Taxonomic review of some Ediacaran acritarchs from the Siberian Platform

Precambrian Research 136 (2005) 283–307

Taxonomic review of some Ediacaran acritarchs from the Siberian Platform Małgorzata Moczydłowska∗ Uppsala University, Department of Earth Sciences, Palaeobiology, Norbyv¨agen 22, 752 36 Uppsala, Sweden Received 13 July 2004; received in revised form 1 December 2004; accepted 10 December 2004

Abstract The Ediacaran radiation of phytoplankton (acritarchs) was one of the most conspicuous biotic events in the Precambrian, including the diversification of the metazoa, and resulted in the appearance of tens of new species with complex morphology and large dimensions. This association of marine autotrophic microbiota lasted for less than ca. 20 million years (Myr), postdating the Snowball Earth episode and preceding the diversification of bilaterian metazoans, and became extinct before the dawn of Cambrian. Several taxa recognized from the Siberian Platform were among the first records of Ediacaran-age acritarchs and these are taxonomically revised here, based on observations of new material and re-examination of the type collection. The diagnoses of the genus Appendisphaera and its originally described species A. grandis, A. fragilis and A. tenuis are emended. The genera Cavaspina and Tanarium, and their species C. acuminata, C. basiconica, T. conoideum, T. irregulare and T. tuberosum, are retained. This taxonomic re-evaluation follows comparison with other Ediacaran species and taxonomic concepts to accommodate the morphologic variety of acritarchs from China and Australia published recently. The synonymy proposed here and the recognition of certain morphologic taxa is intended to simplify the identification and to eliminate some superfluous taxa. The subsequent records of the species described from Siberia in China and Australia, their consistent stratigraphic ranges and wide geographic distribution make these species good index fossils for international correlation. The acritarch-based zonation proposed for a portion of the recently ratified Ediacaran System in Australia also has potential for the global biostratigraphic standard so much needed for the new system. © 2004 Elsevier B.V. All rights reserved. Keywords: Acritarchs; Taxonomy; Phytoplankton; Ediacaran; Neoproterozoic; Siberia

1. Introduction The Ediacaran acritarchs are a group of lavishly ornamented and diverse organic-walled microfossils, ∗

Fax: +46 18 4712749. E-mail address: [email protected].

0301-9268/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.precamres.2004.12.001

recorded approximately in a period of time between 580 and 550 Ma (million years ago (Ma); Knoll and Walter, 1992; Grey, 2005) and representing one of the most conspicuous radiations of phytoplankton, probable green algae. Records extend across the Siberian Platform, China and Australia (Pyatiletov, 1980; Pyatiletov and Rudavskaya, 1985; Rudavskaya

284

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

and Vasileva, 1989; Kolosova, 1991; Moczydłowska et al., 1993; Vidal et al., 1993; Yin, 1985, 1986, 1987; Zhang, 1984; Zhang et al., 1998; Zang, 1992; Zang and Walter, 1992a,b; Yuan and Hofmann, 1998; Grey, 1998, 2005). They originated and spread worldwide rapidly, pre-dating the appearance of Ediacara-type bilaterian metazoans, and became extinct before the end of Neoproterozoic. The causes of their diversification and extinction are not easy to explain but the events coincide within short time intervals with major global climatic and environmental changes. The radiation of Ediacaran acritarchs followed, with a time laps of ca. 10–20 Myr, the Varangerian/Marinoan glaciation, which was the final global stage of the Snowball Earth conditions. The Varangerian/Marinoan glaciation was not the last in the ice-ages of Neoproterozoic and some younger diamictites are glaciogenic as interpreted in China and elsewhere (Xiao et al., 2004), but this was a major episode (Knoll et al., 2004a, 2004b), while the following, such as perhaps the Hankalchough glaciation in North China, was probable more restricted and had less devastating effect on the biosphere. The acritarch radiation was coeval with the ensuing warming and establishing green house conditions, oxygenation of the ocean, recovery of the global gyres and current circulation. The sequence of these changes was interrupted, probably with a profound environmental catastrophic effect, by the Acraman bolide impact ca. 580 Ma (Williams, 1994; Williams and Wallace, 2003; Grey et al., 2003). A terminal Neoproterozoic extinction eliminated most of the photosynthetic marine biota, including cyanobacteria and unicellular and thallophytic algae that are well known from earlier Neoproterozoic fossil records, as well as soft-bodied Ediacaratype metazoans and some other enigmatic multicellular organisms. This is, however, even less clearly understood because there are no evident and directly related environmental changes at the time that may trigger the biotic extinction. The anoxic event bound to the Precambrian–Cambrian transgression in some parts of the world and the extension of the water masses with low oxygen content onto the shelves and platforms surrounding the palaeocontinents, which were the most inhabitable marine ecosystems, may have contributed to the extinction, but there may be only one of several factors. The above-mentioned Hankalchough glaciation was suggested to cause the disappearance of complex acritarchs preserved in the Doushantuo Formation and

the subsequent radiation of macroscopic animals (Xiao et al., 2004). However, the timing of this glaciation is poorly constrained and only by means of lithological and geochemical correlations without a support of agediagnostic fossils. The only fossils in the succession, underlying the Hankalchough Formation, are uncertain vendotaenids in the Shuiquan Formation, whose stratigraphic range is post-Marinoan–Cambrian, and thus providing no more precise age estimation. The Ediacaran acritarchs are in general characterized by complex morphology and large dimensions, which are two to three times the order of magnitude of Phanerozoic specimens. The broad estimation of their diversity is approximately 100–120 species, based on the accounts of morphologic form-taxa (Vidal and Moczydłowska, 1997; Grey, 2005), but it may vary significantly depend on the taxonomic approach and concepts of the identification of species. Inevitably, their number may be under-or overestimated, in relation to the records. A consistent taxonomy is needed to assess more realistically (within feasible palaeontological reliability) the biodiversity of Ediacaran phytoplankton and to depict their morphologic innovations and adaptations to changing ecological conditions and interactions with the evolving metazoan consumers. From the point of view of establishing evolutionary trends among global biota and relationships between primary producers and heterotrophic consumers, Ediacaran acritarch diversity has a basic value for any further interpretation. Needless to say, agreement on identification of taxa regardless of preservation modes and taxonomic concepts would enable their application to biostratigraphy, and could be expected to be of value for the recently accepted terminal Neoproterozoic system, the Ediacaran System (Knoll, 2000; Knoll et al., 2004a, 2004b). The present contribution deals with taxonomic revision of microfossils derived from the Siberian Platform and intends to simplify their recognition and application to stratigraphy and palaeobiogeography. If this taxonomy is accepted, the number of Ediacaran species would be slightly reduced, eliminating some synonymous and superfluous taxa. The distribution of a few species is better constrained, discerning cosmopolitan and restricted species, and may be useful for interregional correlation. The biostratigraphic correlation of the Ediacaran strata containing the species studied is inferred between Australia, Siberia and South China, and

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

the chronologic sequence of environmental and biotic events during the Ediacaran Period is briefly outlined.

2. Material and preservation Microfossils have been extracted from thin-bedded, kerogenous mudstones and shales by standard palynological maceration method and examined in permanent strew slides under transmitted light microscope with interference contrast (Leitz Wetzlar Dialux 20) and high definition real-time 3D microscope (Edge R400). The material is from the original type collection from the Siberian Platform studied by Moczydłowska et al. (1993), and is housed in the palaeontological collections of the All Russian Petroleum Scientific Research Exploration Institute, St. Petersburg, signed with the acronym VNIGRI, and in the Museum of Evolution, Uppsala University (former Paleontologiska Museet Uppsala), with the acronym PMU. The specimens in the present report are newly studied and the observations have never been published before. Moczydłowska et al. (1993) provided detailed information on the derivation of samples, location of boreholes and geological framework of the rock successions. Briefly, samples cut from drill-cores are from several formations underlying the Siberian Platform, which represent shallow marine, siliciclastic and carbonate Neoproterozoic to Lower Cambrian successions. The successions are un-metamorphosed, with a low grade of thermal alteration, un-deformed and almost horizontally underlying, but containing several unconformities. They belong to a single transgressive–regressive depositional cycle on a carbonate platform. The relative Cambrian age of the strata is established by means of diagnostic small shelly fossils, whereas the late Vendian, equivalent to the Ediacaran age of the underlying rocks is documented by acritarchs and cyanobacteria (Grausman and Zhernovskij, 1989; Rudavskaya and Vasileva, 1989; Moczydłowska et al., 1993). The preservation of organic-walled microfossils is excellent or good, and many specimens are threedimensionally preserved or only slightly compressed, displaying a light colouration of organic matter. Some corrosion or compaction folds are observed on the vesicle wall and some loss of processes or deformation in some specimens. The specimens are not affected by

285

impregnation by migrating mineral solutions and diagenetic precipitation as are those preserved in cherts, phosporites and silicified carbonates. Because of this condition, the organic vesicles or processes are not distorted by penetrating and precipitating solutions (“inflated”, “infilled”) and show the original layering of the wall (single-layered walls). By contrast, some of the layers interpreted to be outer envelopes or membranes surrounding the processes or double-layered walls in certain taxa examined in petrographic thinsections from diagenetically altered rocks in China may be artefacts produced by precipitation of mineral solutions and not original permineralized organic membranes (e.g., Asterocapsoides, Pustulisphaera, in Zhang et al., 1998).

3. Taxonomic review New records of late Neoproterozoic acritarchs from China and Australia provided in recent years a great variety of morphotypes preserved in different taphonomic modes (permineralized in China and freely extracted from rock matrix in Australia), and promoted developing new concepts on their subdivisions into form-taxa (Zang and Walter, 1992b; Zhang et al., 1998; Grey, 1998, 2005). A study of additional microfossils from the Siberian Platform in Yakutia, from which several species were recognized as being among the first known ornamented Ediacaran-age acritarchs (Pyatiletov, 1980; Pyatiletov and Rudavskaya, 1985; Rudavskaya and Vasileva, 1989; Moczydłowska et al., 1993), and stimulated the present taxonomic reevaluation. Zang and Walter (1992b) presented the first monographic treatment of Ediacaran acritarchs from the Amadeus Basin in Australia. Their achievements are comprehensive and fundamental and will form the basis for any further studies even though some of their taxonomic assignments may be challenged. Zhang et al. (1998) revised the taxonomic assignment of several Neoproterozoic acritarchs to accommodate microfossils from the Doushantuo Formation in China and, in addition to establishing some new and emending other genera, they transferred several species into certain Phanerozoic genera. They considered Phanerozoic form-genera to be entirely convergent morphotypes that arosed after the terminal

286

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

Proterozoic extinction of phytoplankton without having any direct phylogenetic links. Although used only as a means of morphologic resemblance the choice of the taxa, such as Goniosphaeridium, Micrhystridium and Filisphaeridium, conflict with their taxonomic status established in previous re-evaluations. The genus Goniosphaeridium (Eisenack, 1969, emend. Turner, 1984) is an invalid taxon, being redundant and a junior synonym of Polygonium Vavrdov´a (Le H´eriss´e, 1989; Albani, 1989; Fensome et al., 1990; Moczydłowska and Crimes, 1995; Moczydłowska, 1998). The genus Micrhystridium (Deflandre, 1937) has no application to any of the Neoproterozoic or Cambrian microfossils displaying a single-layered vesicle wall, although formerly attributed to it, because this genus has been diagnosed for microfossils with double-layered wall which derived from Mesozoic (see discussion by Moczydłowska, 1991, pp. 45–46; Moczydłowska, 1998, pp. 41–42). The diagnostic feature of the genus Filisphaeridium (Staplin et al., 1965) are differentiated terminations of processes, which are not observed on the Doushantuo microfossils studied by Zhang et al. (1998). The emendation of this genus by Sarjeant and Stancliffe (1994), which incorporated the presence of simple tips and which was followed by Zhang et al. (1998), is difficult to accept because it makes the genus “polymorphic” and prevents its recognition objectively by any morphologic criterion (see comments by Moczydłowska, 1998, p. 42–43). The Neoproterozic genus Meghystrichosphaeridium retained by Zhang et al. (1998), after the designation of a new type species, is also an invalid taxon because its originally designated type species M. wenganensis was placed in synonymy with Asterocapsoides sinensis, and thus the generic name is no longer available (Grey, 2005; see below). Grey (2005) re-evaluated the taxonomic assignment of Ediacaran acritarchs from Australia and described numerous new species, based on extensive new materials and re-study of the microfossil collection of Zang and Walter (1992b). This work led to a detailed and thorough revision of previous taxonomy and proposal of new concepts in the synonymy of many taxa. The above-mentioned and subsequent contributions changed considerably the assignment of microfossils reported earlier from the Siberian Platform. The present description and emendation deals only with taxa recognized from this region and attributed to the genera Appendisphaera, Cavaspina and Tanarium

(Moczydłowska et al., 1993), after observations on new specimens from the type collection and considering the development of recent taxonomic subdivisions. 3.1. Genus Appendisphaera The genus Appendisphaera (Moczydłowska et al., 1993) has been diagnosed for microfossils with medium to large spherical vesicles bearing relatively long, simple, solid and evenly distributed processes. Three new species established in the type collection from the Siberian Platform, A. grandis, A. fragilis and A. tenuis, display collectively a vesicle diameter in a range of 60–150 ␮m, and a process length of 7–33 ␮m. The length of processes varies between 15 and 25% of the vesicle diameter in A. grandis and A. fragilis, and 6–8% in A. tenuis. The species A.? tabifica (Moczydłowska et al., 1993) was tentatively referred to the genus because it has processes similar in shape but longer (40–46 ␮m; N = 1), which coalesce and form a membrane in the equatorial zone, differing in this way from other species of the genus. At present, only one specimen with such morphology is known and this prevents any further interpretation about whether the nature of the membrane is a persistent trait or a possible taphonomic artefact. Zhang et al. (1998) rejected this species together with A. fragilis, assuming that they present features of diagenetic origin. The studied specimens are, however, quite well preserved and not compressed and provide perfectly adequate material for observations. The circumscribed diagnostic features of Appendisphaera were the solid nature of the processes and their substantial length in proportion to the vesicle diameter, distinguishing it from Ericiasphaera (Vidal, 1990), which has also solid but very short processes. The length of processes in Ericiasphaera is 6–10 ␮m and only 2.0–3.5% of the vesicle diameter, which is approximately 280 ␮m measured on a single available specimen (Vidal, 1990). Previous observations on the process morphology in Appendisphaera under transmitted light microscopy led to the conclusion that the processes were solid (Moczydłowska et al., 1993). Because the processes are thin, slender and densely distributed in the type species, although less numerous in two other species, it was difficult to determine whether an internal cavity was present. Recent examinations using a higher resolution of transmitted light and 3D

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

microscopic images and studies of additional wellpreserved specimens from the type collection, as well as the re-examination of the holotypes of described species, revealed that the processes of Appendisphaera are hollow and freely communicate with the vesicle cavity. The processes have a very small cross-section diameter, and therefore their lumen may be obscured making an apparent appearance of being solid. It is also difficult to see the connection between the process bases and vesicle wall in most cases because the processes are abundant and tightly distributed. These new observations and comparative studies on variously preserved specimens and morphotypes of the Neoproterozoic acritarchs from Australia and China has led to a redefinition of Appendisphaera (see under Palaeontology). The diagnoses of the genus and the three species originally recognized in the type collection, A. grandis, A. tenuis and A. fragilis are emended, whereas A.? tabifica, remains tentatively assigned to the emended genus because of the lack of additional specimens for study. New species of Appendisphaera recognized by Grey (2005) are believed, after the author’s own examination of the Australian collection (in the year 2002), to have hollow processes with free connection to the vesicle cavity and pertain to the herein emended genus. The present emendation does not make Appendisphaera synonymous with other Neoproterozoic genera having hollow processes freely communicating with vesicle cavity. The combination of the shape of processes, their relative length and pattern of distribution in Appendisphaera (Moczydłowska et al., 1993, emend.) is unique and distinctive from other genera, such as Briareus, Cavaspina, Papillomembrana, Trachyhystrichosphaera, Tanarium, Vidalia, and also Echinosphaeridium. The diagnostic morphological features and dimensions of these genera and their species are compared and shown in Figs. 1 and 2. Zhang et al. (1998) considered Appendisphaera (Moczydłowska et al., 1993), to be a junior synonym of Ericiasphaera (Vidal, 1990), because both genera have been diagnosed as having solid processes. This might be true if only the original diagnosis of Appendisphaera is considered and if the relative length of processes and their proportion to diameter of vesicle are not accepted as diagnostic characters. Appendisphaera was assumed to be a distinctive genus because the very short and conical processes in Ericiasphaera contrasted

287

with those relatively long, thin cylindrical or ciliate in Appendisphaera, and because of a sharply differing ratio between the length of processes and the diameter of vesicle (Moczydłowska et al., 1993). Zhang et al. (1998) pointed out that the length of processes in A. tenuis (Moczydłowska et al., 1993), and in E. spjeldnaesii (Vidal, 1990), are within the same size range, but they ignored the fact that the vesicle diameter of E. spjeldnaesii is twice as large as that of A. tenuis, making the proportions substantially different. They also misquoted the original diagnosis of Vidal (1990) by stating that E. spjeldnaesii has cylindrical or conical processes. However, according to the original species diagnosis, E. spjeldnaesii has exclusively conical processes. Their suggested synonymy of A. tenuis as a junior taxon of E. spjeldnaesii is not consistent with regard to the shape of processes in A. tenuis, which are cylindrical with minute and slightly conical bases, and which have a smaller vesicle diameter. Zhang et al. (1998) stated that it was uncertain whether the processes of Appendisphaera grandis (Moczydłowska et al., 1993), were solid or hollow. Moreover, they suggested its transfer to either Ericiasphaera (if solid) or “Meghystrichosphaeridium (Zhang et al., 1998; non Chen and Liu, 1986)” (if hollow). This uncertainty is here clarified by presenting enlarged photomicrographs of process details to show the hollow processes in Appendisphaera (Figs. 2 and 3). Because “Meghystrichosphaeridium” is an invalid taxon (Grey, 2005, and see below), it is impossible to place Appendisphaeraas emended herein into this genus. Grey (2005) retained the genus Appendisphaera (Moczydłowska et al., 1993), and emended its diagnosis by adding that processes are abundant, densely crowded, predominantly ciliate, very thin, with only a minor expansion near the base, may taper near the tips, and are solid or nearly solid. This statement resulted from her examination of the type collection from Siberia stored in Uppsala and observations that some processes were probably hollow, in contrast to those solid in Ericiasphaera. The part of the emendation to the genus by Grey (2005) relating to solid processes is not followed here because subsequent detailed study has clearly demonstrated hollow nature of processes. Other features incorporated into her diagnosis are accepted. Grey (2005) retained within the genus A. grandis, A. tenuis and A.? tabifica, whereas she transferred A. fragilis to Ericiasphaera as a new combination.

288

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

Fig. 1. The identification key to some Ediacaran acritarch genera and selected species with single-walled vesicle and hollow processes, showing the diagnostic morphological features and dimensions. The symbol Ø stands for the vesicle diameter and p. for the process length.

Study of abundant and more diverse collection of Australian specimens attributed to Appendisphaera led to the description of several new species (Grey, 2005), which may need to be re-diagnosed under the emended description of Appendisphaera to recognize the hollow nature of the processes. 3.2. Genus Cavaspina The genus Cavaspina (Moczydłowska et al., 1993) was recognized for microfossils consisting of medium to large spherical vesicles bearing short and simple, hollow processes that freely communicate with the vesicle cavity. It was based on very well preserved al-

though not abundant specimens. The vesicle diameter measured on 15 non- or slightly compressed specimens is 50–133 ␮m (Moczydłowska et al., 1993). Two species were originally described, Cavaspina acuminata (Kolosova, 1991; Moczydłowska et al., 1993), and C. basiconica (Moczydłowska et al., 1993). Subsequently, Zhang et al. (1998) and Grey (2005) rejected the genus and considered it synonymous in parts with other genera by transferring the two species as new combinations. Zhang et al. (1998) transferred Cavaspina acuminata (Kolosova, 1991; Moczydłowska et al., 1993), the type species of Cavaspina, to as Goniosphaeridium acuminatum (Kolosova) new combination and, in

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

289

Fig. 2. The identification key to some Ediacaran acritarch taxa with double-walled vesicle and hollow processes and this with solid processes, showing the diagnostic morphological features and dimensions. The symbol Ø stands for the vesicle diameter and p. for the process length.

effect, rejected the genus. Because Goniosphaeridium is an invalid taxon (Moczydłowska, 1998; see above), this proposal is inappropriate and Cavaspina remains a valid genus. Zhang et al. (1998) included C. basiconica (Moczydłowska et al., 1993) into their synonymy of Meghystrichosphaeridium perfectum (Kolosova) new combination. This transfer could not be followed since the genus Meghystrichosphaeridium Zhang, Yin, Xiao and Knoll non Chen and Liu, 1986 (ibidem, p. 32) is also an invalid taxon. Zhang et al. (1998; p. 24, 34) proposed retention of the name of the latter genus and designated its retained species M. chadianensis (Chen and Liu) new combination, emend., as the type species. This is in contradiction to the fact that they accepted the originally designated type species of Meghystrichosphaeridium, M. wenganensis (Chen and Liu, 1986), to be a junior synonym of Asterocapsoides sinensis (Yin and Li, 1978) emend. Such procedure is not in accord with the rules of I.C.B.N. and the genus “Meghystrichosphaeridium” must be rejected, its name could not be retained nor genus restored with newly chosen type species. In consequence, “Meghystrichosphaeridium” became a junior synonym of Asterocapsoides (Grey, 2005). In the context of this taxonomic puzzle, the authors’ rhetoric (Zhang et al., 1998, p. 34) was that “As Solomon recognized, Gordian knots require solutions appropriate to the problem”. The Gordian knot was, however, cut by Alexander the Great somewhat later than Solomon could advise on the matter.

Nor could the priority of the specific epithet “perfectum” be recognized over “basiconica” as proposed in the synonymy by Zhang et al. (1998), in which Cavaspina basiconica (Moczydłowska et al., 1993) was treated as a junior synonym of “Tanarium perfectum (Kolosova, 1991)” chosen by them as the nominal species of a new combination “Meghystrichosphaeridium perfectum (Kolosova)”. The species “Tanarium perfectum (Kolosova, 1991)” is invalid because Kolosova (1991), describing the new genus Tanarium, has neither provided a diagnosis for “T. perfectum” nor assigned it to a new species. She referred to it as “Tanarium perfectum (Kolosova)” and in the figure caption of photomicrograph referred to it as a holotype. In the same way, another invalid species, “Tanarium densum (Kolosova)” was illustrated and referred to as a holotype in the figure caption, but without a description, diagnosis or indication of being a new species (Kolosova, 1991). The lack of descriptions means that both taxa are nomina nuda. “Tanarium perfectum” and “T. densum”, mentioned by Kolosova (1991) as supposedly new species, were described in a manuscript by Kolosova (1990) but never published. This manuscript was deposited in VINITI (All-Union Institute of Scientific and Technical Information) in Moscow in 1990 as an internal report no. 4997 of the USSR, Academy of Sciences. This is not a valid and distributed publication as required for formal taxonomic description under the I.C.B.N. Kolosova published formal descriptions of the

290

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

Fig. 3. Appendisphaera grandis (Moczydłowska et al., 1993, emend.) (A) Specimen VNIGRI.3758/2-G/42. Dyudan 291-0 borehole at a depth of 3414.3–3420.3 m. (B) Specimen VNIGRI.2128/2-X/35. Talakan 823 borehole, 1534.0–1539.0 m, Khamaka Formation. (C) Specimen VNIGRI.3758/3-N/13/3. Dyudan 291-0 borehole, 3414.3–3420.3 m. (D) Specimen VNIGRI.3349/1-W/36. Nakyn 295-0 borehole, 3062.0–3068.0 m. Scale bar in D equals 50 ␮m for A, C and D; 30 ␮m for B. All specimens in this and following Figures derive from Yakutia, East Siberian Platform, and are of a Neoproterozoic, Ediacaran age. Photomicrographs were taken under a transmitted light microscope (Leitz Wetzlar Dialux 20) with interference contrast and immersion oil.

new genus Tanarium and its type species T. conoideum in 1991 but she unfortunately omitted the two other species. Because of these circumstances, specimens referred to “T. perfectum” or “Meghystrichosphaeridium perfectum” (Kolosova, 1991; Zhang et al., 1998) are considered here as conspecific with Cavaspina basiconica (Moczydłowska et al., 1993), the only validly published and having priority taxon. Grey (2005) included the genus Cavaspina (Moczydłowska et al., 1993) in part, as a junior synonym, into her emended genus Echinosphaeridium (Knoll, 1992), because she proposed a new combination for its type species as Echinosphaeridium acuminatum (Kolosova, 1991). In the emended diagnosis of

Echinosphaeridium, she stated that the vesicle is large and the echinate ornaments in shape of cones or spines are hollow and freely communicate with vesicle cavity. The intension of this emendation has been to remove the specific size requirements from the diagnosis by Knoll (1992) in which the diameter of vesicle had been determined to be above 200 ␮m for the genus and within a range of 200–650 ␮m for the type species Echinosphaeridium maximum (Yin, 1987; Knoll, 1992). It was also emphasized (Grey, 2005) that spines may exceed the length of 5 ␮m (diagnosed originally by Knoll, 1992 as being small up to 5 ␮m), in effect distinguishing the ornament from processes by smaller proportion to the diameter of vesicle. The size limit of the sculpture

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

elements of vesicle wall (or “ornamentation” in Grey’s nomenclature) in Phanerozoic acritarchs has never been and could not be arbitrary and strictly defined but it is rather considered in terms of the ratio between the length of sculpture elements to the diameter of vesicle, clearly contrasting in the proportions with processes being relatively longer. Accordingly, in the taxonomic scheme by Grey (2005), the genus Echinosphaeridium (Knoll, 1992, emend. Grey, 2005) has a large, echinate ornamented vesicle but not true processes. This characteristic is evident in two new species described, E. gravestockii (Grey, 2005) and E. triangulum (Grey, 2005), and is in accord with the type species E. maximum (Yin, 1987; Knoll, 1992). It does not, however, conform consistently with the synonymized species C. acuminata (Kolosova, 1991; Moczydłowska et al., 1993). The latter species has the diameter of vesicle in a range of 50–68 ␮m (Moczydłowska et al., 1993) or even 35–50 ␮m (Kolosova, 1991), being much smaller than Echinosphaeridium (above 200 ␮m according to Knoll, 1992, or by standard of Grey, 2005) or other Ediacaran acritarchs. The length of thorn-like processes in C. acuminata is 3–5 ␮m that in a proportion to the vesicle diameter constitutes 6–10% and could not be treated as the vesicle sculpture. The processes are also sparsely distributed contrasting with a dense “ornamentation” in Echinosphaeridium. The overall morphologic appearance of C. acuminata = Echinosphaeridium acuminatum (Kolosova, 1991) comb. nov. differs from any species included by Grey (2005) into the genus Echinosphaeridium. The species C. acuminata (Kolosova, 1991; Moczydłowska et al., 1993), and by default, the genus Cavaspina (Moczydłowska et al., 1993), of which it is the type species, is herein retained because of the presence of true processes defined by their length in proportion to the diameter of vesicle. Because of the rejection of Cavaspina as a valid genus, since its type species was considered a junior synonym of Echinosphaeridium, (Grey, 2005) transferred the other species, C. basiconica (Moczydłowska et al., 1993), to newly established genus Vidalia although not formally revised it as a new combination. As a result, Cavaspina was included in part also into Vidalia Grey (2005). The latter genus was diagnosed as Cavaspina with regard to the vesicle dimensions, being medium to large, and characteristics of processes, adding that the processes are heteromorphic, being

291

spinose, cylindrical or conical (also “cylindrical or conical” in Cavaspina) and that many processes are biform, having hollow conical bases and solid filamentous tips (Grey, 2005). Moczydłowska et al. (1993) diagnosed C. basiconica in the same sense of processes being biform, by having distinctive conical bases and thin tapering tips, and by showing graphically the variety of process morphology. The species has the diameter of vesicle ranging from 83 to 133 ␮m and the length of processes 7–16 ␮m, as observed on scarce Siberian collection (N = 6), and on one specimen of much smaller dimensions with diameter of vesicle 32 ␮m × 43 ␮m and length of processes 3–5 ␮m (Moczydłowska et al., 1993). Seemingly, the only difference between the new genus Vidalia and C. basiconica is larger vesicle range and length of processes in Vidalia measured on a larger collection, although overlapping with C. basiconica, but having similar ratio between length of processes and diameter of vesicle (mean proportion 1:10). The size limit (around 130 ␮m dividing the genera Cavaspina and Vidalia is again a taxonomic dilemma (both described as “medium to large vesicle”) and the question arises should any limit be strictly followed or what is the significance of the vesicle diameter variation? The commonly called “large” Ediacaran acritarchs, such as Echinosphaeridium, Ericiasphaera or Papillomembrana are in a range of 200–650 ␮m, whereas Appendisphaera, Cavaspina, Tanarium and Briareus are in average below 200 ␮m in diameter. Grey (2005) argued that the size classes reflect different populations and taxonomic entities and that C. basiconica = Vidalia basiconica is a distinct species from V. multispinulosa and V. pulchra, although having a similar morphology. By incorporating C. basiconica into a new genus Vidalia, this genus would embrace microfossils with a very wide range of vesicle diameter, from 83 to 450 ␮m. Accepting such size variation as less diagnostic and recognizing the biform character of processes as a major diagnostic trait, a new combination of C. basiconica within genus Vidalia could be agreeable. In this option, the genus Cavaspina would remain with only its type species (C. acuminata, with homomorphic, thorn-like processes). The second option is that by retaining the genus Cavaspina, the genus Vidalia may be treated as congenetic and its junior synonym. The overall morphologic characteristic of the latter genus is similar and

292

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

the vesicle diameter is also overlapping with that of Cavaspina. Accordingly, the new combination by Grey (2005) as Vidalia basiconica (Moczydłowska et al., 1993; Grey, 2005) would not be followed. Vidalia multispinulosa (Grey, 2005) conforms morphologically to the diagnosis of C. basiconica and differs only in larger dimensions of both the vesicle diameter and process length, which overlap, however, in their lower ranges. The ratio of the diameter of vesicle to length of processes is similar. The two species may be considered synonymous. Vidalia pulchra is not clearly biform, and thus may be re-combined as Cavaspina pulchra (Grey, 2005) new. comb. The third option is to retain both genera, Cavaspina and Vidalia, in which Cavaspina contains both species, C. acuminata and C. basiconica in their primary assignation, and Vidalia (with heteromorphic, biform processes and larger diameter of vesicle) contains the species V. multispinulosa and V. pulchra. This option is favoured here, however the re-examination of all concerned taxa is required and intended. 3.3. Genus Tanarium The genus Tanarium (Kolosova, 1991, emend. Moczydłowska et al., 1993) has been established for microfossils consisting of medium to large vesicles, spherical to sub-spherical, bearing large processes or protrusions (long and wide in cross-section diameter), heteromorphic, hollow and freely connected with the vesicle cavity. Processes or protrusions are conical or cylindrical, simple or occasionally divided, tapering or rounded distally (Moczydłowska et al., 1993). The ratio between length of processes and diameter of vesicle is generally high and in the primarily described species, T. conoideum, T. irregulare and T. tuberosum, it varies between 12 and 50%. The processes are relatively wide at the bases and also in their stem portions, and may become conical or tuberous. Morphologically and dimensionally heteromorphic processes may occur on a single specimen, including divided process tips seen on some specimens representing undoubtedly the type species T. conoideum (Kolosova, 1991, emend. Moczydłowska et al., 1993; text-fig 10D). The heteromorphic nature of the processes is expressed most clearly in T. irregulare and T. tuberosum, and Moczydłowska et al. (1993) (text-fig 12) summarized the variety of process morphology. Zhang et al. (1998), referring to the exam-

ination of the type collection by one of the authors, suggested that the heteromorphism in Tanarium is an artefact of preservation. This is not the case as seen on the original illustrations of type specimens and on other specimens reported here (Fig. 7). Two nomina nuda species of Tanarium from the Siberian Platform, “T. densum” and “T. perfectum”, were mentioned and illustrated by Kolosova (1991), but not formally described as new species (see above under Cavaspina). Specimens attributed to nomen nudum T. perfectum are considered here to be synonymous with Cavaspina basiconica, whereas those of nomen nudum T. densum may belong to Vidalia multispinulosa. Zhang et al. (1998) rejected the genus Tanarium because they transferred its species to other, allegedly senior synonymous genera, but Grey (2005) reviewed the taxonomy and retained the genus; she recognized several new species additional to those previously described. Zhang et al. (1998) considered the type species, T. conoideum (Kolosova, 1991, emend. Moczydłowska et al., 1993), to be a junior synonym of their Goniosphaeridium conoideum (Kolosova) new combination, and consequently rejected Tanarium as being a junior synonym of Goniosphaeridium. The genus Goniosphaeridium (Eisenack, 1969, emend. Kjellstr¨om, 1971, emend. Turner, 1984), is accepted by majority of researchers on Palaeozoic acritarchs, for which it has been established, as a redundant taxon and a junior synonym of Polygonium (Vavrdov´a, 1966; Le H´eriss´e, 1989; Albani, 1989; Fensome et al., 1990; Moczydłowska and Crimes, 1995; Moczydłowska, 1998; see above and under Cavaspina). Therefore, its retention for Neoproterozoic microfossils is inappropriate in the sense of taxonomic rules of I.C.B.N. and it would be biostratigraphically confusing, even if correctly used. Zhang et al. (1998) included the nomen nuda species “T. densum (Kolosova, 1991)” and “T. perfectum (Kolosova, 1991)” as new combinations into their re-defined genus “Meghystrichosphaeridium (Zhang et al. non Chen and Liu, 1986)”. This genus is, however, an invalid taxon (Grey, 2005; see above under Cavaspina), and its name is not available for new combinations. Zhang et al. (1998) treated another species of Tanarium, T. tuberosum (Moczydłowska et al., 1993), as a junior synonym of Asterocapsoides sinensis (Yin and Li, 1978) emended by them and being the type species of the nominal genus, which is

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

supposed to have membrane-like outer wall layer. The double-layered wall diagnosed for A. sinensis, and by default Asterocapsoides, has never been observed in T. tuberosum, neither as the obtusely conical processes among another characteristic features. The synonymy proposed by Zhang et al. (1998) is inappropriate to the observations on both taxa and Grey (2005) retained the species T. tuberosum (Moczydłowska et al., 1993). Grey (2005) emended Tanarium (Kolosova, 1991, emend. Moczydłowska et al., 1993), and incorporated into the diagnosis the fact that the parameters of processes and protrusions are various (additionally to the various shapes originally diagnosed), and that they are heteromorphic, randomly distributed with bases being separated, and their length usually above 20% of the vesicle diameter. This emendation enhanced the significance of variability of process morphology (heteromorphism), which has also been evident from the previous emendation and stated in remarks by Moczydłowska et al. (1993). On the other hand, the presence of branching processes among those non-branching ones observed in the same specimens was excluded as not enough common feature. The length of processes in usually more than 20% of the diameter of vesicle introduced by Grey (2005) into the genus diagnosis is in disagreement with the actual dimensions of the type species from the Siberian collection, in which the length of processes varies within a range of 12–50% of the diameter of vesicle (N = 6). The limited number of specimens may account for this size range, although confirmed by the present study, but it should not perhaps be defined in the diagnosis. The emendation by Grey (2005) does not change substantially the characteristic and variability of the processes or protrusions in Tanarium but it defines the narrower size range of process length, and therefore is not followed here. Grey (2005) retained all species of Tanarium described from the Siberian Platform and transferred by Zhang et al. (1998) to other genera as valid and separate taxa. She recognized several new species from Australia and proposed a new combination for Solisphaeridium ? araithecum (Tanarium araithecum) described by Zang and Walter (1992b), after taxonomic revision of their collection and based on new materials. In summary, there are 10 species in the genus making it one of the most morphologically diverse and common among Ediacaran acritarchs.

293

4. Palaeontology 4.1. Group Acritarcha (Evitt, 1963) Genus Appendisphaera (Moczydłowska et al., 1993) emended Type species. Appendisphaera grandis (Moczydłowska et al., 1993) emended; Yakutia, Siberian Platform, Nepa-Botuoba region, Zapad 742 borehole, Khamaka Formation, Neoproterozoic, Upper Vendian (Ediacaran; Moczydłowska et al., 1993). Synonymy Appendisphaera gen.nov.—Moczydłowska et al. (1993), pp. 500–503, text-figs 3 and 4. Pro parte Ericiasphaera (Vidal, 1990)—Zhang et al. (1998), pp. 26–28 (Appendisphaera, Moczydłowska et al., 1993). Appendisphaera (Moczydłowska et al., 1993; emend.)—Grey (2005). Pro parte Ericiasphaera (Vidal, 1990)—Grey (2005). [Appendisphaera fragilis = Ericiasphaera fragilis (Moczydłowska et al., 1993)—Grey (2005)]. Emended diagnosis: Organic-walled, acid-resistant microfossils consisting of medium to large circular to oval vesicle (originally spherical) bearing relatively long processes evenly distributed on the vesicle wall. The processes are simple, homomorphic, slim, cylindrical or ciliate with straight or slightly modified (widened) basal portions. Terminations of processes may taper, be rounded or blunt. The processes are hollow, although very narrow in cross-section diameter, and freely communicate with the vesicle cavity. The excystment structure, if present, is in a shape of circular pylome. Remarks: The proximal portions of processes may be slightly widened and form minute bases whereas their distal portions may taper to form sharp-pointed or rounded tips or be blunt, but not divided or flared. The processes, if not well preserved, may not always be clearly seen as hollow, because of a small cross-section diameter, and may appear as being thread-like. A circular opening (a possible pylome) with a diameter of 17 ␮m × 25 ␮m has been observed on a single specimen of the type species (Fig. 3B).

294

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

Grey (2005) described several new species attributed to Appendisphaera and emended the diagnosis of the genus, in which she stated that the processes are solid or “nearly solid”. An examination of Grey’s microfossil collection (in the year 2002) and holotypes of new species, together with a consideration of their state of preservation and comparison with the Siberian microfossils, incline the author to interpret the nature of processes in Australian specimens as being hollow. In new Appendisphaera anguina (Grey, 2005), the processes are clearly hollow although very thin indeed. This species differs from A. grandis (Moczydłowska et al., 1993), emended, by having less abundant, much longer (several folds) and flexible processes, which proportion to the vesicle diameter is also distinctly higher (40%). The vesicle diameter of A. anguina (N = 3) exceeds the dimensions of A. grandis but overlaps with it in some range. The Australian microfossils attributed to Appendisphaera are in overall dimensions larger and of various ratios of process length to vesicle diameter (Grey, 2005). Another new species, A. barbata (Grey, 2005), resembles very much A.? tabifica (Moczydłowska et al., 1993), by having dense and coalesced processes (that could be a morphologic feature although this is not certain), or by being welded into interstitial organic matter (preservation mode). Because of this appearance, it is difficult to depict the nature of the processes (solid or hollow), and therefore to transfer it to as emended herein Appendisphaera. The species A. barbata is left, similarly like A.? tabifica, for further taxonomic evaluation if better preserved specimens are recovered. The nature of processes in a new species A. centoreticulata (Grey, 2005) is also uncertain because the processes are densely clogged together and the examined specimens (those illustrated by Grey (2005)) are strongly degraded and thermally altered. The appearance of processes being grouped and distributed in a reticulate pattern may be taphonomic. Specimens of a new combination A. dilutopila (Zang in Zang and Walter, 1992b; Grey (2005) have not been examined by the author, because they belong to another collection, however the specimens illustrated by Grey (2005) resemble also A.? tabifica. The new species A. minutiforma Grey (2005) is poorly preserved and its processes seem to be coalesced into a membrane, obscuring the observations on the nature of processes.

4.2. Appendisphaera grandis (Moczydłowska et al., 1993, emended) Fig. 3A–D; Fig. 4A–F Synonymy Baltisphaeridium (?) strigosum Jankauskas— Pyatiletov and Rudavskaya (1985), p. 152, pl. 63, Fig. 7 and 9. Baltisphaeridium strigosum Jankauskas— Rudavskaya and Vasileva (1989), pl. 1, Figs. 2–4; pl. 2, Figs. 1 and 2. Appendisphaera grandis sp. nov.—Moczydłowska et al. (1993), pp. 503–505, pl. 1, Figs. 1 and 2, textfig 5. Types: Holotype specimen PMU-Sib.1-R/63/2 (textfig 5A–D); paratype specimen PMU-Sib.1-L/27/1 (pl.1, Figs. 1 and 2). Yakutia, Siberian Platform, NepaBotuoba region, Zapad 742 borehole at a depth of 1887.0–1894.0 m, Khamaka Formation, Neoproterozoic, Upper Vendian (Ediacaran; Moczydłowska et al., 1993, p. 503). Emended diagnosis: Vesicle circular in outline, originally spherical, bearing very abundant long processes evenly distributed over its surface. The processes are homomorphic, simple, slim cylindrical in shape, proximally slightly widened and distally tapering. Their tips are sharp-pointed. The processes are hollow and freely communicate with the vesicle cavity. They are densely distributed but clearly separated from each other and attached to the vesicle without clearly defined basal structures. The excystment structure is by a circular pylome. Material: Twelve additional very well-preserved specimens have been observed from the Siberian type collection and some more in a poorer state of preservation. Three-dimensionally preserved specimens (Fig. 3A and B; Fig. 4B and F) demonstrate that the processes are hollow inside and communicate with the vesicle cavity. Dimensions: Newly measured specimens are within the size range of the species described by Moczydłowska et al. (1993). Diameter of the vesicle is 95–132 ␮m; length of processes is 16–26 ␮m (N = 12). The length of processes in a proportion to the vesicle diameter is 17–20%. Remarks: The morphological features added in the emendation to the species diagnosis, and the genus of which it is the type species, are the hollow nature of

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

295

Fig. 4. Appendisphaera grandis (Moczydłowska et al., 1993, emend.) (A, B and D) Specimen PMU-Sib.1-L/42/4. Zapad 742 borehole at a depth of 1887.0–1899.0 m, Khamaka Formation; (A) enlarged fragment (left upper quarter) of the specimen shown in B, with long, slim but hollow processes freely communicating with vesicle cavity; (B) entire specimen showing tightly distributed processes, which are of equal lengthl; (D) enlarged fragment (right lower quarter) of the specimen shown in B with processes clearly hollow inside. (C, E and F) Specimen PMU-Sib.2P/63/2. Zapad 742 borehole, 1887.0–1899.0 m, Khamaka Formation; (C and F) enlarged fragments (left upper quarter and right lower quarter, respectively) of the specimen shown in E showing processes hollow inside and freely communicating with the vesicle cavity. Scale bar in E equals 20 ␮m for A and D; 50 ␮m for B and E; 10 ␮m for C and F.

296

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

the processes and their free communication with the vesicle cavity, and the presence of pylome. Occurrence: Yakutia, Siberian Platform, NepaBotuoba region, boreholes Zapad 742, depth 1887.0–1894.0 m, Ozero 761, depth 1876.0–1884.0 m, and Talakan 823, depth 1534.0–1539.0 m, Khamaka Formation; Syugdzer Saddle, boreholes Dyudan 291-0, depth 3414.3–3420.3 m, and Nakyn 295-0, depth 3062.0–3068.0; Upper Vendian (Ediacaran; Moczydłowska et al., 1993); boreholes Ozero 759, depth 1835.0–1837.0 m, and Byuk 715, depth 1964.8 m, Kursov Formation (Pyatiletov and Rudavskaya, 1985). No new records outside the Siberian Platform are known. 4.3. Appendisphaera fragilis (Moczydłowska et al., 1993, emended) Fig. 6D Synonymy Appendisphaera fragilis sp. nov.—Moczydłowska et al. (1993), p. 505, text-fig 6A and B. Ericiasphaera fragilis (Moczydłowska et al., 1993) comb. nov.—Grey (2005), Figs. 159D and 160B. non Ericiasphaera fragilis (Moczydłowska et al., 1993) comb. nov.—Grey (2005), Figs. 159 A–C, E and F and 160A and C. Holotype: Specimen PMU-Sib.1-Y/37/3 (text-fig 6A and B). Yakutia, Siberian Platform, NepaBotuoba region, Zapad 742 borehole at a depth of 1887.0–1894.0 m, Khamaka Formation, Neoproterozoic, Upper Vendian (Ediacaran; Moczydłowska et al., 1993, p. 505). Emended diagnosis: Vesicle oval in outline, originally spherical, bearing long, slender and fragile processes. The wall of the vesicle is smooth. The processes are approximately of an equal length, thin, ciliate, but hollow inside and communicate with the vesicle cavity. Their tips are blunt. The processes are widely spaced and directly attached to the vesicle without any basal structure. Material: No new specimens are known apart from those three previously examined (Moczydłowska et al., 1993). Dimensions: Diameter of the vesicle is 57–121 ␮m; length of processes is 11–20 ␮m (N = 3). The length of processes in a proportion to the vesicle diameter is 16–19%.

Remarks: Specimens from Australia are larger in their vesicle diameter (100–221 ␮m; N = 28), and length of processes (28–75 ␮m; N = 18; Grey, 2005). Some specimens attributed to the species are not synonymized here because they seem to have elongated, tapering conical processes (own examination) and slightly conical bases (Grey, 2005), which does not conform to the characteristic of A. fragilis. Occurrence: Yakutia, Siberian Platform, NepaBotuoba region, Zapad 742 borehole, depth 1887.0– 1894.0 m, Khamaka Formation; Syugdzer Saddle, Dyudan 291-0 borehole, depth 3414.3–3420.3 m; Upper Vendian (Ediacaran; Moczydłowska et al., 1993). Australia, Officer Basin, Munta 1 borehole, depth 1443.6 m, Tanana Formation, Ediacaran (Grey, 2005). 4.4. Appendisphaera tenuis (Moczydłowska et al., 1993, emended) Fig. 5A–F Synonymy Appendisphaera tenuis sp. nov.—Moczydłowska et al. (1993), pp. 506–508, text-fig 7. non Ericiasphaera spjeldnaesii (Vidal, 1990)— Zhang et al. (1998), pp. 26–28. Appendisphaera tenuis (Moczydłowska et al., 1993)—Grey (2005), Fig. 109B. non Appendisphaera tenuis (Moczydłowska et al., 1993)—Grey (2005), Fig. 109A and C. Holotype: Specimen PMU-Sib.1-M/33; Yakutia, Nepa-Botuoba region, Zapad 742 borehole at a depth of 1887.0–1894.0 m, Khamaka Formation, Neoproterozoic, Upper Vendian (Ediacaran; Moczydłowska et al., 1993, p. 506, text; Fig. 7A–C) (Fig. 5A–F). Emended diagnosis: Vesicle circular in outline, originally spherical, with smooth or psilate wall surface bearing numerous, evenly distributed, short and slender processes. The processes are hollow and freely communicate with the inner vesicle cavity. They have a narrow diameter in cross-section, are cylindrical in the stem portion and have sharp-pointed, rounded or blunt tips and slightly expanded, minute conical bases. No excystment structure was observed. Material: Five additional well-preserved specimens from the same slides as the type collection together with the three specimens originally described by Moczydłowska et al. (1993).

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

297

Fig. 5. Appendisphaera tenuis (Moczydłowska et al., 1993, emend.) (A) Specimen VNIGRI.3758/3-W/29/4. Dyudan 291-0 borehole at a depth of 3414.3–3420.3 m. (B, D and F) Specimen PMU-Sib.1-Y/39/1. Zapad 742 borehole, 1887.0–1899.0 m, Khamaka formation; (B) enlarged fragment (upper half) of the specimen shown in D, displaying slender hollow processes that have slightly widened bases and freely communicate with vesicle cavity; (D) entire specimen showing abundant but clearly separated processes; (F) enlarged fragment (right lower quarter) of the specimen shown in D, with processes tapering towards sharp-pointed or rounded tips. (C and E) Specimen PMU-Sib.1-V/36. Zapad 742 borehole, 1887.0–1899.0 m, Khamaka Formation; (C) entire specimen with slender processes, which are softly deformed during the burial; (E) enlarged fragment (upper left quarter) showing free connection between the hollow processes and vesicle inner cavity. Scale bar in B equals 50 ␮m for A; 20 ␮m for B and F; 40 ␮m for C; 35 ␮m for D; 12 ␮m for E.

Dimensions: Diameter of vesicle is 87–143 ␮m; length of processes is 9–16 ␮m; N = 5. In combination with the previous record from the Siberian Platform, the range of vesicle diameter is 87–147 ␮m, length of

processes is 7–16 ␮m (N = 8). The length of processes in a proportion to the vesicle diameter is 8–11%. Remarks: Among the specimens attributed by Grey (2005) to Appendisphaera tenuis one is considered here

298

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

as synonymous (ibidem, Fig. 109B), whereas the identification of two others (ibidem, Fig. 109A and C) remains dubious. These specimens are poorly preserved and their processes are clotted (as in A.? tabifica; own examination) rendering the observations on morphology uncertain. Their dimensions exceed the size range of the Siberian specimens. The Australian specimens measured from a more numerous collection (N = 28) range from 140 to 415 ␮m in vesicle diameter and 5–50 ␮m in process length (Grey, 2005). Occurrence: Yakutia, Siberian Platform, NepaBotuoba region, Zapad 742 borehole, depth 1887.0– 1894.0 m, Khamaka Formation; Syugdzer Saddle, Dyudan 291-0 borehole, depth 3414.3–3420.3 m; Upper Vendian (Ediacaran; Moczydłowska et al., 1993). Australia, Amadeus Basin, Rodinga 4 borehole, Pertatataka Formation; Officer Basin, boreholes Munta 1, Observatory Hill 1, and Lake Maurice West 1, lower Ungoolya Group; Ediacaran (Grey, 2005), and the Murnaroo 1 borehole, Karlaya Limestone of the lower Ungoolya Group; Ediacaran (unpublished data; Willman et al., submitted for publication). 4.5. Genus Cavaspina (Moczydłowska et al., 1993) Type species: Cavaspina acuminata (Kolosova, 1991; Moczydłowska et al., 1993); Yakutia, Siberian Platform, Peri-Patom Marginal Ridge (Berezov Depression), Torgo G-2 borehole at a depth of 70.0–74.0 m, Torgo Formation, Neoproterozoic, Upper Vendian (Ediacaran; Kolosova, 1991; Moczydłowska et al., 1993). By original designation. Synonymy Cavaspina gen.nov.—Moczydłowska et al. (1993), pp. 508–509. Pro parte Goniosphaeridium (Eisenack, 1969, emend. Turner, 1984)—Zhang et al. (1998) pp. 28–32 [Cavaspina acuminata (Kolosova, 1991) Moczydłowska et al. (1993) = Goniosphaeridium acuminatum (Kolosova) new combination]. Pro parte Meghystrichosphaerdium (Zhang et al., 1998; non Chen and Liu, 1986)—Zhang et al. (1998), p. 34, 36 [Cavaspina basiconica Moczydłowska et al. (1993) = Meghystrichosphaerdium perfectum (Kolosova) new combination].

Pro parte Echinosphaeridium (Knoll, 1992: emend.)—Grey (2005), text-fig 39; [Echinosphaeridium acuminatum (Kolosova, 1991) comb. nov.]. Pro parte Vidalia new genus—Grey (2005). [Vidalia basiconica (Moczydłowska et al., 1993) comb. nov.]. 4.6. Cavaspina acuminata (Kolosova, 1991; Moczydłowska et al., 1993) Fig. 6A and B Synonymy Unnamed specimen—Rudavskaya and Vasileva (1989), pl. 1, Fig. 5. Baltisphaeridium pilosiusculum Jankauskas— Rudavskaya and Vasileva (1989), pl. 2, Figs. 4–6. Baltisphaeridium sp.—Rudavskaya and Vasileva 1989), pl. 2, Fig. 7. Baltisphaeridium (?) acuminatum (Kolosova) sp. nov.—Kolosova (1991), pp. 57–58, Fig. 4:1–3. Cavaspina acuminata (Kolosova, 1991) comb. nov.—Moczydłowska et al. (1993), pp. 509–510, textfig 10A and B. ? Goniosphaeridium acuminatum (Kolosova) new combination—Zhang et al. (1998), p. 28, 32, Fig. 8.3. Echinosphaeridium acuminatum (Kolosova, 1991) comb. nov.—Grey (2005). Holotype: Specimen YIGS Nr 87–123 (Kolosova, 1991, Fig. 4:1); Yakutia, Siberian Platform, Peri-Patom Marginal Ridge (Berezov Depression), Torgo G-2 borehole at a depth of 70.0–74.0 m, Torgo Formation, Neoproterozoic, Upper Vendian (Ediacaran; Kolosova, 1991; Moczydłowska et al., 1993) (Fig. 6A and B). Description: Vesicle circular to oval in outline, originally spherical, bearing numerous short conical processes, which are hollow inside and freely, communicate with the vesicle cavity. Tips of processes are sharp-pointed. The processes appear in general to be stiff although some bend distally as a result of taphonomic deformation. Material: Four new and well-preserved specimens from the Siberian collection containing the type specimens. Dimensions: Diameter of vesicle is 52–70 ␮m; length of processes is 3–4 ␮m; width of process bases is around 1 ␮m (N = 4). All available specimens from the Siberian collection have the following size range: diameter of vesicle 50–70 ␮m, length of processes 3–5 ␮m,

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

299

Fig. 6. (A and B) Cavaspina acuminata (Kolosova, 1991; Moczydłowska et al., 1993). (A) Specimen VNIGRI.1091/1-J/34. Talakan 806 borehole at a depth of 1467.0–1473.9 m, Khamaka Formation. (B) Specimen VNIGRI.1091/1-W/52. Talakhan 806 borehole, m. 1467.0–1473.9 m, Khamaka Formation. (C) Cavaspina basiconica (Moczydłowska et al., 1993). Specimen VNIGRI.2128/3-S/48. Central Talakan 823 borehole, 1534.0–1539.0 m, Khamaka Formation. (D) Appendisphaera fragilis (Moczydłowska et al., 1993, emend.) Specimen VNIGRI.3758/2-G/43/3. Dyudan 291-0 borehole, 3414.3–3420.3 m. Fragile and flexible processes characteristic for the species are partly preserved due to the poor state of preservation. Scale bar in C equals 20 ␮m for A and B; 30 ␮m for C and D.

width of process bases around 1 ␮m (N = 12). The length of processes in a proportion to the vesicle diameter is 6–10%. Remarks: Two specimens recorded from China and synonymized with Cavaspina acuminata by Zhang et al. (1998) (pp. 28–32, Fig. 8.3) are much larger but have a similar ratio between the process length and vesicle diameter (6–8%). They range from 200 to 240 ␮m in diameter of vesicle and 15–20 ␮m in length of processes, thus 3–4 times the size of the Siberian specimens. A fragment of a specimen illustrated by Zhang et al. (1998) (Fig. 8.3) shows substantially softly distorted outline of the vesicle caused probably by permineralization during the diagenesis of chert, in which it is preserved, with a few conical processes. The estimated diameter of vesicle of this fragmentary specimen is

also highly uncertain. Although Zhang et al. (1998) accepted a wide size variation in Neoproterozoic acritarch species and the specimen illustrated has a morphologic characteristic of Cavaspina acuminata, the identification of the Chinese specimens is uncertain, and thus the new combination based on such limited material is not followed here. Occurrence: Yakutia, Siberian Platform, Berezov Depression, borehole Torgo G-2, depth 70.0–74.0 m, Torgo Formation (Kolosova, 1991); Nepa-Botuoba region, Talakan 806 borehole, depth 1467.0–1473.9 m, Khamaka Formation; Lena-Anabar Depression, Charchyk 1 borehole, depth 2683.0–2712.3 m, Turkut Formation (Moczydłowska et al., 1993). South China, Yangtze Gorges, upper Doushantuo Formation (upper cherts; Zhang et al., 1998).

300

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

4.7. Cavaspina basiconica (Moczydłowska et al., 1993) Fig. 6C Synonymy Baltisphaeridium (?) strigosum Jankauskas— Pyatiletov (1980), p. 11, pl. 1, Figs. 5–8, pl. 2, Figs. 1–4. Baltisphaeridium (?) strigosum Jankauskas, 1976—Pyatiletov and Rudavskaya (1985), p. 152, pl. 63, Fig. 8. Baltisphaeridium strigosum Iank.—Rudavskaya and Vasileva (1989), pl. 1, Figs. 2–4, 6; pl. 2, Figs. 1 and 2. Nomen nudum, Tanarium perfectum (Kolosova)—Kolosova (1991), Fig. 6:1–6. Pro parte Comasphaeridium sp. B—Zang and Walter (1992b), p. 34, Fig. 28F and G. Cavaspina basiconica sp. nov.—Moczydłowska et al. (1993), p. 510–512, text-fig 11. Invalid Meghystrichosphaeridium perfectum (Kolosova) new combination—Zhang et al. (1998) p. 36, Fig. 10.7 and 10.8. Vidalia basiconica (Moczydłowska et al., 1993) comb. nov.—Grey (2005). Holotype: Specimen PMU-Sib.1-Y/55/2 (text-fig 1A, B and D); paratype specimen PMU-Sib.1-O/562 (text-fig 11C); Yakutia, Siberian Platform, NepaBotuoba region, Zapad 742 borehole at a depth of 1887.0–1894.0 m, Khamaka Formation, Neoproterozoic, Upper Vendian (Ediacaran; Moczydłowska et al., 1993). By original designation. Description: Vesicle circular to oval in outline, originally spherical, bearing abundant and evenly distributed processes, which are almost equal in length and have distinctive conical, swollen bases forming slightly wavy outline. The processes taper from wide bases into slender distal portions and sharp-pointed or blunt tips. The bases are hollow inside and freely communicate with the vesicle cavity and distal portions are solid. Material: Five specimens relatively well-preserved. Dimensions: Diameter of vesicle is 85–110 ␮m; length of processes is 9–13 ␮m; width of process bases is 3–5 ␮m (N = 5). The combined size range of the Siberian specimens recorded be Moczydłowska et al. (1993) and herein is as follows: diameter of vesicle is 83–133 ␮m; length of processes is 7–16 ␮m; width of

process bases is 3–5 ␮m (N = 11). The length of processes in a proportion to the vesicle diameter is 8–12%. Remarks: The species has not been recorded in Australia but Grey (2005) transferred it to the new genus Vidalia because she considered that the generic name Cavaspina is no longer available. The genus Cavaspina is retained herein, as is the species basiconica original attribution. Cavaspina basiconica is morphologically similar to new species V. multispinulosa (Grey, 2005) and V. pulchra (Grey, 2005), but it lies outside the size class of these two species (Grey, 2005). Some of the microfossils from the Amadeus Basin in Australia described by Zang in Zang and Walter (1992b) (p. 34, Fig. 28F and G) under an open nomenclature as Comasphaeridium sp. B are considered to belong to C. basiconica. This informal taxon was diagnosed (ibidem) as having solid processes and commonly thickened at the tip. However, among the illustrated specimens the two considered here as conspecific with C. basiconica show clearly similar, small, conical and hollow bases of the processes and simple, rather blunt or tapering, terminations of processes. The dimensions are also in the same range. Zhang et al. (1998) included these specimens, together with C. basiconica, into the synonymy of their “Meghystichosphaeridium perfectum (Kolosova) new combination”. Two specimens from China described under invalid name “Meghystichosphaeridium perfectum (Kolosova) new combination” by Zhang et al. (1998) (p. 36, Figs. 10.7 and 10.8) are convincingly conspecific with C. basiconica. The diameter of the vesicle measured on a strongly flattened specimen provided extreme size limits of 42–200 ␮m, which after correction to the original spheroid vesicle would be similar to the dimensions of the Siberian specimens. The length of processes is 14–21 ␮m, which is slightly larger than in specimens in our collection. The positive morphological and dimensional class identification of well-preserved specimens, though only two, from China and from Australia, also in a limited number, makes C. basiconica the cosmopolitan species known from three palaeocontinents of the time. Occurrence: Yakutia, Siberian Platform, Byuk 715 borehole, depth 1964.8 m, Kursov Formation (Pyatiletov and Rudavskaya, 1985); Nepa-Botuoba region, boreholes Zapad 742, depth 1887.0–1894.0 m, and Talakan 823, depth 1534.0–1539.0 m, Khamaka

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

301

Fig. 7. (A, C and E) Tanarium conoideum (Kolosova, 1991, emend. Moczydłowska et al., 1993). (A) Specimen VNIGRI.3758/3-J/11/2. Dyudan 291-0 borehole, at a depth of 3414.3–3420.3 m. (C) Specimen VNIGRI.3758/3-X/33/3. Dyudan 291-0 borehole, 3414.3–3420.3 m. (E) Specimen VNIGRI.2021/3-R/49/2. Charchyk 1 borehole, 2703.0–2712.3 m, Turkut Formation. (B and D) Tanarium tuberosum (Moczydłowska et al., 1993); (B) specimen VNIGRI.3349/1-R/29. Nakyn 295-0 borehole, 3062.0–3068.0 m; (D) Specimen VNIGRI.3142/2-R/36. Nakyn 295-0 borehole, 3062.0–3068.0 m. (F) Tanarium irregulare (Moczydłowska et al., 1993). Specimen PMU-Sib.1-O/40. Zapad 742 borehole, 1887.0–1899.0 m, Khamaka Formation. Scale bar in E equals 40 ␮m for A and F; 30 ␮m for B; 50 ␮m for C and E; 45 ␮m for D.

Formation, Upper Vendian (Ediacaran; Moczydłowska et al., 1993). Australia, Amadeus Basin, Rodinga 4 borehole, Pertatataka Formation (Zang and Walter, 1992b); Officer Basin, Murnaroo 1 borehole, lower Ungoolya Group, Karlaya Limestone and Wilari Dolomite (Tanana Formation; unpublished data; Willman et al., submitted for publication). South China, Hubei Province, Xiaofenghe and Tianjiayuanzi sections,

Doushantuo Formation, terminal Proterozoic (Zhang et al., 1998). 4.8. Genus Tanarium (Kolosova, 1991, emend. Moczydłowska et al., 1993) Type species. Tanarium conoideum (Kolosova, 1991, emend. Moczydłowska et al., 1993). Yakutia,

302

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

Siberian Platform, Byuk-Tanar 715 borehole at a depth of 1964.0–1970.6 m, Kursov Formation, Upper Proterozoic, Upper Vendian (Ediacaran; Kolosova, 1991; Moczydłowska et al., 1993). By original designation. Synonymy Nomen nudum, Tanarium (Kolosova), gen.nov.— Kolosova (1990), pp. 24–25 (unpublished manuscript). Tanarium (Kolosova), gen.nov.—Kolosova (1991), pp. 56–57. Hocosphaeridium gen.nov.—Zang in Zang and Walter (1992b), p. 61. Solisphaeridium (Staplin et al., 1965)—Zang in Zang and Walter (1992b), p. 100. Pro parte Goniosphaeridium (Eisenack emend. Kjellstr¨om, 1971)—Zang in Zang and Walter, 1992b, p. 50, 54, Fig. 45H. (Goniosphaeridium sp. A = Tanarium conoideum). Tanarium (Kolosova, 1991) emend.—Moczydłowska et al. (1993), pp. 512–514. Pro parte Goniosphaeridium (Eisenack, 1969, emend. Turner, 1984)—Zhang et al. (1998), p. 32. (Tanarium conoideum = “Goniosphaeridium conoideum”). Tanarium (Kolosova, 1991; emend. Moczydłowska et al., 1993; emend.)—Grey (2005). Remarks: The hook-like terminations of processes interpreted as a diagnostic feature of Hocosphaeridium Zang in Zang and Walter (1992b) are a result of taphonomic degradation, and thus the genus is a junior synonym of Tanarium (Grey, 2005). 4.9. Tanarium conoideum (Kolosova, 1991, emend. Moczydłowska et al., 1993) Fig. 7A, C and E Synonymy Baltisphaeridium primarium Jankauskas—Pyatiletov (1980), p. 11, pl. 1, Figs. 1–4. Baltisphaeridium primarium Jankauskas—Pyatiletov and Rudavskaya (1985), p. 152, pl. 63, Figs. 1–4. Baltisphaeridium primarium Jankauskas— Rudavskaya and Vasileva (1989), pl. 1, Fig. 7. Nomen nudum, Tanarium conoideum (Kolosova), gen. et sp. nov.—Kolosova (1990), pp. 25–26, pl. 1, Figs. 1–2 (Unpublished manuscript).

Tanarium conoideum (Kolosova) sp. nov.—Kolosova (1991), p. 56, Fig. 5:1–3. Pro parte Hocosphaeridium scaberfacium gen. et sp. nov.—Zang in Zang and Walter (1992b), p. 61, Fig. 45 A–F (non G). Goniosphaeridium sp. A—Zang in Zang and Walter (1992b), p. 54, Fig. 45H. Tanarium conoideum (Kolosova, 1991, emend.)—Moczydłowska et al. (1993), pp. 514–516, text; Fig. 10C–D. Goniosphaeridium conoideum (Kolosova) new combination—Zhang et al. (1998), p. 32, Fig. 9.1–9.4. Meghystrichosphaeridium conoideum (Kolosova) Zhang et al.—Knoll (2000), Fig. 3G [sic! Goniosphaeridium conoideum (Kolosova) Zhang et al., 1998]. Tanarium conoideum (Kolosova, 1991; emend. Moczydłowska et al., 1993)—Grey (2005). Holotype: YAIGN, No. 87–115, prep. 503-80/2. Yakutia, Siberian Platform, Byuk-Tanar 715 borehole at a depth of 1964.0–1970.6 m, Kursov Formation, Vendian (Kolosova, 1991, p. 57, Fig. 5:1–2). By original designation. Material: Six specimens relatively well-preserved. Dimensions: Diameter of vesicle is 124–168 ␮m; length of processes is 24–50 ␮m; width of process bases is 9–22 ␮m (N = 6). The length of processes in a proportion to the vesicle diameter is 7–18%. Description: Vesicle circular to oval in outline, originally spherical, having unevenly distributed, sparse, heteromorphic processes. The processes are conical or cylindrical, both may occur on one specimen, with widened bases of various width and tapering or rounded terminations. The processes are hollow and freely communicate with the vesicle cavity. Remarks: Occasionally divided tips of processes were observed on a paratype illustrated by Kolosova (1991) (Fig. 5:3), and on the specimen shown by Moczydłowska et al. (1993) (text-fig 10D). These are not preservation artefacts produced by superposition or splitting of the process terminations but true morphological features. A few measured specimens from China (Zhang et al., 1998) are within the size class of those from the Siberian Platform. The specimens of the synonymous species from the Amadeus Basin recorded by

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

Zang and Walter (1992b) (N = 15) are also of the same dimensions. The Australian specimens measured on a more numerous collection from the Officer Basin (Grey, 2005) are of larger dimensions, having diameter of vesicle 96–395 ␮m (N = 61), length of processes 12–90 ␮m, and width of process bases 5–50 ␮m (N = 57). Occurrence: Yakutia, Siberian Platform; NepaBotuoba region, boreholes Byuk 715, depth 1968.8 m, Kursov Formation (Pyatiletov and Rudavskaya, 1985), and Ozero 761, depth 1876.3–1884.6 m (Kolosova, 1991); Syugdzer Saddle, Dyudan 291-0 borehole, depth 3414.3–3420.3 m; Lena-Anabar Depression, Charchyk 1 borehole, depth 2703.0–2712.3 m; Upper Vendian (Ediacaran; Moczydłowska et al., 1993). Australia, Amadeus Basin, Ooraminna 1 and Rodinga boreholes, Pertatataka Formation, Ediacaran (Zang and Walter, 1992b); Officer Basin, Munta 1 and Observatory Hill 1 boreholes, Tanana Formation (Grey, 2005), and Murnaroo 1 borehole, lower Ungoolya Group, Karlaya Limestone and Wilari Dolomite (Tanana Formation; unpublished data; Willman et al., submitted for publication). South China, Hubei Province, Liantuo region, Shipai section, and Guizhou Province, Weng’an-Fuguan region, Doushantuo Formation, terminal Proterozoic (Zhang et al., 1998). 4.10. Tanarium irregulare (Moczydłowska et al., 1993) Fig. 7F Synonymy Baltisphaeridium varium Volkova—Rudavskaya and Vasileva (1989), pl. 2, Fig. 8. Tanarium irregulare sp. nov.—Moczydłowska et al. (1993), p. 516, text-fig 14A–D. Tanarium irregulare (Moczydłowska et al., 1993)—Grey (2005), Figs. 204, 205. Types: Holotype specimen PMU-Sib.2-J/57/1 (textfig 14A–B); paratype specimen PMU-Sib.1-Q/51/3-4 (text-fig 14C–D); Yakutia, Siberian Platform, NepaBotuoba region, Zapad 742 borehole at a depth of 1887.0–1894.0 m, Khamaka Formation, Neoproterozoic, Upper Vendian (Ediacaran; Moczydłowska et al., 1993, p. 516). By original designation. Material: Three relatively well-preserved specimens.

303

Description: Vesicle irregularly oval in outline, bearing unevenly distributed, numerous, heteromorphic processes. The processes are long, flexible, gradually conical or cylindrical with tapering terminations characterized by wide or inconspicuous bases and sharp-pointed tips. Both types may occur on a single specimen. The processes are hollow and communicate freely with the vesicle cavity. Dimensions: Diameter of vesicle is 80–168 ␮m, length of processes is 25–54 ␮m (N = 3). The length of processes in a proportion to the vesicle diameter is 31–32%. Remarks: Together with the previously described specimens from the same Siberian collection (Moczydłowska et al., 1993), the dimensions of the species are: diameter of vesicle 75–168 ␮m, length of processes 23–54 ␮m (N = 6). More numerous specimens from Australia (N = 31) display slightly larger diameter of vesicle in a range of 52–218 ␮m, and length of processes 13–60 ␮m (Grey, 2005). Occurrence: Yakutia, Siberian Platform, NepaBotuoba region, Zapad 742 borehole at a depth of 1887.0–1894.0 m, Khamaka Formation, Neoproterozoic, Upper Vendian (Ediacaran; Moczydłowska et al., 1993). Australia, Officer Basin, Munta 1, Observatory Hill 1, and Lake Maurice West 1 boreholes, lower Ungoolya Group, Ediacaran (Grey, 2005), and Murnaroo 1 borehole, lower Ungoolya Group, Karlaya Limestone (unpublished data; Willman et al., submitted for publication). 4.11. Tanarium tuberosum (Moczydłowska et al., 1993) Fig. 7B–D Synonymy Baltisphaeridium primarium Jankauskas— Rudavskaya and Vasileva (1989), pl. 2, Fig. 3. Tanarium tuberosum sp. nov.—Moczydłowska et al. (1993), pp. 516–518, text-fig 15A–D. Non Asterocapsoides sinensis (Yin and Li, 1978)— Knoll (1992), pp. 762–764, pl. 6, Figs. 5–6. Non Asterocapsoides sinensis (Yin and Li, 1978, emend.)—Zhang et al. (1998), pp. 24, Fig. 5.10. Holotype: Specimen PMU-Sib.4-J/30/3; Yakutia, Siberian Platform, Nepa-Botuoba region, Zapad 742 borehole at a depth of 1876.0–1884.0 m, Khamaka Formation, Neoproterozoic, Upper Vendian (Ediacaran;

304

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

Moczydłowska et al., 1993, p. 517, text-fig 15A, B and D). By original designation. Material: Seven well-preserved specimens, with intact processes but with the vesicle surface slightly corroded. Description: Vesicle circular to oval in outline, originally spherical, bearing a few but large and robust conical processes of various dimensions on one specimen. The processes are hollow and freely connected with the vesicle inner cavity. Dimensions: Diameter of vesicle is 70–109 ␮m, length of processes is 22–66 ␮m, and width of process bases is 10–37 ␮m (N = 7). The dimensions of present specimens are within the range observed by Moczydłowska et al. (1993). The length of processes in a proportion to the vesicle diameter is 31–60%. Remarks: The synonymy proposed by Zhang et al. (1998) in which T. tuberosum is a junior synonym of Asterocapsoides sinensis could not be accepted on the grounds of a basic diagnostic difference between the species. According to the emendation to the diagnosis by Zhang et al. (1998), Asterocapsoides sinensis has a membranous outer wall layer in a double-layered vesicle whereas T. tuberosum consistently displays a single-layered vesicle wall. The selected neotype of A. sinensis, because of the loss of the holotype, shows in general a similar shape of the processes (Zhang et al., 1998, p. 24, Fig. 5.10), although the proportion of their length to the vesicle diameter is different in comparison to the robust conical protrusions in T. tuberosum. The specimen referred to A. sinensis by Knoll (1992) (pl. 6, Figs. 5–6) seems conspecific with T. tuberosum but if it possesses the double-layered vesicle wall, and this assumption is reflected by the synonymy by Zhang et al. (1998), then it precludes it as being a senior synonym of T. tuberosum. Occurrence: Yakutia, Siberian Platform, NepaBotuoba region, boreholes Zapad 844, depth 1700.0– 1715.6 m, and Ozero 761, depth 1876.0–1884.0 m, Khamaka Formation; Syugdzher Saddle, borehole Nakyn 295-0, depth 3062.0–3068.0 m; Lena-Anabar Depression, borehole Charchyk 1, depth 2703.0– 2712.3 m; Neoproterozoic, Upper Vendian (Ediacaran; Moczydłowska et al., 1993). Australia, Officer Basin, Murnaroo 1 borehole, lower Ungoolya Group, Dey Dey Mudstone and Karlaya Limestone (Tanana Formation; unpublished data; Willman et al., submitted for publication).

5. Biostratigraphic implications The emended taxonomy of acritarch species from Siberia and revision of some microfossils from Australia and South China (the Yangtze and South China platforms), render possible the synonymy and recognition of taxa in common for biostratigraphic correlation. It appears that among eight species examined here only one, Appendisphaera grandis, is known exclusively from Siberia at the moment. The best taxonomic and palaeogeographic fit of this association is with the successions in Australia where, except of A. grandis and Cavaspina acuminata, six other species are present, whereas three species, C. acuminata, C. basiconica, and Tanarium conoideum, occur in Siberia and S. China. The most significant biostratigraphically are the species T. conoideum and C. basiconica, because they occur in all three palaeocontinents and additionally across various basins in each of the palaeocontinent, and because T. conoideum is a nominal index species for the acritarch zone in Australia. The first appearance of the latter species defines, together with other species, the base of the T. conoideum–Schizofusa risoriaVariomargosphaeridium litoschum Assemblage Zone, but it has a wider range and extends throughout the two succeeding zones (Grey, 2005). The entire range of T. conoideum recorded in the stratotype sections for the Ediacaran acritarch zones in Australia, the Officer Basin, embraces approximately 150 m of strata, including the upper Dey Dey Mudstone (unpublished data; Willman et al., submitted for publication), and the Karlaya Limestone and Wilari Dolomite Member (the two latter referred also to as the Tanana Formation; Grey, 2005). In the Amadeus Basin, it is known from the upper Pertatataka Formation (Zang and Walter, 1992b), whereas in S. China in the upper Doushanuo Formation of the Hubei and Guizhou provinces (Zhang et al., 1998; see synonymy). Cavaspina basiconica is recorded in the Officer Basin for the first time, in the Karlaya Limestone and Wilari Dolomite in the Murnaroo 1 borehole (unpublished data; Willman et al., submitted for publication), but previously it has been recovered in the Amadeus Basin in the upper Pertatataka Formation and in S. China, Hubei Province, in the upper chert of the Doushantuo Formation (see synonymy). The distribution both of species, T. conoideum and C. basiconica, in Siberia is in a narrow interval of correlative strata

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

of the Khamaka and Kursov formations, and it is most likely partially recognized, because of the scarce sampling across the sedimentary successions and basins. Thus, the correlation of the Ediacaran strata, which contain the species studied here, between the three palaeocontinents is suggested to be between the lower Ungoolya Group (upper Dey Dey Mudstone; Karlaya Limestone and Wilari Dolomite or the Tanana Formation) in the Officer Basin and the upper Pertatataka Formation in the Amadeus Basin in Australia, the upper part of the Doushanuo Formation in S. China, and portions of the Khamaka and Kursov formations in the Siberian Platform. The exact time equivalence between various intervals of these formations may not be established more precisely at the moment. However, it is based on hard evidence, i.e., fossils, to correlate the strata inter-continentally within the time span that took to accumulate approximately 150 m of sediments in the stratotypes in the Officer Basin. This may be just a few million years and such time resolution in the Ediacaran Period is worth of doing acritarch biostratigraphy and very satisfactory, indeed. The chronologic sequence of environmental and biotic events, deduced from data compiled from various sources (Zang and Walter, 1992b; Moczydłowska et al., 1993; Vidal and Moczydłowska, 1997; Zhang et al., 1998; Grey et al., 2003; Grey, 2005; Hill et al., 2004; Knoll et al., 2004a, 2004b; Xiao et al., 2004) and arranged biochronologically in part by acritarchbased correlation, seems to be as it follows. The Marinoan glaciation at ca. 635–600 Ma, which was the final and truly global stage of the Snowball Earth, was followed by warming up and recovery of the environments. In the interval between 600 and 580 Ma simple, spheroidal acritarchs persisted worldwide (Vidal and Moczydłowska, 1997; Grey, 2005) and low-grade yet undetermined metazoans producing embryos evolved, what is recorded in the lower Doushanuo Formation (Zhang et al., 1998; Xiao and Knoll, 2000). At ca. 580 Ma, a post-Marinoan and geographically more limited glaciation occurred, as evidenced by the Gaskiers Formation in Newfoundland (Bowring et al., 2003) and some other diamictites including perhaps the Hankalchough Formation in North China (Xiao et al., 2004). The relative age of the Hankalchough Formation is uncertain because it is inferred from the composite lithological succession without a conclusive biostratigraphic control. However, if the correla-

305

tion with the Gaskiers Formation suggested by Xiao et al. (2004) were correct, the Hankalchough glaciation episode would pre-date the major radiation of phytoplankton recorded in Australia and S. China and not to the opposite as they have interpreted. Subsequently, the Ediacaran phytoplankton, assigned to the Ediacaran Complex Acanthomorpic Palynoflora (ECAP), radiated and diversified soon after ca. 580–570 Ma (Grey et al., 2003; Grey, 2005). This major acritarch radiation is marked by the appearance of some 50 or so new species and is well constrained in Australia. The latter age is determined by the isotopic dating of the Acraman impact ejecta layer, which stratigraphic position is evidently post-Marinoan and pre-dating the phytoplankton radiation, because both events are documented convincingly in the same sedimentary successions and in several localities. The acritarch radiation has been considered to be global (Vidal and Moczydłowska, 1997; Grey, 2005), and is supported by the worldwide distribution of certain taxa shown here. The ECAP radiation post-dates the Acraman bolide impact but it may be contemporaneous to the appearance of the earliest macroscopic Ediacaran biota, which are rangeomorphs of the Mistaken Point assemblage in Newfoundland, at 575 Ma (Narbonne and Gehling, 2003; Narbonne, 2004). The frondose Ediacara-type metazoans evolved and persisted between 575 and 543 Ma (Brasier and Antcliffe, 2004), and bilaterians emerged meantime around 555 Ma (Martin et al., 2000). The phytoplankton characterized by the ECAP became extinct before the end of the Ediacaran Period and the minimum age of its duration is around 550 Ma. This time limit is provided by the age of the Ediacaran metazoans in Australia, which are preserved in the same sedimentary successions as acritarchs in the Amadeus Basin (Zang and Walter, 1992b; Grey et al., 2003; Grey, 2005), when the palynoflora vanished.

Acknowledgements The studies were supported through grant from The Swedish Research Council (Vetenskapsr˚adet). Reexamination of the type collection from the Siberian Platform by K. Grey and A.H. Knoll added to author’s own concerns about the nature of processes in Appendisphaera and helped to review its taxonomic assignation. The vigorous discussions on the taxon-

306

M. Moczydłowska / Precambrian Research 136 (2005) 283–307

omy of some Ediacaran acritarchs, which will probably never end, with Kath Grey, Andy Knoll, Wenlong Zang and Leiming Yin are greatly appreciated but the opinions expressed here are the responsibility of the author. I thank Kath Grey for reading the early version of the manuscript and two anonymous reviewers for their comments. Gary Wife, Evolutionary Biology Centre, Uppsala University, is acknowledged for his help with image processing.

References Albani, R., 1989. Ordovician (Arenigian) acritarchs from the Solanas sandstone formation, Central Sardinia, Italy. Bolletino della Societ`a Paleontologica Italiana 28, 3–37. Bowring, S., Myrow, P., Landing, E., Ramezani, J., Grozinger, J., 2003. Geochronological constraints on terminal Neoproterozoic events and the rise of metazoans. Geophys. Res. Abstracts 5, 13219. Brasier, M., Antcliffe, J., 2004. Decoding the Ediacaran enigma. Science 305, 1115–1117. Chen, M., Liu, K., 1986. The geological significance of newly discovered microfossils from the Upper Sinian (Doushantuo age) phosphorites. Scientia Geological Sinica 1, 46–53 (In Chinese). Deflandre, G., 1937. Microfossiles des silex Cretaces. Deuxi`eme partie. Flagell´es incertae sedis Hystrichosphaerid´es sarcodin´es. Organisme Divers. Annales de Pal´eontologie 26, 51–103. Eisenack, A., 1969. Zur Systematic einiger pal¨aozoischer Hystrichosph¨aren (Acritarcha) des baltischen Gebietes. Neues Jahrbuch fur Geologie und Pal¨aontologie, Abhandlungen 133, 245–266. Evitt, W.R., 1963. A discussion and proposals concerning fossil Dinoflagellates, Hystrichospheres and Acritarchs. (U.S) National Academy of Sciences Proceedings 49, 158–164, 298–302. Fensome, R.A., Williams, G.L., Sedley Barss, M., Freeman, J.M., Hill, J.M., 1990. Acritarchs and fossil prasinophytes: an index to genera, species and infraspecific taxa. AASP Contributions Series Number 25, 771 pp. Grausman, V.V., Zhernovskij, V.P., 1989. Late Precambrian and Cambrian transitional beds in the deep-drilling sections of the Western Yakutia. In: Khomentovski, B.B., Sovetov, Y.K. (Eds.), Later Precambrian and Early Palaeozoic in Siberia. Institute of Geology and Geophysics, Novosibirsk, pp. 75–92 (in Russian). Grey, K., 1998. Ediacarian palynology of Australia. Ph.D. Thesis. Macquarie University. Grey, K., 2005. Ediacarian palynology of Australia. Association of Australasian Palaeontologists Memoir 25, in press. Grey, K., Walter, M.R., Calver, C.R., 2003. Neoproterozoic biotic diversification: “Snowball Earth” or aftermath of the Acraman impact? Geology 31, 459–462. Hill, A.C., Grey, K., Gostin, V.A., Webster, L.J., 2004. New records of late neoproterozoic acraman ejecta in the officer basin. Aust. J. Earth Sci. 51, 47–51.

Kjellstr¨om, G., 1971. Ordovician Microplankton (Baltisphaerids) from the Gr¨otlingbo Borehole No. 1 in Gotland, Sweden. Sveriges Geologiska Unders¨okning, Ser. C 655, 1–75. Knoll, A.H., 1992. Vendian microfossils in metasedimentary cherts of the Scotia Group, Prins Karls Forland, Svalbard. Palaeontology 35 (4), 751–774. Knoll, A.H., 2000. Lerning to tell Neoproterozoic time. Precambrian Res. 100, 3–20. Knoll, A.H., Walter, M.R., 1992. Latest Proterozoic stratigraphy and Earth history. Nature 356, 673–678. Knoll, A.H., Walter, M.R., Narbonne, G.M., Christie-Blick, N., 2004a. A new period for the Geological time scale. Science 305, 621–622. Knoll, A.H., Walter, M.R., Narbonne, G.M., Christie-Blick, N., 2004b. The Ediacaran Period: a new addition to the geologic time scale. Lethaia 37, in press. Kolosova, S.P., 1990. The ancient acanthomorphs from the Eastern Siberian Platform. Internal report no. 4997 in All-Union Institute of Scientific and Technical Information, Moscow, 1–45. (In Russian). Kolosova, S.P., 1991. Late Precambrian spiny microfossils from the eastern part of the Siberian Platform. Algologia 1, 53–59 (in Russian). Le H´eriss´e, A., 1989. Acritarches et kystes d’algues Prasinophycees du Silurien de Gotland, Suede. Palaeontograph. Italica 76, 57–302. Martin, M.W., Grazhdankin, D.V., Bowring, S.A., Evens, D.A.D., Fedonkin, M.A., Kirschvink, J.L., 2000. Age of Neoproterozoic bilaterians body and trace fossils, White Sea, Russia: Implications for metazoan evolution. Sciences 288, 841–845. Moczydłowska, M., 1991. Acritarch biostratigraphy of the lower Cambrian and the Precambrian–Cambrian boundary in southeastern Poland. Fossils Strata 29, 127. Moczydłowska, M., 1998. Cambrian acritarchs from Upper Silesia Poland—biochronology and tectonic implications. Fossils Strata 46, 121. Moczydłowska, M., Crimes, T.P., 1995. Late Cambrian acritarchs and their age constraints on an Ediacara-type fauna from the Booley Bay Formation, Co. Wexford. Eire. Geol. J. 30, 11– 128. Moczydłowska, M., Vidal, G., Rudavskaya, V.A., 1993. Neoproterozoic (Vendian) phytoplankton from the Siberian platform, Yakutia. Palaeontology 36 (3), 495–521. Narbonne, G.M., 2004. Modular constuction of early Ediacaran complex life forms. Science 305, 1141–1144. Narbonne, G.M., Gehling, J.G., 2003. Life after snowball: The oldest complex Ediacaran fossils. Geology 31, 27–30. Pyatiletov, V.G., 1980. Yudoma complex microfossils from southern Yakutia. Geologiya i Geofizika 7, 8–20 (in Russian). Pyatiletov, V.G., Rudavskaya, V.A., 1985. Acritarchs from the Yudomian complex. In: Sokolov, B.S., Ivanovskij, A.B. (Eds.), Vendian System 1. Nauka, Moscow, pp. 151–158 (in Russian). Rudavskaya, V.A., Vasileva, N.J., 1989. Talsy assemblage of acritarchs from the Nepa-Botuoba anticline. In: Timoshina, N.A. (Ed.), Phytostratigraphy and spore morphology of the ancient plants in the oil–gas provinces in the USSR. VNIGRI, Leningrad, pp. 5–11 (in Russian).

M. Moczydłowska / Precambrian Research 136 (2005) 283–307 Sarjeant, W.S.A., Stancliffe, R.P.W., 1994. The Micrhystridium and Veryhachium complexes (Acritarcha: Acanthomorphitae and Polygonomorphitae): a taxonomic reconsideration. Micropalaeontology 40, 1–77. Staplin, F.L., Jansonius, J., Pocock, S.A.J., 1965. Evaluation of some acritarchous hystrichosphere genera. Neues Jahrbuch f¨ur Geologie und Pal¨aontologie Abh 123, 167–201. Turner, R.E., 1984. Acritarchs from the type area of the Ordovician Caradoc Series, Shropshire, England. Palaeontographica Abt. B 190, 87–157. Vavrdov´a, M., 1966. Palaeozoic microplankton from Central Bohemia. Casopis pro mineralogii a geologii 11, 409–414. Vidal, G., 1990. Giant acanthomorph acritarchs from the upper Proterozoic in southern Norway. Palaeontology 33 (2), 287–298. Vidal, G., Moczydłowska, M., 1997. Biodiversity, speciation, and extinction trends of Proterozoic and Cambrian phytoplankton. Paleobiology 23, 230–246. Vidal, G., Moczydłowska, M., Rudavskaya, V., 1993. Biostratigraphical implications of a Chuaria-Tawuia assemblage and associated acritarchs from the Neoproterozoic of Yakutia. Palaeontology 36 (2), 387–402. Williams, G.E., 1994. Acraman: a major impact structure from the Neoproterozoic of Australia. In: Dressler, B.O., Grieve, R.A.F., Sharpton, V.L. (Eds.), Large Meteorite Impacts and Planetary Evolution, 293. Geological Society of America, pp. 209–224 (Special Papers). Williams, G.E., Wallace, M.W., 2003. The Acraman asteroid impact, South Australia: magnitude and implications for the late Vendian environment. J. Geol. Soc. London 160, 545–554. Willman, S., Moczydłowska, M., Grey, K. Neoproterozoic (Ediacaran) diversification of acritarchs—A new record from the Murnaroo 1 drillcore, eastern Officer Basin, Australia. Review of Palaeobotany and Palynology, submitted for publication. Xiao, S., Bao, H., Wang, H., Kaufman, A., Zhou, C., Li, G., Yuan, X., Ling, H., 2004. The Neoproterozoic Quruqtagh Group in eastern Chinese Tianshan: evidence for a post-Marinoan glaciation. Precambrian Res. 130, 1–26.

307

Xiao, S., Knoll, A.H., 2000. Phosphatized animal embryos from the Neoproterozoic Doushantuo formation at Weng’an, Guizhou Province, South China. J. Paleontology 74, 767–788. Yin, L., 1986. Microfossils of the Doushantuo Formation in the Yangtze Gorge district, western Hubei. Palaeontologia Cathayan 2, 229–249. Yin, Leiming, 1985. Microfossils of the Doushantuo formation in the Yangtze Gorge district. Western Hubei Palaeontologia Cathayanadkjdot 2, 229–249. Yin, Leiming, 1987. New data of microfossils from Precambrian– Cambrian cherts in Ningqiang, southern Shaanxi. Acta Palaeontol. Sinica 26, 187–195. Yin, L., Li, Z., 1978. Precambrian microflora of Southwest China with reference to their stratigraphical significance. Nanjing Institute of Palaeontology Memoirs 10, 41–108 (In Chinese). Yuan, X., Hofmann, H.J., 1998. New microfossils from the Neoproterozoic (Sinian) Doushantuo Formation , Wengan, Guizhou Province, southwestern China. Alcheringa 22, 189–222. Zang, W., 1992. Sinian and Early Cambrian floras and biostratigraphy on the South China Platform. Palaeontographica Abt. B 224, 75–119. Zang, W., Walter, M.R., 1992a. Late Proterozoic and early Cambrian microfossils and biostratigraphy, northern Anhui and Jiangsu, central eastern China. Precambrian Res. 57, 243– 323. Zang, W., Walter, M., 1992b. Late Proterozoic and Cambrian microfossils and biostratigraphy, Amadeus Basin, Central Australia. Assoc. Aust. Palaeontol. Memoir 12, 132. Zhang, Z., 1984. Microflora of the late Sinian Doushantuo Formation, Hubei Province, China. In: Xie, L., Zhang, J. (Eds.), Scientific Papers on Geology for International Exchange: Prepared for the 27th International Geological Congress. Geological Publishing House, Beijing, pp. 129–142. Zhang,Y., Yin, L., Xiao, S., Knoll, A.H., 1998. Permineralized fossils from the terminal Proterozoic Doushantuo Formation, South China. J. Paleontol. 72 (4), The Paleontological Society Memoir 50, pp. 1–52.