Type species

Blastanosphaira kokkoda, by monotypy

Diagnosis

As for type species.

Etymology

From the greek βλασταυω, to bud or to germinate, σφαιρα, sphere, and κοκκωδη, granular.

Blastanosphaira kokkoda new species

Figure 2.1–2.11

Figure 2 Photographs of Roper organic-walled microfossils: (1–11) Blastanosphaira kokkoda n. gen. n. sp.; (2) specimen starting budding; (3) specimen showing an elongate expansion; (4) specimen showing circular opening; (6) the bottom specimen’s wall is peeling off the vesicle; (8) thick folds between attached specimens; (5–8) specimens showing multiple budding; (11) SEM picture showing details of granular wall. (12–13) Chlorogloeaopsis contexta. (14) Coneosphaera artica. (15) Dictyosphaera delicata. (16–18) Eomicrocystis magilca: (17) detail of (16) showing oval cells and absence of external envelope. Scale bar in (1) is: (1, 2, 8, 9, 10) 13 µm; (3, 14, 16, 18) 20 µm; (4, 13, 17) 10 µm; (5) 80 µm; (6, 7) 15 µm; (11) 500 nm; (12) 50 µm. Slides and England coordinates are (1) U5 569.1 m .2 Q42, (2, 3) U5 569.1 m .2 Q40/2, (4) U5 569.1 m .2 R43, (5) U5 569.1 m .2 R/S42, (6) U5 569.1 m .2 R43, (7–10) U5 536.6 m .2 P33, (12, 13) U6 240.2 m .2 S16, (14) A82/3 311.3 m O5/2, (15) GG1 48.75 m .2 J43/4, (16) U5 125.1 m .2 N33/2, (18) U6 230.8 m H16.

Holotype

Specimen Figure 2.1, palynological slide U5 569.1 m, England finder coordinates R/S42, from the Wood Duck Member of the Mainoru Formation, Roper Group.

Diagnosis

Spheromorph, a few up to ~100 µm in diameter, with very thin chagrinate wall, small sinuous folds, and one lanceolate fold predominantly near the margins of compressed vesicles. Division by budding, with one or several large spherical scars left by detaching buds; serial budding without cells detaching common, leading to a colonial habit. Commonly, taphonomic alteration results in the thin wall peeling off the vesicle from an equally tenuous internal layer.

Occurrence

Mesoproterozoic, Wood Duck Member of the Mainoru Formation, Roper Group, Australia.

Description

Spheromorph with very thin chagrinate wall and small sinuous folds, and one lanceolate fold predominantly near the margins of compressed vesicles. Size 3–93 µm in minimum diameter (mean: 28.7 µm, σ=16.8 µm, N=149). Two specimens oval shaped (52–104 µm long and 32–64 µm wide), and one specimen (27 µm in diameter) bears an elongate expansion (40 µm long x 8 µm wide) (Fig. 2.3). Division by budding, with cells staying attached and forming irregular colonies, cells rarely isolated, often attached to one to four other cells, commonly with large spherical scars left by detaching buds or adjacent cells. Range of diameter and morphology may vary greatly, from spherical to oval to filamentous. Commonly, taphonomic alteration results in the thin wall peeling off the vesicle from an equally tenuous internal layer.

Remarks

The Roper population forms an essentially monospecific assemblage in euxinic basinal shales, and is rare in other facies. It differs from Gemmuloides by the thin chagrinated wall, circular scars, and multiple attached buds forming colonies. It also differs from Eosaccharomyces ramosus Hermann, another budding spheromorph forming colonies, by the chagrinate ornamentation of the vesicle wall, and taphonomic features such as circular scars (Fig. 2.4) and one large lanceolate fold at periphery and very thin folds more centrally distributed (Fig. 2.1, 2.10). The attachment to a biofilm reported and illustrated by Hermann (Reference Hermann1990, pl. 14) and Hermann and Podkovyrov (Reference Hermann and Podkovyrov2012) is not observed for the Roper population, although it is not mentioned as a diagnostic character (Jankauskas et al., Reference Jankauskas, Mikhailova and Hermann1989). Growth of oval cells oriented in the direction of the “branches” of the colony do occur in the Lakhanda material, as underscored by Knoll et al. (Reference Knoll, Javaux, Hewitt and Cohen2006), but this is not always the case (see Hermann Reference Hermann1990, pl. 14, figs. 5, 7), and is not reported as a diagnostic criterion in Jankauskas et al. (Reference Jankauskas, Mikhailova and Hermann1989). The chagrinate spheromorphs commonly show evidence of budding (Fig. 2.2–2.8), forming spheres (Fig. 2.6–2.8) or elongate extensions (Fig. 2.3), with up to seven specimens attached. Some specimens bear a distinct circular hole rimmed by a fold in the wall (with a diameter up to more than 60% of the vesicle diameter) (Fig. 2.4). Because budding specimens may bear this hole (Fig. 2.7), it cannot be interpreted as a pylome (excystment structure), but rather as a scar left when connected individuals detached. Commonly, the thin wall has partially peeled off, exposing the lighter inner side of the vesicle wall (Fig. 2.6). Cells can be isolated, or more commonly attached to 1 to 4 other cells (Fig 2.7). Blastanosphaira kokkoda differs also from other spheromorphs with chagrinate walls, such as L. obsuleta and L. atava, by its prominent budding habit and consequent colonial association, very thin wall, and circular scars.

The chagrinate appearance seems to be an ornamentation rather than taphonomic alteration, suggesting eukaryotic affinity. SEM shows a granular wall and occasional taphonomic holes (Fig. 2.11). Budding is also consistent with eukaryotic affinities, resembling yeast behavior, but detailed ultrastructural and microchemical analyses will be required to confirm the affinity of this population. Due to its budding without cells detaching and forming colonies, E. ramosus has been interpreted as a possible fungus (yeast-like) by Hermann and Podkovyrov (Reference Hermann and Podkovyrov2012) or as social amoebae, although these are difficult to preserve as compressions (Porter, Reference Porter2006), except in stages of their life cycle when they can produce cellulose walls. Interestingly, cells of the modern yeast Saccharomyces may bear several circular scars, and when budding rapidly, form pseudomycelia. However, budding as a form of asexual reproduction also occurs in some bacteria (cyanobacteria, prosthecate proteobacteria; Angert, Reference Angert2005), in addition to some protists, fungi (yeast), and animals. The chagrinate ornamentation of the wall combined with large size suggest the Roper fossils are probable eukaryotes, and their common budding and pseudocolonial habit shows they represent metabolically active, reproducing vegetative cells. Their restricted distribution in deeper anoxic facies may suggest an anaerobic metabolism (see Muller et al., 2012 for a review of modern anaerobic eukaryotes) or facultatively aerobic metabolism at low oxygen tensions. Alternatively, they could have been planktonic, but in this case, their limitation to deeper anoxic facies is difficult to explain.

Genus Chlorogloeaopsis Maithy, Reference Maithy1975, emend. Hofmann and Jackson, Reference Hofmann and Jackson1994

Type species

Chlorogloeaopsis zairensis Maithy, Reference Maithy1975, from the Bushimay (now Mbuyi-Mayi) Supergroup, RDC, Meso-Neoproterozoic.

Other species

Chlorogloeaopsis kanshiensis (Maithy, Reference Maithy1975), n. comb. Hofmann and Jackson, Reference Hofmann and Jackson1994; Chlorogloeaopsis contexta (Hermann, 1976) n. comb. Hofmann and Jackson, Reference Hofmann and Jackson1994.

Chlorogloeaopsis contexta (Hermann in Timofeev, Hermann, and Mikhailova, Reference Timofeev, Hermann and Mikhailova1976), emend. Hofmann and Jackson, Reference Hofmann and Jackson1994

Figure 2.12–2.13

1976 Polysphaeroides contextus Hermann in Reference Timofeev, Hermann and MikhailovaTimofeev, Hermann, and Mikhailova, p. 42, pl. 14, fig. 3

1989 Polysphaeroides contextus; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 119, pl. 27, figs. 10a, b

1990 Polysphaeroides contextus; Reference HermannHermann, p. 26, pl. 8, fig. 8

1994 Chlorogloeaopsis contexta; (Hermann in Timofeev et al., Reference Timofeev, Hermann and Mikhailova1976), emend. Reference Hofmann and JacksonHofmann and Jackson, p. 19, figs. 12.13–12.15

Holotype

Polysphaeroides contextus Hermann, 1976 in Timofeev, Hermann, and Mikhailova, p. 42–43, pl. 14, fig. 3; from the late Riphean (Tonian) Miroedikha Formation of the Turukhan Uplift, Siberia.

Occurrence

Mesoproterozoic and Neoproterozoic successions worldwide, such as the Mbuyi-Mayi Supergroup, RDC; the Miroedikha Formation of the Turukhan Uplift, Siberia; the Roper Group, Australia; the Bylot Supergroup, Canada.

Description

One cylindrical colony without envelope, composed of several indistinctly defined rows of cells 3–5 µm wide; colony 400 µm long and 25 µm wide.

Remarks

The spelling of the genus was corrected by Hofmann and Jackson (Reference Hofmann and Jackson1994, p. 18–19) and simultaneously (both in July 1994) by Butterfield et al. (Reference Butterfield, Knoll and Swett1994, p. 72). Hofmann and Jackson (Reference Hofmann and Jackson1994) recognized three species of Chlorogloeaopsis: C. contexta (Hermann, 1976) n. comb. Hofmann and Jackson, Reference Hofmann and Jackson1994, has indistinct rows of cells and cell diameter ranging from 1 to 5 µm; C. zairensis Maithy, Reference Maithy1975 with cells 8 to 10 µm in diameter, two to four in a row, while C. kanshiensis has cells 10–15 µm in diameter, two or three distinct rows of cells. The Roper population differs from C. kanshiensis, defined by two or three rows of cells, and from Polysphaeroides spp., which are loose aggregates of spheroidal dispersed cells or pairs, tetrads, octads, and spheroidal colonies of up to 10–20 cells in a sheath.

Genus Coneosphaera Luo, Reference Luo1991

Type species

Coneosphaera inaequalalis Luo, Reference Luo1991, from the Changlongshan Formation, Neoproterozoic, China.

Other species

Coneosphaera artica Hofmann and Jackson, Reference Hofmann and Jackson1994; Coneosphaera sp. Hofmann and Jackson, Reference Hofmann and Jackson1994.

Coneosphaera sp.

Figure 2.14

Description

50–51 µm thin-walled light brown spheromorphs loosely associated with many smaller 2–4 µm vesicles on the wall surface and close to their periphery. Three specimens observed.

Remarks

Our specimens differ from C. artica, which shows larger diameters of both large and small vesicles (79–130 µm and 8–11 µm, respectively) and a higher number of the loosely attached or closely associated small vesicles. It also differs from C. sp. in the Bylot Group (Hofmann and Jackson, Reference Hofmann and Jackson1994), which has a few vesicles firmly attached to a larger central one and resembles a specimen illustrated by Hermann (Reference Hermann1990, p. 20, pl. 5.11) in the Miroedikha Formation, Siberia. It differs from C. inaequalalis, which is characterized by a large cell three or four times bigger than the attached smaller cells, and one cell much smaller than the others (Luo, Reference Luo1991, p. 193).

Genus Dictyosphaera Xing and Liu, Reference Xing and Liu1973

Type species

Dictyosphaera macroreticulata Xing and Liu, Reference Xing and Liu1973, from the Chuanlingguo Formation, Yenliao region; Chih County of Hopei, northern China, Mesoproterozoic.

Dictyosphaera macroreticulata Xing and Liu, Reference Xing and Liu1973

Figure 2.15

1973 Dictyosphaera macroreticulata Reference Xing and LiuXing and Liu, p. 22, 58, pl. 1, 16–17.

1982 Dictyosphaera delicata; Reference Hu and FuHu and Fu, p. 108, pl. 2, figs. 3–6.

2001 Dictyosphaera sp.; Reference Javaux, Knoll and WalterJavaux et al., fig 1e.

2003 Dictyosphaera delicata; Reference Kaufman and XiaoKaufman and Xiao, fig. 1.

2005 Dictyosphaera delicata; Reference Yin, Yuan, Meng and HuYin et al., p. 52, fig. 2.1, 2.2, 2.4, 2.5, 2.7, 2.9, 2.10.

2007 Dictyosphaera delicata; Reference Yin and YuanYin and Yuan, p. 351, fig. 1.1.

2009 Dictyosphaera delicata; Reference Schiffbauer and XiaoSchiffbauer and Xiao, fig. 3f.

?2011 “ellipsoidal vesicle with a micro-reticulate wall” Reference Strother, Battison, Brasier and WellmanStrother et al., fig. 1i, j.

2015 Dictyosphaera macroreticulata; Reference Agic, Moczydłowska and YinAgic et al., p. 32, figs. 2–4.

Lectotype

Specimen originally described as Dictyosphaera sinica Xing and Liu, Reference Xing and Liu1973, from the Chuanlingguo Formation, Yenliao region, Chih County of Hopei, northern China, Mesoproterozoic, and junior synonym of D. macroreticulata Xing and Liu (Reference Xing and Liu1973, pl. I:18) (Agic et al., Reference Agic, Moczydłowska and Yin2015).

Occurrence

Paleoproterozoic and Mesoproterozoic of China (Ruyang and Gaoshanhe Groups) (Xing and Liu, Reference Xing and Liu1973), Australia (Roper Group) (Javaux et al., Reference Javaux, Knoll and Walter2001), Belt Supergroup (Adam, Reference Adam2014).

Description

Only three specimens observed in the Roper population, one specimen measured: 50 µm in diameter with polygonal plates less than 2 µm wide. No excystment structure observed.

Remarks

Agic et al. (Reference Agic, Moczydłowska and Yin2015) revised the taxonomy of the genus Dictyosphaera and synonymized all the species previously described (D. delicata, D. sinica, D. gyrorugosa, D. incrassata) to the senior species D. macroreticulata, described as 10 to 300 µm vesicles ornamented by a reticulate polygonal pattern consisting of interlocking 1–6 µm polygonal plates. Excystment by pylome or medial split. Because the holotype was not available for re-examination, they selected a lectotype from the same material as the holotype. In their original diagnosis, Hu and Fu (Reference Hu and Fu1982) described a reticulate surface ornamentation, but did not comment on its fine structure. TEM analysis by Yin et al. (Reference Yin, Yuan, Meng and Hu2005) subsequently demonstrated that the wall is made of interlocked polygonal plates 1–3 µm wide, perforated by nanopores observed with SEM on both the exterior and interior vesicle surfaces (Kaufman and Xiao, Reference Kaufman and Xiao2003). The wall ultrastructure is multilayered (FIB-EM analyses; Schiffbauer and Xiao, Reference Schiffbauer and Xiao2009), and excystment by partial rupture or a circular opening (pylome) has also been observed (Yin et al., Reference Yin, Yuan, Meng and Hu2005).

Dictyosphaera macroreticulata is reported from the ~1580–1460 Ma Lower Belt Group, USA (Adam, Reference Adam2014), as well as the 1400–1700 Ma Ruyang and broadly correlative Gaoshanhe groups of China, where it co-occurs with abundant Shuiyousphaeridium macroreticulatum, an acanthomorph with similar wall ornamentation but bearing many processes (Xiao et al., Reference Xiao, Knoll, Kaufman, Yin and Zhang1997; Schiffbauer and Xiao, Reference Schiffbauer and Xiao2009). In the Chinese assemblages, Dictyosphaera specimens may include life cycle or taphonomic variants of Shuiyousphaeridium (Xiao et al., Reference Xiao, Knoll, Kaufman, Yin and Zhang1997) that either lost or never formed the outer wall layer from which processes arise (Javaux et al., Reference Javaux, Knoll and Walter2004). The Chinese population includes vesicles ranging from 28 to 240 µm in diameter, with 1–4 µm platelets (Agic et al., Reference Agic, Moczydłowska and Yin2015). In the Roper Group, however, D. macroreticulata (=D. delicata) is rare and Shuiyousphaeridium absent. Dictyosphaera possibly occurs, as well, in the ~1000 Ma Stoer and lower Torridon groups, Scotland (Javaux, personal observation, 2008), although it is unnamed in Strother et al. (Reference Strother, Battison, Brasier and Wellman2011), who described a population as ellipsoidal fossils with walls made of highly ordered circular pits, creating a reticulate pattern and, therefore, differing from the plate-like wall structure of the Mesoproterozoic Dictyosphaera.

Kaufman and Xiao (Reference Kaufman and Xiao2003) suggested that D. macroreticulata (=D. delicata) was a photosynthetic eukaryote based on its complex morphology and C-isotopic composition. Neither morphology nor isotopic composition, however, is diagnostic with respect to energy metabolism, although the eukaryotic nature of this ornamented acritarch is convincing. Functionally, D. macroreticulata is most likely a cyst or resting stage common to the life cycles of metabolically diverse eukaryotes (see below).

Recently, Tang et al. (Reference Tang, Pang, Yuan, Wan and Xiao2015) described a new species, D. tacita, based on two specimens that differ from the other species by their smooth external surface and the presence of hexagonal platelets only on the interior vesicle surface. The hexagons are smaller (0.5–0.9 µm) and the vesicle diameter larger (100–120 µm) than those of D. macroreticulata (2–6 µm platelets, 10–20 µm vesicle diameter), D. sinica (0.5–1.5 µm platelets, 15–45 µm vesicle diameter), and D. delicata (1–3 µm platelets, 50–300 µm vesicle diameter). However, Agic et al. (Reference Agic, Moczydłowska and Yin2015) proposed a synonymy among D. delicata, D. macroreticulata, and other species of the genus based on the overlapping size range of the vesicles and wall platelets, and similar morphologies. Tang et al. (Reference Tang, Pang, Yuan, Wan and Xiao2015) argued that this needs reevaluation.

Genus Eomicrocystis Golovenok and Belova, Reference Golovenok and Belova1986

Type species

Eomicrocystis magilca Golovenok and Belova, Reference Golovenok and Belova1986

Other species

Eomicrocystis elegans Golovenok and Belova, Reference Golovenok and Belova1986

Eomicrocystis magilca Golovenok and Belova, Reference Golovenok and Belova1986

Figure 2.16–2.18

1986 Eomicrocystis magilca Reference Golovenok and BelovaGolovenok and Belova, p. 95 [English version p. 89], pl. 7., figs. 5–7.

1989 Eomicrocystis magilca; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 91, pl. 19, fig. 7.

1994 Eomicrocystis magilca; Reference Hofmann and JacksonHofmann and Jackson, p. 25, pl. 18, figs. 2–4.

1997 Eomicrocystis magilca; Reference CotterCotter, p. 258, fig. 7A, B.

2016 Eomicrocystis magilca; Baludikay et al., Reference Baludikay, Storme, François, Baudet and Javaux2016, p. 179, fig. 12f.

Holotype

Eomicrocystis malgica Golovenok and Belova, Reference Golovenok and Belova1986, pl. 7, fig. 5, from the Malgina Formation in the Uchur-Maya region, eastern Siberia.

Description

Small ovoid or spheroidal colonies of light brown, loosely packed, small spheroidal to ovoid vesicles of uniform size, sometimes dividing by binary fission, without enclosing envelope. Three colonies observed, with cells 3 µm wide and 6–7 µm long.

Occurrence

Mesoproterozoic and early Neoproterozoic, Roper Group, Australia; Malgina Formation in the Uchur-Maya region, eastern Siberia (Golovenok and Belova, Reference Golovenok and Belova1986); Bylot Supergroup, Canada (Hofmann and Jackson, Reference Hofmann and Jackson1994); Belt Supergroup, USA (Adam et al., 2016); Mbuyi-Mayi Supergroup, RDC (Baludikay et al., Reference Baludikay, Storme, François, Baudet and Javaux2016).

Remarks

Eomicrocystis differs from the genus Coleogleba (Strother et al., Reference Strother, Knoll and Barghoorn.1983) in lacking an organic matrix or distinct envelope enclosing the cell clusters, and from the genus Coniunctiophycus by the absence of a single dense mass less than a micron in diameter within cells, the smaller cell size (10 µm in C. sp), and the shape of the colony described in the Belt Supergroup as “spheroidal colony of tens of individuals, from which a wide, linear extension of more cells emerges and folds back onto itself to form a single reticulate fold” (Adam et al., Reference Adam, Skidmore and Mogk2016, p. 16). It also differs from described species of Myxococcoides (Schopf, Reference Schopf1968) in the size and organization of constituent cells. Eomicrocystis malgica differs from E. elegans by the smaller size of the cells’ minimum diameter (3–5 µm versus 6–9 µm) and more regular shape of the aggregate. The Roper colonies have cell diameters intermediate between the two species, but also have an irregular aggregate shape, and therefore are identified as E. malgica.

Genus Gemmuloides Samuelsson and Butterfield, Reference Samuelsson and Butterfield2001

Type species

Gemmuloides doncooki Samuelsson and Butterfield Reference Samuelsson and Butterfield2001

cf. Gemmuloides doncooki Samuelsson and Butterfield, Reference Samuelsson and Butterfield2001

Figure 4.1

2001 Gemmuloides doncooki Reference Samuelsson and ButterfieldSamuelsson and Butterfield, p. 248, fig 7, D–F.

2014 Gemmuloides doncooki; Reference AdamAdam, p. 35, fig. 13.

Holotype

Gemmuloides doncooki Samuelsson and Butterfield, Reference Samuelsson and Butterfield2001, p. 248, 249, GSC 117042 (Fig. 7D), Lone Land Formation, NW flank of Cap Mountain (63°24'11''N, 123°14'12''W), Canada, approximately 2 m above carbonate ledge. Sample 94-LL-8. GSC loc. C-404520.

Description

Two spheromorphs, 260 and 85 µm diameter, with chagrinate wall were observed, each with a dark central sphere; only one shows evidence of budding. The presence of a dark central body is not included in the original description, but this may reflect taphonomic rather than systematic differences. The presence of a bud allies the Roper fossils with Gemmuloides doncooki.

Occurrence

Roper Group, Australia; Lone Land Formation, Canada (Samuelsson and Butterfield, Reference Samuelsson and Butterfield2001); Belt Supergroup, USA (Adam, Reference Adam2014).

Remarks

The Roper assemblage includes another budding spheromorph, Blastanosphaira kokkoda, which differs from cf. G. doncooki by its colonial habit, smaller diameter, thinner chagrinate wall with thin folds, and multiple buds of larger size relative to the mother cell, as well as by the presence of circular scars left by detached buds. Coneosphaera sp. in the Bylot Group (Hofmann and Jackson, Reference Hofmann and Jackson1994) has several smaller vesicles attached to a central one, resembling a specimen illustrated by Hermann (Reference Hermann1990, p. 20, pl. 5.11) from the Miroedikha Formation, Siberia, which also differs from cf. G. doncooki. Gemmuloides doncooki is also reported in the Belt Supergroup, Montana, USA (Adam, Reference Adam2014).

Genus Leiosphaeridia Eisenack, Reference Eisenack1958, emend. Downie and Sarjeant, Reference Downie and Sarjeant1963, emend. Turner, Reference Turner1984

Type species

Leiosphaeridia baltica Eisenack, Reference Eisenack1958.

Remarks

Jankauskas (1989) revised the taxonomy of the genus Leiosphaeridia (see for detailed synonymy) and proposed an operational approach to species recognition within the genus Leiosphaeridia, essentially diagnosing species based on a combination of two characters: size and wall texture. Subsequent workers have tended to follow this scheme, with some modifications (e.g., Butterfield et al., Reference Butterfield, Knoll and Swett1994; Hofmann and Jackson, Reference Hofmann and Jackson1994). Jankauskas (1989) discriminated four smooth-walled Leiosphaeridia species: L. crassa and L. jacutica are thick-walled leiospheres, smaller or larger than 70 µm in diameter, respectively; L. minutissima and L. tenuissima are thin-walled vesicles, again smaller or larger than 70 µm in diameter, respectively. A fifth species, L. ternata differs from other species in having a distinctively rigid, opaque wall that fractures radially. Chuaria circularis is also a smooth-walled spheromorph, but can be discriminated from the leiospheres by its much thicker wall (at least 2 µm thick), concentric folds and wrinkles, and large diameter (0.43–3.5 mm), leaving textured imprints on bedding surfaces (Butterfield et al., Reference Butterfield, Knoll and Swett1994).

The difficulty of applying the modified Jankauskas classification lies in the potential challenge of estimating wall thickness (underscored by Butterfield et al., Reference Butterfield, Knoll and Swett1994) and in classifying populations that do not fit neatly within the proposed size classes, as also noticed by Porter and Riedman (in press) in populations from the Neoproterozoic Chuar Group. Thus, while Butterfield et al. (2004) and Hofmann and Jackson (Reference Hofmann and Jackson1994) reported a taxonomic break at 70 µm, there is little in the size frequency diagrams they present to justify this. Wall thickness has commonly been estimated on the basis of color or fold morphology, but wall color can vary as a function of taphonomy, thermal maturity, or original composition. Butterfield (in Butterfield et al., Reference Butterfield, Knoll and Swett1994, p. 11–12) has discussed the distinction between the thickness of folds and the thickness of the wall, which are not necessarily correlated. Previous study of wall ultrastructure in different Leiosphaeridia species from the Roper Group (Javaux et al., Reference Javaux, Knoll and Walter2003, Reference Javaux, Knoll and Walter2004) showed that L. crassa with thick lanceolate folds had a thinner wall than L. tenuissima with thin sinuous folds. We suggest that fold morphology, which reflects the taphonomy of walls with biological differences in flexibility, provides a more objective criterion than wall thickness or color. In this view, L. crassa and L. jacutica have thick lanceolate folds, whereas L. minutissima and L. tenuissima have thin sinuous folds.

Size frequency distribution presents a second complication, because many leiosphaerid populations transgress the 70 µm boundary taken to separate species. For example, we measured the minimum diameter of specimens of different color (dark brown, medium brown, light brown) and fold morphology (broad lanceolate or thin sinuous folds) within the Roper assemblage and observed no size break around 70 µm in these different morphotypes (Figs. 3.1–3.7, 4.4–4.8). This difficulty has also been underlined by Porter and Riedman (2016) for Chuar Group populations. We suggest that species should be distinguished on the basis of modal rather than maximum diameter, so that Leiosphaeridia with lanceolate folds and a modal size <70 µm would be assigned to L. crassa, whereas populations with lanceolate folds and a modal size >70 µm would be placed in L. jacutica. This has the advantage of removing ambiguity in size frequency distributions while retaining the species distinctions used in many previous publications.

Figure 3 Size frequency distribution of leiospheres: (1) Size frequency distribution of all Leiosphaeridia crassa/jacutica (dark-, medium-, and light-brown walls); (2) Size frequency distribution of dark-brown Leiosphaeridia crassa/jacutica; (3) Size frequency distribution of medium-brown Leiosphaeridia crassa/jacutica; (4) Size frequency distribution of light-brown Leiosphaeridia crassa/jacutica; (5) Size frequency distribution of all Leiosphaeridia minutissima/tenuissima (medium- and light-brown walls); (6) Size frequency distribution of light-brown Leiosphaeridia minutissima/tenuissima; (7) Size frequency distribution of medium-brown Leiosphaeridia minutissima/tenuissima.

Figure 4 Photographs of Roper organic-walled microfossils (color figures are available in the online version of this paper): (1) cf. Gemmuloides doncooki. (2, 3) Leiosphaeridia atava. (4) Light-brown Leiosphaeridia crassa/jacutica. (5) Medium-brown Leiosphaeridia crassa/jacutica. (6) Dark-brown Leiosphaeridia crassa/jacutica. (7) Light-brown Leiosphaeridia minutissima/tenuissima. (8) Medium-brown Leiosphaeridia minutissima/tenuissima. (9) Leiosphaeridia ternata. (10–12) Leiosphaeridia sp., (11) showing details of wall texture of specimen in (10). Scale bar in (1) is: (1) 85 µm; (2) 12 µm; (3) 15 µm; (4) 14 µm; (5) 17 µm; (6) 10 µm; (7–8) 6 µm; (9) 90 µm; (10) 30 µm; (11) 60 µm; (12) 10 µm. Slides and England coordinates are (1) U6 230.8 m .2 L2Y/1; (2) U6 305.1 m.2A O26 ¾; (3) U6 305.1 m.2A U37/1; (4, 7) U6 230.8 m .2 H46/G46 (area); (5) U6 240.2 m .2 O34/3; (6) U6 305.1 m .2A T26/1; (8) U6 305.1 m .2A U20; (9) U5 125.1 m; (10, 11) U6 305.1 m 2A N20; (12) U6 230.8 m.2 S24/2.

Based on the presence of a multilayered recalcitrant wall, Roper leiospheres have been interpreted as eukaryotic (Javaux et al., Reference Javaux, Knoll and Walter2004). In the absence of supporting TEM analyses of wall ultrastructure, this attribution cannot be extended to all Proterozoic leiospheres; very likely the genus Leiosphaeridia is polyphyletic and their simple morphologies may record both prokaryotes and eukaryotes. Occasionally, medial split excystment structures have been observed in Roper specimens, suggesting that at least some of these fossils were resting cysts; however, even here, caution is advisable, because baeocyte-producing cyanobacterial cells can split in ways that resemble medial split excystment (Waterbury and Stanier, Reference Waterbury and Stanier1978, p. 13, fig. 4).

Leiospheres may occur as isolated specimens assigned to Leiosphaeridia, compact colonies called Synsphaeridium spp., or loose colonies named Symplassosphaeridium spp., possibly reflecting cyst and vegetative stages of the same population or life stages of different organisms. Single leiospheres might also be detached specimens from a colony (Hofmann and Jackson, Reference Hofmann and Jackson1994). The simple morphologies of leiospheres make it difficult to choose among these hypotheses, but more detailed analyses of wall ultrastructure and chemistry may provide the requisite tests (Javaux et al., Reference Javaux, Knoll and Walter2004; Javaux and Marshall, Reference Javaux and Marshall2006).

Leiosphaeridia atava (Naumova, Reference Naumova1960) Jankauskas, Mikhailova, and Hermann, Reference Jankauskas, Mikhailova and Hermann1989

Figure 4.2–4.3

1960 Megasacculina atava Reference NaumovaNaumova, pl. 3, fig. 15.

1989 Leiosphaeridia atava (Naumova, Reference Naumova1960); Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 74, pl. 10, figs. 4–7.

2016 Leiosphaeridia atava; Reference Sergeev, Knoll, Vorob’eva and SergeevaSergeev et al., fig. 4.5.

Holotype

Preparation 452/1, paleontological collection at the Institute of Precambrian Geology and Geochronology, St. Petersburg, Russia, upper Riphean (Tonian), Lakhanda Group, Neryuen Formation, Uchur-Maya region, Siberia. (The holotype was lost, as mentioned by Sergeev and Lee, Reference Sergeev and Lee2006).

Occurrence

The Mainoru Formation, Roper Group, Australia; the Lakhanda Group, Neryuen Formation, Uchur-Maya region, Siberia (Jankauskas, 1989); the Koltasy Formation, Russia (Sergeev et al., Reference Sergeev, Knoll, Vorob’eva and Sergeeva2016); the El Mreiti Group, Taoudeni Basin, Mauritania (Beghin et al., in Reference Beghin, Storme, Blanpied, Gueneli, Brocks, Poulton and Javauxreview).

Description

Spheroidal to oval vesicle with a fine granular, flexible wall, with numerous folds, 46 to 56 µm in diameter (N=4); two specimens with a dark, internal bleb of organic matter. No excystment structures observed.

Remarks

Leiosphaeridia atava differs from L. obsuleta by its diameter larger than 70 µm (Jankauskas, 1989).

Leiosphaeridia crassa (Naumauva, Reference Naumova1949), emend. Jankauskas in Jankauskas, Mikhailova, and Hermann, Reference Jankauskas, Mikhailova and Hermann1989

Figure 4.4–4.6

1949 Leiotriletes crassus Reference NaumovaNaumova, p. 54, pl. 1, figs. 5, 6; pl. 2, figs 5, 6.

1989 Leiosphaeridia crassa; Jankauskas in Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 75, pl. 9, figs. 5–10.

1989 Leiosphaeridia minutissima; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 75, pl. 9, figs. 2, 3.

Holotype

No holotype was designated by Naumova (Reference Naumova1949), from the Lontova Formation, lower Cambrian, Estonia. A lectotype was designated by Jankauskas (in Jankauskas et al., Reference Jankauskas, Mikhailova and Hermann1989, p. 75) from Naumova (Reference Naumova1949, pl. 1, fig. 3), but this specimen was part of Leiotriletes simplicissimus, which is a species that Jankauskas et al. (Reference Jankauskas, Mikhailova and Hermann1989) synonymized with a different species of L. minutissima (Porter and Riedman, 2016).

Emended diagnosis

A species of Leiosphaeridia with smooth, pliant walls with lanceolate folds and a modal diameter of less than 70 µm.

Occurrence

Proterozoic and lower Paleozoic, worldwide.

Description

Smooth-walled leiospheres with large lanceolate folds (Fig. 3.1–3.4). Minimum diameter ranges from 5 to 390 µm (mean: 58.1±40.2 µm, N=669). No statistical differences among dark brown, medium, and light brown subpopulations, with mean diameters and standard deviations of, 54.5±21.6 µm (N=61), 55.3±30.7 µm (N=191 µm), and 56.0±27.7 µm (N=116). Excystment by partial rupture and medial split.

Remarks

As noted above, the rationale for emending the diagnosis of this species stems from the desire to focus on observed rather than inferred wall characters and to articulate size distinctions in a way that will minimize ambiguity in observed populations. The emended diagnosis considers the presence of lanceolate folds on a smooth wall as a diagnostic character as opposed to the wall color, which is not considered as a valid character.

Leiosphaeridia jacutica (Timofeev, Reference Timofeev1966), emend. Mikhailova and Jankauskas in Jankauskas, Mikhailova, and Hermann, Reference Jankauskas, Mikhailova and Hermann1989

Figure 4.4–4.6

1966 Kildinella jacutica Reference TimofeevTimofeev, p. 30, pl. 7, fig. 2.

1989 Leiosphaeridia jacutica (Timofeev, Reference Timofeev1966); Mikhailova and Jankauskas in Jankauskas et al., Reference Jankauskas, Mikhailova and Hermann1989, p. 77, pl. 9, fig. 12; pl. 12, figs. 3, 6, 7, 9.

Holotype

Preparation number 452/1, Biostratigraphy Laboratory, Maya River Collection, late Mesoproterozoic/early Neoproterozoic Lakhanda Group, Russia (Timofeev, Reference Timofeev1966, pl. 7, fig. 2).

Emended diagnosis

A species of Leiosphaeridia characterized by smooth, pliant walls with lanceolate folds and a modal diameter greater than 70 µm.

Occurrence

Proterozoic worldwide.

Description

A species of Leiosphaeridia characterized by smooth, pliant walls with lanceolate folds and a modal diameter greater than 70 µm. Excystment by partial rupture and medial split. While we cannot exclude the possibility that these represent a long right-hand tail of the L. crassa population, we suspect that, by comparison to other mid-Proterozoic assemblages, distinct populations of large leiosphaerids were present in the Roper seaway.

Remarks

As noted above, the rationale for emending the diagnosis of this species stems from the desire to focus on observed rather than inferred wall characters and to articulate size distinctions in a way that will minimize ambiguity in observed populations. The emended diagnosis considers the presence of lanceolate folds on a smooth wall as a diagnostic character, as opposed to wall color, which is not considered as a valid character.

Leiosphaeridia minutissima (Naumova, Reference Naumova1949), emend. Jankauskas in Jankauskas, Mikhailova, and Hermann, Reference Jankauskas, Mikhailova and Hermann1989

Figure 4.7–4.8

1949 Leiotreletes minutissimus Reference NaumovaNaumova, p. 52, pl. 1, figs. 1, 2; pl. 2, figs. 1, 2.

1989 Leiosphaeridia minutissima (Naumova); Jankauskas in Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 79, pl. 9, figs. 1, 4, 11.

Lectotype

No holotype was designated by Naumova (Reference Naumova1949). Jankauskas (in Jankauskas et al., Reference Jankauskas, Mikhailova and Hermann1989, p. 80) designated a specimen of Leiotriletes minutissimus (pl. 1, fig. 1) from Naumova (Reference Naumova1949) as lectotype.

Emended diagnosis

A species of Leiosphaeridia characterized by smooth walls with sinuous folds and a modal diameter less than 70 µm.

Description

Smooth-wall spheromorphs with sinuous folds and a modal diameter less than 70 µm. Minimum diameter 21–117 µm (mean: 50.6±18.2 µm, N=216) (Figure 3.5–3.7). Light brown specimens 21–117 µm in minimum diameter (N=116, mean: 50.8±17.9 µm) and medium brown specimens 27–111 µm (N=47, mean: 49.6±19.1 µm). No dark brown specimens observed.

Occurrence

Proterozoic worldwide.

Remarks

As noted above, the rationale for emending the diagnosis of this species stems from the desire to focus on observed rather than inferred wall characters and to articulate size distinctions in a way that will minimize ambiguity in observed populations. The emended diagnosis considers the presence of sinuous folds on a smooth, thin wall as a diagnostic character, as opposed to wall color, which is not considered as a valid character.

Leiosphaeridia tenuissima Eisenack, Reference Eisenack1958 emend.

Figure 4.7–4.8

1958 Leiosphaeridia tenuissima Reference EisenackEisenack, p. 391, pl. 1, figs. 2, 3.

1989 Leiosphaeridia tenuissima; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 81, pl. 9, fig. 13.

Holotype

Preparation A3, 3 number 4 from the Dictyonema-shales of the lower Ordovician, St Petersburg area, Russia (Eisenack, Reference Eisenack1958, pl. 1, fig. 2).

Emended diagnosis

A species of Leiosphaeridia characterized by smooth walls with sinuous folds and a modal diameter (rather than maximum diameter) greater than 70 µm; the wall color is not a diagnostic criteria.

Description

Smooth wall spheromorphs with sinuous folds and a modal diameter greater than 70 µm. These may reflect a larger, uncommon population of Leiosphaeridia in Roper shales.

Occurrence

Proterozoic worldwide.

Remarks

As noted above, the rationale for emending the diagnosis of this species stems from the desire to focus on observed rather than inferred wall characters and to articulate size distinctions in a way that will minimize ambiguity in observed populations. The emended diagnosis considers the presence of sinuous folds on a smooth, thin wall as a diagnostic character as opposed to wall color, which is not considered as a valid character.

Leiosphaeridia ternata (Timofeev, Reference Timofeev1966), emend. Mikhailova and Jankauskas in Jankauskas et al., Reference Jankauskas, Mikhailova and Hermann1989

Figure 4.11

1966 Turuchanica ternata Reference TimofeevTimofeev, p. 45, pl. 9, fig. 8.

1989 Leiosphaeridia ternata (Timofeev); Mikhailova and Jankauskas in Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 81, pl. 11, figs. 2–4; pl. 12, figs. 4, 5, 8.

2016 Leiosphaeridia ternata; Reference Sergeev, Knoll, Vorob’eva and SergeevaSergeev et al., fig. 4.3, 4.4.

Holotype

Preparation 169/1, Biostratigraphical laboratory LAGED AN SSSR, Turukhansk collection, lower Tungunska, Turukhansk district; Miroedikhinsk series, Riphean (Mesoproterozoic and early Neoproterozoic boundary), rarely Ordovician (Timofeev, Reference Timofeev1966).

Occurrence

Found globally in worldwide Proterozoic successions.

Description

Compressed opaque spheromorph with thick, rigid walls commonly showing characteristic radial fractures. Diameter 15 to 110 µm.

Description

Large medium to dark brown spheroidal to oval vesicles with a characteristic cork-like wall texture made of 5–11 µm, irregular patchy areas of different colors and fabric; this texture may well be taphonomic, but if so, it reflects original differences in wall composition, compared to other leiosphaerids. Concentric folds at the periphery. The minimum diameter of 19 spheroidal specimens is 56–455 µm (mean: 159.8±96.3 µm). Three oval specimens measured 75–210 µm wide and 160–330 µm long.

Remarks

This species differs from another large leiosphere L. jacutica by its particular cork-like wall texture and a morphology that ranges from spheroidal to ovoidal. It also differs from Chuaria circularis, which has a thicker opaque, smooth wall. These specimens are left in open nomenclature until further characterization by SEM and TEM.

Genus Lineamorpha Vorob’eva, Sergeev, and Yu, Reference Vorob’eva, Sergeev and Yu2015

Type species

Lineamorpha elongata Vorob’eva, Sergeev, and Yu, Reference Vorob’eva, Sergeev and Yu2015, by monotypy.

Lineamorpha elongata Vorob’eva et al., Reference Vorob’eva, Sergeev and Yu2015

Figure 5.1–5.4

Figure 5 Photographs of Roper organic-walled microfossils: (1–4) Lineaforma lineata: (2) showing hollow extremity of specimen in (1), (3) specimen in situ in thin section. (5) Paleolyngbya catenata. (6–9) Satka favosa: (6) showing medial split and hollow interior, (8) showing hollow interior. (10) Siphonophycus kestron (bottom specimen) and S. typicum (top specimen). (11) Siphonophycus robustum. (12) Siphonophycus septatum. (13) Siphonophycus thulenema. (14) Squamosphaera colonialica. (15) Symplassophaeridium sp, (16–18) Synsphaeridium spp. Scale bar in (1) is: (1) 60 µm; (2) 100 µm; (3) 50 µm; (4) 110 µm; (5, 7) 15 µm; (6, 8) 20 µm; (9) 40 µm; (10, 13) 20 µm; (11, 12) 10 µm; (14) 50 µm; (15, 16) 33 µm; (17, 18) 15 µm. Slides and England coordinates are (1, 2) U5 125.1 m C13/3; (3) thin section 3785a R47/1; (4) A82/3 328.35 m.3 N41/4; (5) U5 130.5 ker E21; (6) U6 240.8 m .2 K23/3; (7) U6 305.1 m . E29; (8) U6 230.8 m.2 F14; (9) U6 230.8 m .2 J26/4; (10) U6 240.2 m .2 Z27/2; (11) U5 125.1 m .2 X48/4; (12) GG1 340.2 m.3 M13; (13) U6 240.2 m .2 Q18/3; (14) A82/3 328.35 m .3 K/L35; (15) A82/3 311.3 m .2 O5/2; (16) U5 125.1 m .2 R34/3; (17) A82/3 311.3 m .2 H40/4; (18) U5 151.3 m .2 Q/R29.

2004 “large striated tubes” Reference Javaux, Knoll and WalterJavaux et al., p. 126, fig 3 g–k.

2015 Lineamorpha elongata; Reference Vorob’eva, Sergeev and YuVorob’eva et al., p. 216, figs. 7 1–7.5.

2016 Lineamorpha elongata; Adam et al., fig. 9 A–D.

Holotype

Figure 7.4, Vorob’eva et al., Reference Vorob’eva, Sergeev and Yu2015, GINPC 14711-804, locality AK-14, Kotuikan River valley, Kotuikan Formation, Anabar Uplift, northern Siberia.

Occurrence

Early Mesoproterozoic, Jalboi, Crawford, and upper Mainoru formations, Roper Group, Australia; Belt Supergroup, Montana, US (Adam, Reference Adam2014); and Kotuikan Formation, northern Siberia (Vorob’eva et al., Reference Vorob’eva, Sergeev and Yu2015).

Description

Longitudinally striated hollow tubes (not a sheath around bundled filamentous sheaths) that often break into fragments, so maximum length is unknown but millimetric, 34 to 150 µm in diameter, fragment length: 131 to 473 µm (N=25).

Remarks

In the Roper population, there seems to be no relation between diameter and fragment length, nor dominant fragment length, suggesting random fragmentation of longer, probably millimetric, tubes. Light microscopy shows longitudinal, micron-scale striations along the tubes while SEM reveals a thick multilayered wall of densely packed granules, but no longitudinal striations. At the ultrastructural level (TEM), however, transverse sections of the wall show a clear alternation of electron-dense and electron-tenuous bands that correspond in size and distribution to the striations observed by light microscopy (Javaux et al., Reference Javaux, Knoll and Walter2004). The wall is ~1 μm thick, occasionally with an outer, electron-dense layer. The striations, thus, are not wall sculpture, but reflect original compositional heterogeneities in the tube wall, indicating complex physiological controls on wall formation.

The Roper material appears to be indistinguishable from the type of Lineaforma elongata from the lower Mesoproterozoic Kotuikan Formation, northern Siberia (Vorob’eva et al., Reference Vorob’eva, Sergeev and Yu2015). In the Roper Group, these filaments occur as transported fragments, contributing less than 3% to the entire assemblage, but up of 40% in lower-shoreface to inner-shelf shales. The rounded, closed tube ends observed in the Russian population were not observed in fragmental Roper specimens. The large size and complex wall ultrastructure of these microfossils suggest a eukaryotic affinity (Javaux et al., Reference Javaux, Knoll and Walter2004).

Genus Palaeolyngbya Schopf, Reference Schopf1968

Type species

Palaeolyngbya barghoorniana Schopf, Reference Schopf1968

Palaeolyngbya catenata Hermann, Reference Hermann1974

Figure 5.5

1974 Palaeolyngbya catenata Reference HermannHermann, p. 8, pl. 6, fig. 5.

1980 Oscillariopsis robusta; Reference Horodyski and DonaldsonHorodyski and Donaldson, p. 149, fig. 13H.

1994 Palaeolyngbya catenata; Butterfield et al., Reference Butterfield, Knoll and Swett1994, p. 61, fig. 25F–G.

Holotype

No holotype designated by Hermann, Reference Hermann1974, p. 8, 9, pl. 6, fig. 5, Tonian, Miroedikha Formation, Russia.

Description

Cellular trichome within a single encompassing sheath, cells 26 µm wide and 6 µm long.

Type species

Satka favosa Jankauskas, Reference Jankauskas1979a

Satka favosa Jankauskas, Reference Jankauskas1979a

Figure 5.6–5.9

1979a Satka favosa Reference JankauskasJankauskas, pl. 4, fig. 2.

1980 “polygonally segmented sphaeromorphs” Reference HorodyskiHorodyski, p. 658, pl. 2, figs. 8–12.

1989 Satka favosa; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 51, pl. 4, figs. 1, 2?

1989 Satka elongata; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 51, pl. 4, figs. 3, 5.

1989 Satka granulosa; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 51, pl. 4, fig. 8.

1994 Satka spp. Reference Hofmann and JacksonHofmann and Jackson, pl. 18, figs. 26–31.

2001 Satka favosa; Reference Javaux, Knoll and WalterJavaux et al., pl. 1e, f.

2003 Satka favosa; Reference Javaux, Knoll and WalterJavaux et al., figs. 1–10, 11.

2004 Satka favosa; Javaux et al., Reference Javaux, Knoll and Walter2004, p. 125, fig. 3a–f.

Holotype

Specimen pl. 4, fig. 2, preparation 16-1815-635, lower and middle Riphean (Mesoproterozoic) successions of the southern Urals, Russia (Jankauskas, 1989).

Description

Hollow oval spheromorph, 24 to 100 µm wide and 29 to 100 µm long (N=122), with walls made of tessellated 6 to 16 µm (minimum diameter) polygonal plates and with no external envelope. Excystment by medial split (Fig. 5.6).

Occurrence

Satka favosa, as described here, seems to be restricted to Mesoproterozoic rocks, including lower Mesoproterozoic shales of the Belt Supergoup (“polygonally segmented sphaeromorphs” of Horodyski, Reference Horodyski1980; Adam, Reference Adam2014), the Bylot Supergroup of the Canadadian Arctic (Hofmann and Jackson, Reference Hofmann and Jackson1994, as Satka spp., pl. 18, figs. 26–31), and lower and middle Riphean (Mesoproterozoic) successions of the southern Urals (Jankauskas et al., Reference Jankauskas, Mikhailova and Hermann1989).

Remarks

The wall construction of S. favosa identifies it as a eukaryote, most likely the resting stage of some protist. Great confusion exists in the literature concerning Satka and its species. Jankauskas (1989) differentiated S. favosa from S. elongata (40–70 µm) by its smaller size and the characteristic shape of its inward-curving plates; S. colonialica (up to 150 µm) was segregated because of its simpler regular shape and better-defined plates; and S. granulosa (40–50 µm wide to 75–125 µm long) was differentiated by its smaller size and granular appearance (linked to the presence of internal bodies). The specimens illustrated by Jankauskas (1989) as Satka elongata (pl. 4, figs. 3, 5) and Satka granulosa (pl. 4, fig. 8) also resemble Satka favosa as described here. Satka squamifera is described as having rounded plates and an external envelope. From our observations, however, the “plates” of S. squamifera represent the imprints of spheroidal cells on an encompassing envelope; therefore, we interpret this population as a colonial microorganism, perhaps cyanobacterial, which is unlikely to be linked to S. favosa at the domain level, and recently placed within the new genus Squamosphaera (Tang et al., Reference Tang, Pang, Yuan, Wan and Xiao2015).

Genus Siphonophycus Schopf, Reference Schopf1968, emend. Knoll, Swett, and Mark, Reference Knoll, Swett and Mark1991

Type species

Siphonophycus kestron Schopf (Reference Schopf1968).

Occurrence

Widespread in Proterozoic assemblages, common throughout the Roper Group.

Description

Fragments of smooth, non-septate tubes, commonly interpreted as the sheaths of oscillatorialean cyanobacteria.

Remarks

Different species are distinguished on the basis of cross-sectional diameter (revision in Butterfield et al., Reference Butterfield, Knoll and Swett1994): S. thulenema: 0.5 µm; S. septatum: 1–2 µm; S. robustum: 2–4 µm; S. typicum: 4–8 µm; S. kestron: 8–16 µm; and S. solidum: 16–32 µm. Five species occur in Roper shales: S. kestron, S. robustum, S. septatum and S. typicum occur as transported fragments; and S. thulenema forms small balls of thin filamentous sheaths. Siphonophycus spp. are commonly interpreted as the sheaths of oscillatorialean cyanobacteria.

Siphonophycus kestron Schopf, Reference Schopf1968

Figure 5.10

1968 Siphonophycus kestron Reference SchopfSchopf, p. 671, pl. 80, figs. 1–3.

1971 Siphonophycus kestron; Reference Schopf and BlacicSchopf and Blacic, pl. 109, figs. 3, 4.

1992 Siphonophycus kestron; Reference SergeevSergeev, p. 95, pl. 16, figs. 8, 9.

1992 Siphonophycus kestron; Reference SchopfSchopf, pl. 31, fig. J.

1994 Siphonophycus kestron; Reference Butterfield, Knoll and SwettButterfield et al., fig. 21D.

2001 Siphonophycus kestron; Reference Sergeev and LeeSergeev and Lee, p. 8, pl. 1, fig. 1.

2006 Siphonophycus kestron; Reference Sergeev and LeeSergeev and Lee, pl. 1, fig. 10.

2006 Siphonophycus kestron; Reference SergeevSergeev, p. 214, pl. 22, figs. 1, 2; pl. 28, fig. 3; pl. 36, fig. 3; pl. 44, fig. 11; pl. 45, figs. 3, 6.

Holotype

Specimen pl. 80, fig. 1 (Schopf, Reference Schopf1968), thin section Bit. Spr. 6-3, Paleobotanical Collections, Harvard University number 58469, from Neoproterozoic Bitter Springs Formation, Amadeus Basin, Australia.

Description

Fragments of smooth, non-septate tubes, 8–16 µm in diameter, most specimens 8–9 µm, a few up to 16 µm.

Holotype

Specimen pl. 83, fig. 1 (Schopf, Reference Schopf1968), thin section Bit. Spr. 10-1, Paleobotanical Collections, Harvard University number 58491 from Neoproterozoic Bitter Springs Formation, Amadeus Basin, Australia.

Description

Smooth filamentous sheaths 2–4 μm in diameter, most specimens 2–3 µm in diameter.

Holotype

Specimen pl. 86, fig. 11 (Schopf, Reference Schopf1968), thin section Bit/Spr 6–3, Paleobotanical collections, Harvard University, number 58527 from the Neoproterozoic Bitter Springs Formation, Amadeus Basin, Australia.

Description

Fragments of smooth, non-septate tubes, 1–2 µm in diameter. Common, as transported fragments.

Holotype

HUPC 62718, fig. 22I, slide 86-G-62-46, R-28-3, Algal Dolomite Member, Svanbergfjellet Foramtion, Geerabukta (79°35'30''N, 17°44''E), 55 m above base of member.

Description

Fragments of thin, smooth, non-septate tubes, 0.5 µm in diameter, forming small balls of enrolled filamentous sheaths.

Holotype

Specimen pl. 6, figs. 1, 2 (Hermann, Reference Hermann1974), preparation number 49/2T, Neoproterozoic Miroyedikha Formation, Krasnoyarsk Krai in Turukhansk region, near Maya River, Siberia.

Description

Fragments of thin smooth, non-septate tubes, 4–8 µm in diameter.

Type species

Squamosphaera colonialica (Jankauskas, Reference Jankauskas1979b) Tang et al., Reference Tang, Pang, Yuan, Wan and Xiao2015 by monotypy

Squamosphaera colonialica (Jankauskas, Reference Jankauskas1979b) Tang et al., Reference Tang, Pang, Yuan, Wan and Xiao2015

Figure 5.14

1979b Satka colonialica Reference JankauskasJankauskas, p. 192, pl. 1, figs. 4, 6.

1985 Satka colonialica; Reference Knoll and SwettKnoll and Swett, p. 468, pl. 53, figs. 4–6, 8.

1989 Satka colonialica; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 51, pl. 4, figs. 4, 7.

1989 Satka squamifera; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 52, pl. 4, fig. 10; pl. 5, fig.1–8

1997 Satka colonialica; Reference SamuelssonSamuelsson, p. 175, fig. 9A, B.

1999 Satka colonialica; Reference CotterCotter, p. 77, fig. 7C.

1999 Satka colonialica; Reference Samuelsson, Dawes and VidalSamuelsson et al., fig. 4G.

2015 Squamosphaera colonialica; Tang et al., Reference Tang, Pang, Yuan, Wan and Xiao2015, p. 312, fig. 12 A–C2, fig. 13 A–F2

in press Squamosphaera colonialica; Reference Porter and RiedmannPorter and Riedman, fig. 17, 1–7. [See for complete synonymy]

Holotype

Number 16-62-4762/22, slide 1. Well Kabakovo-62, 4762-4765 m. Neoproterozoic Zigazino-Komarovo Formation, Ufa, Bashkirian Urals (Jankauskas, 1979, fig. 4).

Description

Single-walled, spheroidal, tomaculate, or irregularly shaped vesicles with irregular outline characterized by numerous broadly domical bulges. Vesicles 29–166 µm wide and 66–184 µm long (N=37); individual bulges 11 to 14 µm in diameter.

Remarks

The Roper population closely matches the emended diagnosis provided by Porter and Riedman (in Reference Porter and Riedmannpress). Populations assigned here to the genus Squamosphaera were originally classified as a species of the genus Satka (Jankauskas, Reference Jankauskas1979b). As discussed above, the type species of Satka, S. favosa, is characterized by a wall of tessellated plates, which is far different from the vesicles observed in S. colonialica. The two species should not be placed in the same genus and doubtfully belong to the same domain. Tang et al. (Reference Tang, Pang, Yuan, Wan and Xiao2015) gave formal recognition to this by segregating populations of Satka colonialica into the new genus. Tang et al.’s (Reference Tang, Pang, Yuan, Wan and Xiao2015) diagnosis and description suggest that Squamosphaera was a cyst wall ornamented by broadly domical processes, but this conflicts with the irregular morphology of individual vesicles, both within Tang et al.’s (Reference Tang, Pang, Yuan, Wan and Xiao2015) illustrated materials and populations observed elsewhere. For this reason, Porter and Riedman (in Reference Porter and Riedmannpress) emended the diagnosis of Squamosphaera, identifying the domical surface features simply as bulges. Roper populations closely resemble those from the Chuar Group, and we interpret them as enveloped marked by imprints of internal cells no longer present.

Hofmann and Jackson (Reference Hofmann and Jackson1994, p. 28) described Satka colonialica from the Bylot Supergroup, the Canadadian Arctic, as a colony of packaged cells in “distinct belt-like rows transverse to the long axis of the colony,” with a smooth surface and distinct curvilinear folds. They further suggested that S. squamifera, S. granulosa, and S. elongata might be taphonomic variants of the same taxon, and mentioned S. elongata Jankauskas, 1989 as the senior synonym to which other species should be referred. Satka favosa, however, is actually the senior species of the genus Satka (Jankauskas, Reference Jankauskas1979b). Hofmann and Jackson (Reference Hofmann and Jackson1994) also include in their suggestion of synonymy a Bylot population referred to Satka spp. that we interpret as S. favosa (see above). Several types of coccoidal cyanobacteria (Chroococcales and Pleurocapsales) and green algae (such as Pandorina) can produce colonies of packed spheroidal cells embedded in an envelope of amorphous mucilage matrix. Less commonly, the individual cells have a single wall rather than a multilamellate envelope, are closely packed, and the colony is surrounded in a structurally defined envelope, such as in modern cyanobacteria that produce baeocytes (endospores) within a parental wall (Chroococcidiopsis and Staniera/Dermocarpa). Squamosphaera colonialica resembles these pleurocapsalean cyanobacteria, with the internal cells not preserved, only their imprints on the wall. Squamosphaera differs from Synsphaeridium spp., which are colonies without an envelope.

Genus Symplassosphaeridium Timofeev, Reference Timofeev1959

Symplassosphaeridium sp.

Figure 5.15

Description

Aggregates of loosely packed, smooth-walled vesicles of variable size, but with similar morphology and size within a colony. Differs from Synsphaeridum by the loose packing of vesicles.

Type species

Synsphaeridium gotlandicum Eisenack, Reference Eisenack1965.

Synsphaeridium sp.

Figure 5.16–5.18

Occurrence

Widespread in Proterozoic and Phanerozoic rocks.

Description

Aggregates of contiguous smooth-walled vesicles, sometimes with internal inclusions, without envelope. Vesicles are similar in morphology and size within a colony. Colonies have variable size, from broadly spherical to elongated and irregular. Cell diameter ranges from 4 to 40 µm, and colonies can be up to 180 µm or more in diameter.

Type species

Tappania plana Yin, Reference Yin1997.

Other species

Tappania tubata Yin, Reference Yin1997; Tappania gangaei Prasad and Asher, Reference Prasad and Asher2001.

Tappania plana Yin, Reference Yin1997

Figure 6.1–6.15

Figure 6 Photographs of Roper organic-walled microfossils: (1–15) Tappania plana: arrow in (1) showing furcating process, arrows in (2–4) showing septae in processes, (3) showing details from specimen in (2), arrow in (11) showing the area of locally grouped small processes shown in (12), arrow in (15) shows open neck-like expansion, suggesting excystment structure. (16) Tortunema sp. (17, 18) Trachytrichoides sp.: (18) showing details of cells morphology in filaments in (17). Scale bar in (1) is: (1, 2) 40 µm; (3, 11) 10 µm; (4, 8, 14) 20 µm; (5, 9, 16, 17) 30 µm; (6, 10, 12, 15, 18) 15 µm; (7) 27 µm; (13) 25 µm. Slide and England finder coordinates: (1) GG1 340.2 m .3 B X36/2, (2, 3) GG1 340.2 m .2 A J47/2, (4) GG1 340.2 m .3B T40/2, (5) GG1 340.2 m .2A E28/4, (6) U5 151.3 m .2 Q28/3, (7) GG1 326.2 m .2 V33/1, (8) U5 151.3 m .2 Y14/2, (9) GG1 340.2 m .3 H26/2, (10) GG1 326.2 m .3 F39/1, (11, 12) GG1 340.2 m .2 E17/1, (13) GG1 326.2 m .2 Y28/4, (14) GG1 340.2 m .3 O19/1, (15) U5 130.5 m .2 U9, (16) A82/3 379.1M G57/0, and (17) U6 240.2 m .2B J34/1.

1997 Tappania plana Reference YinYin, p. 23, pl. 1, figs. 4, 6, 7.

1997 Tappania tubata Reference YinYin, p. 23, 24, pl. 2, figs. 1, 3, 4, 6.

1997 Tappania plana; Reference Xiao, Knoll, Kaufman, Yin and ZhangXiao et al., p. 205, fig. 3c.

2001 Tappania plana; Reference Prasad and AsherPrasad and Asher, p. 73, pl. 2, figs. 1–3, 9; pl. 3, figs. 1–6.

2001 Tappania tubata; Reference Prasad and AsherPrasad and Asher, p. 74, pl. 2, figs. 4–7.

2001 Tappania gangaei; Reference Prasad and AsherPrasad and Asher, p. 74, pl. 2, figs. 8, 10.

2001 Tappania plana; Reference Javaux, Knoll and WalterJavaux et al., pl. 1a–c.

2004 Tappania plana; Reference Javaux, Knoll and WalterJavaux et al., p. 124, fig. 2a–e.

2009 Tappania plana; Reference NagovitsinNagovitsin, fig. 2 a–e.

Holotype

Sample and slide M 9208-1, L4/37, Shuiyou section, southern Shanxi, North China; lower shales of Beidajian Formation of the Ruyang Group (Meso-Neoproterozoic) (Yin, Reference Yin1997, pl. 1, fig. 7).

Description

Size 15 to 158 µm (N=48), irregularly spheroidal vesicle bearing zero to 21 tubular, heteromorphic, sometimes branching, sometimes septate processes with closed relatively dark, rounded ends; zero to four neck-like expansions; zero to three bulbous protrusions. Process length up to 8 µm; bulbous expansions 2 µm wide; neck up to 2 µm high and 2 µm wide; two specimens show septate processes (Fig. 6.2–6.4), two others with branching processes. One specimen with a neck-like expansion shows a concentration of small (~8 µm long) processes with dark ends in one area of the vesicle surface, and another has small (3–5 µm long), hair-like spines, which are probably developing processes (not shown). The vesicle occasionally includes a dark cytoplasmic remnant. Specimens may bear only broad neck-like extensions (Fig. 6.6, 6.7, 6.10), or only processes (zero to 21) (Fig. 6.2, 6.5, 6.9, 6.13), or both. Neck-like extensions usually have a dark rim. In one specimen without processes, this trapezoidal extension is open, possibly indicating excystment (Fig. 6.15). Some specimens also show bulbous expansions suggestive of division by budding (Fig. 6.1); buds have semi-circular to oval convex morphology, whereas neck-like expansions have a trapezoidal shape, with side walls flaring outward and a convex end.

Occurrence

Tappania plana seems to be restricted to uppermost Paleoproterozoic and Mesoproterozoic rocks, including, in addition to the Roper Group, Australia (Javaux et al., Reference Javaux, Knoll and Walter2001); the Ruyang Group, China (Xiao et al., Reference Xiao, Knoll, Kaufman, Yin and Zhang1997; Yin, Reference Yin1997); the Bahraich and Kheinjua groups, India (Prasad and Asher, Reference Prasad and Asher2001; Prasad et al., Reference Prasad, Uniyal and Asher2005); the Kamo Group of Siberia (Nagovitsin Reference Nagovitsin2009; Nagovitsin et al., Reference Nagovitsin, Stanevich and Kornilova2010); and the Lower Belt Group, USA (Adam, Reference Adam2014).

Remarks

We observed a wide range of morphologies within Tappania, ranging from specimens with only broad, neck-like extensions, or only processes, to individuals with both broad, neck-like extensions and processes. On one fragmented specimen bearing a neck-like expansion, very small processes with dark, rounded closed ends are locally grouped on the vesicle wall. This is the first time this morphology has been reported in Tappania plana, however a single fragmented specimen and the large variability of the species precludes the creation of a new species at this time. Rare specimens show processes with septa, suggesting Tappania was multicellular. Ultrastructural analyses show a unilayered homogenous wall (Javaux et al., Reference Javaux, Knoll and Walter2004). The Roper population shows division by budding, and possible excystment through the opening of a neck-like extension. Specimens from the Kotuikan Formation illustrated by Nagovitsin (Reference Nagovitsin2009) suggest that Tappania could also reproduce by a simple binary division of the vesicle.

Yin (Reference Yin1997) described a second species of Tappania, T. tubata, that co-occurs with T. plana and has a broad tube-like extension but not trapezoidal neck-like extension, with a fimbriate distal margin and a few small processes on its extension surface. The Roper Tappania population displays the range of morphological characters originally ascribed to T. plana and T. tubata, occasionally on a single specimen. Therefore, we consider T. tubata to be a synonym of the senior species, Tappania plana. Prasad and Asher (Reference Prasad and Asher2001) described a third species, Tappania gangaei, based on the rounded bulbous extension, rather than trapezoidal or tube-like. However, in the Roper population, specimens may bear both neck-like and rounded extension (interpreted as budding structures), therefore here too, we consider T. plana as the senior synonym.

Vesicles bearing neck-like expansions but no processes are reported as cf. Tappania? in the late Mesoproterozoic–early Neoproterozoic Mbuyi-Mayi Supergroup, RDC (Baludikay et al., Reference Baludikay, Storme, François, Baudet and Javaux2016). However, the absence of processes on any of the six specimens observed so far and the younger age of these fossils leaves this occurrence ambiguous, even though Tappania populations elsewhere also include similar morphologies without processes. Indeed, so far, Tappania plana seems to be restricted to uppermost Paleoproterozoic to Mesoproterozoic rocks. Butterfield (Reference Butterfield2005a) described specimens from the mid-Neoproterozoic Wynniatt Formation, the Canadian arctic as Tappania, but these show a complex pattern of septation, peripheral branching and anastomosis not found in Mesoproterozoic populations and lack the neck-like expansions or the closed and rounded process terminations characteristic of older fossils. Therefore, the Neoproterozoic population might usefully be placed into a separate genus.

Genus Tortunema Hermann, 1976

Type species

Tortunema wernadskii (Schepeleva, Reference Schepeleva1960) Butterfield et al., Reference Butterfield, Knoll and Swett1994.

Tortunema sp.

Figure 6.16

Description

Fragmental remains of compressed cylindrical sheaths, 250–300 µm long and 30 µm wide (N=2), marked by thin, regularly spaced, transverse annulations that record cell boundaries of originally ensheathed trichomes. Spacing of prominent annulations 6 µm, commonly with less-pronounced annulations between them.

Type species

Trachytrichoides ovalis Hermann in Timofeev et al., Reference Timofeev, Hermann and Mikhailova1976.

Trachytrichoides sp.

Figure 6.17–6.18

Description

Multicellular filaments with ovoid cells and thick intercellular septa, no external sheath, 157 µm long and 5 µm wide (N=3), with individual ellipsoidal cells 5 µm wide x 6 µm long.

Remarks

A rare component of the Roper Group, differs from other filamentous taxa by the oval shape of the cells and absence of ellipsoidal fold between the cells (as in Arctacellularia), and from the type species T. ovalis by the smaller cell size than those of the holotype (25–35 µm wide and 30–60 µm long).

Genus Valeria Jankauskas, Reference Jankauskas1982, emend. Nagovitsin, Reference Nagovitsin2009

Type species

Valeria lophostriata (Jankauskas, Reference Jankauskas1979b) Jankauskas, Reference Jankauskas1982.

Valeria lophostriata (Jankauskas, Reference Jankauskas1979b) Jakauskas, Reference Jankauskas1982

Figure 7.1–7.4

Figure 7 Photographs of Roper organic-walled microfossils: (1–4) Valeria lophostriata: (1) showing half enrolled vesicle following medial split, (2) showing start of medial split, (3, 4) showing wall ornamentation by characteristic concentric striations. (5, 6) Unnamed form A, large compartmentalized colonial forms. (7, 8) Unnamed form B, opaque spheromorph, (8) showing details of folds at periphery. (9) Unnamed form C, spheromorphs connected by a filamentous expansion. (10) Unnamed form D, spheromorph with a filamentous expansion. (11) Unnamed form E, large smooth thick brittle spheromorph. (12) Unnamed form F, large filament in indented sheath. Scale bar in (1) is: (1) 100 µm, (2, 4, 8) 25 µm, (3) 10 µm, (5) 70 µm, (6) 120 µm, (7) 45 µm, (9) 18 µm, (10, 15) 30 µm, (11) 80 µm, and (12) 55 µm. Slide and England finder coordinates: (1) U6 305.1 m .2A S41, (2) U6 230.8 m .2 N27/2, (4) U6 233.6 B45/0, (5) U6 305.1 m .2A O/N39, (6) U6 305.1 m B45/1, (7) GG1 340.2 m .3B U30, (9) U5 125.1 m .2 M41/3, (10) GG1 326.2 m .2 E20/1, (11) U6 240.2 m .2U27/2, (12) U5 436.7 m .2 S51.

1979b Kildinella lophostriata Reference JankauskasJankauskas, p. 153, fig. 1.13–1.15.

1982 Valeria lophostriata; Reference JankauskasJankauskas, p. 109, pl. 39, fig. 2.

1983 Kildinosphaera lophostriata; Reference Vidal and SiedleckaVidal and Siedlecka, p. 59, fig. 6A–G.

1985 Kildinosphaera lophostriata; Reference Vidal and FordVidal and Ford, p. 361, fig. 4C, E–F.

1989 Valeria lophostriata; Reference Jankauskas, Mikhailova and HermannJankauskas et al., p. 86, pl. 16, figs. 1–5. [See for additional synonymy]

1994 Valeria lophostriata; Hofmann and Jackson, Reference Hofmann and Jackson1994, p. 24, pl. 17, figs. 14–15; pl. 19, fig. 4.

1997 Valeria lophostriata: Reference Xiao, Knoll, Kaufman, Yin and ZhangXiao et al., p. 201, fig. 3e.

1999 Valeria lophostriata; Reference Samuelsson, Dawes and VidalSamuelsson et al., p. 15, fig. 8E.

2001 Valeria lophostriata; Reference Javaux, Knoll and WalterJavaux et al., fig. 1D.

2004 Valeria lophostriata; Reference Javaux, Knoll and WalterJavaux et al., fig. 2F–I.

2009 Valeria lophostriata; Reference Nagy, Porter, Dehler and ShenNagy et al., fig. 1A, B.

2009 Valeria lophostriata; Reference NagovitsinNagovitsin, p. 144, fig. 4E.

2009 ovoidal acritarch with striated ornamentation Reference Peng, Bao and YuanPeng et al., fig. 4.

2009 ovoidal acriatrch with striated ornamentation Reference Lamb, Awramik, Chapman and ZhuLamb et al., fig. 4 A.

?2012 “dark walled megasphaeric coccoid with a subradial striation” Reference Battison and BrasierBattison and Brasier, fig. 8B.

2015 Valeria lophostriata; Reference Tang, Pang, Yuan, Wan and XiaoTang et al., p. 315, fig. 11.

in press Valeria lophostriata; Reference Riedman and PorterRiedman and Porter, p. 10, fig. 4.1.

in press Valeria lophostriata; Reference Porter and RiedmannPorter and Riedman, fig. 19.1–19.3.

(For additional synonymy see Jankauskas et al., Reference Jankauskas, Mikhailova and Hermann1989, and Hofmann and Jackson, Reference Hofmann and Jackson1994)

Holotype

Number 16-62-4762/16, sp. 1, DH Kabakovo 62 drill core, depth 4762 to 4765 meters, Neoproterozoic Zigazino-Komarovo Formation, southern Urals (Jankauskas, Reference Jankauskas1979b, fig. 1.14).

Description

Large vesicle, 104–160 µm in minimum diameter, with lanceolate folds and a distinctive ornamentation of concentric ridges, giving the appearance of a “target” (Fig. 7.3, 7.4).

Occurrence

This taxon is found worldwide (Hofmann, Reference Hofmann1999) from the late Paleoproterozoic Era (Javaux et al., 2004; Lamb et al., Reference Lamb, Awramik, Chapman and Zhu2009; Peng et al., Reference Peng, Bao and Yuan2009) to the Cryogenian (Nagy et al., Reference Nagy, Porter, Dehler and Shen2009).

Remarks

SEM analyses show that the striations are 1-µm ridges located on the inside of the vesicle wall (Javaux et al., Reference Javaux, Knoll and Walter2004). Excystment by medial split gives rise to two half vesicles that commonly enroll onto themselves (Fig. 7.1, 7.2).

Unnamed form A

Figure 7.5–7.6

Description

A large ovoidal or irregular and globular envelope including several contiguous compartments, each surrounded by an envelope and containing closely packed spheroidal cells. Two fragmented specimens are 350 µm wide and 600–700 µm long, internal compartments surrounded by an inner envelope 39–85 µm in diameter, containing poorly defined, closely packed cells. The external envelope is 8–13 µm thick.

Description

Black opaque vesicles, 141 and 215 µm in diameter (N=2), with medial split and folds at periphery.

Remarks

These vesicles differ from Chuaria circularis by the translucent margin showing folds.

Unnamed form C

Figure 7.9

Description

Vesicles with smooth to chagrinate walls, 30 and 35 m in diameter (N=2), connected by a 14-µm-long filamentous expansion.

Description

Vesicle 40 µm in diameter, attached to a large 80 µm filamentous expansion, but not communicating with the cell interior (thus distinct from Germinosphaera).

Description

Large, smooth-walled, thick, brittle, brown-orange wall fragment of a spheromorph, 310 µm in diameter.

Description

Large, 16 to 29 µm wide filament in a 72 µm x 171 µm smooth indented sheath.

Remarks

This large filamentous fossil differs from other sheathed filamentous taxa by the indentation of the sheath and absence of septae in the filament, although these characters could be taphonomic. Other taxa, such as Rugosoopsis, can reach large diameters, but have a distinct transverse fabric not observed here. Palaeolyngbya may also have a wide sheath, but is characterized by regular uniseriate array of well-preserved cells (Butterfield et al., 1994).