, Sutton and Edgecombe2013; Moysiuk and Caron, Reference Moysiuk and Caron2019), but as this study throws no further light on the higher-level affinity of the group, we treat them alongside Trilobita.

Systematic paleontology

Family Glyptagnostidae Whitehouse, Reference Whitehouse1936
Genus Glyptagnostus Whitehouse, Reference Whitehouse1936

Type species

Glyptagnostus toreuma Whitehouse, Reference Whitehouse1936 (=Agnostus reticulatus Angelin, Reference Angelin1851; Öpik, Reference Öpik1961), from the Georgina Limestone of Queensland, Australia, by original designation.

Glyptagnostus reticulatus (Angelin, Reference Angelin1851)
 Figure 3.1

Reference Peng, Lin and Zhu2000

Glyptagnostus reticulatus; Peng and Robison, p. 87, fig. 71 (see for synonymy to date).

Reference Peng and Robison2000

Glyptagnostus reticulatus; Peng, Lin, and Zhu, fig.1.

Reference Peng, Babcock, Lin, Chen and Zhu2001

Glyptagnostus reticulatus; Peng et al., pl. 4.1–4.4, 5.1–5.3, 6.1, 6.6, 6.14.

Reference Ahlberg2003

Glyptagnostus reticulatus; Ahlberg, fig. 3E–G.

Reference Peng, Babcock, Lin, Chen, Qi and Zhu2004a

Glyptagnostus reticulatus; Peng et al., pl. 1.5–1.9.

Reference Peng, Babcock, Robison, Lin, Rees and Saltzman2004b

Glyptagnostus reticulatus; Peng et al., fig. 8C–E.

Reference Peng, Babcock, Lin and Chen2005

Glyptagnostus reticulatus; Peng et al., fig.10.1, 10.2.

Reference Varlamov, Pak and Rosova2006

Glyptagnostus reticulatus; Varlamov, Pak, and Rosova, p. S29, pl. 1, figs. 1–3.

Reference Ergaliev and Ergaliev2008

Glyptagnostus reticulatus; Ergaliev and Ergaliev, p. 88, pl. 28, figs. 1, 4, 6.

Reference Ergaliev and Ergaliev2008

Glyptagnostus angelini Resser, Reference Resser1938; Ergaliev and Ergaliev, p. 89, pl. 28, figs. 5, 7.

Reference Westrop and Eoff2012

Glyptagnostus reticulatus; Westrop and Eoff, p. 235, fig. 22.9–22.15.

Reference Ahlberg and Terfelt2012

Glyptagnostus reticulatus; Ahlberg and Terfelt, fig. 3a, b.

Reference Schwimmer and Montante2012

Glyptagnostus reticulatus; Schwimmer and Montante, p. 34, fig. 2.5–2.8.

Reference Makarova2013

Glyptagnostus reticulatus; Makarova, p. 13, fig. 1a.

Reference Peng, Babcock, Robison, Lin, Rees and Saltzman2013

Glyptagnostus reticulatus; Peng et al., fig. 2.7c–g.

Reference Danukalova, Kuzmichev and Korovnikov2014

Glyptagnostus reticulatus; Danukalova, Kuzmichev, and Korovnikov, pl. 3, figs. 4, 5.

Reference Peng, Hou and Wang2016

Glyptagnostus reticulatus; Peng, Hou, and Wang, fig. 4.45.

Figure 3. Trilobites from Changgou section, Daliang area, Menyuan County, Qinghai Province, except the holotype of Pterocephalops granulus Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979 (=Baikadamaspis sinensis [Yang in Zhou et al., Reference Zhou, Liu, Meng and Sun1977]) (20) and the holotype of Corynexochus chinensis Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979 (12) from Chuancigou, Qilian County, Qinghai Province. (1) Glyptagnostus reticulatus (Angelin, Reference Angelin1851), cephalon, scale bar = 1 mm, NIGPAS174370. (2–4) Pseudagnostus idalis Öpik, Reference Öpik1967: (2) cephalon, scale bar = 0.5 mm, NIGPAS174371; (3) pygidium, scale bar = 1 mm, NIGPAS174372; (4) pygidium, scale bar = 0.5 mm; NIGPAS174373. (5, 6) Innitagnostus inexpectans (Kobayashi, Reference Kobayashi1938): (5) cephalon, scale bar = 1 mm, NIGPAS174374; (6) pygidia, scale bar = 1 mm, NIGPAS174375. (7–11) Paraacidaspis hunanica Egorova in Poletaeva, Reference Poletaeva1960: (7) cranidium, scale bar = 5 mm, NIGPAS174376; (8) cranidium, scale bar = 5 mm, NIGPAS174377; (9) cranidium, scale bar = 5 mm, NIGPAS174378; (10) pygidium, scale bar = 2 mm, NIGPAS174379; (11) pygidium, scale bar = 2 mm, NIGPAS174380. (12–19) Corynexochus plumula Whitehouse, Reference Whitehouse1939: (12) cranidium, scale bar = 1 mm, NIGPAS44654 (the holotype of Corynexochus chinensis Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979, transferred to C. plumula in this paper); (13) cranidium, scale bar = 1 mm, NIGPAS174381; (14) cranidium, scale bar = 1 mm, NIGPAS174382; (15) cranidium, scale bar = 1 mm, NIGPAS174383; (16) cranidium, scale bar = 1 mm, NIGPAS174384; (17) pygidium, scale bar = 1 mm, NIGPAS174385; (18, 19) dorsal and left lateral view of pygidium, scale bar = 1 mm, NIGPAS174386. (20–23) Baikadamaspis sinensis (Yang in Zhou et al., Reference Zhou, Liu, Meng and Sun1977): (20) cranidium, scale bar = 1 mm, NIGPAS44665 (the holotype of Pterocephalops granulus Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979, transferred to Baikadamaspis sinensis in this paper); (21) cranidium, scale bar = 1 mm, NIGPAS174387; (22, 23) dorsal and right lateral view of cranidium, scale bar = 2 mm, NIGPAS174388. (24) Librigena of Shengia shergoldi Peng, Babcock, and Lin, Reference Peng, Babcock and Lin2004c, scale bar = 2 mm, NIGPAS174389.

Lectotype

Cephalon (Westergård, Reference Westergård1947, pl. 1, fig. 2, RM, no. Ar. 9794), Scania, Andrarum, Sweden, Furongian, Olenus Zone.

North Qilian material

One cephalon.

Remarks

Albeit slightly broken, the cephalon is assigned to Glyptagnostus reticulatus with certainty. The reticulate pattern on the genae and pleural fields of Glyptagnostus reticulatus varies ontogenetically and stratigraphically (Peng and Robison, Reference Peng and Robison2000). The new material, with dense reticulate sculpture, is similar to those commonly occurring in younger strata within the zone. The anteroglabella in our specimen is sagittally bipartite. This feature is also found in the material of Bennett Island (Danukalova et al., Reference Danukalova, Kuzmichev and Korovnikov2014).

Family Agnostidae M'Coy, Reference M'Coy1849
Genus Pseudagnostus Jaekel, Reference Jaekel1909

Type species

Agnostus cyclopyge Tullberg, Reference Tullberg1880, from the Furongian of Sweden, by original designation.

Pseudagnostus idalis Öpik, Reference Öpik1967
Figure 3.2–3.4

Reference Öpik1967

Pseudagnostus idalis Öpik, p. 153, pl. 62, figs. 8, 9, pl. 63, figs.1, 3.

Reference Hill, Playford and Woods1971

Pseudagnostus idalis; Hill, Playford, and Woods, pl. 12, figs. 1, 2.

Reference Ergaliev1980

Pseudagnostus (Pseudagnostus) idalis Öpik, Reference Öpik1967; Ergaliev, p. 107, pl. 11, fig. 9.

Reference Shergold1982

Pseudagnostus (Pseudagnostus) idalis; Shergold, p. 26, pl. 2, figs. 1–5, pl. 3, figs. 1–8.

Reference Shergold1982

Pseudagnostus (Pseudagnostus) idalis sagittus; Shergold, p. 27, pl. 3, figs. 1–8.

Reference Xiang and Zhang1985

Pseudagnostus idalis; Xiang and Zhang, p. 84, pl. 12, figs. 1–7.

Reference Jago1987

Pseudagnostus (Pseudagnostus) idalis denisonensis; Jago, p. 210, pl. 24, figs. 4–12.

Reference Lu and Lin1989

Pseudagnostus (Pseudagnostus) vigilax; Lu and Lin, p. 116 (233), pl. 14, figs. 5–11.

Reference Jago and Brown1992

Pseudagnostus (Pseudagnostus) idalis huskissonensis; Jago and Brown, p. 63, pl. 1, figs. U–W, pl. 2, figs. A–O.

Reference Peng1992

Pseudagnostus (Pseudagnostus) idalis transversus; Peng, p. 26, figs. 11M–Q.

Reference Peng1992

Pseudagnostus (Pseudagnostus) ampullatus Öpik, Reference Öpik1967; Peng, p. 26, figs. 11I–L.

Reference Shergold, Bordonaro and Liñán1995

Pseudagnostus (Pseudagnostus) idalis Öpik, Reference Öpik1967; Shergold, Bordonaro, and Liñán, p. 251, pl. 3, figs. 1–6.

Reference Shergold, Bordonaro and Liñán1995

Pseudagnostus (Pseudagnostus) sp. cf. P. idalis Öpik, Reference Öpik1967 sensu lato; Shergold, Bordonaro, and Liñán, p. 251, pl. 3, figs. 7–12.

Reference Peng and Robison2000

Pseudagnostus josepha (Hall, Reference Hall1863); Peng and Robison, p. 16, figs. 10.1–10.10.

Reference Paterson and Laurie2004

Pseudagnostus idalis; Paterson and Laurie, p. 93, figs. 6B–D, F–N.

Reference Varlamov, Pak and Rosova2006

Pseudagnostus (Pseudagnostus) idalis; Varlamov, Pak, and Rosova, p. s31, pl. 1, figs. 5–10.

Reference Ergaliev and Ergaliev2008

Pseudagnostus (Pseudagnostus) idalis; Ergaliev and Ergaliev, p. 168, pl. 29, figs. 5–13, pl. 31, figs. 1–3, 8–14, pl. 34, figs. 6–25, pl. 35, figs. 1, 2, 4–13, 15, pl. 39, figs. 5–7.

Holotype

Pygidium (Öpik, Reference Öpik1967, pl. 62, fig. 8, CPC5908), Glenormiston, Queensland, Australia, Furongian, Idamean, Corynexochus plumula Zone.

Description

Cephalon subcircular with deliquiate border furrow, axial furrow and median preglabellar furrow deep, gena smooth. Glabella rounded at front, slightly constricted at F2; F3 slightly bowed rearward. Basal lobes prominent, triangular. Pygidia suboval with deliquiate border furrow, acrolobe weakly constricted, pleural fields smooth; axial furrow behind F2 becoming shallower or entirely effaced when reaching to border furrow; posterolateral spines small; axis constricted at M2, F1 short and weak, and F2 deep to weak and interrupted by median tubercle.

North Qilian material

One cephalon and two pygidia.

Remarks

This species is commonly confused with Pseudagnostus josepha (Hall, Reference Hall1863), and their relationship has been fully discussed (Peng and Robison, Reference Peng and Robison2000; Laurie in Paterson and Laurie, Reference Paterson and Laurie2004; Varlamov et al., Reference Varlamov, Pak and Rosova2006; Westrop and Eoff, Reference Westrop and Eoff2012). The type specimens of Pseudagnostus josepha, collected from the Sunwaptan Lone Rock Formation of Wisconsin, are poorly preserved (Shergold, Reference Shergold1977, pl. 15, figs. 9, 10). Westrop (Reference Westrop1986) assigned better material, collected from the coeval Bison Creek Formation, Alberta, to this species. Until new topotypes of Pseudagnostus josepha prove it to be synonymous with Pseudagnostus idalis, we prefer to treat them as separate species.

Genus Innitagnostus Öpik, Reference Öpik1967

Type species.—Innitagnostus innitens Öpik, Reference Öpik1967 from the Pomegranate Limestone, Willis Creek, northwestern Queensland, Australia, by original designation.

Remarks

This genus is controversial currently. Some workers regarded it as a junior synonym of Agnostus or Micragnostus (e.g., Robison, Reference Robison1994; Peng and Robison, Reference Peng and Robison2000; Høyberget and Bruton, Reference Høyberget and Bruton2008), whereas others treated it as a separate genus (e.g., Shergold and Laurie, Reference Shergold, Laurie and Kaesler1997; Laurie in Paterson and Laurie, Reference Paterson and Laurie2004; Westrop and Eoff, Reference Westrop and Eoff2012). In Innitagnostus, the glabella has an angulate recess at the base to accommodate the basal lobes, and lateral portions of glabellar M2 are commonly separated from the midmost glabella by weak longitudinal (exsag.) furrows. These two characters differentiate Innitagnostus from Agnostus and Micragnostus. At present, we regard them as three valid genera.

Innitagnostus inexpectans (Kobayashi, Reference Kobayashi1938)
Figure 3.5, 3.6

Reference Peng and Robison2000

Agnostus inexpectans; Peng and Robison, p. 12, fig. 7 (see for synonymy).

Reference Paterson and Laurie2004

Innitagnostus inexpectans; Paterson and Laurie, p. 93, figs. 6O–Q.

Reference Ergaliev and Ergaliev2008

Innitagnostus inexpectans; Ergaliev and Ergaliev, p. 43, pl. 30, figs. 1–10.

Reference Schwimmer and Montante2012

Agnostus inexpectans; Schwimmer and Montante, p. 34, fig. 2.1.

Reference Westrop and Eoff2012

“Innitagnostus” inexpectans; Westrop and Eoff, p. 231, figs. 21, 22.1–22.8.

Lectotype

Cephalon (Westrop and Eoff, Reference Westrop and Eoff2012, fig. 22.1–22.3, GSC12006), locality P6/6, British Columbia, Furongian, “Taenicephalus”- (=Taenicephalites) bearing black limestone.

Description

Cephalon subcircular with moderate convexity, clearly furrowed, and smooth. Border narrow, slightly wider anteriorly; border furrow narrow. Preglabellar median furrow narrow, moderately deep. Glabella tapering forward; anterior glabellar subquadrate with a short frontal sulcus. F3 deep, narrow, and nearly straight; F2 and F1 fairly well defined and connected by weak longitudinal (exsag.) furrows. Glabellar node obscure. Basal lobes trapezoid with moderate size.

Pygidium subcircular, smooth with moderate convexity. Axial furrow deep, narrow. Axis constricted across M2. M1 trilobate; F1 shallow with moderate width, arching forward; F2 narrow and shallow, bent rearward by strong axial node. Posteroaxis ogival, terminal node obscure. Border narrow, slightly wider posteriorly. Posterolateral border spine small.

North Qilian material

One cephalon and one pygidium.

Remarks

Our new material is very similar to that described by Westrop and Eoff (Reference Westrop and Eoff2012) and is regarded as conspecific.

?Family Harpididae Whittington, Reference Whittington1950
Genus Baikadamaspis Ergaliev, Reference Ergaliev1980

Type species

Baikadamaspis proprius Ergaliev, Reference Ergaliev1980, from the Glyptagnostus reticulatus Zone and Homagnostus longiformis Zone, Malyi, Karatau, Kazakhstan, by original designation.

Baikadamaspis sinensis (Yang in Zhou et al., Reference Zhou, Liu, Meng and Sun1977)
Figure 3.20–3.23

Reference Zhou, Liu, Meng and Sun1977

Loganopeltoides sinensis Yang in Zhou et al., p. 244, pl. 73, fig. 18.

Reference Yang1978

Loganopeltoides sinensis; Yang, p. 70, pl. 13, figs. 11, 12.

Reference Zhu, Lin and Zhang1979

Pterocephalops granulus; Lin and Zhang in Zhu, Lin, and Zhang, p. 92, pl. 38, fig. 2.

Reference Liu and Li1982

Loganopeltoides sinensis; Liu, pl. 230, fig. 18.

Reference Zhou, Cao, Hu and Zhao1996

Loganopeltoides sinensis; Zhou et al., p. 46, pl. 7, figs. 9, 10.

Reference Peng, Babcock and Lin2004c

Baikadamaspis sinensis; Peng, Babcock, and Lin, p. 159, pl. 74, figs. 6–12; text-fig. 21.

Holotype

Cranidium (Zhou et al., Reference Zhou, Liu, Meng and Sun1977, pl. 73, fig. 18; also Yang, Reference Yang1978, pl. 13, fig. 12, CUGB [China University of Geosciences] 0308001), Tingziguan, Chatian Town, Fenghuang County, Hunan Province, southwest China, Furongian, Chuangia–Prochuangia Zone.

North Qilian material

Two cranidia.

Remarks

Our material was assigned originally to Loganopeltoides by Zhou et al. (Reference Zhou, Cao, Hu and Zhao1996) and later transferred to Baikadamaspis by Peng et al. (Reference Peng, Babcock and Lin2004c). This transfer is accepted. Pterocephalops granulus Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979 was transferred to Pterocephalopsinus by Jell in Jell and Adrain, Reference Jell and Adrain2003, as its genus name is preoccupied. It was later transferred to Baikadamaspis by Peng et al., Reference Peng, Babcock and Lin2004c. The holotype has been refigured herein (Fig. 3.20). It is similar to the holotype of Baikadamaspis sinensis (Peng et al., Reference Peng, Babcock and Lin2004c, p. 160, text-fig. 21) and our material and is regarded as a junior synonym of Baikadamaspis sinensis.

Family Pterocephalidae Kobayashi, Reference Kobayashi1935
Genus Aphelaspis Resser, Reference Resser1935

Type species

Aphelaspis walcotti Resser, Reference Resser1938, from the Furongian of Virginia, subsequently designated by Palmer (Reference Palmer1953).

Aphelaspis granulata Kuo in Egorova et al., Reference Egorova, Xiang, Li, Nan and Kuo1963
 Figure 4.14–4.25

Reference Egorova, Xiang, Li, Nan and Kuo1963

Aphelaspis granulata Kuo in Egorova et al., p. 59, pl. 14, figs. 7–11.

Reference Lu, Zhang, Zhu, Qian and Xiang1965

Aphelaspis granulata; Lu et al., p. 177, pl. 30, figs. 1–4.

Reference Peng1992

Aphelaspis granulata; Peng, p. 57, figs. 27D–G.

Figure 4. Trilobites from Changgou section, Daliang area, Menyuan County, Qinghai Province except the holotype of Shengia intermedia Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979 (=Shengia shergoldi Peng, Babcock, and Lin, Reference Peng, Babcock and Lin2004c) (9) from Chuancigou, Qilian County, Qinghai Province. (1–13) Shengia shergoldi Peng, Babcock, and Lin, Reference Peng, Babcock and Lin2004c: (1) cranidium, scale bar = 1 mm, NIGPAS174390; (2) cranidium, scale bar = 1 mm, NIGPAS174391; (3, 4) dorsal and left lateral view of cranidium, scale bar = 2 mm, NIGPAS174392; (5) cranidium, scale bar = 2 mm, NIGPAS174393; (6) cranidium, scale bar = 1 mm, NIGPAS174394; (7) cranidium, scale bar = 1 mm, NIGPAS174395; (8) cranidium, scale bar = 2 mm, NIGPAS174396; (9) cranidium, scale bar = 2 mm, NIGPAS44701 (the holotype of Shengia intermedia Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979, transferred to S. shergoldi in this paper); (10) pygidium, scale bar = 1 mm, NIGPAS174397; (11) pygidium, scale bar = 1 mm, NIGPAS174398; (12) pygidium, scale bar = 2 mm, NIGPAS174399; (13) pygidium, scale bar = 2 mm, NIGPAS174400. (14–25) Aphelaspis granulata Kuo in Egorova et al., Reference Egorova, Xiang, Li, Nan and Kuo1963: (14) pygidium, scale bar = 2 mm, NIGPAS174401; (15) pygidium, scale bar = 2 mm, NIGPAS174402; (16) pygidium, scale bar = 2 mm, NIGPAS174403; (17) pygidium, scale bar = 2 mm, NIGPAS174404; (18) cranidium, scale bar = 2 mm, NIGPAS174405; (19) cranidium, scale bar = 2 mm, NIGPAS174406; (20) cranidium, scale bar = 2 mm, NIGPAS174407; (21, 22) dorsal and left lateral views of cranidium, scale bar = 2 mm, NIGPAS174408; (23) cranidium, scale bar = 2 mm, NIGPAS174409; (24) cranidium, scale bar = 2 mm, NIGPAS174410; (25) cranidium, scale bar = 2 mm, NIGPAS174411. (26) Eugonocare (Olenaspella) transversa Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979, cranidium, scale bar = 2 mm, NIGPAS174412.

Holotype

Cranidium (Egorova et al., Reference Egorova, Xiang, Li, Nan and Kuo1963, pl. 14, fig. 11, GMC (Geological Museum of China) F281, Chuandong Town, Tongren County, Guizhou Province, southwest China, Furongian.

Description

Cranidium subquadrate with high convexity. Glabellar tapering forward, obtusely round or truncate anteriorly. Four pairs of lateral glabellar furrows shallow. Eye ridges prominent, extending backward slightly; palpebral lobe moderately large, located at the mid-length of glabella. Anterior branch of facial sutures divergent, and posterior branch of facial sutures diagonally extending outward and backward. Preglabellar field long (sag.), anterior border furrow shallower medially, and anterior border narrower abaxially. Occipital furrow arching backward, shallower medially; occipital ring wider proximally, occipital tubercle small. Posterior border furrow deep and wide. Exoskeleton covered with small granules.

Pygidia inverted trapezoid in outline with small granules. Axis as wide as half of pleural region, tapering backward gently, composed of three axial rings and terminal axial piece; terminal axial piece divided by a shallow transverse furrow. Postaxial ridge narrow. Four pairs of pleural furrows deep and wide, interpleural furrow undeveloped. Border furrow shallow. Border narrow, wider posteriorly, and gently arching forward medially.

North Qilian material

Abundant cranidia and pygidia.

Remarks

This is the first time that a pygidium associated with this species has been found. The species is easily differentiated from Aphelaspis qilianensis Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979 by its granulose cranidia and relatively narrow pygidial axis.

Genus Eugonocare (Olenaspella) Wilson, Reference Wilson1956

Type species

Parabolinella? evansi Kobayashi, Reference Kobayashi1938, from McKay Group, British Columbia, Canada, by original designation.

Eugonocare (Olenaspella) transversa Lin and Zhang in Zhu, Lin, and Zhang, Reference Zhu, Lin and Zhang1979
Figure 4.26

Reference Zhu, Lin and Zhang1979

Olenaspella transversa Lin and Zhang in Zhu, Lin, and Zhang, p. 93, pl. 38, figs. 9, 10.

Holotype

Cranidium (Zhu et al., Reference Zhu, Lin and Zhang1979, pl. 38, fig. 9, NIGPAS44672), eastern branch of Chuancigou, Qilian County, Qinghai Province, northwest China, Furongian.

North Qilian material

One cranidium.

Remarks

Although our specimen is broken, its wide (tr.) cranidium, short (sag.) and wide (tr.) glabella, long (exs.) eye ridge, and wide (tr.) fixigena warrant its assignment to this species. The diagnosis of Eugonocare has been revised by Peng (Reference Peng1992, p. 59) and included three subgenera, Eugonocare, Olenaspella, and Pseudeugonocare, distinguished by their pygidial marginal spines, which are not represented in our collection. The latter two genera have been found in China. Eugonocare (Olenaspella) usually occurs in the Jiangshanian Stage, and Eugonocare (Pseudeugonocare) occurs earlier in the Paibian Stage in China. Given this, our specimens are more likely Eugonocare (Pseudeugonocare). As the pygidium of this species has not been found at this locality, and Zhu in Zhou and Zhen (Reference Zhou and Zhen2008) has already ascribed this species to Eugonocare (Olenaspella), at present we follow Zhu in Zhou and Zhen's (Reference Zhou and Zhen2008) assignment and tentatively assign it to Eugonocare (Olenaspella).

Family Eoacidaspidae Poletaeva, Reference Poletaeva1957
Genus Paraacidaspis Poletaeva, Reference Poletaeva1960

Type species

Paraacidaspis hunanica Egorova in Poletaeva, Reference Poletaeva1960 from the Chuangia–Prochuangia Zone, Huaqiao Formation, Tingziguan, Chatian, Fenghuang, northwestern Hunan, China, by original designation.

Paraacidaspis hunanica Egorova in Poletaeva, Reference Poletaeva1960
Figure 3.7–3.11

Reference Peng, Babcock and Lin2004c

Paraacidaspis hunanica; Peng, Babcock, and Lin, p. 147, pl. 46, figs. 1–16, text-fig. 24 (see for synonymy).

Holotype

Cranidium (Poletaeva, Reference Poletaeva1960, pl. 3, fig. 1; GMC [Geological Museum of China] 2604), Huaqiao Formation, Tingziguan, Chatian, northwestern Hunan, China, Furongian.

North Qilian material

Three cranidia and two pygidia.

Remarks

Peng et al. (Reference Peng, Babcock and Lin2004c) have discussed the morphological variation of this species, and our material falls within the range of it.

Family Lisaniidae Zhang, Reference Zhang1963
Genus Shengia Xiang in Egorova et al., Reference Egorova, Xiang, Li, Nan and Kuo1963

Type species

Shengia quadrata Xiang in Egorova et al., Reference Egorova, Xiang, Li, Nan and Kuo1963, from the Glyptagnostus reticulatus Zone, Huaqiao Formation, northwestern Hunan, by original designation.

Shengia shergoldi Peng, Babcock, and Lin, Reference Peng, Babcock and Lin2004c
Figures 3.24, 4.1–4.13

Reference Zhu, Lin and Zhang1979

Shengia intermedia Lin and Zhang in Zhu, Lin, and Zhang, p. 102, pl. 40, fig. 13.

Holotype

Cranidium (Zhu et al., Reference Zhu, Lin and Zhang1979, pl. 40, fig. 13, NIGPAS44701), eastern branch of Chuancigou, Qilian County, Qinghai Province, China; Furongian.

Description

Cranidium subquadrate in outline with high convex. Glabella long (sag.), almost parallel-sided to slightly tapering forward, obtusely rounded to truncated anteriorly, with four pairs of weakly incised lateral furrows. S1 bifurcated; S2 extending inward and backward; S3 transversely or slightly backward extending; S4 short and narrow, extending inward and upward. Occipital furrow wide medially, narrowing abaxially, and almost indiscernible laterally. Occipital ring broad (sag.) and narrowing distally; occipital tubercle small. Fixigena narrow (tr.), evenly convex. Eye ridge narrow and short (tr.); palpebral lobe long, arcuate, opposite to cranidial midpoint. Anterior border narrow and longer adaxially, gently arching forward, covered with terrace ridges. Posterior border furrow deep and wide; posterolateral projection long and wide. Librigena broad (tr.); lateral border generally tapering posteriorly and extending into a strong genal spine.

Pygidium semicircular; length (sag.) half of width (tr.). Axis strongly convex, with six rings and a terminal piece. Postaxial ridge weak. Pleural region evenly divided by five pairs of wide pleural furrows. Interpleural furrows indiscernible. Border wide and slightly arching forward medially, covered with weak terrace ridges.

North Qilian material

Abundant cranidia and pygidia and one librigena.

Remarks

This species is originally named Shengia intermedia Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979. It is homonymous with S. intermedia (Resser and Endo, Reference Resser and Endo1937), and Peng et al. (Reference Peng, Babcock and Lin2004c) renamed it S. shergoldi. The holotype of this species is refigured (Fig. 4.9), and larger Changgou materials (Fig. 4.3, 4.8) are closely similar to it. The meraspid is differentiated by its relatively narrower fixigena and more curved anterior border. These differences are regarded as ontogenetic variations.

Family Corynexochidae Angelin, Reference Angelin1854
Genus Corynexochus Angelin, Reference Angelin1854

Type species

Corynexochus spinulosus Angelin, Reference Angelin1854 from the middle Cambrian of Sweden, by original designation.

Corynexochus plumula Whitehouse, Reference Whitehouse1939
Figure 3.12–3.19

Reference Zhu, Lin and Zhang1979

Corynexochus chinensis Lin and Zhang in Zhu, Lin, and Zhang, p. 88, pl. 37, fig. 5.

Reference Peng1992

Corynexochus chinensis; Peng, p. 34, fig. 16J, non-fig. 16K.

Reference Peng1992

Corynexochus plumula; Peng, p. 34, figs. 16B–I, P (see for synonymy).

Reference Pratt1992

Corynexochus plumula; Pratt, p. 45, pl. 9, figs. 17–21.

Reference Zhou, Cao, Hu and Zhao1996

Corynexochus plumula; Zhou et al., pl. 7, figs. 13, 14.

Reference Duan, Yang and Shi1999

Corynexochus plumula; Duan, Yang, and Shi, p. 164, figs. 12A, 13F.

Reference Paterson and Laurie2004

Corynexochus plumula; Paterson and Laurie, p. 96, fig. 7A–C.

Holotype

Cranidium (Whitehouse, Reference Whitehouse1939, pl. 24, fig. 8), Georgina Limestone, Queensland, Australia, Miaolingian.

North Qilian material

Four cephala and two pygidia.

Remarks

This widespread and well-known species has been fully discussed by Whitehouse (Reference Whitehouse1939) and Öpik (Reference Öpik1967). The posterior branch of the facial suture extends backward and straightly outward in small cranidia (pl. 3, fig. 15) but is gently curved in larger cranidia (pl. 3, fig. 16) and curved in the largest cranidium (pl. 3, figs. 12, 14). This ontogenetically related variation can also be observed in northwestern Queensland material (Öpik, Reference Öpik1967, pl. 3, figs. 1, 2, 4).

Corynexochus chinensis Lin and Zhang in Zhu et al., Reference Zhu, Lin and Zhang1979 and C. pulcher Zhou in Zhou et al., Reference Zhou, Li and Qu1982, the other two late Cambrian species, are reminiscent of this species. Lin and Zhang in Zhu et al. (Reference Zhu, Lin and Zhang1979) separated C. chinensis from C. plumula by the former's nearly straight cranidial axial furrow, relatively less expanding glabella, longer palpebral lobe, and narrower fixigena. The holotype of C. chinensis is a cranidium and refigured herein (Zhu et al., Reference Zhu, Lin and Zhang1979, pl. 3, fig. 12). As seen herein, all cranidial features of these two species are similar, and it is hard to differentiate them. Therefore, C. chinensis is regarded as a junior synonym of C. plumula. The pygidium of C. chinensis, ascribed to this species by Peng (Reference Peng1992), is easily differentiated from that of C. plumula by its relatively larger width/length ratio. It may belong to another species of this genus. As mentioned by Peng (Reference Peng1992), because C. pulcher is based on meraspid materials, it may also be a junior synonym of C. plumula.

Acknowledgments

This work was supported by grants from the National Natural Science Foundation of China (41672002, 41672028, 41521061, 41330101, 41672142, and 41290260), the Chinese Academy of Sciences (XDB26000000) and State Key Laboratory of Palaeobiology and Stratigraphy, and the U.S. National Science Foundation EAR-1849963. This is a contribution to IGCP 668 project “The stratigraphic and magmatic history of Early Paleozoic equatorial Gondwana and its associated Evolutionary Dynamics.” We are grateful for the comments of two reviewers and editors that significantly improved the paper.

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Figure 0

Figure 1. (1) Schematic map showing major tectonic units of China (modified from Song et al., 2013). (2) Geological sketch of Qilian Mountain area, northwest China (modified from Lin et al., 2013). (3) Geological map of Changgou section, Daliang area (modified from unpublished data, Qinghai Geological Bureau, 1969). C3 - Miaolingian, C4 - Furongian, O2 - Middle Ordovician, O3 - Late Ordovician, S1 - Llandovery, P - Permian, T - Triassic, Q - Quaternary.

Figure 1

Figure 2. Stratigraphic column of the unnamed formation at Changgou section, Daliang area, Menyuan County, Qinghai Province, showing fossiliferous limestone layer occurring within a thick sequence of spilitic basalts and other volcanogenic rocks.

Figure 2

Figure 3. Trilobites from Changgou section, Daliang area, Menyuan County, Qinghai Province, except the holotype of Pterocephalops granulus Lin and Zhang in Zhu et al., 1979 (=Baikadamaspis sinensis [Yang in Zhou et al., 1977]) (20) and the holotype of Corynexochus chinensis Lin and Zhang in Zhu et al., 1979 (12) from Chuancigou, Qilian County, Qinghai Province. (1) Glyptagnostus reticulatus (Angelin, 1851), cephalon, scale bar = 1 mm, NIGPAS174370. (2–4) Pseudagnostus idalis Öpik, 1967: (2) cephalon, scale bar = 0.5 mm, NIGPAS174371; (3) pygidium, scale bar = 1 mm, NIGPAS174372; (4) pygidium, scale bar = 0.5 mm; NIGPAS174373. (5, 6) Innitagnostus inexpectans (Kobayashi, 1938): (5) cephalon, scale bar = 1 mm, NIGPAS174374; (6) pygidia, scale bar = 1 mm, NIGPAS174375. (7–11) Paraacidaspis hunanica Egorova in Poletaeva, 1960: (7) cranidium, scale bar = 5 mm, NIGPAS174376; (8) cranidium, scale bar = 5 mm, NIGPAS174377; (9) cranidium, scale bar = 5 mm, NIGPAS174378; (10) pygidium, scale bar = 2 mm, NIGPAS174379; (11) pygidium, scale bar = 2 mm, NIGPAS174380. (12–19) Corynexochus plumula Whitehouse, 1939: (12) cranidium, scale bar = 1 mm, NIGPAS44654 (the holotype of Corynexochus chinensis Lin and Zhang in Zhu et al., 1979, transferred to C. plumula in this paper); (13) cranidium, scale bar = 1 mm, NIGPAS174381; (14) cranidium, scale bar = 1 mm, NIGPAS174382; (15) cranidium, scale bar = 1 mm, NIGPAS174383; (16) cranidium, scale bar = 1 mm, NIGPAS174384; (17) pygidium, scale bar = 1 mm, NIGPAS174385; (18, 19) dorsal and left lateral view of pygidium, scale bar = 1 mm, NIGPAS174386. (20–23) Baikadamaspis sinensis (Yang in Zhou et al., 1977): (20) cranidium, scale bar = 1 mm, NIGPAS44665 (the holotype of Pterocephalops granulus Lin and Zhang in Zhu et al., 1979, transferred to Baikadamaspis sinensis in this paper); (21) cranidium, scale bar = 1 mm, NIGPAS174387; (22, 23) dorsal and right lateral view of cranidium, scale bar = 2 mm, NIGPAS174388. (24) Librigena of Shengia shergoldi Peng, Babcock, and Lin, 2004c, scale bar = 2 mm, NIGPAS174389.

Figure 3

Figure 4. Trilobites from Changgou section, Daliang area, Menyuan County, Qinghai Province except the holotype of Shengia intermedia Lin and Zhang in Zhu et al., 1979 (=Shengia shergoldi Peng, Babcock, and Lin, 2004c) (9) from Chuancigou, Qilian County, Qinghai Province. (1–13) Shengia shergoldi Peng, Babcock, and Lin, 2004c: (1) cranidium, scale bar = 1 mm, NIGPAS174390; (2) cranidium, scale bar = 1 mm, NIGPAS174391; (3, 4) dorsal and left lateral view of cranidium, scale bar = 2 mm, NIGPAS174392; (5) cranidium, scale bar = 2 mm, NIGPAS174393; (6) cranidium, scale bar = 1 mm, NIGPAS174394; (7) cranidium, scale bar = 1 mm, NIGPAS174395; (8) cranidium, scale bar = 2 mm, NIGPAS174396; (9) cranidium, scale bar = 2 mm, NIGPAS44701 (the holotype of Shengia intermedia Lin and Zhang in Zhu et al., 1979, transferred to S. shergoldi in this paper); (10) pygidium, scale bar = 1 mm, NIGPAS174397; (11) pygidium, scale bar = 1 mm, NIGPAS174398; (12) pygidium, scale bar = 2 mm, NIGPAS174399; (13) pygidium, scale bar = 2 mm, NIGPAS174400. (14–25) Aphelaspis granulata Kuo in Egorova et al., 1963: (14) pygidium, scale bar = 2 mm, NIGPAS174401; (15) pygidium, scale bar = 2 mm, NIGPAS174402; (16) pygidium, scale bar = 2 mm, NIGPAS174403; (17) pygidium, scale bar = 2 mm, NIGPAS174404; (18) cranidium, scale bar = 2 mm, NIGPAS174405; (19) cranidium, scale bar = 2 mm, NIGPAS174406; (20) cranidium, scale bar = 2 mm, NIGPAS174407; (21, 22) dorsal and left lateral views of cranidium, scale bar = 2 mm, NIGPAS174408; (23) cranidium, scale bar = 2 mm, NIGPAS174409; (24) cranidium, scale bar = 2 mm, NIGPAS174410; (25) cranidium, scale bar = 2 mm, NIGPAS174411. (26) Eugonocare (Olenaspella) transversa Lin and Zhang in Zhu et al., 1979, cranidium, scale bar = 2 mm, NIGPAS174412.