Organic-walled microfossils from the early Neoproterozoic Liulaobei Formation in the Huainan region...

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Precambrian Research 236 (2013) 157– 181

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Precambrian Research

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rganic-walled microfossils from the early Neoproterozoic Liulaobeiormation in the Huainan region of North China and theiriostratigraphic significance

ing Tanga,b, Ke Panga,b, Shuhai Xiaob,∗, Xunlai Yuana, Zhiji Oua, Bin Wana

State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008,hinaDepartment of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA

r t i c l e i n f o

rticle history:eceived 19 March 2013eceived in revised form 3 July 2013ccepted 18 July 2013vailable online xxx

eywords:arly Neoproterozoiccritarchiulaobei Formationorth Chinarachyhystrichosphaera

a b s t r a c t

Biostratigraphic subdivision and correlation of early Neoproterozoic strata is hampered by the limitednumber of widely distributed and age diagnostic fossils. The acanthomorphic acritarch Trachyhystrichos-phaera aimika, among a few other microfossil taxa, has emerged as a potential early Neoproterozoic indexfossil, but its temporal and spatial ranges have not been thoroughly documented. To improve our knowl-edge about early Neoproterozoic biodiversity, we carried out a micropaleontological investigation of theearly Neoproterozoic Liulaobei Formation in northern Anhui of North China. Our investigation using alow-manipulation maceration technique revealed a diverse assemblage of organic-walled microfossilsdominated by sphaeromorphs and filaments, with relatively few acanthomorph taxa. A total of 23 taxawere recovered, including three new species (Eotylotopalla? grandis n. sp., Siphonophycus gigas n. sp., andTrachyhystrichosphaera botula n. sp.). Also present in the Liulaobei Formation are Trachyhystrichosphaeraaimika (a species widely present in pre-Cryogenian Neoproterozoic and latest Mesoproterozoic rocks)and Pololeptus rugosus (a species characterized by an ellipsoidal vesicle with transverse annulations).The new data add to the growing diversity of early Neoproterozoic fossils and strengthen the basis forimproved biostratigraphic correlation of early Neoproterozoic strata. Correlation with other geochrono-
logically dated successions that contain Trachyhystrichosphaera confirms Trachyhystrichosphaera and T.aimika as promising index fossils to define and subdivide the pre-Cryogenian Neoproterozoic Era interms of Global Boundary Stratotype Section and Point (GSSP), as opposed to current system usingGlobal Standard Stratigraphic Age (GSSA). Available biostratigraphic data, including the occurrence ofTrachyhystrichosphaera, Chuaria, Tawuia, and Sinosabellidites, suggest that the Liulaobei Formation is ofpre-Cryogenian Neoproterozoic age, not Cryogenian–Ediacaran age as some have suggested in the past.
. Introduction

Proterozoic paleontological data are crucial for the study of earlyukaryote evolution, biostratigraphic correlation, and paleoenvi-onmental reconstruction (Butterfield and Chandler, 1992; Knoll,994; Knoll et al., 2006). Organic-walled microfossils preserved inne-grained siliciclastic rocks have been a major source of Protero-oic paleontological information (Jankauskas et al., 1989), and theaphonomic window of small carbonaceous compression continueso offer new insights into Proterozoic and Paleozoic paleobiology
Butterfield and Harvey, 2012). The aim of this study is to inves-igate, using low-manipulation maceration techniques (Butterfieldt al., 1994), organic-walled microfossils from marine shales of the
∗ Corresponding author. Tel.: +1 5402311366.E-mail address: [email protected] (S. Xiao).

301-9268/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.precamres.2013.07.019

© 2013 Elsevier B.V. All rights reserved.

Neoproterozoic Liulaobei Formation in the Huainan region, north-ern Anhui Province, North China (Fig. 1).

Neoproterozoic successions in the Huainan region, particularlythe Liulaobei and Jiuliqiao formations, have been a target of pale-ontological investigation since the 1980s (Dong et al., 2008; Duan,1982; Qian et al., 2009; Sun et al., 1986; Wang, 1982; Wanget al., 1984; Yin, 1985; Zheng, 1979, 1980). The Liulaobei For-mation contains macroscopic carbonaceous compression fossilssuch as Chuaria Walcott, 1899, Tawuia Hofmann in Hofmann andAitken (1979), and Sinosabellidites Zheng, 1980. In addition to thesemacrofossils, the Jiuliqiao Formation also contains macroscopicribbon-shaped fossils Pararenicola huaiyuanensis Wang, 1982 andProtoarenicola baiguashanensis Wang, 1982. The Chuaria-Tawuia
assemblage provided the first biostratigraphic support for a Neo-proterozoic age of the Liulaobei and Jiuliqiao formations, whichhave been correlated with the Chuaria- and Tawuia-bearing LittleDal Group in the Mackenzie Mountains of northwestern Canada
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158 Q. Tang et al. / Precambrian Research 236 (2013) 157– 181

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ig. 1. (A) Paleogeographic placement of the North China Block in early Neoproteuainan region, Anhui Province, China, modified from Li et al. (2013), showing sam

ocation of the Huainan region in the North China Block.

Duan, 1982; Hofmann and Aitken, 1979). Sinosabellidites, Parareni-ola, and Protoarenicola are transversely annulated ribbon-shapedacrofossils that have been variously interpreted as mobile worms

Chen, 1988; Sun, 1986; Sun et al., 1986) or epibenthic macroalgaeDong et al., 2008). The recent discovery of similar fossils from Neo-roterozoic rocks in the Timan Ridge of Russia (Gnilovskaya, 1998;nilovskaya et al., 2000) and the Bhima Basin of southern India

Sharma and Shukla, 2012) indicates that they too may have wideeographic distribution and biostratigraphic significance.

Although the macroscopic carbonaceous fossils of the Liu-aobei and Jiuliqiao formations have been studied thoroughly,rganic-walled microfossils in these units have not been sys-ematically investigated, despite the fact that both units contain
ne-grained siliciclastic rocks that have the potential to preserveicroscopic carbonaceous fossils. Indeed, previous reconnaissance
tudies have demonstrated that both units contain leiospheric andare acanthomorphic acritarchs including Trachyhystrichosphaera

Rodinia supercontinent, modified from Li et al. (2008). (B) Geological map of thecality at the Diangeda–Baieshan section (star). White box in inset map denotes the

aimika Hermann in Timofeev et al., 1976 (Hong et al., 2004; Wanget al., 1984; Yin, 1985; Yin and Sun, 1994; Zang and Walter, 1992b),suggesting that the Liulaobei and Jiuliqiao formations are promisingin providing useful micropaleontological data to understand Neo-proterozoic eukaryote evolution and biostratigraphic correlation.To improve the micropaleontological yield and quality, we appliedlow-manipulation maceration techniques to analyze shale sam-ples from the Liulaobei Formation in the Huainan region, and ourstudy revealed a diverse assemblage of organic-walled microfossils,including several new species and the biostratigraphically usefulgenus Trachyhystrichosphaera Timofeev and Hermann in Timofeevet al., 1976.

2. Geological setting

The Huainan region is located in the southern part of the NorthChina Block (Fig. 1). The paleogeographic location of the North

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hina Block during the early Neoproterozoic has not been com-letely resolved, largely because of the poor paleomagnetic datarom North China due to Mesozoic tectonic overprinting (Zhangt al., 2006). However, tectonostratigraphic analysis suggests thathe North China Block was likely located in the tropical peripheryf the Rodinia supercontinent (Fig. 1A; Li et al., 2008). Indeed, thenitiation of the sedimentary basin in the Huainan region may beelated to the rifting and drifting phases during the breakup of theodinia in the early Neoproterozoic.

In the Huainan area, the Neoproterozoic sedimentary sequences up to 2000 m thick and sits on metamorphic rocks of thealeoproterozoic-Mesoproterozoic Fengyang Group (Bureau ofeology and Mineral Resources of Anui Province, 1987; Yao andhang, 1985). The sequence consists of, in ascending order, theuainan Group, Feishui Group, and Fengtai Formation (Fig. 2). Theuainan and Feishui groups each represents a sedimentary cycle

Fig. 2; Sun et al., 1986; Yang et al., 1980; Zhu et al., 1964). The loweredimentary cycle or the Huainan Group, which consists of Bagong-han and Liulaobei formations, is dominated by siliciclastic rocks.he Bagongshan Formation, several meters to more than 500 m inhickness, consists of a basal conglomerate followed by fluvial tohoreface sandstone, and onlaps over the Fengyang Group. The con-ormably overlying Liulaobei Formation, approximately 530 m inhickness measured at the Diangeda–Baieshan section near Shoux-an (star in Fig. 1B), can be subdivided in three members. Theower member is composed of purple and yellowish green, thino medium bedded, argillaceous limestone and dolomitic lime-tone intercalated with purplish red calcareous shale. The middleember consists of gray and yellowish green shale and silty mud-

tone with calcareous siltstone and limestone interbeds. The upperember is characterized by yellowish green and gray shale with

hin-bedded fine-grained quartz sandstone, calcareous siltstone,nd argillaceous limestone. The lack of cross-stratified sandstonen the Liulaobei Formation suggests a depositional environment inhe transitional to offshore zones. As mentioned above, shales of theiulaobei Formation contain well-preserved organic-walled micro-ossils (Wang et al., 1984; Yin, 1985; Yin and Sun, 1994; Zang and

alter, 1992b) and macroscopic carbonaceous compression fossilsuch as Chuaria, Tawuia and Sinosabellidites (Sun et al., 1986; Wangt al., 1984; Zheng, 1980).

The upper sedimentary cycle of the Feishui Group consists ofhe Shouxian, Jiuliqiao and Sidingshan formations in an ascend-ng order (Sun et al., 1986). The Shouxian Formation is about5–90 m in thickness and consists of feldspathic and calcare-us sandstone with common planar and trough cross-beddingtructures as well as wave ripples, indicating a shoreface to transi-ional depositional environment (Xing et al., 1996). The succeedingiuliqiao Formation, 26–119 m in thickness, is characterized byhin-bedded and laminated argillaceous limestone and stromat-litic limestone with siltstone interbeds. Numerous macroscopicarbonaceous compression fossils, including Chuaria, Tawuia, Sinos-bellidites, Pararenicola, and Protoarenicola, have been reportedrom the Jiuliqiao Formation (Chen, 1988; Chen and Zheng, 1986;ong et al., 2008; Fu, 1989; Niu and Zhu, 2002; Qian et al., 2009;un et al., 1986; Wang, 1982; Wang et al., 1984; Zheng, 1980).n addition, a moderately diverse assemblage of organic-walled

icrofossils dominated by leiospheres has also been reported fromhe Jiuliqiao Formation (Hong et al., 2004). Conformably overlyinghe Jiuliqiao Formation is the ∼300-m-thick Sidingshan Formation,hich consists of intertidal stromatolitic dolomites with chert lay-

rs and nodules.The Sidingshan Formation is separated from the Fengtai Forma-

ion by an erosion surface. The Fengtai Formation consists of poorlytratified diamictites with outsized clasts in a calcareous mudstonend dolostone matrix. The Fengtai diamictite has been interpreteds glacial deposits (Wang et al., 1984), and has been correlated with

rch 236 (2013) 157– 181 159

late Ediacaran glacial diamictites along the southern margin of theNorth China Block (Guan et al., 1986; Shen et al., 2007, 2010, 2011;Xiao et al., 2004). The Fengtai diamictite is unconformably overlainby the Houjiashan Formation with a basal phosphatic conglom-erate followed by carbonate rocks. The presence of small shellyfossils and trilobites in the Houjiashan Formation indicates an earlyCambrian age (Zhang and Zhu, 1979; Zhang et al., 1979).

As the Huainan and Feishui groups are underlain by thePaleo-Mesoproterozoic Fengyang Group and overlain by the lateEdiacaran Fengtai Formation, their depositional age is constrainedbetween the Mesoproterozoic and Ediacaran. However, their exactage has been a matter of uncertainty. For example, the Huainan andFeishui groups have been variously regarded as Cryogenian and Edi-acaran deposits (Xing, 1989; Xing et al., 1996) or pre-CryogenianNeoproterozoic rocks (Cao, 2000; Cao et al., 1989). In recent years,the latter opinion has gained more support from paleontologi-cal data and regional correlation. Although there are no volcanicashes in the Huainan and Feishui groups that allow for precisezircon U–Pb dating, whole rock K–Ar and Rb–Sr ages from theserocks are between 900 Ma and 750 Ma (see summary in Dong et al.,2008). Additionally, the Huainan and Feishui groups are often cor-related with the middle-upper Qingbaikou Group in the Jixian areanear Beijing and equivalent rocks in Liaoning Province, based onsimilar fossil assemblages (Du et al., 2009; Duan, 1982); the middle-upper Qingbaikou Group is radiometrically constrained to be earlyNeoproterozoic in age (Gao et al., 2009, 2010). Finally, the occur-rence of Trachyhystrichosphaera aimika in the Liulaobei Formation(Yin, 1985) is also inconsistent with a Cryogenian-Ediacaran age.Thus, when considered together, the available biostratigraphic evi-dence and regional correlation reinforce the interpretation that theorganic-walled microfossil assemblage reported in this paper ispre-Cryogenian Neoproterozoic in age.

3. Materials and methods

In this study, twenty mudstone samples were collected from ameasured section of the Liulaobei Formation at Diangeda–Baieshannear the city of Shouxian (Figs. 1 and 2). The section was mea-sured downward from the Liulaobei-Shouxian boundary, becausethis boundary is easily recognizable and also because the basalLiulaobei Formation at this section is not well exposed. Sampleswere processed using low-manipulation HF maceration techniques(Butterfield et al., 1994) in the Nanjing Institute of Geology andPalaeontology. Eleven samples were productive, with exception-ally abundant and well-preserved microfossils from a single sample(11-LLB-A; star in Fig. 2), which supplies the majority of micro-fossils illustrated in this paper. Organic-walled microfossils weremanually removed from maceration residues and individuallymounted on glass slides for light and electron microscopy. All illus-trated specimens are reposited in Nanjing Institute of Geology andPalaeontology (NIGPAS), Chinese Academy of Sciences.

4. Summary of microfossils from the Liulaobei Formation

Consistent with the previous studies, our study shows thatorganic-walled microfossils from the Liulaobei Formation are dom-inated by sphaeromorphic acritarchs and cyanobacterial filaments(Fig. 3; Yin, 1985; Yin and Sun, 1994; Zang and Walter, 1992b).Nearly all fossiliferous samples contain the sphaeromorph genusLeiosphaeridia, which ranges from less than 30 �m to more than500 �m in diameter. Previous studies of the Liulaobei Formation
reported more than 20 Leiosphaeridia species distinguished by vesi-cle size and the presence of folds and other vesicle ornaments(Wang et al., 1984; Yin, 1985; Yin and Sun, 1994; Zang and Walter,1992b). However, some of these features (e.g., vesicle folds and


F ), withD by bla

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ig. 2. Stratigraphic column of the Huainan and Feishui groups (Sun et al., 1986iangeda–Baieshan locality. Sampled horizons (11-LLB-A to 11-LLB-T) are marked

utative ornaments) are likely of taphonomic origin and should note considered as species-defining features. We follow Butterfieldt al. (1994) in recognizing just five Neoproterozoic Leiosphaeridiapecies, in addition to the type species L. baltica Eisenack, 1958.hese five species are L. minutissima (Naumova, 1949) Jankauskas inankauskas et al., 1989 (thin-walled, less than 70 �m in diameter);. tenuissima Eisenack, 1958 (thin-walled, 70–200 �m in diame-er); L. crassa (Naumova, 1949) Jankauskas in Jankauskas et al.,989 (thicker-walled, less than 70 �m in diameter); L. jacuticaTimofeev, 1966) Mikhailova and Jankauskas in Jankauskas et al.,989 (thicker-walled, 70–800 �m in diameter); and L. wimaniiBrotzen, 1941) Butterfield in Butterfield et al., 1994 (800–2500 �mn diameter, often with medial split). Noting that L. wimanii wasriginally described as Chuaria wimanii and that Chuaria is commonn the Liulaobei Formation, it is possible that all five Leiosphaeridiapecies are present in the Liulaobei Formation (Figs. 3 and 4A–D).

Simia simica (Jankauskas, 1980) Jankauskas in Jankauskas et al.,989, and S. annulare (Timofeev, 1969) Mikhailova in Jankauskast al., 1989, are also common in our collection (Fig. 4E–G).imia Mikhailova and Jankauskas in Jankauskas et al., 1989 is

a detailed stratigraphic column of the Liulaobei Formation as measured at theck dots and star (most productive sample).

very similar to Pterospermopsimorpha Timofeev, 1966. When com-pressed, both Simia and Pterospermopsimorpha appear to havea dark inner body surrounded by a light outer zone, althoughSimia was originally described as a pteromorph (but classifiedunder the prismatomorphs) and Pterospermopsimorpha as a dis-phaeromorph (Jankauskas et al., 1989). Compressed pteromorphs(spherical vesicle with an extended equatorial ring or flange) anddisphaeromorphs (an inner vesicle surrounded concentrically byan outer vesicle) can appear very similar and can be difficult to dis-tinguish (Hofmann and Jackson, 1994). Nonetheless, our specimensare similar to Simia simica and S. annulare described by Jankauskaset al. (1989). The inner body of S. simica is circular, opaque, about22 �m in diameter, and surrounded by a ∼3-�m-wide ring of amor-phous material (Fig. 4E). In contrast, the inner body of S. annulare issubcircular and sometimes with folds (likely due to deformation),translucent with psilate surface, 92–140 �m in diameter, and sur-
rounded by a lighter-colored membranous ring that is 18–35 �mwide (Fig. 4F–G). One specimen shows a small vesicle attachedto the outer ring (upper left of Fig. 4G), an association that couldrepresent a taphonomic accident or reproductive budding.

Q. Tang et al. / Precambrian Research 236 (2013) 157– 181 161

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Fig. 3. List of microfossil ta

Abundant aggregated vesicles were recovered from the Liu-aobei samples, including Synsphaeridium sp., Myxococcoides ovatanoll, 1982, Fabiformis baffinensis Hofmann in Hofmann and

ackson, 1994, and Ostiana microcystis Hermann, 1976. Vesicles ofynsphaeridium sp. are 10–25 �m in diameter and are arranged inrregular aggregates 40–65 �m in maximum dimension (Fig. 4H–J).

hen disaggregated, Synsphaeridium vesicles can be indistinguish-ble from Leiosphaeridia or Myxococcoides vesicles. However, theggregation habit provides biological information about colonialityHofmann and Jackson, 1994). Considering the constantly incom-lete preservation of this form genus, we follow the practice of

ankauskas et al. (1989) to leave the fossils in an open nomen-lature. The aggregates of Myxococcoides ovata from Liulaobeiollection consist of dozens of spheroidal vesicles, each with aiameter of approximately 20 �m (Fig. 4K–M). The aggregatesre commonly covered by a translucent matrix. The thin vesicleall and the relatively large aggregates distinguish Myxococcoides

vata from other Myxococcoides species. Cylindrical aggregationsf vesicles, with or without a translucent enclosing membraneFig. 5A, B), are here tentatively assigned to Fabiformis baffinensisofmann in Hofmann and Jackson, 1994. Our specimens, which

m the Liulaobei Formation.

are approximately 10 �m in vesicle diameter, 40 �m in aggregatediameter, and 180–280 �m in aggregation length, show distinctspheroidal cell units forming straight or curved, cylindrical ortubular aggregates. These specimens are also somewhat similarto Chlorogloeaopsis species, but their cells are larger than thoseof Chlorogloeaopsis contexta (Hermann in Timofeev et al., 1976)Hofmann in Hofmann and Jackson, 1994, and their cells are moreabundant and more tightly arranged than those of Chlorogloeaop-sis kanshiensis (Maithy, 1975) Hofmann in Hofmann and Jackson,1994. Large planar colonies of coccoidal vesicles from the Liu-laobei Formation are identified as Ostiana microcystis Hermann,1976 (Fig. 5C–G), which is also a common Riphean element inRussia (Hermann, 1990; Vorob’eva et al., 2009b). The colonies canbe single- or double-layered, with or without an enclosing mem-brane. Double-layered colonial structure can be observed in SEMimages, where two layers of cells are superimposed on each other(Fig. 5D). One of our specimens consists of perforated colonies
that are superficially similar to Eosaccoromyces ramosus Hermann,1979, but unlike the latter species, vesicles in our specimen are notarranged in “cell chains” and are enclosed by a thin outer membrane(Fig. 5F).


Fig. 4. (A) Leiosphaeridia minutissima, specimen 11-LLB-A-53-3. (B) Leiosphaeridia crassa, specimen 11-LLB-A-55-2. (C) Leiosphaeridia tenuissima, specimen 11-LLB-A-17-1.(D) Leiosphaeridia jacutica, specimen 11-LLB-A-41-10. (E) Simia simica, specimen 11-LLB-A-53-1. (F and G) Simia annulare. (F) Specimen 11-LLB-A-40-9. (G) Specimen 11-LLB-A-47-5, with a small bud-like vesicle. (H–J) Synsphaeridium sp., specimens 11-LLB-A-54-1, 11-LLB-A-55-4 and 11-LLB-A-55-5, respectively. (K–M) Myxococcoides ovata,specimen 11-LLB-A-57-15, 11-LLB-A-S-6 and 11-LLB-A-S-7, respectively.


Fig. 5. (A, B) Fabiformis baffinensis, specimen 11-LLB-A-46-20, 11-LLB-A-49-10, respectively. (C–G) Ostiana microcystis. (C) Scanning electron microscopy (SEM) image,specimen 11-LLB-A-S-1. (D) Magnification of box area in C, showing superimposed vesicles in a double-layered colony. (E) Transmitted light microscopy (TLM) image ofspecimen illustrated in C. (F) Magnification of box area in G, showing mono-layered, perforated colonial sheet covered by a translucent membrane. (G) Specimen 11-LLB-A-49-12. (H) Navifusa majensis, specimen 11-LLB-A-55-3.


Fig. 6. Pololeptus rugosus. (A) Specimen 11-LLB-B-S-1, SEM micrograph. (B) Magnification of box area in A, showing ruptured vesicle wall. (C) Same specimen as in A, TLMmicrograph. (D) Specimen 11-LLB-A-S-2, TLM micrograph, showing transverse annulations. (E) Same specimen as in D, SEM micrograph. (F) Magnification of right box areain E, showing transverse annulations on vesicle surface. (G) Magnification of box area in D. (H) Magnification of left box area in E and same area as in G, showing rupturedvesicle wall.


Fig. 7. Transmitted light micrographs of Pololeptus rugosus. (A) Specimen 11-LLB-A-23-9. (B) Specimen 11-LLB-A-20-12, with transverse annulations in the equatorial regionand pitted texture in the polar regions. (C) Specimen 11-LLB-A-40-1, two chained vesicles. (D) Specimen 11-LLB-A-40-11, three chained vesicles. (E) Specimen 11-LLB-B-S-2.(F) Magnification of box area in E, showing a close view of transverse annulations.

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The Liulaobei Formation also contains morphologically moreomplex netromorphs and acanthomorphs, including Navifusaajensis Pyatiletov, 1980, Pololeptus rugosus (Yin, 1985) Yin and

un, 1994, Trachyhystrichosphaera aimika Hermann, 1976, T. botula. sp., and Eotylotopalla? grandis n. sp. Navifusa majensis (Fig. 5H)

s a netromorphic form with smooth vesicle walls, and our spec-mens are 42–71 �m in length and 17–26 �m in width, largerhan N. bacillaris (Hermann, 1981) Hofmann and Jackson, 1994,ut smaller than N. actinomorpha (Maithy, 1975) Hofmann andackson, 1994 (Hofmann and Jackson, 1994). Navifusa is morpho-ogically similar to Leiovalia Eisenack, 1965, but the latter genus isaid to be more rounded rather than elongate than Navifusa (Fatkand Brocke, 2008; Volkova et al., 1979). Liulaobei specimens iden-ified as Pololeptus rugosus (Figs. 6 and 7) are similar to Navifusan their sausage-shaped morphology, but they are larger (vesiclespproximately 40–280 �m in length and 30–145 �m in width) andharacterized by transverse annulations and terminal pitted orna-ents. This species has been previously reported from the Liulaobei

ormation (Yin and Sun, 1994), but an emended diagnosis based onew observations is presented here.

Perhaps the most biostratigraphically important discoverys the documentation of the acanthomorphs Trachyhystrichos-haera aimika and T. botula n. sp. in the Liulaobei FormationFigs. 8–11 and 12A). Although T. aimika was previously illustratedrom the Liulaobei Formation (Yin, 1985), no detailed descriptionas provided. Our analysis recovered about 140 Trachyhystri-

hosphaera specimens from a single horizon (11-LLB-A) in theiulaobei Formation. A larger sample size allows more detailedescription and the recognition of a new species, which will beescribed under the Systematic Paleontology section. In additiono Trachyhystrichosphaera botula n. sp., another new acanthomorphharacterized by large vesicle and a sparse number of obtuseemispherical processes has been recovered from the Liulaobeiormation; this form is described as Eotylotopalla? grandis n. sp.Fig. 12D–F).

Filamentous microfossils are common in Precambrian fossilif-rous successions, and the Liulaobei Formation is no exception.ost Liulaobei filaments can be placed in the genus Siphonophy-

us Schopf, 1968. We follow Knoll et al. (1991) and Butterfieldt al. (1994) in distinguishing Siphonophycus species on the basisf filament diameter: S. thulenema Butterfield in Butterfield et al.,994 (0.5 �m in diameter); S. septatum (Schopf, 1968) Knoll, Swett,nd Mark, 1991 (1–2 �m); S. robustum (Schopf, 1968) Knoll, Swett,nd Mark, 1991 (2–4 �m); S. typicum (Hermann, 1974) Butterfieldn Butterfield, Knoll, and Swett, 1994 (4–8 �m); S. kestron Schopf,968 (8–16 �m); S. solidum (Golub, 1979) Butterfield in Butterfield,noll, and Swett, 1994 (16–32 �m); and S. punctatum Maithy, 1975

32–64 �m). Our collection includes all these species except S. thu-enema (Fig. 13A–H, L–M). In addition, we describe a new species. gigas that is characterized by large filaments 64–128 �m inidth (Fig. 13I, N). Sometimes, Siphonophycus filaments of different

izes form a mat-like structure (Fig. 13J), apparently representing aulti-species community. Also, some Siphonophycus filaments are

oiled to form a circular roll-up structure up to 55 �m in diameterFig. 13M), similar to a coiled Leiotrichoides specimen illustrated inermann (1990). In addition to Siphonophycus, bundled filaments

dentified as Polythrichoides lineatus Hermann, 1974, are present inhe Liulaobei assemblage, and some of these filaments have well-reserved trichomes (Fig. 14).

. Systematic paleontology

Group Acritarcha Evitt, 1963

Genus Eotylotopalla Yin L., 1987

Type species: Eotylotopalla delicata Yin L., 1987.

rch 236 (2013) 157– 181

Eotylotopalla? grandis n. sp.Figure 12D–F

Holotype: The specimen illustrated in Fig. 12E is designated asthe holotype; Nanjing Institute of Geology and Palaeontology, spec-imen 11-LLB-A-52-2.

Type locality: Liulaobei Formation; 60 m below the top of theformation.

Diagnosis: A species of Eotylotopalla with a large vesicle anda sparse number of hemispherical processes that are terminallyrounded and thickened.

Material: Two specimens from sample 11-LLB-A.Description: Single-walled spheroidal vesicle, ∼400 �m in

diameter, ornamented with ∼12 regularly distributed processes.Processes hollow, communicate freely with vesicle interior,20–45 �m in length, and 100–120 �m in basal width.

Remarks: Eotylotopalla? grandis n. sp. is similar to severalother Eotylotopalla species in its sparsely distributed, bulbous tohemispherical processes that are sometimes terminally thickened.However it is much larger than all existing Eotylotopalla species(Liu et al., in press; Xiao et al., in press), and for this reason it isprovisionally placed in this genus. For comparison, E. delicata Yin,1987, is 40–50 �m in vesicle diameter and has small bulbous andsometimes bifurcating processes; E. dactylos Zhang et al., 1998, is35–45 �m in vesicle diameter and has cylindrical to digitate pro-cesses that are distally truncated; and E. strobilata (Faizullin, 1998)Sergeev et al., 2011, is 65–85 �m in vesicle diameter and has a largenumber of small hemispherical processes. Eotylotopalla? grandisis somewhat similar to Asterocapsoides sinensis in vesicle size andsparsely distributed processes (Zhang et al., 1998). However, theprocesses of A. sinensis are conical and have pointed terminations.

Eotylotopalla is widely distributed in Ediacaran Doushantuo For-mation, southern China (Yin, 1987). The occurrence of Eotylotopallain the Liulaobei Formation is consistent with the argument thatacanthomorphic acritarchs can be dated back to early Neoprotero-zoic or even Mesoproterozoic eras (Xiao et al., 1997).

Etymology: Species epithet derived from Latin grandis, with ref-erence to the much larger vesicle and processes compared to otherEotylotopalla species.

Genus Pololeptus Yin L. in Yin and Sun, 1994, emend.

1994 Pololeptus Yin L. in Yin and Sun, p. 101–102.

Type species: Pololeptus rugosus (Yin, C., 1985) Yin and Sun, 1994.Emended diagnosis: Single-walled vesicles, ovoidal to tomacu-

late (or sausage-like) in shape, with rounded or constricted ends.Vesicle wall smooth or ornamented with transverse annulations(particularly in the equatorial region). Either or both ends (polarregions) of the vesicle are characterized with pitted textures, whichappear to be present on the inner surface of the vesicle wall or in theinner layer of a double-layered vesicle wall. Occasionally, severalvesicles are chained to form a linear series.

Remarks: Acritarchs of this genus were originally describedby Yin (1985) from the Liulaobei Formation under three speciesof Teophipolia Kirjanov, 1979, which is a Cambrian netromorphicacritarch with a circular or an irregular opening at one end. Yin(1985) remarked that the Liulaobei fossils are characterized by“thinner areas” with reticulate ornamentation at either or bothends of their netromorphic vesicles, and that some of them have anirregular or circular rupture at one end of their vesicles, with thelatter feature being a basis for a taxonomic assignment to Teophipo-lia. Yin and Sun (1994), however, noted that the “thinner areas” inthe Liulaobei fossils are dark-colored “worm-like or netted struc-
tures” at either or both ends of the vesicle, and that no biologicallyprogramed opening (e.g., excystment structures) are present in theLiulaobei fossils. They thus argued that the Liulaobei fossils cannotbe accommodated by Teophipolia and erected the genus Pololeptus.


Fig. 8. Transmitted light micrographs of Trachyhystrichosphaera aimika. (A) Specimen 11-LLB-A-61-1, with several small processes. (B) Specimen 11-LLB-A-26-12, with pro-cesses of different sizes. (C) Specimen 11-LLB-A-20-11, with well-preserved outer membrane. (D) Specimen 11-LLB-A-24-2, with outer membrane and relatively longprocesses. (E) 11-LLB-A-24-9, with a dark-colored, discoidal inner body. (F) Specimen 11-LLB-A-21-17, with perforations on vesicle wall that match the processes ofTrachyhystrichosphaera aimika in size and density; these perforations are interpreted as resulting from broken processes.


Fig. 9. SEM and TLM micrographs of Trachyhystrichosphaera aimika. (A) Specimen 11-LLB-A-S-3, TLM micrograph. (B) Magnification of box area in A, showing a distallydilated process which becomes wider after penetrating outer membrane. (C) SEM micrograph of same specimen as in A. (D) Magnification of box area in C. (E) Specimen11-LLB-A-20-2, TLM micrograph. (F) Magnification of box area in E, showing two tubular processes that gradually taper distally and remain more or less cylindrical afterpenetrating outer membrane.


Fig. 10. SEM and TLM micrographs of Trachyhystrichosphaera aimika. (A) Specimen 11-LLB-A-S-4, TLM micrograph. (B) SEM micrograph of same specimen as in A. (C)Magnification of box area in B. (D) Backscattered electron (BSE) micrograph of same specimen in A, showing dark inner body. (E) Specimen 11-LLB-A-47-18, TLM micrographof dyads. (F) Specimen 11-LLB-A-46-27, TLM micrograph of dyads surrounded by outer membrane. Also note perforations on vesicle wall that correspond to broken processes.


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ig. 11. TLM micrographs of Trachyhystrichosphaera botula n. sp. (A) Specimen 1pecimen 11-LLB-A-52-4. (D) Holotype, specimen 11-LLB-A-50-13. (E) Specimen 1plit and a dark inner body. (H) Magnification of box area in F, showing broken proc

While we agree with Yin and Sun (1994) that the Liulaobei fos-ils are distinct from Teophipolia and should be placed in Pololeptus,e also made several new observations that warrant an emenda-

ion of the latter genus. First, a close examination of the terminal

A-51-9, with an irregularly shaped inner body. (B) Specimen 11-LLB-A-20-6. (C)-A-22-16. (F) Specimen 11-LLB-A-42-6. (G) Specimen 11-LLB-A-40-4. Note medial.

“worm-like or netted structures” shows that they are more appro-priately described as pitted textures (Figs. 6C, D and 7A, B). Suchpitted textures appear superficially similar to sediments trappedin the polar regions, although it is unclear how sediments would


Fig. 12. (A) Trachyhystrichosphaera botula n. sp., specimen 11-LLB-A-27-6. (B, C) Sinosabellidites huainanensis. (B) Specimen 11-LLB-M-1. (C) Magnification of box area in B,showing transverse annulations. (D–F) Eotylotopalla? grandis n. sp. (D) Magnification of box area in F, showing obtuse hemispherical process with terminal thickening. (E)Holotype, specimen 11-LLB-A-52-2. (F) Specimen 11-LLB-A-50-1.


Fig. 13. (A) Siphonophycus septatum, specimen 11-LLB-A-53-5. (B) Siphonophycus robustum, specimen 11-LLB-A-53-2. (C, D) Siphonophycus typicum, specimens 11-LLB-A-53-6 and 11-LLB-A-49-1, respectively. (E) Siphonophycus kestron, specimen 11-LLB-A49-9. (F–G) Siphonophycus solidum, specimens 11-LLB-A-45-13 and 11-LLB-A-46-4,respectively. (H and L) Siphonophycus punctatum, specimens 11-LLB-A-45-2 and 11-LLB-A-45-8, respectively. (I and N) Siphonophycus gigas n. sp. (I) Holotype, specimen 11-LLB-A-47-2. (N) Specimen 11-LLB-A-37-8. (J) Microbial mat consisting of Siphonophycus septatum and S. typicum, specimen 11-LLB-A-47-13. (K) Possibly a twisted specimeno obustu

btrc(pjodlc(sd

f Siphonophycus gigas n. sp. Specimen 11-LLB-A-40-18. (M) Coiled filaments of S. r

e introduced into the vesicle. SEM observation shows that the pit-ed textures are not on the external surface of the vesicle wall;ather, they are present either on the inner surface of the vesi-le wall or on the inner layer of a double-layered vesicle wallFig. 6A, B). Yin and Sun (1994) speculated that these terminalitted structures may represent “contact traces formed by con-

uncted vesicles”. This speculation is consistent with the presencef chained vesicles (Fig. 7C, D). Second, we have identified a newiagnostic feature of Pololeptus: transverse annulations. Such annu-

ations are best seen in the equatorial region of larger vesicles and
an be observed in both scanning electron and light microscopyFigs. 6D, E and 7A, B, E, F), but they may not be present in smallerpecimens (Figs. 6A and 7C, D) or in polar regions. Thus, the genusiagnosis is here emended to reflect these new observations.
m. The 20-�m scale bar is for M, and the 100-�m scale bar is for all others.

Our new observations of Pololeptus also shed new light on itsontogeny, reproduction, and taphonomy. The preferential occur-rence of transverse annulations in lager vesicles, but not in smallerones, indicates that these annulations may have developed dur-ing active growth of vesicles. Hence, the vesicles are not restingcysts, but actively growing organisms. This inference is furthersupported by the chained vesicles (Fig. 7C, D), which are best inter-preted as a strategy for asexual reproduction. Finally, the absenceof an excystment opening is also consistent with our interpre-tation that the available material of Pololeptus does not include
a resting cyst stage. Some specimens in our collection do haveV-shaped or irregular ruptures (Fig. 6A–C), but these are likelytaphonomic artifacts rather than biologically programed excyst-ment openings.


Fig. 14. SEM and TLM micrographs of Polytrichoides lineatus. (A) Specimen 11-LLB-A-44-18, with septa at the arrow. (B) Specimen 11-LLB-A-S-5, TLM micrograph, filamentswith capitate terminations. (C) SEM micrograph of same specimen as in B. (D) Magnification of box area in B. (E) Magnification of box area in C. (F) Specimen 11-LLB-A-40-16,filaments with blunt terminations.

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Although much smaller in overall size and in length/widthatios, the annulated vesicles of Pololeptus are somewhat similaro the macrofossil Sinosabellidites Zheng, 1980 and Pararenicola

ang, 1982, from the Huainan and Huaibei regions in northernnhui (Dong et al., 2008). Sinosabellidites can sometimes co-occurith Pololeptus on the same bedding surface in the Liulaobei For-ation. Both Sinosabellidites and Pararenicola are ribbon-shaped

ompressions with transverse annulations. Although the annu-ations of Pararenicola are distributed along the entire length ofheir ribbons, those of Sinosabellidites appear to be restricted tohe equatorial region as in Pololeptus (Fig. 12B). In addition, someararenicola specimens consist of chained ribbons of millimetersn width and length, similar to but much larger than the chainedesicles of Pololeptus. And the chained ribbons of Pararenicolare also interpreted as a strategy for asexual reproduction (Dongt al., 2008). However, there are important differences betweenhe transverse annulations in Sinosabellidites and Pararenicola andhose in Pololeptus. In the best preserved specimens, transversennulations in Sinosabellidites and Pararenicola are more promi-ent (with slightly positive relief), more complete (reaching acrosshe entire width of compressed ribbons), and more regularly andidely spaced (Fig. 12B, C). In contrast, transverse annulations in

ololeptus are thinner, wrinkle-like, more irregularly distributed,nd more closely spaced (Fig. 6F). Nonetheless, the possibility thathese differences may be ontogenetic and there may be some devel-pmental linkages among these morphotaxa cannot be ruled outith available evidence, and should be further investigated in the

uture.Several Ediacaran and Cambrian fossils are also characterized

ith transverse annulations, but these can be easily differenti-ted from Pololeptus. For example, two Ediacaran genera fromhe Dengying Formation of southern Shaanxi Province in Southhina—Gaojiashania Yang, Zhang and Yin in Lin et al., 1986,nd Shaanxilithes Xing, Yue, and Zhang in Xing et al., 1984—areharacterized with transverse annulations, but they are veryong tubular organisms rather than tomaculate vesicles (Chent al., 2003; Cai et al., 2010). Similarly, the annulated ribbon-likeossil Sabellidites Yanichevsky, 1926, from early Cambrian rocksan be differentiated from Pololeptus by its tubular morphologySun et al., 1986). Finally, uniserially chained vesicles also occurn the Proterozoic genus Arctacellularia Hermann in Timofeevt al., 1976, but unlike Pololeptus, the vesicles of Arctacellu-aria are spheroidal rather than tomaculate and they are notnnulated.

Pololeptus rugosus (Yin, C., 1985) Yin and Sun, 1994, emend.Figures 6, 7

985 Teophipolia rugosa Yin, C., p. 108, pl. 2, figs. 17 and 18.985 Teophipolia tenera Yin, C., p. 108, pl. 2, fig. 19.985 Teophipolia biacris Yin, C., p. 108, pl. 2, fig. 20.994 Pololeptus rugosa (Yin, C.) Yin and Sun, p. 101–102, fig. 4a, 4c, 4d, 4h, 4k.994 Pololeptus biacris (Yin, C.) Yin and Sun, p. 102, fig. 4e, 4f, 4j, 4l.

Orthography: The species epithet is declined to rugosus to matchhe genus name.

Material: Twenty three specimens have macerated from shaleamples 11-LLB-A and 11-LLB-B.

Emended diagnosis: Ovoidal to tomaculate vesicles, with smoothr psilate walls decorated with fine and closely spaced trans-erse annulations, particularly in the equatorial region. Vesicles areccasionally chained, and isolated vesicles have bluntly roundederminal ends (polar regions). Pitted textures are characteristics
f one or both polar regions, particularly in larger specimens,nd they appear to be present on the inner surface of theesicle wall or in the inner layer of a double-layered vesicleall.
rch 236 (2013) 157– 181

Dimension: Vesicles are 40–280 �m long and 30–145 �m wide.Length/width ratios range from 1.3 to 4. Approximately 13 annula-tions per 10 �m length of vesicle.

Remarks: Pololeptus rugosus is here emended to reflect the newobservations of transverse annulations and pitted textures in thepolar region. Yin (1985) established three species of Teophipoliabased on Liulaobei material. These three species were differentiatedbased on the presence of large folds on vesicle walls and pitted tex-ture in one polar region (T. rugosa), fine wrinkles on vesicle wallsand pitted texture in one polar region (T. tenera), and large foldson vesicle walls and pitted texture in both polar regions (T. biacris).Large folds on vesicle walls are likely taphonomic features. Further-more, if the pitted textures represent attachment scars on chainedvesicles, then whether such textures are present in one or bothpolar regions depends on whether a vesicle is located in a terminalor intercalary position. Thus, we regard these three species to besynonymous, with T. rugosa taking priority.

Pololeptus rugosus is similar to several other netromorphs inoverall vesicle morphology (particularly Navifusa and Leiovalia;Eisenack, 1965; Combaz et al., 1967; Fatka and Brocke, 2008;Hofmann and Jackson, 1994; Volkova et al., 1979), but is distinctfrom all other netromorphs by its transverse annulations and pittedtextures in polar regions.

Occurrence: Neoproterozoic Liulaobei Formation, HuainanGroup, North China (Yin, 1985; Yin and Sun, 1994).

Genus Trachyhystrichosphaera Timofeev and Hermann, 1976, emend.

See Butterfield et al. (1994) for synonyms.1992 Prolatoforma Mikhailova in Mikhailova and Podkovyrov, p. 122.non 1999 “Trachyhystrichosphaera truncata” Hermann and Jankauskas;

Samuelsson et al., fig. 8a, b.non 1999 Trachyhystrichosphaera parva Mikhailova; Sergeev, pl. 1, figs. 5, 6

(the same specimens were subsequently identified asShorikhosphaeridium knolli Sergeev, 2001, p. 445, fig. 8.3–8.6).

non 2006 Trachyhystrichosphaera aimika Hermann; Sergeev, pl. 20, figs. 1, 2(the same specimen was previously identified as Pterospermopsimorpha?sp. in Sergeev, 1999, pl. 1, fig. 7).

Type species: Trachyhystrichosphaera aimika Hermann inTimofeev et al., 1976.

Emended diagnosis: Large spheroidal, ovoidal, or tomaculatevesicles with a small number of highly heteromorphic, hollow,basally separate, and irregularly distributed processes. Processescommunicate freely with vesicle cavity. An outer membrane maybe present surrounding the processes, and an inner body may bepresent in the vesicle.

Remarks: The diagnosis of Trachyhystrichosphaera was previ-ously emended by Butterfield et al. (1994). The diagnosis is herefurther emended to accommodate T. botula n. sp., which has atomaculate vesicle rather than a spheroidal vesicle that character-izes the two other recognized species of Trachyhystrichosphaera—T.aimika and T. polaris. In addition, the presence of bifurcating pro-cesses is removed from the emended diagnosis. Butterfield et al.(1994) illustrated one specimen of T. aimika with basally bifurcat-ing processes (their fig. 18H), but the evidence is unconvincing asthe bifurcation appears to be an artifact of overlapping processes.

Butterfield et al. (1994) discussed extensively on Trachy-hystrichosphaera. To summarize their main points, the genusTrachyhystrichosphaera is characterized by significant variabilityin vesicle size, process density and morphology, and the pres-ence/absence of an enclosing membrane. Thus, Butterfield et al.(1994) recognized only two species, T. aimika and T. polaris.Other published Trachyhystrichosphaera species were either syn-
onymized with T. aimika or excluded from Trachyhystrichosphaerabecause they do not have the characteristic features of this genus.Butterfield et al. (1994) also regarded Nucellohystrichosphaera Tim-ofeev and Hermann in Timofeev et al., 1976, as a synonym of

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rachyhystrichosphaera, a synonymization accepted here too. Addi-ionally, we also propose that the genus Prolatoforma Mikhailovan Mikhailova and Podkovyrov, 1992, be a junior synonymy of Tra-hyhystrichosphaera. The type species of Prolatoforma, P. aculeata,hares the most salient features of Trachyhystrichosphaera aimika:pheroidal to sub-spheroidal vesicle with sparsely distributed andollow processes surrounded by an outer membrane. Its bipolaristribution of processes (Vorob’eva et al., 2009b) appears to be

taphonomic artifact. Butterfield et al. (1994) have already com-ented on Trachyhystrichosphaera truncate, which they excluded

rom the genus Trachyhystrichosphaera, and this exclusion was pro-isionally accepted in Samuelsson et al. (1999) when they describedTrachyhystrichosphaera truncata”. Additionally, Trachyhystrichos-haera parva from the Shorikha Formation (Sergeev, 1999) doesot belong to this genus, because they appear to have bifurcatedrocesses; indeed, these specimens have later been publisheds Shorikhosphaeridium knolli Sergeev, 2001. Finally, a specimenriginally identified as Pterospermopsimorpha? sp. (Sergeev, 1999)ut subsequently as Trachyhystrichosphaera aimika (Sergeev, 2006)oes not seem to have processes and should be excluded fromrachyhystrichosphaera too.

The degree of morphological variation is also seen in the Liu-aobei material of Trachyhystrichosphaera, particularly T. aimika for

hich a large number of specimens are available for a statisti-al analysis. The vesicle diameter of T. aimika, calculated as theeometric mean of the maximum and minimum dimensions forach specimen, ranges from 39 �m to 373 �m, number of processeser vesicle from 2 to 40, process length from 1 �m to 36 �m, androcess basal width from 0.7 �m to 11.8 �m (Fig. 15A). The pro-esses of T. aimika can be cylindrical, conical, distally expanded,erminally capitate, or tufted, and an enclosing membrane mayr may not be present. Certainly, the morphological variability isartly due to taphonomic alteration: processes can be abradedr broken (Figs. 8F, 10F, 11H), and the enclosing membrane iso thin that it may be taphonomically lost. Such taphonomiclteration partly explains the large variation in process lengthnd the poor correlation between vesicle diameter and numberf processes (Fig. 15A). However, as argued in Butterfield et al.1994), there is also an ontogenetic signature in the morpho-ogical variation of Trachyhystrichosphaera aimika. For example,ome of our specimens show that very thin and short pro-esses with pointed tips (thus not broken) co-exist with thicker,arger, and often broken processes (Fig. 8A–D), indicating that pro-esses continuously erupted and lengthened during active vesiclerowth.

The Liulaobei material of Trachyhystrichosphaera also showswo other features that have been previously illustrated but notescribed in detail: nucleus-like internal bodies (Jankauskas et al.,989; Butterfield, 2005; Vorob’eva et al., 2009a,b) and dyad vesi-les (Butterfield, 2005). The internal bodies are darker than vesiclealls, 12–39% of hosting vesicle diameter (for T. aimika), irregularly

haped and centrally or peripherally located within the hostingesicles (Figs. 8E, 10A, D, F, 11A, B, 12A). Backscattered electronicroscopy shows the internal bodies are darker than the hosting

esicle (Fig. 10D), indicating that they are compositionally and/ortructurally distinct from the compressed vesicle walls (Schiffbauert al., 2012). There have been other reports of nucleus-like internalodies in Proterozoic acritarchs, notably in Shuiyousphaeridium andictyosphaera from the Mesoproterozoic Ruyang Group of Northhina (Li et al., 2012; Schiffbauer and Xiao, 2009; Yin et al., 2005).ut the Liulaobei internal bodies are comparatively smaller andore irregularly shaped. Measurements of T. aimika show a poor

orrelation between the diameter of inner body and correspondingesicle (Fig. 15C). At the present, we regard the inner bodies of Tra-hyhystrichosphaera as possibly representing condensed cytoplasmGolubic and Barghoorn, 1977; Knoll and Barghoorn, 1975).

rch 236 (2013) 157– 181 175

Several dyads are found among Trachyhystrichosphaera aimikaspecimens from the Liulaobei Formation (Fig. 10E, F). The dyadsconsist of two vesicles of unequal to subequal sizes. The vesiclesare in close contact and are held together by the enclosing mem-brane or amorphous organic matter. Just like the chained vesiclesof Pololeptus rugosus, these dyads of T. aimika may also repre-sent a strategy for asexual reproduction (e.g., budding). Furtherinvestigation with additional material is needed to test the con-sistency of such dyad associations and their possible biologicalsignificance.

Trachyhystrichosphaera aimika Hermann in Timofeev et al., 1976Figures 8–10

1976 Trachyhystrichosphaera aimika Hermann; Timofeev et al., p. 48, pls.19.6, 19.8, 20.1–20.3

1984 Trachyhystrichosphaera vidalii Knoll, p. 154–156, fig. 8A–K.1992 Prolatoforma aculeata Mikhailova in Mikhailova and Podkovyrov, p.

122, pl. 2, figs. 7–8.1994 Trachyhystrichosphaera aimika Hermann; Butterfield et al., p. 46–47,

figs. 18A–K, 19G; and synonyms therein.1995 Trachyhystrichosphaera sp. cf. T. aimika Hermann; Zang, p. 169, fig.

26A–G.1995 Trachyhystrichosphaera?stricta Zang, p. 169–170, fig. 25H–J.1995 Trachyhystrichosphaera vidalii Knoll; Zang, p. 170, fig. 23A–E.1998 Trachyhystrichosphaera sp.; Butterfield and Rainbird, fig. 3H.2001 Trachyhystrichosphaera aimika Hermann; Samuelsson and

Butterfield, fig. 10E.2005 Trachyhystrichosphaera aimika Hermann; Butterfield, p. 178, fig. 9.2008 Trachyhystrichosphaera aimica [sic] Hermann; Nagovitsin,

Grazhdankin, and Kochnev, fig. 2e–f.2008 Prolatoforma aculeata Mikhailova; Nagovitsin, Grazhdankin, and

Kochnev, fig. 2g–h.2009a Prolatoforma aculeata Mikhailova; Vorob’eva et al., p. 166, fig. 4v.2009b Prolatoforma aculeata Mikhailova; Vorob’eva et al., p. 180, figs. 8.10,

8.12; and synonyms therein.2009 Trachyhystrichosphaera sp.; Srivastava, fig. 4.

Material: More than 125 specimens isolated from shale sample11-LLB-A.

Description: Spheroidal to sub-spheroidal vesicle with hetero-morphic, hollow, cylindrical and conical, and sometimes tuftedprocesses. An outer membrane and an irregularly shaped internalbody may be present. Vesicles are sometimes found in dyads. Someprocesses penetrate outer membrane and become distally dilated(Fig. 9A–D). Vesicles 39–373 �m in diameter (average = 165 �m;n = 112). Processes 0.7–11.8 �m in basal width (average = 3.5 �m;n = 539) and 1–36 �m in length (average = 11 �m; n = 146).

Remarks: We follow Butterfield et al. (1994) to treat Tra-chyhystrichosphaera vidalii as a junior synonym of T. aimika. Asdiscussed above under the genus Trachyhystrichosphaera, Prolato-forma aculeate is also regarded as synonymous with T. aimika;polar distribution of processes in P. aculeate specimens illustratedin Vorob’eva et al. (2009b) appears to be due to taphonomic lossbecause the outer membrane is also lost where processes areabsent.

Occurrence: Trachyhystrichosphaera aimika is known frompre-Cryogenian Neoproterozoic and latest Mesoproterozoic suc-cessions in Siberia, Southern Urals, Spitsbergen, Yukon Territory,Arctic Canada, South Australia, Central India, and North China(Table 1).

Trachyhystrichosphaera botula n. sp.Figures 11 and 12A

Holotype: The specimen illustrated in Fig. 11D is designated asthe holotype; Nanjing Institute of Geology and Palaeontology, spec-imen 11-LLB-A-50-13.


Material: Twenty four specimens from shale sample 11-LLB-A.Diagnosis: A species of Trachyhystrichosphaera characterized by

tomaculate or sausage-like vesicle with bluntly rounded ends.


Table 1List of unambiguous occurrences of Trachyhystrichosphaera aimika published in the literature, with likely ages and selected co-existing taxa.

Likely age (Ma) Formation (locality) Trachyhystrichosphaera and co-existing taxa Reference

Late Riphean Lower Vychegda Fm. Chuaria circularis Vorob’eva et al. (2006)(South Timan, Russia) Ostiana microcystis Vorob’eva et al. (2009a,b)

Polytrichoides lineatus.Prolatoforma aculeata (=T. aimika)Simia nerjenicaSiphonophycus typicumTrachyhystrichosphaera aimika

630–850 Sirbu Shale Fm. Cymatiosphaera Srivastava (2009)(Central India) leiosphaerids

Trachyhystrichosphaera sp. (=T. aimika)Vase-shaped microfossils

717–812 Fifteenmile Group Cymatiosphaeroides kullingii Allison and Awramik (1989)(Yukon Territory, Canada) leiosphaerids Macdonald et al. (2010a)

Sphaeranasillos irregularisTrachyhystrichosphaera magna (=T. aimika)T. vidalii (=T. aimika)

700–750 Svanbergfjellet Fm. Chuaria circularis Knoll et al. (1991)Draken Conglomerate Fm. Cymatiosphaeroides kullingii Butterfield et al. (1994)(Spitsbergen) Germinosphaera bispinosa

G. fibrillaleiosphaeridsTawuia dalensisTrachyhystrichosphaera aimikaT. polarisT. vidalii (=T. aimika)Valkyria borealis

700–800 Ryssö Fm. Chuaria circularis Knoll and Calder (1983)750–800 Hunnberg Fm. Cymatiosphaeroides kullingii Knoll (1984)

(Svalbard) Kildinella hyperboreicaTawuia dalensisTrachysphaeridium spp.Trachyhystrichosphaera vidalii (=T. aimika)

750–800 Upper Alinya Fm. Cymatiosphaeroides kullingii Zang (1995)(Officer Basin, South Australia) leiosphaerids

Satka compactaSimia annulareValeria lophostriataTrachyhystrichosphaera sp. cf. T. aimikaT.?stricta (=T. aimika)T. vidalii (=T. aimika)

Late Riphean Khajpakh Fm. Chuaria circularis Vidal et al. (1993)(700–840) (Northern Yakutia, Eastern Siberia) leiosphaerids

Simia annulareTawuia dalensisTrachyhystrichosphaera vidalii (=T. aimika)

Late Riphean Karatau Group leiosphaerids Jankauskas et al. (1989)(Urals) Pterospermopsimorpha insolita

Simia simicaTrachyhystrichosphaera aimikaT. vidalii (=T. aimika)

820–870 (K–Ar) Miroyedikha Fm. Colonial coccoid microfossils Hermann (1990)1025 ± 40 Lakhanda Fm. leiosphaerids Jankauskas et al. (1989)(Pb–Pb) (Uchur-Maia, Siberia) Nucellosphaeridium bellum Pjatiletov (1988)

Nucellohystrichosphaera megalea Timofeev et al. (1976)Polysphaeroides contextus Nagovitsin et al. (2008)Polytrichoides lineatus Semikhatov et al. (2000)Prolatoforma aculeata (=T. aimika)Pterospermopsimorpha granulataTrachyhystrichosphaera aimikaT. cyathophora (=T. aimika)T. megalia (=T. aimika)T. membranacea (=T. aimika)T. stricta (=T. aimika)T. vidalii (=T. aimika)

800–900 Wynniatt Fm. Cymatiosphaeroides Butterfield and Rainbird (1998)(Arctic Canada) Germinosphaera

leiosphaeridsPolytrichoidesSiphonophycusTrachyhystrichosphaera aimika

Pre-Cryogenian Neoproterozoic Lone Land Fm. leiosphaerids Samuelsson and Butterfield (2001)Blackwater Lake G-52 drill core Navifusa majensis(Franklin Mountains, northwestern Canada) Ostiana microcystis

Siphonophycus robustumS. typicumTrachyhystrichosphaera aimika


Fig. 15. Measurements of Trachyhystrichosphaera aimika and T. botula. (A) Cross-plot and frequency distribution of vesicle diameter (geometric mean of maximum andm iamea hosphp . aimik

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s

inimum dimensions for each specimen), number of processes, and process basal dimika. (B) Frequency distribution of the vesicle length/width ratios of Trachyhystricool distribution that justifies the distinction of the two species. (C) Cross-plot of T

Description: Flattened vesicles elliptical in shape, 195–365 �mn length (average = 284 �m; n = 22), 81–162 �m in width (aver-ge = 112; n = 22), and 2.0–4.2 in length/width ratio. Processeseteromorphic, cylindrical or conical, 1.7–8 �m in diameter, and
–39 �m in length. An outer membrane and an irregularly shaped
nternal body may be present.Remarks: A few specimens in our collection have poorly pre-

erved processes (Figs. 11A, G, 12A) and ruptured vesicles (Fig. 11F).

ter (measured on the thickest process of each specimen) of Trachyhystrichosphaeraaera aimika and T. botula from the Liulaobei Formation. Note a natural break in thea vesicle diameter and inner body diameter (correlation coefficient R = 0.52).

Despite so, they are easily recognizable as Trachyhystrichosphaerabotula n. sp. The new species is similar to T. aimika in process mor-phology and variability, but it is different from T. aimika and T.polaris in its tomaculate rather than spheroidal vesicle. We adopt
a vesicle length/width ratio of 2 as a cut-off between T. botulaand T. aimika, guided by a break in the pooled distribution of thelength/width ratio of these two species (Fig. 15B). Considering theexistence of dyad vesicles of T. aimika, it is possible that T. botula

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ay represent an ontogenetic transitional form between monadsnd dyads of T. aimika; in other words, after reaching certain size,

spheroidal vesicle of T. aimika may become elongate (tomaculateesicle of T. botula) and then divide into two vesicles (dyads of T.imika). This is an interesting speculation that needs to be inves-igated with more specimens. At the present, however, we followhe principle of form taxonomy to distinguish T. aimika and T. botulaased on vesicle morphology.

Etymology: Species epithet derived from Latin botulus, with ref-rence to the sausage-shaped vesicle of the new species.

Incertae Sedis

enus Polytrichoides Hermann, 1974, emend. Hermann in Timofeev et al., 1976

Type species: Polytrichoides lineatus Hermann, 1974, emend. Her-ann in Timofeev et al., 1976

olytrichoides lineatus Hermann, 1974, emend. Hermann in Timofeev et al., 1976Figure 14

974 Polytrichoides lineatus Hermann, p. 7–8, pl. 6, figs. 3, 4.976 Polytrichoides lineatus Hermann; Timofeev et al., p. 37, pl. 14, fig. 7.985 Polytrichoides formosus Yin C., p. 109, pl. 4, fig. 8.985 Polytrichoides lineatus Hermann; Yin C., pl. 4, fig. 7.989 Polytrichoides lineatus Hermann; Jankauskas et al., p. 119–120, pl. 30,figs. 5a, 5b 6, 7.

990 Polytrichoides lineatus Hermann; Hermann, pl. 9, figs. 8, 8a.991 Polytrichoides lineatus Hermann; Yin L., p. 263, pl. 4, fig. 11.991 Polytrichoides lineatus Hermann; Knoll et al., p. 563, figs. 4.3, 4.5.992b Polytrichoides lineatus Hermann; Zang and Walter, p. 315–316, pl.17, figs. A–E.

994 Polytrichoides lineatus Hermann; Yin and Sun, p. 102, figs. 5b, 6m.994 Polytrichoides lineatus Hermann; Hofmann and Jackson, p. 12–13,figs. 11.13–11.17.

Material: More than 36 specimens isolated from shale sample1-LLB-A.

Description: Bundled filaments with one or two capitate ends.ach filament may represent the cylindrical sheath of uniseriateyanobacteria, but a common sheath surrounding the entire bun-le is absent. Filaments sometimes spread out or disaggregated athe ends of bundles. Septate filaments are occasionally preservedFig. 14A) and they are interpreted as cellular trichomes or theirmpressions within individual sheaths.

Bundles 154–700 �m in length (average = 404; n = 31) and8–75 �m in width (average = 39 �m; n = 31), with each bun-le consisting of 4–27 filaments (average = 12; n = 25). Filaments–9 �m in diameter (average = 7 �m; n = 110), and cells in tri-homes ∼6 �m in length.

Remarks: Bundled filaments are common among modernyanobacteria. Some of them such as Schizothrix and Micro-oleus have a common sheath surrounding the bundled filaments,hereas others such as Aphanizomenon and Trichodesmium areaked multi-trichomous cyanobacteria without a common sheathLee and Golubic, 1998). The absence of a common sheath inolytrichoides lineatus suggests a comparison with Aphanizomenonnd Trichodesmium, although Hermann (1974) and Timofeev et al.1976) compared Polytrichoides lineatus with Microcoleus chthono-lastes. It is possible that the absence of a common sheath in P.

ineatus may be due to taphonomic loss. However, it has been shownxperimentally that cyanobacterial sheaths are more resistant toegradation than cellular trichomes (Bartley, 1996). Thus, the con-istent absence of a common sheath around the bundled filamentsn many P. lineatus populations suggests that it is a biological fea-ure.

Occurrence: Early Neoproterozoic Liulaobei Formation, Huainan
roup, North China (Yin and Sun, 1994; Zang and Walter,992b); Mesoproterozoic Bylot Supergroup, Baffin Island,anada (Hofmann and Jackson, 1994); Early Neoproterozoicraken Conglomerate, Spitsbergen (Knoll et al., 1991); Early
rch 236 (2013) 157– 181

Neoproterozoic Mirojedikha Formation, Siberia (Hermann,1974).

Genus Siphonophycus Schopf, 1968, emend. Knoll et al., 1991

Type species: Siphonophycus kestron Schopf, 1968.

Siphonophycus gigas n. sp.Figure 13I and N

1999 Siphonophycus sp.; Buick and Knoll, p. 761–762, fig. 6.1, 6.5.

Holotype: The specimen illustrated in Fig. 13I is designated asthe holotype; Nanjing Institute of Geology and Palaeontology, spec-imen 11-LLB-A-47-2.


Material: Three specimens from shales of Liulaobei Formation.Diagnosis: A species of Siphonophycus with a diameter of

64–128 �m.Description: Flattened, unbranched, nonseptate, tubular fila-

ments that are often deformed, twisted, or folded. Filaments73–102 �m in diameter (average = 85; n = 3) and up to 1072 �min length.

Remarks: Siphonophycus gigas n. sp. can be distinguishedfrom other Siphonophycus species by its large size. According toButterfield et al. (1994) and Buick and Knoll (1999), S. thulenemahas a diameter of 0.5 �m, S. septatum 1–2 �m, S. robustum 2–4 �m,S. typicum 4–8 �m, S. kestron 8–16 �m, S. solidum 16–32 �m, andS. punctatum 32–64 �m, all smaller than S. gigas (64–128 �m indiameter). The specimen illustrated in Fig. 13K may be a stronglydeformed and twisted tubular fossil, and it could also be identifiedas S. gigas given its size.

Etymology: Species epithet derived from Latin gigas, with refer-ence to the large size of this species.

6. Biostratigraphic implications

The organic-walled microfossil assemblage of the Liulaobei For-mation is characterized by abundant sphaeromorphs and filaments,with a relatively low diversity of acanthomorphs (although a mod-erate abundance of Trachyhystrichosphaera aimika). Overall, thisassemblage is distinct from well-known Ediacaran acritarch assem-blages dominated by diverse acanthomorphs (Grey, 2005; Liu et al.,in press; Moczydłowska, 2005; Moczydłowska and Nagovitsin,2012; Sergeev et al., 2011; Vorob’eva et al., 2009b; Xiao et al.,in press; Zhang et al., 1998), but similar to Proterozoic assem-blages from the Khajpakh, Mirojedikha and Lakhanda formations inSiberia (Hermann, 1990; Jankauskas et al., 1989; Pjatiletov, 1988;Timofeev et al., 1976; Vidal et al., 1993), the Karatau Group inthe Urals (Jankauskas et al., 1989), the Fifteenmile Group, Black-water Lake G-52 drill core, and Wynniatt Formation in northernCanada (Allison and Awramik, 1989; Butterfield and Rainbird,1998; Samuelsson and Butterfield, 2001), the Sirbu Shale Forma-tion in central India (Srivastava, 2009), the Svanbergfjellet andDraken Conglomerate formations in Spitsbergen (Butterfield et al.,1994; Knoll et al., 1991), the Ryssö and Hunnberg formations inSvalbard (Knoll, 1984; Knoll and Calder, 1983), and the upperAlinya Formation in South Australia (Zang, 1995) (Table 1). On thebasis of available geochronological data and stratigraphic correla-tion, these assemblages are of pre-Cryogenian Neoproterozoic age.The only possible exception is the Lakhanda Formation, which is
intruded by 1005 ± 4 Ma and 974 ± 7 Ma sills (baddeleyite U–Pbages; Rainbird et al., 1998) and gives a Pb–Pb isochron age of1025 ± 40 Ma (Semikhatov et al., 2000); thus the Lakhanda For-mation may straddle right at the Mesoproterozoic-Neoproterozoic

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oundary as defined by the Global Standard Stratigraphic AgeGSSA).

The comparison of the Liulaobei assemblage with otherre-Cryogenian Neoproterozoic assemblages suggests that thecanthomorph Trachyhystrichosphaera and particularly T. aimikaay be a useful index fossil to define, subdivide, and corre-

ate the early Neoproterozoic Era using the concept of Globaloundary Stratotype Section and Point (GSSP). Although thereere several reports of Trachyhystrichosphaera from Ediacaran

uccessions (Awramik et al., 1985; Yin et al., 2007; Zang andalter, 1992a), all of these have been questioned (Butterfield

t al., 1994). For example, various Ediacaran Trachyhystrichosphaerapecies from the Amadeus Basin of central Australia (Zang and

alter, 1992a) have been subsequently transferred to the gen-ra Appendisphaera, Gyalosphaeridium, and Knollisphaeridium (Grey,005). Similarly, the Trachyhystrichosphaera-like specimen fromhe Ediacaran Doushantuo Formation in South China (Awramikt al., 1985) has been subsequently reassigned to Tianzhushaniapinosa (Zhang et al., 1998). Although Yin C. and colleagues (Yin,001; Yin et al., 2001) have suggested that the Ediacaran speciesianzhushania spinosa is somewhat similar to Trachyhystrichos-haera vidalii (which is here considered as a junior synonym of T.imika following Butterfield et al., 1994), it is important to pointut that T. spinosa has much more abundant and more uniformrocesses than T. vidalii. Thus, there have been no reliable reportsf Trachyhystrichosphaera or T. aimika in Ediacaran successions.nstead, as shown in Table 1, all reliable reports of T. aimika comerom pre-Cyogenian Neoproterozoic rocks, with a possible excep-ion of the Lakhanda Formation which could be either earliesteoproterozoic or latest Mesoproterozoic in age. Revised strati-raphic correlation suggests that the occurrence of T. aimika and. vidalii (=T. aimika) in the upper Fifteenmile Group, Yukon Terri-ory, northwestern Canada, is constrained between 811.5 Ma and17.4 Ma (Allison and Awramik, 1989; Macdonald et al., 2010a,b,011). These age constraints, when considered together with thebsence of Trachyhystrichosphaera in any Ediacaran or Cryogenianuccessions (Huntley et al., 2006; Knoll et al., 2006), suggest that theeographically widespread acanthomorph taxa Trachyhystrichos-haera and T. aimika are potential index fossils to define, subdivide,nd correlate the Tonian System (or pre-Cryogenian Neoprotero-oic rocks) using the concept of GSSP.

The paleontological similarities between the Liulaobei assem-lage and other pre-Cryogenian Neoproterozoic assemblages alsouggest that the Liulaobei Formation is more likely pre-Cryogenianeoproterozoic (Cao, 2000; Cao et al., 1989) than Cryogenian-diacaran in age (Xing, 1989; Xing et al., 1996). A pre-Cryogenianeoproterozoic age assessment for the Liulaobei Formation is alsoonsistent with other paleontological data. In addition to Tra-hyhystrichosphaera and T. aimika, the Liulaobei Formation alsoontains abundant leiosphaerids, Chuaria, Tawuia, possible vase-haped microfossils, Cymatiosphaera, Trachysphaeridium, Satka, andimia (Wang et al., 1984; Yin, 1985; Zang and Walter, 1992b).lthough not age diagnostic by themselves, many of these fossilsre common elements in early Neoproterozoic successions else-here (Hofmann and Aitken, 1979; Hofmann and Jackson, 1994;

orter et al., 2003; Sergeev, 1999).

. Conclusions

The organic-walled microfossil assemblage from the Liu-aobei Formation is dominated by sphaeromorphic acritarchs
nd filaments, with relatively few acanthomorphic taxa includ-ng Trachyhystrichosphaera aimika, T. botula n. sp., and Eoty-otopalla? grandis n. sp. Comparison with other microfossilssemblages (Table 1) shows that the Liulaobei assemblage is likely
rch 236 (2013) 157– 181 179

pre-Cryogenian Neoproterozoic in age. In particular, available evi-dence indicates that the genus Trachyhystrichosphaera and its typespecies T. aimika occur in pre-Cryogenian Neoproterozoic succes-sions and they can be important index fossils for the definition ofthe base of the Neoproterozoic and for the biostratigraphic subdivi-sion and correlation of early Neoproterozoic rocks using the GSSPconcept. Based on the presence of Trachyhystrichosphaera aimika,the Liulaobei Formation is considered pre-Cryogenian Neoprotero-zoic in age, rather than Ediacaran or Cryogenian (Xing, 1989). Thisassessment is also consistent with other less decisive evidence suchas the presence of Chuaria, Tawuia, possible vase-shaped microfos-sils, Cymatiosphaera, Trachysphaeridium, Satka, and Simia.

Acknowledgements

This work was supported by Chinese Academy of Sciences(KZZD-EW-02 and KZCX2-YW-153), Chinese Ministry of Scienceand Technology (2013CB835000), National Natural Science Foun-dation of China (41272011, 41130209), and US National ScienceFoundation (EAR-1250800). We thank Lei Chen for field work assis-tance, Fengbao Huang and Jinlong Wang for sample preparation,Yongqiang Mao and Dr. James D. Schiffbauer for SEM photography,Dr. Leiming Yin and Dr. Chuanming Zhou for taxonomic discussion,and two anonymous reviewers for constructive comments.

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Organic-walled microfossils from the early Neoproterozoic Liulaobei Formation in the Huainan region...

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