Cambrian Trilobite Ovatoryctocara Granulata Tchernysheva, 1962 and Its Biostratigraphic Significance

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Progress in Natural Science 19 (2009) 213–221 www.elsevier.com/locate/pnsc

Cambrian trilobite Ovatoryctocara granulata Tchernysheva, 1962 and its biostratigraphic signiﬁcance

Jinliang Yuan a,*, Yuanlong Zhao b, Jin Peng b, Xuejian Zhu a, Jih-pai Lin c

a Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, East Beijing Road 39, Nanjing 210008, China b College of Resource and Environment Science, Guizhou University, Guiyang 550003, China c School of Earth Sciences, Ohio State University, Columbus, OH 43210, USA

Received 28 March 2008; received in revised form 27 May 2008; accepted 14 August 2008

Abstract

The genus Ovatoryctocara Tchernysheva, 1962, and its key species Ovatoryctocara granulata Tchernysheva, 1962, are revised. Ovatoryctocara granulata occurs near the base of the Ovatoryctocara Zone and ranges up into the lower portion of the Kounamkites Zone in the Siberian Platform. O. granulata also appears in southeastern Guizhou, South China, but O. granulata in northern Greenland may represent an indefinite species. Specimens of Ovatoryctocara from Newfoundland cannot be identified to species level. Specimens including two cranidia and three pygidia from the lower part of the Aoxi Formation at Yaxi Village, Shizhu Town, eastern Tongren, northeastern Guizhou, were previously assigned to O. granulata, which is now reassigned as a new species O. yaxiensis sp. nov. It bears the following main features: glabella club-shaped, slightly expanded medially, with four pairs of lateral furrows, of which S1–S3 are triangular pits, S4 is shallow, connecting with axial furrow; shorter palpebral lobe situated a little anterior to the midway of facial suture across the fixigenae, longer posterolateral area (exsag.); semielliptical pygidium consisting of seven axial rings with a terminal piece and with eight pairs of marginal tips giving a sawtooth-like shape of the lateral margins in dorsal view. Although O. granulata is a widely distributed species, the FAD of O. granulata, for a global stage boundary, still has some disadvantages. First, its distribution is not as wide as that of Oryctocephalus indicus (Reed, 1910). Second, specimens of O. granulata are common only in Siberia. Third, the stratigraphic range of the species has not been studied in detail in all continents. Fourth, O. granulata is relatively small and easily affected by post-burial distortion. Last but not least, there exists obviously a facies change between the Ovatoryctocara Zone (lower Amgan Stage; deeper water facies) and the underlying Anabaraspis splendens Zone (Toyonian Stage; shallow water facies) in Siberian Platform. Nev- ertheless, the stratigraphic correlation utility of O. granulata in South China and Siberia is discussed. Ó 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.

Keywords: Trilobites; Ovatoryctocara granulata Tchernysheva, 1962; Cambrian; Biostratigraphy

1. Introduction Siberia. It is a fairly common trilobite in the lower Amgan strata (Ovatoryctocara Zone) of the Yudoma-Olenek Ovatoryctocara Tchernysheva, 1962, was first described region, where Oryctocara (= Ovatoryctocara) was used to as a subgenus Oryctocara (Ovatoryctocara), with the type define the base of Amgan Stage, namely the base of tradi- species Oryctocara ovata Tchernysheva by Kryskov et al. tional Middle Cambrian in Siberia. Oryctocara Zone is here [1] and Tchernysheva [2] from the Amgan strata of eastern replaced by Ovatoryctocara Zone because of lack of any species of Oryctocara in this Zone. Ovatoryctocara granulata Tchernysheva, 1962, was proposed as a key species to * Corresponding author. Tel.: +86 25 86082532; fax: +86 25 83357026. E-mail addresses: [email protected], [email protected] (J. define a global Cambrian stage boundary [3,4], and the Yuan). FAD of O. granulata defining the base of Ovatoryctocara

1002-0071/$ - see front matter Ó 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved. doi:10.1016/j.pnsc.2008.08.002 214 J. Yuan et al. / Progress in Natural Science 19 (2009) 213–221

Zone coincides with the base of the Amgan Stage in the with deep pleural furrows and distinct interpleural furrows; Kuonamka Formation along the Molodo River in the north border furrow and border not defined; surface covered with of the Siberian Platform, Russia. Since 1977, extensive or without granules. Known species: O. ovata Tchernysh- discussions and reinvestigations on Oryctocara granulata eva, 1960, O. granulata Tchernysheva, 1962, O. angusta Tchernysheva, 1962, or on O. granulata Tchernysheva, Tchernysheva, 1962, O. yaxiensis sp. nov. The Ovatorycto- 1962, and its stratigraphic significance have been carried cara sp. in the upper portion of the Amecephalus arrojosen- out [5–13]. However, the definitions of both Ovatoryctocara sis Zone of western North America [14] may be a juvenile Tchernysheva, 1962, and the species O. granulata specimen of Euarthricocephalus sp. or Arthricocephalus Tchernysheva, 1962, are still problematic; therefore, the sp. because of the absence of developed interpleural main aim of this study is to revise the genus Ovatoryctocara grooves on pleural regions of pygidium as in Ovatorycto- Tchernysheva, 1962, and its species. cara Tchernysheva, 1962. Based on the characteristics of the type species Orycto- 2. Revised diagnosis of Ovatoryctocara Tchernysheva, 1962 cara ovata Tchernysheva [1], Tchernysheva [2] (Fig. 1a and aa0) and Sovorova [15] elevated the subgenus Orycto- The revised diagnosis of Ovatoryctocara Tchernysheva, cara (Ovatoryctocara) Tchernysheva, 1962. Later, Whit- 1962: small oryctocarid trilobite with subcylindrical gla- tington [16] diagnosed the genus Ovatoryctocara as bella, slightly expanded forward, widest anteriorly; lateral characterized by ‘‘the proparian facial suture, the genal glabellar furrows with S1–S3 developed as deeper circular angle rounded and lacking a spine, four thoracic segments, pits near but isolated from the axial furrows, and S4 merely the relatively long pygidium with 10 – 12 axial rings and 10 as very shallow pits; preglabellar field absent; palpebral – 1; pleural ribs. The cheeks and pleurae are not granu- lobe short situated about at the midlength of fixigenae; lated, but bear a network of fine ridges” (Fig. 1aand eye ridge narrow and distinct, inclined backward; facial aa0). However, these features with the exception of the rel- suture proparian; librigenae small, without genal spine; atively shorter and less segmented pygidium and different posterior lateral limb very wide (tr.) and moderately long patterns of lateral glabellar furrows are also shared by (exsag.); thorax of four segments, with pleural tips subtrun- the Arthricocephalus Bergeron with A. chauveaui Bergeron, cate; semielliptical to semicircular pygidium with axis of 1899, as the type species [17] (see also Lane et al. [18] seven to eleven rings and a terminal piece; pleural regions (Fig. 1candcc0).

Fig. 1. Ovatoryctocara Tchernysheva, 1962, and its related genera based on their type species. a and aa0: Ovatoryctocara ovata (Tchernysheva in Kryskov et al., 1960) from Tchernysheva, 1962; b and bb0: Oryctocara geikiei Walcott, 1908, from Yuan et al., 2002; c and cc0: Arthricocephalus chauveaui Bergeron, 1899, from Yuan, Zhao et Yang, 2006, assigned to Arthricocephalites xinzhaiheensis Chien et Lin in Lu et al., 1974; d and dd0: Shergoldiella vincenti Geyer, 2006, from Geyer, 2006, Scale bars are 1 mm. J. Yuan et al. / Progress in Natural Science 19 (2009) 213–221 215

Arthricocephalus chauveaui Bergeron, 1899, is character- are most similar to Shergoldiella sequei (Linãń et Gozalo, ized by slightly expanded forwardly subrectangular gla- 1999), which was previously described either as Tonkinella bella, with four pairs of lateral pits, of which S1–S3 are sequei or as a specimen of ‘‘Hamatolenus (Myopsolenus)? transglabellar furrows, palpebral lobes situated anteriorly, jilocanus” in Linãń et Gozalo [24] from Lower Cambrian eight thoracic segments, semicircular pygidium with nar- of Spain. row border and distinct narrow border furrow. It differs Oryctocara Walcott [25] and its type species O. geikiei from Ovatoryctocara ovata (Tchernysheva, 1960) in the Walcott, 1908 (Fig. 1b and bb0), from the Spence Shale presence of three transglabellar furrows, much wider fixige- (lower portion of Cambrian Series 3 or traditional early nae between palpebral lobes, eight thoracic segments Middle Cambrian) in Idaho, USA, can be easily distin- (instead of four thoracic segments in the latter), shorter guished from Ovatoryctocara by its rather broader cylindri- semicircular pygidium with narrow pygidial border, dis- cal glabella consisting of four pairs of glabellar furrows as tinct border furrow, and with five axial rings and five pleu- rounded pits, far from the axial furrows and two pairs of ral ribs (instead of 10–12 axial rings and 10 pleural ribs in transglabellar furrows (S1–S2), gonatoparian facial suture, the latter). Therefore, a few figured specimens that were 12 thoracic segments and a shorter pygidium with seven previously assigned to Arthricocephalus granulus Chien et segments. In addition, Oryctocara lata Tchernysheva, Lin in Zhou et al. [19] from the early Cambrian Dachenling 1952 [26], from Amgan strata of Siberia (Tchernysheva Formation of Hetang, Jiangshan, western Zhejiang [20,21] [2]) should belong to Euarthricocephalus Ju, 1983 [20],as should belong to Ovatoryctocara. On the other hand, a few having rod-shaped glabella consisting of four pairs of lat- illustrated specimens that were previously assigned to Arth- eral glabellar furrows as rounded pits, of which S1 is bifur- ricocephalus chauveaui Bergeron, 1899, from the Dachen- cated axially and connected laterally to axial furrows to ling Formation of Dongzi, southern Anhui [22] should be form a pair of small lateral basal glabellar lobes, wider fix- reinterpreted as Shergoldiella cf. S. sequei (LinãńetGoz- igenae between palpebral lobes, and 8–9 thoracic segments alo, 1999) [23], because it has the slightly expanded for- with much wider pleural lobes. wardly glabella with four pairs of lateral glabellar Shergoldiella Geyer, 2006, and its type species Shergoldi- furrows, of which S1–S3 developed as circular pits near ella vincenti Geyer [27] (Figs. 1d and 2d) from the base of the axial furrows, shorter palpebral lobes situated anteri- Cephalopyge notabilis Zone of Jbel Wawrmast Formation orly, very long and moderately wide (exsag.) posterior lat- in the eastern Anti-Atlas of Morocco is mostly similar to eral limb (tr.); eight thoracic segments, with subtruncate Ovatoryctocara, because both genera have subcylindrical pleural tips; semielliptical to semicircular pygidium with glabella, with four pairs of lateral glabellar furrows as cir- axis of 5–6 rings and a terminal piece; pleural regions with cular pits, short palpebral lobe, proparian facial suture, but deep pleural furrows and distinct interpleural furrows; it differs from the latter in having slightly expanded glabella pygidial border furrow and border not defined. In compar- medially, widest across S2 or S3, four pairs of lateral circu- ison with other species of Shergoldiella, the specimens of lar furrows, of which S1 is transglabellar furrow, shorter Arthricocephalus chauveaui mentioned in Zhu et al. [23] palpebral lobe situated slightly anterior to the midway of

Fig. 2. Ovatoryctocara granulata Tchernysheva, 1962, and its related form from South China. (a and b) Ovatoryctocara granulata Tchernysheva, 1962, from the Bathynotus holopygus–Ovatoryctocara granulata Zone of the Kaili Formation, southeastern Guizhou; of which (a) (GK6003, Yuan et al., 2002) from Wuliu-Zengjiayan section and (b) from (CD 1000-89; GK6801) Jianshan section, Chuandong Village, Jianhe County. (c) Arthricocephalus sp. from the Bathynotus holopygus–Ovatoryctocara granulata Zone of the Kaili Formation, (GK6803) from Jianshan section, Chuandong Village, Jianhe County, southeastern Guizhou. Scale bars are 1 mm. 216 J. Yuan et al. / Progress in Natural Science 19 (2009) 213–221 facial suture across the fixigenae, wider (exsag.) posterior [28] were considered as O. granulata Tchernysheva, 1962, lateral area of fixigenae, thorax of 6–8 segments (instead by Geyer [8] (Fig. 3f and g). However, these Greenland of four segments in Ovatoryctocara); pygidium with axis specimens are rather small (about less than 1.35 mm in of six rings and a terminal piece (instead of 7–11 rings plus length) and apparently represent meraspid specimens. a terminal piece in Ovatoryctocara). The differences The cranidium of Greenland specimens has four pairs of between Ovatoryctocara and other genera mentioned above lateral furrows connecting with axial furrow and without are illustrated in Fig. 1. longitudinal furrows, shorter palpebral lobe situated a little anterior to the midway of facial suture across the fixigenae, wider posterolateral area (exsag.), and semielliptical pygid- 3. Ovatoryctocara granulata (Tchernysheva, 1962) ium (Fig. 3g) consists of eight narrow axial rings and a terminal piece. The differences between O. granulata and Tchernysheva (1962) selected one cranidium as the holo- other related forms mentioned above are shown in Fig. 3. type of O. granulata [2]. This species is distinct from the type species Ovatoryctocara ovata (Tchernysheva, 1960) in having an expanded glabella medially, S1–S3 connected 4. Ovatoryctocara yaxiensis sp. nov. and associated species with shallow longitudinal furrows, a relatively longer palpebral lobe, a semicircular pygidium with only 6–7 axial Ovatoryctocara yaxiensis sp. nov. (Fig. 4a–e; aa´ and bb´) rings and the surface with granules. O. granulata is not a is described here based on cranidium (a and aa´) as the junior synonym of Arthricocephalus chauveaui Bergeron, holotype from the Aoxi Formation at Yaxi, Shizhu Town, 1899 [28], because it has distinctly different patterns of gla- Tongren County, eastern Guizhou. The new species is bellar furrows. In addition, specimens (Fig. 2a and b) from characterized by the following features: cranidium trape- the Bathynotus holopygus–O. granulata Zone of the Kaili zoidal; glabella club-shaped, slightly expanded medially, Formation, southeastern Guizhou are nearly identical to with four pairs of lateral furrows, of which S1–S3 are trian- the type material from Siberia with the exception of slightly gular pits, S4 is shallow, connecting with axial furrow; nar- shorter palpebral lobes situated more anteriorly and wider rower fixigenae (tr.), shorter palpebral lobe situated a little posterolateral area (exsag.). anterior to the midway of facial suture across the fixigenae, Other specimens of O. granulata have been reported wider posterolateral area (exsag.); semielliptical pygidium from Avalon Peninsula, southeastern Newfoundland [3]. with seven axial rings and a terminal piece and with seven The cranidium of O. granulata from Newfoundland pairs of marginal tips giving a sawtooth-like shape of the (Fletcher, 2003 [3]), shown in Fig. 3d, shows (1) rather short lateral margins in dorsal view; pleural region with seven palpebral lobes situated a little anterior to the midway of pairs of deep pleural furrows and distinct narrow interple- facial suture across the fixigenae, (2) S1–S3 connected with- ural furrows; exoskeleton with a few coarser and fine gran- out shallow longitudinal furrows, wider (exsag.) posterior ules. It differs from O. granulata mainly in having club- lateral area of fixigenae, (3) the pygidium (Fletcher, 2003 shaped glabella with triangular glabellar furrows (S1–S3), [3]) shown in Fig. 3e, with eight axial rings and a terminal shorter palpebral lobe situated a little anterior to the mid- piece and (4) sculpture on the surface of cranidium and way of facial suture across the fixigenae, longer posterolat- pygidium being not as strong as Siberian type material. eral area (exsag.), and semielliptical pygidium with eight Therefore, the assignment of these Newfoundland speci- pairs of marginal tips giving a sawtooth-like shape of the mens to O. granulata is questionable, and these specimens lateral margins in dorsal view. The new species occurs may represent an indefinable species of Ovatoryctocara. together with Barklyella sp. (Fig. 4f), Deiradonyx sp. In addition, two cranidia and seven pygidia formerly (Fig. 4g) and Xiaofangshangia sp. (Fig. 4h–m). Barklyella assigned to Ovatoryctocara sp. A. from North Greenland Shergold, 1969 [29], with its type species B. expansa Sher-

Fig. 3. Reconstruction of Ovatoryctocara granulata Tchernysheva, 1962, and its related forms from Siberia, South China, SE Newfoundland and North Greenland. (a and b) Ovatoryctocara granulata Tchernysheva, 1962, from Siberian Platform; (c) Ovatoryctocara granulata Tchernysheva, 1962, from South China; (d and e) O. sp. from southeastern Newfoundland; (f and g) O. sp. A from North Greenland. Scale bars are 1 mm. J. Yuan et al. / Progress in Natural Science 19 (2009) 213–221 217

Fig. 4. Ovatoryctocara yaxiensis sp. nov. and associated species from the Aoxi Formation,Yaxi, Shizhu Town, Tongren County, eastern Guizhou. (a–e), aa0 and bb0: Ovatoryctocara yaxiensis sp. nov. from Yuan et al., 2002 as O. granulata (pl. 31, Figs. 10–13, NIGP 133180–133180, cranidium (a and aa’), holotype) and as Barklyella sp. (pl. 28, Fig. 5, NIGP133178); (f) Barklyella sp. from Yuan et al., 2002 (pl. 28, Fig. 4, NIGP133177); (g) Deiradonyx sp. (NIGP 133184); (h–m) Xiaofangshangia? sp. (NIGP 133185–133190). Scale bars are 1 mm. gold, 1969 [28], was originally described from the Dinesus- a narrower anterior border. Furthermore, the illustrated Xystridura fauna of the Beetle Creek Formation, Dingo Xiaofangshangia sp. (Fig. 4h–m) is quite similar to Xiaof- Creek, Northwest Queensland, which is considered as early angshangia divergens Qiu [34], which comes from the upper Middle Cambrian in age. However, Laurie [30] assigned part of the Mantou Formation (the upper part of Redlichia the Xystridura negrina assemblage and Redlichia forresti chinensis Zone) in Dananzhuang, Tongshan County, assemblage to the Early Cambrian Ordian Stage. Recently, northern Jiangsu. Xiaofangshangia sp. differs from Xiaof- Laurie [31] reported the occurrences of Pagetia aff. edura angshangia divergens in having a less tapering glabella for- Jell, Xystridura altera O¨ pik, ptychoparioid sp.1, Arthrico- wardly with four pairs of deeper lateral glabellar furrows. cephalus sp. nov. and Itagnostus sp. from the Jigaimara Comparing with older literatures on the related forms of Formation, Arafura Basin, Northern Territory. Among Ovatoryctocara, O. yaxiensis sp. nov. may occur elsewhere. them, Itagnostus sp. is similar to ‘‘Peronopsis” normata For example, Ovatoryctocara sp. (Fig. 3d and e) at the top from the early Templetonian Beetle Creek Formation. of the Branch Cove Marl Member of the Brigus Formation Thus, the Beetle Creek Formation may include partly tra- in the Easter Cove of Branch, St. Mary’s Bay, southeastern ditional, latest Early Cambrian and earliest Middle Cam- Newfoundland (upper Cephalopyge Zone) is more similar brian based on trilobite correlations. In South China, the to O. yaxiensis sp. nov. (Fig. 3a–e;aa´ and bb´) than O. gran- LAD of Arthricocephalus Bergeron, 1899, is below the Ory- ulata Tchernysheva, 1962, because of lack of longitudinal ctocephalus indicus, which is the key species for defining the furrows on glabella, and having shorter palpebral lobes, base of Cambrian Series 3 (Yuan et al.) [32], therefore, the much wider posterolateral area (exsag.), and rather ele- Ordian Stage and the lower portion of the Templetonian vated relief of cranidium and pygidium. Stage in Australia may be time-equivalent to the Long- wangmiaon or late Duyunnian in South China. 5. Intra- and inter-cratonic biostratigraphic correlations Deiradonyx O¨ pik, 1982 [33], is ranging from the Ordian to early Templetonian Stages in Australia. Figured Deirad- In China, the oldest representative of Shergoldiella, cf. onyx sp. (Fig. 4g) is similar to Deiradonyx toddi O¨ pik [33] S. sequei (Linãń et Gozalo, 1999) [23], is from the early from the Northern Territory, Australia, except for having Cambrian Dachenling Formation of Dongzi, southern 218 J. Yuan et al. / Progress in Natural Science 19 (2009) 213–221

Anhui [22]. The Dachenling Formation is time-equivalent by the ﬁrst occurrence of typical Middle Cambrian trilo- to the Tsinghsutung Formation in northeastern and south- bites, including Paradoxides, Schistocephalus, and Orycto- eastern Guizhou. Based on the reported ranges of associ- cephalidae (Oryctocara = Ovatoryctocara), and associated ated species mentioned above, Ovatoryctocara yaxiensis agnostoids [38]. However, Schistocephalus was considered sp. nov. occurs relatively higher than Shergoldiella cf. S. as a synonym of Palaeolenus Mansuy, 1912 [39], and Palae- sequei. Thus, the Ovatoryctocara yaxiensis assemblage olenus antiquus (Tchernysheva, 1956) [40] is interpreted as a from the Aoxi Formation may be older than the B. holopy- cospecies with Megapalaeolenus deprati (Mansuy, 1912) gus–O. granulata Zone in the lower part of the Kaili For- [39]. Therefore, the base of the Amgan Stage can roughly mation, Guizhou (Table 1). correlate with the upper part of the Megapalaeolenus Zone Based on the ranges of key traditional Early Cambrian or Arthricocephalus chauveaui Zone in South China. trilobite taxa from southwestern China and North China If this correlation is correct, the upper range of O. gran- [12,20,21,34–37], the Early Cambrian trilobite successions ulata occurs in the lower portion of both Kounamkites in the platform facies include the Chittidilla plana-Paragra- Zone in Siberia and B. holopygus–O. granulata Zone in ulos kunmingensis Zone, Redlichia guizhouensis Zone, R. South China. In other words, the lower portion of Koun- murakamii–Hoﬀetella Zone, Megapalaeolenus Zone, Palae- amkites Zone in Siberia is a time-equivalent of the upper olenus Zone, Paokannia–Ushbaspis Zone, and Drepanuro- Duyunian Stage in South China. In Newfoundland, the ides Zone in descending order. The trilobite zonations in Hupeolenus Zone consists of many key correlatable trilo- the slope facies consist of the B. holopygus–O. granulata bite taxa, including Protolenus (Hupeolenus), Orodes, Zone, Protoryctocephalus wuxunensis Zone, Arthricocepha- Chelediscus, Tannudiscus, Condylopyge, Cobboldites and lus taijiangensis Zone, A. chauveaui Zone, A. jiangkouensis Ovatoryctocara [3]. Besides Ovatoryctocara sp. that is sim- Zone, Protolenella conica Zone and Drepanuroides Zone. ilar to O. yaxiensis sp. nov. in South China, Protolenus The stratigraphic correlation of upper portion of the Cam- (Hupeolenus) mckillopi [3] is similar to Sichuanolenus nanji- brian Series 2 between platform and slope facies in China is angensis from the upper part of the Yanwangbian Forma- summarized in Table 1. tion, as mentioned in Zhang et al. [35]. Based on both In Siberia platform, the base of the Amgan Stage coin- accounts, the base of the Hupeolenus Zone (Agdzian Stage) cides with the base of the Schistocephalus Zone. In other in Newfoundland should be correlatable to the base of Pro- words, the beginning of the Amgan Stage is determined tolenella conica Zone (Nangaoan) in South China.

Table 1 Correlation chart of the upper portion of the Cambrian Series 2 between platform and slope facies in China based on key early Cambrian trilobite species (data of ranges of key genera and species from Yin et Lee, 1978; Zhang et al., 1980; Qiu, 1980; Yuan et al., 1999, 2002, 2006). J. Yuan et al. / Progress in Natural Science 19 (2009) 213–221 219

The correlation between South China and Laurentia is ary is not being supported by this study. First, the distribu- achieved based on redlichiid trilobites in South China and tion of O. granulata is not as wide as that of Oryctocephalus olenellid trilobites in Greenland and western United States. indicus, which is another candidate species for defining a The interval of Ovatoryctocara sp. A. [28] (Fig. 4fandg) global Cambrian stage boundary. Second, the specimens from the upper part of the Henson Gletscher Formation, of O. granulata are only common in Siberia, only a few North Greenland, may be correlatable to the A. taijiangen- specimens have been found in southeastern Guizhou, sis Zone in South China. The stratigraphic correlation of South China. Third, taxonomic identifications of known the upper portion of the Cambrian Series 2 between China Ovatoryctocara are sometimes questionable. The Ovator- and selected regions is summarized in Table 2. yctocara sp. in the upper portion of the Amecephalus arro- josensis Zone of western North America [14] may be a 6. Conclusions juvenile specimen of Euarthricocephalus sp. or Arthrico- cephalus sp. because of the absence of developed interpleur- Based on the review of Ovatoryctocara Tcherysheva, al grooves on pleural regions of pygidium as in 1962, a new species O. yaxiensis sp. nov. is erected in the Ovatoryctocara. Fourth, correlation utility of O. granulata present paper. The new species bears the following main has not been validated. In South China, Arthricocephalus features: glabella club-shaped, slightly expanded medially, has a long stratigraphic range from the base of the Balang with four pairs of lateral furrows, of which S1–S3 are trian- Formation (A. jiangkouensis Zone, Nangao Stage) into the gular pits, S4 is shallow, connecting with axial furrow; top of the Duyunian (O. granulata–B. holopygus Zone), shorter palpebral lobe situated a little anterior to the mid- and the LAD of the Arthricocephalus provides additional way of facial suture across the fixigenae, wider posterolat- evidence to strengthen the coeval level of the FAD of O. eral area (exsag.); semielliptical pygidium with seven axial indicus. In the same way, the LAD of O. granulata provides rings and a terminal piece, and with eight pairs of marginal evidence about the synchronicity of the FAD of O. indicus, tips giving a sawtooth-like shape of the lateral margins in an additional potential criterion for international correla- dorsal view. O. granulata was previously regarded as a tion. Last but not least, there exists obviously a facies widespread species, however, the FAD of O. granulata as change between Ovatoryctocara Zone (lower Amgan Stage; a key horizon for defining a global Cambrian stage bound- deeper water facies) and Anabaraspis splendens Zone

Table 2 Correlation chart of the upper portion of the Cambrian Series 2 between China and selected regions. 220 J. Yuan et al. / Progress in Natural Science 19 (2009) 213–221

(Toyonian Stage; shallow water facies) in Siberian Plat- [11] Korovnikov IV. Lower and Middle Cambrian boundary and form, however, where Ovatoryctocara has a relatively trilobites from northeast Siberian platform. Palaeoworld longer range (from the base of the Ovatoryctocara Zone 2001;13:270–5. [12] Yuan JL, Zhao YL, Li Y, et al. Trilobite fauna of the Kaili formation into the lower portion of the Kounamkites Zone). Based (uppermost Lower Cambrian-lower Middle Cambrian) from south- on all the factors mentioned above, the LADs of O. gran- eastern Guizhou, South China. Shanghai: Shanghai Science and ulata in both South China and Siberia can be correlated to Technology Press; 2002, p. 422. each other, but not precisely elsewhere. [13] Zhao YL, Yuan JL, Peng SC, et al. New data on the Wuliu- Zhengjiayan section (Balang, South China), GSSP candidate for the base of Cambrian Series 3. Memoir of the association of Australasian Acknowledgements palaeontologists 2007;33:57–65. 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