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-Science Reviews 212 (2021) 103382

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Earth-Science Reviews

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Review Article non-marine of —Distributions, natural T affinities and ecological implications ⁎ Chris Maysa,b, , Vivi Vajdaa, Stephen McLoughlina a Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden b Monash University, School of Earth, Atmosphere and Environment, 9 Rainforest Walk, Clayton, VIC 3800,

ARTICLE INFO ABSTRACT

Keywords: The abundance, diversity and of non-marine algae are controlled by changes in the physical and Permian–Triassic chemical environment and community structure of continental ecosystems. We review a range of non-marine algae algae commonly found within the Permian and Triassic strata of Gondwana and highlight and discuss the non- mass marine algal abundance anomalies recorded in the immediate aftermath of the end-Permian extinction interval Gondwana (EPE; 252 Ma). We further review and contrast the marine and continental algal records of the global biotic freshwater ecology crises within the Permian–Triassic interval. Specifically, we provide a case study of 17 (in 13 genera) palaeobiogeography from the succession spanning the EPE in the , eastern Australia. The affinities and ecological ­im plications of these -genera are summarised, and their global Permian–Triassic palaeogeographic and stra­ tigraphic distributions are collated. Most of these fossil taxa have close extant algal relatives that are most common in freshwater, brackish or terrestrial conditions, and all have recognizable affinities to groups known to produce chemically stable biopolymers that favour their preservation over long geological intervals. However, these compounds (e.g., sporopollenin and algaenan) are not universal, so the fossil record is sparse for most algal groups, which hinders our understanding of their evolutionary histories. Owing partly to the high preservational potential of , a of freshwater charophyte algae and sister to land , this group has a particularly diverse and abundant Permian–Triassic fossil record in Gondwana. Finally, we review and contrast the marine and continental algal records of the global biotic crises within the Permian–Triassic interval. In continental settings, Permian algal assemblages were broadly uniform across most of southern and eastern Gondwana until the EPE; here, we propose the Peltacystia Microalgal Province to collectively describe these distinct and prolonged freshwater algal assemblages. In the immediate aftermath of the EPE, relative increases in non-marine algae have been consistently recorded, but the distributions of prominent taxa of Permian freshwater algae became severely contracted across Gondwana by the . We highlight the paucity of quantitative, high-resolution fossil evidence for this key group of primary producers during all biotic crises of the Permian and Triassic periods. This review provides a solid platform for further work interpreting abundance and diversity changes in non-marine algae across this pivotal interval in evolutionary history.

1. Introduction et al., 2004, 2012). As such, the fossil records of these groups may provide independent proxies of specific environmental changes, but Aquatic algae provide excellent measures of past and present only if their natural affinities can be established reliably. changes in marine and terrestrial environments. Nutrient, salinity, pH The Permian–Triassic algal record reveals major changes in regional and temperature changes can all lead to significant fluctuations in algal and global environmental conditions. Several distinct and abrupt ex­ abundances within modern terrestrial waterways (Wehr and Sheath, tinction pulses are recognised through this interval (Retallack, 2013; 2015). Some groups are extremely sensitive to specific aquatic para­ Wignall, 2015), such as the end- event (ca 259.8 Ma; meters; for example, the development of ‘blooms’ of zygnematacean Rampino and Shen, 2019) and the Smithian-Spathian event (ca 249 Ma; algae in lakes and rivers under low-pH conditions (Turner et al., 1995; Lindström et al., 2019), all of which have been associated with a dis­ Kleeberg et al., 2006; Watson et al., 2015), or of prasinophyte algae in tinct pulse of marine extinctions. This interval also includes the most marginal marine settings enriched in nutrients (O'Kelly et al., 2003; Not extreme mass of all, the end-Permian extinction (EPE),

⁎ Corresponding author at: Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden. E-mail address: [email protected] (C. Mays). https://doi.org/10.1016/j.earscirev.2020.103382 Received 6 July 2020; Received in revised form 21 September 2020; Accepted 22 September 2020 0012-8252/ © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/). C. Mays, et al. Earth-Science Reviews 212 (2021) 103382 which resulted in the loss of > 80% of marine species (Stanley, 2016) interpretations for the most common forms of algae and possible algae and an unparalleled overturn of terrestrial plants (McElwain and (acritarchs) found in non-marine Permian and Triassic strata of Punyasena, 2007; Cascales-Miñana et al., 2016) and (Ward Gondwana. et al., 2005). The abundances of organic have long been employed as indicators of regional (e.g., Micrhystridium evansii; Price, 1983, 1997) or global (e.g., Reduviasporonites; Eshet et al., 1995; 2. Permian–Triassic palaeoenvironmental conditions of eastern Visscher et al., 1996) environmental changes, thus serving as key Australia biostratigraphic markers for the Permian and Triassic periods. Simi­ larly, modifications in algal (or ) morphology have been uti­ The stratigraphic successions of eastern Australia provide a near- lised to signal changes in local marine conditions (van Soelen et al., continuous record of Permian (Fielding et al., 2008; Phillips et al., 2018; Lei et al., 2019). Furthermore, distinct changes in algal com­ 2017) to Triassic (Banks, 1978; Totterdell et al., 2009) near-shore munities have been identified concurrent with the EPE from almost marine to continental sedimentation. These strata are preserved pri­ every examined marine succession (e.g., Twitchett et al., 2001; Grice marily in the Bowen-Gunnedah-Sydney basin complex (BGSBC), a large et al., 2005; Grice et al., 2007; Schneebeli-Hermann et al., 2012b; van meridional foreland encompassing > 160,000 km2 of Queens­ Soelen and Kürschner, 2018), although probably not all of these strictly land and New South Wales, Australia (Fig. 1). In the to represent ‘algal blooms’ since the absolute concentrations of cysts tend Guadalupian epochs (early to middle Permian), the basin system un­ to decline across the EPE strata in some cases (Shen et al., 2013; Lei derwent broad extension and thermal subsidence, which facilitated the et al., 2019). accommodation of thick (locally > 10 km) sedimentary packages Linking the specific environmental parameters undergoing change (Korsch and Totterdell, 2009). The early to middle Permian subsidence to algal diversities and abundances has been hindered by ambiguous phase is represented by a transgressive trend and the formation of an affinities and ecological tolerances of the algae. Tappan (1980) carried epicontinental shelf, with shallow marine to coastal plain environments out a major review of fossil algae and their probable biological affi­ prevalent (Fielding et al., 2001). This marine phase was followed by a nities, and further significant advances were made for Palaeozoic and regression from the (late Permian) to Early Triassic caused by Triassic groups by Colbath and Grenfell (1995) and Brenner and Foster foreland thrust loading, in addition to sediment loading by erosion of an (1994), respectively. Since that time, significant advances have been active volcanic arc to the east, the New England Orogen (Rosenbaum, made to our understanding of algal chemistry and wall microstructures 2018). This regression led to the establishment of predominantly non- (e.g., de Leeuw et al., 2006; Baudelet et al., 2017), thus facilitating marine environments across the BGSBC from the Lopingian to Middle direct comparisons between and their extant counterparts (e.g., Triassic (Fielding et al., 2001). Broad alluvial plains hosting forested Moczydłowska and Willman, 2009; Steemans et al., 2010; (in the Lopingian) and ephemeral lakes (in the Early Triassic) Moczydłowska et al., 2011), and highlighting the contrasting pre­ with an overall southward fluvial drainage system prevailed during this servational potential of algae groups over geological time (Versteegh interval (Cowan, 1993; Herbert, 1997; Fielding et al., 2020). The EPE and Blokker, 2004). Furthermore, molecular phylogenies of extant represented a major biotic collapse in the late Lopingian, and the onset groups have provided a robust framework for interpreting the evolu­ of continental ecosystem collapse likely preceded the Permian–Triassic tionary histories of (Leliaert et al., 2012; Del Cortona et al., boundary by > 300,000 based on CA-ID-TIMS dating of zircons 2020). from tuff beds intercalated with the fossiliferous succession in both Here, we document algal occurrences through four stratigraphic Australia and South (Fielding et al., 2019, 2020; Gastaldo et al., sections spanning the uppermost Permian to Lower Triassic of the 2020). Lopingian floras of the Sydney Basin are dominated byglos­ Sydney Basin, Australia. We build on earlier reviews, and provide up­ sopterid , with subsidiary coniferous and cordaitalean dated stratigraphic and global geographic distributions, and ecological woody canopy plants and a rich understorey of , sphenophytes, and lycopsids (Holmes, 1995; Shi et al., 2010; McLoughlin et al., 2019).

Fig. 1. Geological maps of Australia, indicating the distributions of Permian and Triassic strata. A) Australian basins with Permian and/or Triassic strata, dotted lines indicate basins that extend offshore, adapted from Shi et al. (2010), McLoughlin (2011b) and McLoughlin et al. (2017). B) Detail of southeastern Sydney Basin, the successions with newly reported fossil occurrences are indicated; CCC-27: Cliff Colliery DDH 27; PHKB-1: Pacific Power Hawkesbury Bunnerong DDH 1.

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Fig. 2. Stratigraphic ranges of potential algal taxa within the Sydney Basin successions. -pollen and provide the key para­ meters for correlations between successions. PHKB-1 litholog from Fielding et al. (2019), biostratigraphy from Mays et al. (2020); CCC-27 litholog and biostrati­ graphy from Mays et al. (2020); Coalcliff outcrop litholog and biostratigraphy from Fielding et al. (2020); Frazer Beach outcrop litholog and biostratigraphy from Vajda et al. (2020). Note, vertical scales for the outcrops are equivalent, but vertical scales for the well successions are unique. C = claystone, Md = mudrock, Ht = heterolithic, Sa = sandstone, Gr = (gravel) conglomerate; L. p. = Lunatisporites pellucidus Zone.

The EPE was notably marked in the Sydney Basin by the disappearance BGSBC (Korsch et al., 2009). Middle and Upper Triassic non-marine of glossopterid-dominated peat-forming communities followed by strata are represented in other small intracratonic basins of eastern water-table rise and extensive ponding of the floodbasins in the­ im Australia (e.g., the Esk Basin [], Tasmania, Ipswich mediate aftermath (Vajda et al., 2020). Immediate post-EPE biotas in­ and Tarong basins [], Callide Basin [Carnian–Rhae­ corporate a low-diversity sclerophyllous flora dominated by small- tian], and the Telford Basin [Carnian–Lower ]; Walkom, 1928; leafed peltasperms and voltzialean (Retallack, 1980; Vajda Banks, 1978; Barone-Nugent et al., 2003; Pattemore, 2016; Fig. 1). et al., 2020; Mays et al., 2020) and similarly impoverished Throughout the Permian and Triassic periods, the BGSBC remained and faunas represented mostly by sparse trace fossils consistently in middle to high southern latitudes (50–80°S; Veevers, (McLoughlin et al., 2020; Fielding et al., 2020). Peat-forming conditions 2006; Klootwijk, 2016). This region preserves four extensive glacial were absent from the basin complex for the entire Early Triassic intervals from the earliest Permian to early Lopingian (early late Per­ (Retallack et al., 1996; Mays et al., 2020). Tectonic inversion in the late mian, ca 255 Ma; Fielding et al., 2008), with glacial deposits distributed resulted in termination of sedimentation within the as far north as 40°S (Frank et al., 2015). In contrast, the global

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Fig. 3. Common zygnematophycean algae from the Permian–Triassic fossil record of the Sydney Basin, Australia, and possible extant representatives; all scales = 20 μm, England Finder coordinates in parentheses below. A–D) Circulisporites sp. A sensu Backhouse, 1991; A, B) S200869-2 (S38), Frazer Beach: 146–148 cm, upper ; A) polar focus; B) equatorial focus; C) S200869-2 (G30[2]), Frazer Beach: 146–148 cm, upper Changhsingian; D) S200864-2 (T21), Frazer Beach: 153–155 cm, upper Changhsingian. E) Circulisporites parvus de Jersey, 1962, S014103-2 (H35), PHKB-1: 801.11 m, upper Changhsingian. F, G) Maculatasporites delicatus Foster, 1975, S014120-2 (N21[4]), PHKB-1: 699.07 m, Smithian; F) equatorial focus; G) polar focus. H–J) Ovoidites scissus (Balme and Hennelly, 1956) Zavattieri et al., 2020; H) S014134-2 (W34[4]), PHKB-1: 320.1 m, Spathian; I) S200868-2, Frazer Beach: 148–150 cm, upper Changhsingian; J) S200864-2 (R22[4]), Frazer Beach: 153–155 cm, upper Changhsingian. K, L) Modern zygospores of elongata (Vaucher) Dumortier, 1822, arrows indicate dehiscence marks, image credits: C. Carter; K) equatorial focus; L) top focus. temperatures of the Early Triassic were extremely warm (Sun et al., with which Circulisporites has strong sculptural similarities, and the 2012). However, the global climate underwent a relative cooling phase oospores of extant members of Oedogoniaceae (). approximately concurrent with the Smithian-Spathian boundary (mid- However, unlike Chomotriletes, Circulisporites has continuous striae , ca 249 Ma; Romano et al., 2013). Despite the high and a consistent equatorial excystment rupture (see de Jersey, 1962; palaeolatitude and assertions of Middle to glacial striae at Norris, 1965). a single site (Spenceley, 2001), convincing evidence for glaciation in eastern Australia during this interval is lacking (Gore and Taylor, 3.1.1.3. Ecological implications. Modern live almost 2003). exclusively in freshwater settings, such as lakes, ponds and rivers (Van Geel, 2001), and can occur as surface mats or phytoplankton (Hall 3. Common Permian and Triassic non-marine algal palynomorphs and McCourt, 2017). Among the alternative affinities, extant and fossil of Gondwana representatives noted above are almost exclusively non-marine (Table 1); e.g., Transeauina is an indicator of well-oxygenated, Algal palynomorphs are common organic-walled microfossils shallow, stagnant, mesotrophic freshwater conditions (Head, 1992; encountered in Permian and Triassic strata. The most frequently Miranda, 2020). Circulisporites is common in non-marine documented non-marine algal palynomorph genera from Gondwana are sedimentary facies (e.g., Norris, 1965; Foster, 1979; Backhouse, 1991; listed and discussed below. The genera are grouped by their interpreted Zippi, 1998), but is also known from estuarine and shallow marine botanical affinity, and the key features distinguishing morphologically deposits (McLoughlin, 1988; Dehbozorgi et al., 2013), having likely similar taxa are outlined, together with summaries of their ecological been transported from adjacent continental settings. tolerances and potential alternative affinities (Table 1). Global stratigraphic and geographic distributions for all epochs of the Permian 3.1.1.4. Sydney Basin occurrences. Circulisporites is generally rare in the and Triassic periods, along with a list of the sources for these data, are upper Lopingian to Lower Triassic strata of the Sydney Basin (, provided (Supplementary Table 2). Newly reported occurrences of algal 1970; Helby, 1970). However, Circulisporites sp. A (Fig. 3A–D) is locally species from the Sydney Basin (Fig. 1B) are tabulated (Supplementary abundant directly following the disappearance of the flora Table 3) and plotted against sections logged for sedimentology (Fig. 2). at the top of the uppermost Permian coal seam, particularly within the See Appendix for Sydney Basin fossil locality details, imaging Dooralong Shale (lowermost Narrabeen Group) at Frazer Beach, specifications and additional notes on algal nomenclature. northern Sydney Basin (Vajda et al., 2020); these strata correspond to Our survey is by no means exhaustive, since many alga-like mi­ the upper Changhsingian–?lower Griesbachian stages (uppermost crofossils reported from Gondwana have been placed under open no­ Permian–?lowermost Triassic; lower Playfordiaspora crenulata Zone; menclature, or the illustrations are inadequate to provide confident Fig. 2). taxonomic assignments. Moreover, some microfossils reminiscent of algae may have alternative (e.g., cyanobacterial or fungal) affinities. 3.1.2. Maculatasporites Tiwari, 1964 (Fig. 3F, G) Here, we focus on those groups most commonly encountered in 3.1.2.1. Taxonomic justification. Both Maculatasporites and Gondwanan Permian–Triassic continental palynoassemblages. Cymatiosphaera include cysts with a complete reticulum and no apparent dehiscence mechanism. The absence of a tetrad mark 3.1. Zygnematophycean algae distinguishes them from reticulate trilete miospore genera, such as Dictyotriletes (Naumova, 1939) Ishchenko, 1952 or Reticulatisporites 3.1.1. Circulisporites de Jersey, 1962 emend. Norris, 1965 (Fig. 3A–E) (Ibrahim, 1933) Neves, 1964. Some Permian specimens of 3.1.1.1. Taxonomic justification. The specimens reported herein have Maculatasporites have been identified with small dehiscence marks circular to subcircular outlines and a series of circumpolar ribs. (micropyloma; Zavattieri et al., 2017), but this is not a diagnostic Crucially, they tend to exhibit a (sub)equatorial rupture (Fig. 3A–C), criterion (Tiwari, 1964), and Australian Permian–Triassic specimens distinguishing them from the broader diagnosis of Chomotriletes tend to lack this feature (Segroves, 1967; Backhouse, 1991; this study). Naumova, 1939 ex Naumova, 1953 (see Grenfell, 1995, p. 209). They Maculatasporites has a broader morphological range than are very similar to Concentricystes Rossignol, 1962, but lack the Cymatiosphaera, but species of the latter have wide lumina and characteristic rugulate/spiral polar sculpture of that genus. tall membranous muri, which, as noted by Backhouse (1991), can be used to distinguish them from the broader diagnosis of Maculatasporites. 3.1.1.2. Affinity. The complete excystment rupture is typical of However, there remains substantial overlap in the diagnoses of these conjugating algae (Zygnemataceae; Krutzsch and Pacltová, 1990). genera, and an emendation of one or both should be considered. As Furthermore, at least one circumpolar ring occurs on the zygospores noted by Anderson (1977), the morphology and structure of of some extant and extinct zygnematacean taxa, e.g., Transeauina Guiry, Maculatasporites is similar to Spongocystia Segroves, 1967. Following 2013 and Lecaniella Cookson and Eisenack, 1962b (Grenfell, 1995). Grenfell (1995); (also see Souza et al., 2016), we consider the described Brenner and Foster (1994) noted similarities between Circulisporites and sculptural features to be inadequate for distinguishing these genera, the ribbed sculpture of some modern chlorophyte taxa (e.g., Scotiella and consider the latter genus a junior synonym of Maculatasporites. [=Chloromonas Gobi, 1900], Chlamydomonadaceae; Scotiellopsis [=Coelastrella Chodat, 1922], ). However, these taxa 3.1.2.2. Affinity. Grenfell (1995) highlighted the similar gross have longitudinal rather than concentric ribs, and tend not to rupture morphology of Maculatasporites and some modern charophyte , equatorially. Zippi (1998) drew comparisons between Chomotriletes, specifically the zygospores of Zygnemataceae (e.g., Agardh,

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1817, Zygnemopsis [Skuja] Transeau, 1934, Zygogonium Kützing, 1843). within Lopingian to Lower Triassic strata elsewhere in the Sydney Basin zygnemataceous zygospores (“Zygnema-type”) similar to (Grebe, 1970; Helby, 1970). Maculatasporites have also been reported (Van Geel and Van der Hammen, 1978, figs 49–54). 3.1.4. Peltacystia Balme and Segroves, 1966 (Fig. 4A, B) 3.1.4.1. Taxonomic justification. The Sydney Basin examples are small, 3.1.2.3. Ecological implications. Maculatasporites is a very common and with circular outlines and a complete excystment rupture, splitting into diverse element across Gondwana, particularly within Permian non- two approximately equal hemispheres. The presence of a prominent marine facies (e.g., Tiwari, 1964; Foster, 1975, 1979; Playford and circumpolar ridge allows placement in Peltacystia rather than the more Rigby, 2008; Zavattieri et al., 2017, 2020), but also extending into the broadly defined Lecaniella Cookson and Eisenack, 1962a. On this basis, Lower Triassic (McLoughlin et al., 1997). As noted by Grenfell (1995), these two genera are not considered synonyms (cf. Head, 1992). this lends support for a freshwater affinity, in addition to its placement Paralecaniella Cookson and Eisenack, 1970, emend. Elsik, 1977, within Zygnemataceae (see ecological preferences of Circulisporites differs from Peltacystia by having a narrow marginal flange. above). Some morphologically similar extant freshwater taxa (e.g., Zygnemopsis) are tolerant of highly acidic water (Zettler et al., 2002). 3.1.4.2. Affinity. Peltacystia has been compared consistently with the zygospores of several Quaternary and species of Transeauina 3.1.2.4. Sydney Basin occurrences. Maculatasporites is extremely rare Guiry, 2013 (formerly: Debarya Wittrock, 1872; Van Geel and Van der within the Sydney Basin, and has only been reported from the Lower Hammen, 1978; Head, 1992; Van Geel and Grenfell, 1996; Cook et al., Triassic of from the Coal Cliff Sandstone, Scarborough Sandstone, and 2011), a member of the conjugating green algae (Zygnemataceae). Bulgo Sandstone within the Pacific Power Hawkesbury Bunnerong DDH 1 (PHKB-1) succession, corresponding to the Griesbachian–Smithian 3.1.4.3. Ecological implications. This fossil-genus is most common in stages (Lower Triassic; P. crenulata–Protohaploxypinus samoilovichii non-marine facies (Segroves, 1967; Zavattieri and Prámparo, 2006); for zones; Fig. 2). example, the type species was described from Permian coal deposits of Western Australia (Balme and Segroves, 1966). It may be locally 3.1.3. Ovoidites Potonié, 1951 ex Thomson and Pflug, 1953 emend. transported into deltaic and shallow marine settings (Fielding and Krutzsch, 1959 (Fig. 3H–J) McLoughlin, 1992). Extant Transeauina inhabit clean, oxygen-rich, 3.1.3.1. Taxonomic justification. Ovoidites includes ellipsoid and ovoid, mesotropic freshwater bodies of Europe, Asia, North America, and simple-walled cells with a partial to complete excystment rupture. New Zealand (see Valenzuela Miranda, 2020). Specimens from the Sydney Basin are typically ovoid (Fig. 3J), but some are near spherical (Fig. 3H). Because Ovoidites circumscribes ovoid to 3.1.4.4. Sydney Basin occurrences. Peltacystia has an inconsistent ellipsoid forms, the spherical specimens may fall outside the emended distribution within PHKB-1 and the Coalcliff and Frazer Beach diagnosis of Krutzsch (1959). However, there is a continuous gradation outcrop successions (Fig. 2). It has a known stratigraphic range of of forms between the ovoid and spherical forms, and it was deemed uppermost Changhsingian (upper Permian) to ?Spathian (Lower impractical herein to segregate them based on this arbitrary distinction. Triassic) in the Sydney Basin (Grebe, 1970; Helby, 1970; this study), This genus can be distinguished from Schizosporis Cookson and but has not yet been reported from the pre-EPE strata in that region. Dettmann, 1959 emend. Pierce, 1976, by its simple, single-layered wall. Ovoidites has priority over Tiwari and Navale, 1967, and 3.1.5. Naumova, 1939 ex Bolkhovitina, 1953 (Fig. 4C) Schizophacus Pierce, 1976, which are interpreted here as junior 3.1.5.1. Taxonomic justification. This genus has a very simple diagnosis synonyms (see discussion by Zavattieri et al., 2020). encompassing cysts ‘without folds’ and having four pores (see taxonomic history by Jansonius and Hills, 1981). As noted by Colbath 3.1.3.2. Affinity. This broadly defined fossil-genus likely represents a and Grenfell (1995), the ‘pores’ are more accurately described as pits or diverse range of zygnematophycean zygospores. Similarities have been indentations. This genus differs from Horologinella Cookson and drawn to various extant conjugating algae (Zygnemataceae), including Eisenack, 1962b emend. Stover and Evitt, 1978 by the absence of a Hallasia Rosenvinge, 1924, Pleurodiscus Lagerheim, 1895, large, central aperture (archeopyle). Typically, this genus includes Kützing, 1843, Zygnema (Krutzsch and Pacltová, 1990), Spirogyra Link, quadrangular cysts with a thick-rimmed pit in each corner. The 1820 (Fig. 3K, L; Van Geel, 1979; Krutzsch and Pacltová, 1990; Van distinctive elongated apices of the Sydney Basin specimens match the Geel and Grenfell, 1996; Zippi, 1998), and Zygogonium (Zippi, 1998). characters of Tetraporina protrusa Brenner and Foster, 1994. As noted by Additional comparisons have been made to extant non-conjugating Brenner and Foster (1994), T. protrusa can be differentiated from zygnematophyceans (), e.g., Desmidium Agardh ex Ralfs, Schizocystia Cookson and Eisenack, 1962b emend. Jardiné et al., 1848 (Worobiec and Worobiec, 2010). 1972, and Spintetrapidites Krutzsch and Pacltová, 1990 by the presence of pits in the cyst corners. 3.1.3.3. Ecological implications. Ovoidites occurs most commonly in deposits of freshwater palaeoenvironments (Van Geel and Van der 3.1.5.2. Affinity. This genus has been typically compared with the Hammen, 1978; Rich et al., 1982; Batten et al., 1994; Worobiec, 2014; zygospores of Mougeotia Agardh, 1824 (Zygnemataceae; Brenner and Zavattieri et al., 2020), although it has been reported from non-marine Foster, 1994; Van Geel and Grenfell, 1996). For example, M. viridis conditions of elevated salinity into which it was possibly transported (Kützing) Wittrock, 1872 has the same quadrangular form with via freshwater streams (Zavattieri et al., 2017). This is concordant with thickened corners bearing pits where filaments normally attach to the the distributions of extant zygnematacean and desmidiacean algae, zygospores (Fig. 4D). Additionally, Mougeotia spores contain which inhabit a range of freshwater habitats between sub-polar and sporopollenin-like compounds (de Vries et al., 1983), which probably tropical climate zones; zygnemataceans generally flourish in clear, resist degradation over geological timescales. However, Lindgren shallow, well-oxygenated water (Hall and McCourt, 2015). (1980, 1986) found that, in addition to Zygnemataceae, numerous other extant taxa are morphologically similar to Tetraporina for at least 3.1.3.4. Sydney Basin occurrences. Of all the successions examined in one stage of their life cycle. Those that exhibit greatest morphological this study, Ovoidites was identified only in post-EPE strata. Specifically, similarities to T. protrusa are among the O. scissus is present within the upper Changhsingian to Spathian strata (), e.g., zoospores of Chlorotetraëdron MacEntee et al., (uppermost Permian–Lower Triassic; P. crenulata–Aratrisporites 1978 (Neochloridaceae) or Pediastrum Meyen, 1829 (), tenuispinosus zones; Fig. 2). Ovoidites has been reported previously and autospores of Tetraëdron Kützing, 1845 (Hydrodictyaceae). Of

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Table 1 Natural affinities and environmental implications of probable freshwater palynomorph taxa. Where possible, environmental interpretations are based on the pre­ ferred habitats of the extant taxa to which the fossils have the closest affinity. Scale bar = 20 μm, and applies to all figures.1 Krutzsch and Pacltová, 1990; 2Grenfell, 1995; 3Hall and McCourt, 2017; 4Zippi, 1998; 5John and Rindi, 2015; 6Hoffman, 1967; 7Brenner and Foster, 1994; 8Buchheim, 2015; 9Kalina and Puncochárová, 1987; 10McCourt et al., 1986; 11Zettler et al., 2002; 12Parke et al., 1978; 13Tappan, 1980; 14Leliaert et al., 2012; 15O'Kelly et al., 2003; 16Not et al., 2004; 17Van Geel, 1979; 18Van Geel and Grenfell, 1996; 19Worobiec and Worobiec, 2010; 20Van Geel and Van der Hammen, 1978; 21Jarzen, 1979; 22Graham et al., 1996; 23Lindgren, 1980; 24Shubert and Gärtner, 2015; 25Colbath and Grenfell, 1995; 26Dotzler et al., 2007; 27Kustatscher et al., 2014; 28Guy-Ohlson, 1996; 29Fott and Nováková, 1969; 30Wehr and Sheath, 2015; 31Darienko et al., 2010; 32Bock et al., 2013; 33Batten, 1996a; 34Steemans and Wellman, 2018; 35Fensome et al., 1999; 36Sarjeant and Taylor, 1999; 37van Soelen et al., 2018; 38Foster, 1979; 39Helby, 1970; 40Balme, 1995; 41Taylor and Hickey, 1992; 42Retallack, 1997; 43Batten, 1968; 44Husby, 2013; 45Elsik, 1999; 46Visscher et al., 1996; 47Visscher et al., 2011; 48Spina et al., 2015; 49Brooks et al., 2015; 50Afonin et al., 2001; 51Zonneveld et al., 2013; 52Talyzina and Moczydłowska, 2000; 53Marin and Melkonian, 2010; 54Mudie et al., 2011.

Genus Sketch Affinities Environmental preferences

Zygnematophyceae ⁎ ⁎ Circulisporites Green algae: zygospores of Zygnemataceae Non-marine: oxygen-rich freshwater (rarely brackish), ()1,2 shallow conditions with variable nutrient content (generally oligo- to mesotrophic), cosmopolitan climates (arctic to tropical)3 Green algae: oospores of Oedogoniaceae (Chlorophyta)4 Non-marine: freshwater (rarely brackish), standing, shallow and/or ephemeral water bodies5, commonly epiphytic, mostly temperate & subtropical climates5,6 Green algae: cysts of Chlamydomonadaceae or Non-marine: soil, peat pools or ephemeral and/or eutrophic Scenedesmaceae (Chlorophyta)7 lakes8,9 ⁎ ⁎ Maculatasporites Green algae: zygospores of Zygnematophyceae Non-marine: oxygen-rich, generally mesotrophic freshwater, (Charophyta)2 shallow stagnant conditions, cosmopolitan climates (arctic to tropical)3,10, ?tolerant of low pH11

⁎ ⁎ Ovoidites Green algae: zygospores of Zygnematophyceae Non-marine: oxygen-rich, generally mesotrophic freshwater, (Charophyta), Zynemataceae1,8,17,18or Desmidiaceae19 shallow stagnant conditions20, cosmopolitan climates (arctic to tropical)3

⁎ ⁎ Peltacystia Green algae: zygospores of Zygnemataceae Non-marine: oxygen-rich, generally mesotrophic freshwater, (Charophyta)2,17,20 shallow stagnant conditions, seasonally warm climates3

⁎ ⁎ Tetraporina Green algae: zygospores of Zygnemataceae Non-marine: oxygen-rich, generally mesotrophic freshwater, (Charophyta)7,18,21 shallow stagnant conditions, cosmopolitan climates (arctic to tropical)10,21?tolerant of low pH22 Green algae: cells of Sphaeropleales (Chlorophyta)23 Non-marine: planktonic in freshwater, arctic to tropical climates, rarely occurring subaerially in soils24

Prasinophytes ⁎ ⁎ Cymatiosphaera Green algae: phycomata of pyramimonadalean Primarily marine14, rarely freshwater53; often forming prasinophytes (Chlorophyta)12,13,25 monospecific plankton blooms15,16, some prehistoric freshwater representatives4,26,27,54 Green algae: oospores of Oedogoniaceae or Non-marine: freshwater (rarely brackish), standing, shallow (Chlorophyta)4 and/or ephemeral water bodies5, commonly epiphytic, mostly temperate & subtropical climates5,6

Trebouxiophyceae ⁎ ⁎ Green algae: coenobia of Non-marine: planktonic in freshwater, mostly in eutrophic Crucigenioideae32(Chlorophyta)7,33,34 ponds and lakes24

Polyphyletic algal genera ⁎ ⁎ Micrhystridium Polyphyletic; ? stem group35; ?green algal Marginal marine: generally near-shore settings36,37; ?brackish cysts water conditions38

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Table 1 (continued)

Genus Sketch Affinities Environmental preferences

⁎ ⁎ Green algae: phycomata of pyramimonadalean Primarily marine14: often forming monospecific plankton prasinophytes (Chlorophyta)25,28 blooms15,16 ⁎ ⁎ Green algae: vegetative cells of Primarily non-marine: occur as freshwater plankton29,30or in (Chlorophyta)25,52 subaerial conditions in soils, as epiphylls, biofilms or lichen photobionts24,30,31

Incertae sedis ⁎ ⁎ Mehlisphaeridium ?Green algae: oospores of Sphaeropleaceae (Chlorophyta) Non-marine: freshwater (rarely brackish), standing, shallow and/or ephemeral water bodies5

⁎ Pilasporites ?Green algae: zygospores of Zygnematophyceae *Non-marine: oxygen-rich, generally mesotrophic freshwater, (Charophyta)39 shallow stagnant conditions, seasonally warm climates (arctic to tropical)3 Land plants: miospores of Isoëtales (Lycophyta)40 Non-marine: freshwater to brackish, aquatic/wetland plant41, ruderal42 Land plants: miospores of (Polypodiophyta)43 Non-marine: wetland/riparian/ruderal plant44

Reduviasporonites ?Fungi: conidia of Ceratobasidiaceae (Basidiomycota)45 Non-marine: saprotrophic46or -pathogenic47 ?Green algae: zygospores of Zygnematophyceae Non-marine: oxygen-rich, generally mesotrophic freshwater, (Charophyta)50 shallow stagnant conditions, cosmopolitan climates (arctic to tropical)3 Green algae: zoospores of Trentepohliaceae Non-marine: subaerial endophytic and/or plant-parasitic49, (Chlorophyta)48 restricted to humid environments, can occur as lichens5 ⁎ ⁎ Rugaletes ?Green algae: zygospores of Zygnemataceae (Charophyta) Non-marine: oxygen-rich, generally mesotrophic freshwater, shallow stagnant conditions, cosmopolitan climates (arctic to tropical)3 : cysts of stem group Dinophyceae Primarily marine: typically open marine conditions, but can occur as blooms in brackish conditions (e.g., estuaries)51

⁎ Indicates present consensus interpretation. these, some are known to produce chemically stable walls with high (Segroves, 1967; see discussion of this genus above), Cymatiosphaera preservational potential (e.g., Pediastrum, Tetraëdron; Versteegh and commonly lacks apparent excystment structures (e.g., pores, ruptures), Blokker, 2004; Baudelet et al., 2017), and these constitute groups with but cysts with more membranous muri should be assigned to the latter potential alternative natural affinities for Tetraporina. genus (see Backhouse, 1991). Most of the specimens of Cymatiosphaera from the Sydney Basin reported here (Fig. 4G–J) conform to C. 3.1.5.3. Ecological implications. The candidates for extant relatives gondwanensis reported from the Permian of India (Tiwari, 1965) and discussed above all primarily inhabit non-marine settings. Modern Western Australia (Backhouse, 1991). However, despite having the Zygnemataceae most commonly live as freshwater plankton (see distinctly large lumina of this species, their total diameters are at the Circulisporites above), and Mougeotia can thrive in highly acidic low end of the size spectrum, endowing them with the appearance of a lacustrine settings (Graham et al., 1996). Similarly, the potential disproportionately coarse reticulum. Other specimens are tentatively affiliates among the Sphaeropleales are generally planktonic forms compared to Cymatiosphaera (Fig. 4E, F), since they do not possess well- living in lakes across a wide range of climates (Shubert and Gärtner, defined inner walls typical of this genus. 2015), although some species of Chlorotetraëdron occur in soils (Guiry and Guiry, 2020). Tetraporina-like fossils occur most commonly in non- 3.2.1.2. Affinity. Cymatiosphaera has been typically interpreted as the marine strata associated with fluviodeltaic (Playford, 1963; Lindgren, phycomata (resistant outer walls of cysts) of prasinophyte algae 1980), lacustrine (Zavattieri et al., 2017) and floodplain wetland (e.g., (Tappan, 1980; Dotzler et al., 2007; Kustatscher et al., 2014; see Taylor Balme and Hennelly, 1956) palaeoenvironments. et al., 2009), based on morphological similarity to (Chlorophyta), e.g., Pouchet, 1893 (Parke et al., 1978; see 3.1.5.4. Sydney Basin occurrences. Tetraporina occurs rarely within Colbath and Grenfell, 1995). The high infrataxon size variability of Guadalupian to Lower Triassic strata of Sydney Basin (Balme and prasinophytes (see Fig. 4E, F; Tappan, 1980), and their high Hennelly, 1956; Helby, 1970). Here, we record it from post-EPE strata preservational potential even over extremely long geological intervals (upper Changhsingian–Spathian stages; uppermost Permian–Lower (Teyssèdre, 2006), also support a prasinophycean affinity for the studied Triassic; Fig. 2), but pre-EPE Permian (Guadalupian to upper specimens. Prasinophyte phycomata generally have a partial excystment Lopingian) occurrences of Tetraporina have been reported previously rupture, a short linear dehiscence mark along a great circle, but most (Balme and Hennelly, 1956; Mishra et al., 2019). Cymatiosphaera do not express this feature (Backhouse, 1991). Some species of Cymatiosphaera have demonstrable similarities to 3.2. Prasinophyte algae dinoflagellates (Schrank, 2003). Alternatively, Zippi (1998) drew comparisons with extant chlorophycean algae: Sphaeropleaceae (e.g., 3.2.1. Cymatiosphaera Wetzel, 1933 ex Deflandre, 1954 (Fig. 4E–J) Sphaeroplea Agardh, 1824; Fig. 4K, L) or Oedogoniaceae. It has yet to be 3.2.1.1. Taxonomic justification. This genus has a complete reticulum demonstrated that these groups produce sporopollenin in their walls, constructed of thin muri and wide lumina (Deflandre, 1954) that give although algaenan, another durable compound, has been identified in the cysts a continuous to undulate outline. Like Maculatasporites some members of Sphaeropleaceae (Baudelet et al., 2017).

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Fig. 4. Algal microfossils from the Permian–Triassic fossil record of the Sydney Basin, Australia, and possible extant representatives; all scales = 20 μm, England Finder coordinates in parentheses below. A, B) Peltacystia sp. S200864-2 (L39[2]), Frazer Beach: 153–155 cm, upper Changhsingian; A) polar focus; B) equatorial focus. C) Tetraporina protrusa Brenner and Foster, 1994, S014127-2 (X40), PHKB-1: 514 m, Smithian. D) Modern zygospore of Mougeotia viridis (Kützing) Wittrock, 1872, note the apical indentations (inset boxes), image credit: C. Carter. E, F) cf. Cymatiosphaera sp.; E) S200905-2, Frazer Beach: 53–56 cm, upper Changhsingian; F) S014126-2 (X33[2]), PHKB-1: 559.6 m, Smithian. G–J) Cymatiosphaera sp. cf. C. gondwanensis (Tiwari, 1965) Backhouse, 1991; G) S014129-2 (X42), PHKB-1: 439.95 m, Smithian; H) S014127-2 (X41[2]), PHKB-1: 514.85 m, Smithian; I) S014120-2 (R34[1]), PHKB-1: 699.07 m, Smithian; J) S014127-2 (X28[3]), PHKB-1: 514.85 m, Smithian. K, L) Modern oospores of Sphaeroplea soleirolii (Duby) Montagne ex Kützing, 1849, image credits: C. Carter; K) two focal depths of a primary membrane with numerous immature oospores (zygotes), each with reticulate sculpture; L) two isolated oospores at three different focal depths (left: equatorial; centre: sub-polar; right: polar).

3.2.1.3. Ecological implications. Traditionally, extant prasinophytes 1994; Batten, 1996a; Fig. 5I, J), Lemmermania Chodat, 1900; and 2, the were considered to be confined largely to marine systems (Leliaert identification of sporopollenin-like compounds in the cell walls of this et al., 2011), where they can proliferate in large algal bloom events group (see Brenner and Foster, 1994). (e.g., O'Kelly et al., 2003; Not et al., 2004). However, a surprising diversity of prasinophytes in freshwater lakes have been reported 3.3.1.3. Ecological implications. This genus has been consistently recently (Marin and Melkonian, 2010). Furthermore, fossil interpreted as a guide fossil for non-marine palaeoenvironments Cymatiosphaera-like cysts have also been reported from brackish to (Grenfell, 1995). This is supported by the environmental preferences freshwater deposits (Zippi, 1998; Mudie et al., 2011), including several of their probable nearest extant relatives: modern crucigenioid species from the Palaeozoic to early (Clausing, 1993; Dotzler et al., (e.g., Tetrastrum) are freshwater plankton, and are particularly common 2007; Kustatscher et al., 2014). Both Sphaeropleaceae and in eutrophic conditions (Naselli-Flores and Barone, 2010; Shubert and Oedogoniaceae occur most commonly in freshwater conditions, often Gärtner, 2015). Quadrisporites horridus was originally described based in shallow and/or ephemeral lakes and, in some cases, as epiphytes on on specimens recovered from the uppermost Permian strata aquatic plants (e.g., Bulbochaete Agardh, 1817; see John and Rindi, immediately overlying the Bulli Coal, southern Sydney Basin 2015). Additional ultrastructural and/or biochemical analyses may (Hennelly, 1958). Coeval strata from across the Sydney Basin have reveal that this fossil-genus is polyphyletic (cf. Leiosphaeridia), and since been interpreted as lacustrine (Vajda et al., 2020; Fielding et al., that some freshwater fossil occurrences (e.g., Dotzler et al., 2007; 2020) and are associated with continental vertebrate trackways Kustatscher et al., 2014; this study) may be more accurately interpreted (Retallack, 1996) and burrows (McLoughlin et al., 2020). High as chlorophyceans rather than prasinophytes. abundances of this species have been noted from approximately coeval beds across eastern Australia (Sydney Basin, Helby, 1973, 3.2.1.4. Sydney Basin occurrences. Cymatiosphaera occurs only within Mays et al., 2020; Bowen Basin, Evans, 1966; see Balme, 1969). the post-EPE strata of the Sydney Basin (Grebe, 1970; Helby, 1973; this Owing to its very high abundances in this region, Q. horridus has study), extending from the upper Changhsingian to Smithian been interpreted as an opportunist alga that flourished in stagnant (uppermost Permian–Lower Triassic; P. crenulata–P. samoilovichii freshwater conditions during the end-Permian extinction interval (Mays zones; Fig. 2). At Coalcliff, rare Cymatiosphaera are also present et al., 2020). within the ‘dead zone’ interval (sensu Vajda et al., 2020), which was deposited in the immediate aftermath of the EPE. However, since this 3.3.1.4. Sydney Basin occurrences. Quadrisporites horridus is a common interval is characterised by an extreme paucity of non-fungal element within Lopingian and Lower Triassic palynological palynomorphs, and these Cymatiosphaera fossils might have been assemblages of the Sydney Basin (Grebe, 1970; Helby, 1970, 1973; reworked from the underlying Illawarra Coal Measures. Mishra et al., 2019; Vajda et al., 2020; Mays et al., 2020; this study). It is present in all examined successions and extends from the 3.3. Trebouxiophycean algae Changhsingian Stage (uppermost Permian; upper Dulhuntyispora parvithola Zone) to Spathian Stage (Lower Triassic; A. tenuispinosus 3.3.1. Quadrisporites Hennelly, 1958 ex Potonié and Lele, 1961 Zone; Fig. 2). (Fig. 5F–H) 3.3.1.1. Taxonomic justification. These fossils consist of four attached 3.4. Polyphyletic algal palynomorphs from the upper Permian to Lower subspherical cells in a tetragonal (typically rhombic [Fig. 5F]) or Triassic of Gondwana rectangular [Fig. 5G, H]) arrangement, with no clear dehiscence marks. The ornament is variable, but in the type species 3.4.1. Leiosphaeridia Eisenack, 1958c emend. Downie and Sarjeant, 1963 (Quadrisporites horridus Hennelly, 1958 ex Potonié and Lele, 1961), (Fig. 5A–D) the sculptural elements consist of dense verrucae, bacula or spines 3.4.1.1. Taxonomic justification. This broadly defined genus includes (Fig. 5F–H); these elements tend to increase in prominence towards the spherical/ellipsoidal cells with simple, thin and typically smooth walls extremities of each cell. Correct identification of this species is with or without excystment pores (=pylomes). In most cases, this taxon supported by the recovery of specimens in this study from strata is reserved for forms lacking dehiscence ruptures, thus differentiating it coeval with those hosting the Q. horridus type specimens (Hennelly, from Schizosporis Cookson and Dettmann, 1959 or Ovoidites (see above). 1958). This species differs fromQ. variabilis (Cramer, 1966) Ottone and The abundant, simple-walled cysts from the Sydney Basin tend to be Rossello, 1996 by being generally larger, and having coarser, more small (< 50 μm), heavily creased owing to their thin-walls, and most densely packed sculptural elements. no evidence of excystment structures (Fig. 5A, B, D), although rare specimens possess a micropylome (Fig. 5C). 3.3.1.2. Affinity. Quadrisporites horridus was originally interpreted as a spore tetrad of a (Hennelly, 1958), an interpretation 3.4.1.2. Affinity. Given the simple morphology, broad geological reiterated by various authors (e.g., Fensome et al., 1990). More range, variable chemical signatures and wall structures, and diverse recently, this genus has been interpreted as an alga (Strother, 1991; palaeoenvironmental conditions (see below), Leiosphaeridia is probably Wellman et al., 2015; Steemans and Wellman, 2018), specifically the polyphyletic and any single affinity is unlikely to capture the diversity coenobia of Crucigenioideae (Trebouxiophyceae, Chlorophyta; see Bock encompassed by this fossil. Leiosphaeridia has arguably one of the et al., 2013). This affinity is supported by: 1, morphological similarity longest stratigraphic ranges of any known fossil-genus, extending at to extant members, e.g., Tetrastrum Chodat, 1895 (Brenner and Foster, least as far back as the Late Palaeoproterozoic (ca 1600 Ma; Knoll et al.,

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Fig. 5. Algal microfossils from the Permian–Triassic of the Sydney Basin, Australia, and potential extant representatives; scales for E = 50 μm, I, J = 10 μm, all other scales = 20 μm, England Finder coordinates in parentheses below. A–D) Leiosphaeridia sp.; A) S014132-2 (S29[1]), PHKB-1: 362 m, Spathian, reproduced from Fielding et al., 2019; B) S014108-2 (V35[4]), PHKB-1: 786.65 m, Griesbachian–Dieneran; C) micropylome indicated with arrow, S014132-2 (S15[1]), PHKB-1: 362 m, Spathian; D) S200860-SEM, 160 cm, upper Changhsingian. E) Modern phycoma of viridus Schmitz, 1878, note the size difference between Halosphaera and Leiosphaeridia, image credit: R. Raine. F–H) Quadrisporites horridus Hennelly, 1958 emend. Potonié and Lele, 1961; F) S014114-2 (K32), PHKB-1: 745.62 m, Smithian, reproduced from Mays et al., 2020; G) S014117-2 (M9[2]), PHKB-1: 778.57 m, Dienerian; H) S200864-2 (G15[4]), Frazer Beach: 153–155 cm, upper Changhsingian. I, J) Modern four-celled coenobia of Tetrastrum staurogeniiforme (Schröder) Lemmermann, 1900, note elongated spines on apical areas of each cell to aid buoyancy, image credits: K. Bruun. K–M) Micrhystridium evansii Price, 1983; K) S014117-2 (V33), PHKB-1: 745.62 m, Smithian; L) S014117-2 (O18[4]), PHKB-1: 745.62 m, Smithian; M) S014132-2 (Y34[3]), PHKB-1: 362 m, Spathian.

2006). The most commonly inferred derivation for this genus has been 3.4.1.4. Sydney Basin occurrences. Examples of Leiosphaeridia are the as the phycomata of prasinophytes (Chlorophyta). Tappan (1980) most commonly encountered algal fossils within the Lopingian and likened Leiosphaeridia to the extant prasinophyte Halosphaera Schmitz, Lower Triassic strata of the Sydney Basin (Mishra et al., 2019; Vajda 1878 (Pyramimonadales; also see Colbath and Grenfell, 1995, Guy- et al., 2020; Mays et al., 2020; this study). The genus extends from the Ohlson, 1996). However, the cells of the extant species (e.g., Fig. 5E) Changhsingian Stage (uppermost Permian; upper D. parvithola Zone) to are typically much larger than those normally reported from Spathian Stage (Lower Triassic; A. tenuispinosus Zone; Fig. 2). Permian–Triassic non-marine deposits of Gondwana. The occurrence of Pyramimonadales in deep geological time is reinforced by: 1, the 3.4.2. Micrhystridium Deflandre, 1937emend. Staplin, 1961 (Fig. 5K–M) probable presence of sporopollenin-like compounds in their walls, 3.4.2.1. Taxonomic justification. Of the several emendations of the genus, including those of Halosphaera (Parke and den Hartog-Adams, 1965), the relatively well circumscribed emended diagnosis of Micrhystridium by providing durability for fossilisation (Aken and Pienaar, 1985); and 2, Sarjeant and Stancliffe (1994) is followed here. This definition includes the near-basal phylogenetic position of Pyramimonadales among extant small (almost always < 27 μm in diameter), typically single-walled cysts green plants (Lewis and McCourt, 2004; Leliaert et al., 2016). with a range of excystment structures (e.g., partial or lateral rupture, A fruitful alternative to morphology has been to analyse the che­ epityche or cryptopylome). Micrhystridium has a (sub)circular outline, mical signatures and wall structures of Leiosphaeridia forms: some whereas the shapes of some other spiny organic-walled microfossils are species have wall features typical of (Le Hérissé, 1984), triangular or quadrangular, with spines at their angular apices (e.g., whereas others show significant differences (Kjellström, 1968; Jux, Dorsennidium Wicander, 1974, Stellinium Jardiné et al., 1972, and 1969). A chlorophyte affinity has been supported for some species Veryhachium Deunff, 1954 emend. Sarjeant and Stancliffe, 1994). based on the presence of algaenans (Steemans et al., 2010). More Compared to other (sub)spherical genera, Micrhystridium has a smaller specifically, an affinity to trebouxiophycean algae is suggested by the cyst diameter and shorter spines than Baltisphaeridium Eisenack, 1958b morphology (e.g., Chlorella [Beyerinck] Beyerinck, 1890 [Colbath and emend. Eiserhardt, 1989, fewer spines than Filisphaeridium Staplin et al., Grenfell, 1995]) and trilaminar wall ultrastructure (e.g., Coccomyxa 1965 emend. Sarjeant and Stancliffe, 1994, and closed spine apices, unlike Schmidle, 1901, Elliptochloris Tschermak-Woess, 1980 [Talyzina and the branched processes of Gorgonisphaeridium Staplin et al., 1965. The Moczydłowska, 2000; Moczydłowska et al., 2010]). Ultrastructural Sydney Basin specimens can be assigned to M. evansii Price, 1983, because analyses have supported chemical analyses, establishing Leiosphaeridia of the very short (0.5–2 μm), widely spaced spines (2–4 μm) and typical as polyphyletic and including populations of both prasinophyte phy­ presence of a partial rupture. comata and trebouxiophycean vegetative cells (Moczydłowska, 2011; Moczydłowska et al., 2011). 3.4.2.2. Affinity. With more than 200 species published, Micrhystridium ranges from the Neoproterozoic to Cenozoic (Fensome et al., 1990), but was particularly diverse and abundant during the Palaeozoic (Downie, 3.4.1.3. Ecological implications. This genus is a common element of 1967). Although approximately 70% of these species may represent marine palynological assemblages, particularly from the late synonyms (Sarjeant and Stancliffe, 1994), the broad morphological Proterozoic to early Mesozoic (Downie, 1973; Fensome et al., 1990). variation and long geological range has earned Micrhystridium the label In modern oceans, plankton blooms of prasinophyte algae are common of a ‘waste-basket taxon’ (Servais, 1996). In this regard, it is similar to in near-shore eutrophic conditions (see Leliaert et al., 2012). Within the Leiosphaeridia, and has long been regarded as a polyphyletic acritarch Permian–Triassic interval, relative increases in leiospherids have been (Deflandre and Deflandre, 1965). However, it has been noted that the noted from various shallow marine deposits (van Soelen et al., 2018; wall structure and excystment mechanism of many species of van Soelen and Kürschner, 2018; Lei et al., 2019), and these have been Micrhystridium and Veryhachium are reminiscent of dinoflagellates linked to increases in nutrient influx into marine settings and a decrease (Dinophyceae; Downie, 1973). Furthermore, several Micrhystridium in salinity (van Soelen et al., 2018). Although relatively rare, and Micrhystridium-like spiny acritarch species have been compared occurrences of freshwater prasinophytes have been recorded in both with, or assigned to, dinoflagellate genera (e.g., Downie, 1973; Dale, the fossil and modern assemblages (see Cymatiosphaera above). Some 1976; Courtinat, 1983; Fensome et al., 1999). Because the majority of other interpretations for Leiosphaeridia affinity favour non-marine species from these fossil-genera are older than the oldest undisputed conditions; e.g., trebouxiophycean algae occur as freshwater plankton fossil dinoflagellates (Anisian Age, Middle Triassic; Tappan and or occupy diverse subaerial niches (Fott and Nováková, 1969; Darienko Loeblich, 1973; Fensome et al., 1996), these may represent stem et al., 2010; see Wehr and Sheath, 2015; see Quadrisporites above). group taxa on the Dinophyceae evolutionary tree. Although less common than marine reports, Permian–Triassic Leiosphaeridia have also been recorded from non-marine successions 3.4.2.3. Ecological implications. Micrhystridium is found almost (e.g., fluvial and lacustrine deposits of Argentina;Zavattieri et al., 2017, exclusively in marine strata, and is particularly common in 2020). Furthermore, high relative abundances of Leiosphaeridia have successions deposited in shallow, nearshore settings (e.g., Wall, 1965; been noted from strata of the Sydney Basin that represent lacustrine Smith and Saunders, 1970; Schrank, 2003; Vajda et al., 2013). The conditions on the basis of sedimentary facies analysis (Fielding et al., species identified herein, M. evansii, is a common taxon in eastern 2020) in the immediate aftermath of the EPE (Vajda et al., 2020; Mays Gondwanan basins, particularly in Permian successions (Price, 1983; et al., 2020). These continental conditions favour the interpretation Phillips et al., 2018). Four factors collectively suggest that this species that the Sydney Basin post-EPE records of Leiosphaeridia represent may be an indicator of brackish estuarine, lagoonal or restricted freshwater algae (e.g., Trebouxiophyceae). marine, rather than open marine, conditions. Firstly, the short spines

12 C. Mays, et al. Earth-Science Reviews 212 (2021) 103382 of the present species (Fig. 5K–M) are unusual for Micrhystridium, and hollow conical processes. These processes are formed from differential Batten (1996b) proposed a link between short acritarch spine lengths thickening of the outer wall. However, for taxa with relatively small and low salinity conditions. Such a relationship has been demonstrated sculptural elements (e.g., M. regulare Anderson, 1977; Fig. 6A, B), discerning for extant dinoflagellates (Hallett, 1999; Mertens et al., 2009, 2012). the structure of the conical processes may be impractical with light This link was supported by the increased relative abundance of short- microscopy. These specimens have closest morphological similarity to the spined Micrhystridium cysts accompanied by a probable decrease in coarsely and irregularly sculptured ‘M. irregulare’ by Anderson (1977). marine salinity recorded from upper Permian–Lower Triassic However, we concur with Backhouse (1991) that the diagnoses of M. successions of East Greenland (van Soelen et al., 2018). Secondly, the irregulare and M. regulare by Anderson (1977) overlap significantly. distribution of M. evansii includes probable non-marine strata from the Following the guidelines by Turland et al. (2018, Ch. 2, Sect. 3, Art. BGSBC based on sedimentological and palynological criteria (Foster, 11.5), we adopt the usage of M. regulare as proposed by Backhouse (1991) 1979; Fielding et al., 2020; this study). Thirdly, small spiny for the present specimens. The coarse sculpture and absence of a dehiscence palynomorphs of comparable size and morphology have been rupture is similar to Cymatiosphaera and Maculatasporites, but identified within Quaternary brackish to freshwater lake deposits of Mehlisphaeridium is differentiated by the presence of conical processes. Australia, although their affinities are not well understood at present The presence of two walls differentiates this genus from Micrhystridium. (Cook et al., 2011, ‘Type A1’, pl. 3, fig. 3). Finally, a spike in the abundance of M. evansii represents a useful biostratigraphic marker (the 3.5.1.2. Affinity. The sculpture of Mehlisphaeridium is similar to some M. evansii Abundance Zone or ‘acme-zone’; Price, 1983, 1997) for the members of the extant chlorophyte family Sphaeropleaceae (e.g., Stage (lower upper Permian, ca 255 Ma) in the northern Sphaeroplea soleirolii [Duby] Montagne ex Kützing, 1849; Fig. 4K, L). portion of the BGSBC (Smith and Mantle, 2013; Laurie et al., 2016). However, without ultrastructural or chemical analyses of the cysts, the This pulse of acritarchs occurs in the uppermost Peawaddy Formation, affinity of this taxon remains uncertain. inferred to represent deposits of a marine incursion into the basin (Price, 1997; Smith and Mantle, 2013; Phillips et al., 2018), or in the 3.5.1.3. Ecological implications. Grenfell (1995) described basal Black Alley Shale, a unit deposited in a brackish water Mehlisphaeridium as non-marine, but no justification was provided. embayment with restricted access to the ocean (Ayaz et al., 2015). Modern Sphaeropleaceae are common planktonic algae in shallow Dinoflagellates, of which some members of Micrhystridium may bodies of freshwater, and regions of intermittent drying, such as represent stem groups (see above), typically live in open marine ephemeral lakes or floodplains (John and Rindi, 2015). This genus conditions, with a lower diversity in lakes (Pollingher, 1987). occurs most commonly in Permian to Lower Triassic fluviolacustrine to However, modern dinoflagellates can form monospecific ‘algal deltaic strata of Gondwana (e.g., Foster, 1979; McMinn, 1985; blooms’ (cf. Smayda, 1997) caused by nutrient influxes along coastal Backhouse, 1991; Fielding and McLoughlin, 1992; Playford and areas (Slater et al., 2019) or in brackish settings, such as estuaries Rigby, 2008; Zavattieri et al., 2017; Gastaldo et al., 2020). (Saldarriaga and Taylor, 2017). In the fossil record, such nutrient-rich and/or brackish conditions may be reflected by near-monospecific 3.5.1.4. Sydney Basin occurrences. Mehlisphaeridium has been reported acritarch assemblages, such as the M. evansii Abundance Zone. previously from Wuchiapingian (lower upper Permian) coastal plain Spikes in the relative abundances of Micrhystridium and Veryhachium deposits of the northern and western Sydney Basin (McMinn, 1982, are common globally in nearshore, especially restricted marine, settings 1985). Mehlisphaeridium is otherwise a rare element within the post-EPE in the immediate aftermath of the EPE (Balme, 1963; Zhan, 1991; Eshet strata of the Sydney Basin and, in this study, was recorded from the et al., 1995; Schneebeli-Hermann et al., 2012a, 2017; Schneebeli- upper Changhsingian to Smithian stages (uppermost Permian–Lower Hermann and Bucher, 2015; Haig et al., 2015; Rampino and Eshet, Triassic; Playfordiaspora crenulata to Protohaploxypinus samoilovichii 2018; Lei et al., 2019; Peyrot et al., 2019), but spikes also occur in non- zones; Fig. 2). marine Early Triassic successions, such as the , (Peng et al., 2018). Following the Smithian-Spathian event (ca 249 Ma; Mays 3.5.2. Pilasporites Balme and Hennelly, 1956 (Fig. 6C–E) et al., 2020), a global cooling interval during the Early Triassic, the 3.5.2.1. Taxonomic justification. This genus encompasses smooth to shallow marine palynological record reveals a major increase in short- finely sculptured cells with circular to oval outlines. As is typical for spined acritarchs, including Micrhystridium (Lindström et al., 2019). this genus, most of the Sydney Basin specimens lack a distinct aperture (Fig. 6C, E), although some bear a short lateral rupture (Fig. 6D). The 3.4.2.4. Sydney Basin occurrences. Micrhystridium occurs sporadically emended diagnoses by Tiwari and Navale (1967) and Jain (1968) are throughout the upper Lopingian and Lower Triassic non-marine strata here rejected because these included the criteria of a rupture or pore, of the Sydney Basin (Grebe, 1970; Helby, 1973). Here, we report respectively, despite an absence (or inconsistent presence) of these Micrhystridium evansii from the non-marine strata of the Changhsingian features in the type material. The Sydney Basin specimens, which are all to Spathian stages (uppermost Permian–Lower Triassic; upper D. assigned to the type species, P. calculus Balme and Hennelly, 1956, can parvithola to A. tenuispinosus zones; Fig. 2). be distinguished from Leiosphaeridia by the prominent equatorial thickening, and from Ovoidites by the absence of a long equatorial 3.5. Palynomorphs of uncertain affinity from the upper Permian to Lower dehiscence mark. Triassic of Gondwana 3.5.2.2. Affinity. This fossil-genus has generally been interpreted as a Organic microfossils of unknown or controversial affinity also occur vascular plant spore (Equisetales, or ‘horsetails’). For example, in global palynological records of the Permian and Triassic periods; Pilasporites allenii Batten, 1968, was found in association with the below are listed the most commonly encountered genera from Equisetites lyellii (Mantell, 1833) Seward, 1894, and Gondwana for which an algal affinity has been suggested. As above, shows great similarity to the alete spores of various extant each genus includes a discussion of key morphological characters, po­ species (Batten, 1968). As noted by Kelber and van Konijnenburg-van tential affinities and ecological interpretations based on associated Cittert (1998), the in situ spores of some fossil equisetalean strobili depositional environments and potential extant and fossil relatives. generally feature a triradiate mark, but the rare spores without these would fall under Pilasporites. However, the genus is likely polyphyletic, 3.5.1. Mehlisphaeridium Segroves, 1967 (Fig. 6A, B) since Pilasporites-like fossil spores were also found in situ in Isoëtites 3.5.1.1. Taxonomic justification. Mehlisphaeridium encompasses spherical, indicus Bose and Roy, 1964, a herbaceous lycopsid, and member of a double-walled cysts with no apparent excystment mechanism, and coarse, distinct vascular plant lineage (Isoëtaceae; Balme, 1995). Furthermore,

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Fig. 6. Possible algal microfossils from the Permian–Triassic of the Sydney Basin, Australia; all scales = 20 μm, England Finder coordinates in parentheses below. A, B) Mehlisphaeridium regulare Anderson, 1977; A) S014125-2 (T24), PHKB-1: 745.62 m, Smithian; B) S014117-2 (M44[1]), PHKB-1: 587.47 m, Smithian. C–E) Pilasporites calculus Balme and Hennelly, 1956; C) S200864-2 (G24[4]), Frazer Beach: 153–155 cm, upper Changhsingian; D) S200864-2 (L44), Frazer Beach: 153–155 cm, upper Changhsingian; E) S200857-SEM, 164.4 cm, upper Changhsingian. F) Reduviasporonites catenulatus Wilson, 1962, S014126-2 (M34), PHKB-1: 559.6 m, Smithian. G, H) Reduviasporonites chalastus (Foster, 1979) Elsik, 1999; G) arrow indicates impression of inner body on outer cell wall, S200864-2 (O48), Frazer Beach: 153–155 cm, upper Changhsingian; H) S014101-1 (O33[3]), PHKB-1: 805.03 m, upper Changhsingian, reproduced from Mays et al., 2020.

Balme (1995, p. 134) interpreted the species found herein, P. calculus, 3.5.2.4. Sydney Basin occurrences. Pilasporites is an uncommon fossil to be a sphaeromorph acritarch. An algal affinity was advanced by from the Guadalupian to Lower Triassic strata of the Sydney Basin Helby (1970), who observed the co-occurrence of P. calculus with the (Balme and Hennelly, 1956; Grebe, 1970; Helby, 1970). We record P. zygnematacean algae Circulisporites, Peltacystia and Tetraporina. In calculus from the Changhsingian to Spathian stages (uppermost support of this association, the thinner wall compared to most plant Permian–Lower Triassic; upper D. parvithola to A. tenuispinosus zones; spores, equatorial thickening, inaperturate poles and close Fig. 2). morphological similarity with Ovoidites favour an algal (e.g., zygnematacean) affinity for this and similar species of Pilasporites. 3.5.3. Reduviasporonites Wilson, 1962 emend. Foster et al., 2002 (Fig. 6F–H) 3.5.3.1. Taxonomic justification. Reduviasporonites consists of simple, 3.5.2.3. Ecological implications. Pilasporites calculus was originally smooth-walled cells that typically occur as septate, linear chains of recovered from probable non-marine Permian strata of New South two or more cells (Fig. 6F, H), and rarely as single (Fig. 6G) or branched Wales and Tasmania, Australia (Balme and Hennelly, 1956). Pilasporites cells. Two populations were identified in the present material, defined calculus, and similar species of this genus, have been recovered from by their cell shapes and sizes: 1, a larger, approximately cylindrical Permian to Jurassic non-marine facies of (e.g., Farabee et al., form (Reduviasporonites chalastus [Foster, 1979] Elsik, 1999; Fig. 6G, 1990), Australia (de Jersey, 1960; de Jersey, 1962; Helby, 1970), India H); and 2, a smaller form with subspherical cells (R. catenulatus Wilson, (e.g., Tripathi, 1997) and South Africa (e.g., Barbolini and Bamford, 1962; Fig. 6F). The specimens of R. chalastus identified herein have 2014). robust thickenings at the polar ends of each cell, and are similar to the

14 C. Mays, et al. Earth-Science Reviews 212 (2021) 103382 type material from the Bowen Basin, Australia (Foster, 1979), but 2018). Owing to the conflicting interpretations of affinities, divergent generally smaller. Many of these specimens feature inner bodies ecological implications have been drawn from the Reduviasporonites (Fig. 6G), and would fall under R. stoschianus (Balme, 1980) Elsik, abundance ‘spike’ of the EPE. The fungal hypothesis implies the 1999; however, we follow the recommendations of Foster et al. (2002) proliferation of saprotrophic (Visscher et al., 1996) and/or who considered that species to be a junior synonym of R. chalastus. pathogenic (Visscher et al., 2011) fungi on dead or dying terrestrial plant tissues (also see Rampino and Eshet, 2018). In contrast, the algal 3.5.3.2. Affinity. The natural affinity of Reduviasporonites remains hypothesis interprets the abundance spike(s) as a response to stressed controversial and presently unresolved, with arguments advanced for subaqueous conditions (Afonin et al., 2001). Although subaerial both fungal and algal origins (see Zavattieri et al., 2017). The evidence trentepohlialeans may represent a feasible affiliation for for these conflicting interpretations has come from direct fossil data, or Reduviasporonites (Spina et al., 2015), it is not clear why this group indirectly from associated fossils or characteristics of the host strata. should peak in abundance in the wake of the EPE, which is Direct morphological similarities have been noted between characterised by a major collapse of terrestrial plant communities, Reduviasporonites and both green algae (e.g., Mougeotia, Spirogyra since many modern subaerial algae (e.g., endophytic and plant-parasitic [Zygnemataceae: Zygnematophyceae], see Afonin et al., 2001; or e.g., members of Trentepohliales) rely heavily on living plant hosts for their Trentepohlia von Martius, 1817 [Trentepohliaceae: ], see life cycles (Brooks et al., 2015; Škaloud et al., 2018). For this reason, Spina et al., 2015), and fungi (e.g., Rhizoctonia De Candolle, 1815 [see freshwater algal or fungal affinities are considered more likely for Elsik, 1999], a member of Ceratobasidiaceae, Andersen and Stalpers, Reduviasporonites, whereby the overloading of nutrition from decaying 1994). We also note morphological similarities between organic matter and increased salinity due to higher ground-water levels Reduviasporonites and Upper Triassic forms from Europe attributed to following deforestation would fuel both algal and fungal proliferation Jacutianemia Timofeev and Hermann, 1979 by van de Schootbrugge (Vajda et al., 2020). et al. (2020, fig. 8H) that probably represent terrestrial fungi. Additional direct evidence has been drawn from biochemical 3.5.3.4. Sydney Basin occurrences. Reduviasporonites occurs rarely in the analyses, specifically the stable C- and N-isotope and hydrocarbon post-EPE (uppermost Lopingian to Lower Triassic) strata of the Sydney signatures, of Reduviasporonites body fossils. These results have also Basin. Our sampling showed that R. catenulatus ranges from the ?upper contributed to conflicting interpretations, with some favouring algae Changsinghian to Spathian stages (P. crenulata to A. tenuispinosus (Foster et al., 2002), but others suggesting fungi (Sephton et al., 2009). zones), whereas R. chalastus was identified only within the P. However, these biochemical interpretations should be considered with crenulata Zone. This latter zone directly overlies the EPE (upper a high degree of uncertainty owing to unquantified post-burial Changhsingian–?Griesbachian stages; uppermost Permian–?lowermost alteration (Sephton et al., 2009). Reduviasporonites can exhibit Triassic; Fig. 2). autofluorescence, which has been attributed to the remains of chlorophyll or oil globules, thus supporting an algal affinity (Spina 3.5.4. Rugaletes Foster, 1979 (Fig. 7A–D) et al., 2004). However, Sephton et al. (2009) has noted that 3.5.4.1. Taxonomic justification. This genus encompasses single-walled, autofluorescence can also be expressed by fungal remains (Wu and alete cells with subcircular outlines and distinctive rugulate sculpture. Warren, 1984); this property has since been identified within Two populations were identified herein, one with coarse rugulae and Rhizoctonia, a putative extant fungal relative (Guermache et al., relatively thick walls (Rugaletes playfordii Foster, 1979; Fig. 7A, B), the 2012). As such, fluorescence yields inconclusive evidence for other featuring narrow rugulae, and thin walls that have a tendency to establishing the affinity of Reduviasporonites. fold (R. awakinoensis Raine in de Jersey and Raine, 1990; Fig. 7C, D). Indirect evidence of the affinity forReduviasporonites has come from The excystment or germination mechanism is unclear, although some the geochemical and lithological interpretations of the host strata and may have irregular partial ruptures (Fig. 7A). This genus can be the ecological niches of its inferred modern relatives (see Rampino and distinguished from Enzonalasporites Leschik, 1956, and Peroaletes Eshet, 2018). The high abundance of aromatic hydrocarbons typical of Bharadwaj and Singh, 1964, by having a single-layered wall. lichen/fungi (Nabbefeld et al., 2010; Sawada et al., 2012) has been advanced to support a fungal affinity (Rampino and Eshet, 2018). 3.5.4.2. Affinity. When first described byFoster (1979), this ambiguous However, these biochemical fingerprints have been identified only in genus was interpreted as a miospore (also see de Jersey and Raine, the host sediments, and not yet tied directly to Reduviasporonites. The 1990). Since then, it has generally been considered an acritarch or morphology and chemical signatures above are consistent with fungi incertae sedis (Playford and Dring, 1981; Foster and Williams, 1991; that lived in connection to land plants, and the potential affiliates Mory et al., 1998). Here, we consider two distinct affinities to extant among extant algal groups are also non-marine taxa that live mostly in algal groups: 1, zygospores of zygnematacean algae; and 2, cysts of a freshwater (e.g., Zygnematales) or subaerial (e.g., Trentepohliales) dinoflagellate stem group. Rugaletes shares a rounded outline and settings. Thus, the occurrences of this taxon in non-marine pa­ rugulate sculpture with fossils interpreted as zygnematacean laeoenvironments (see below) do not significantly favour the affinity of zygospores, such as Cycloovoidites Krutzsch and Pacltová, 1990 (e.g., one group over another and, on the basis of available data, we can not C. cyclus [Krutzsch, 1959] Krutzsch and Pacltová, 1990), or Lecaniella yet resolve whether this taxon has algal or fungal affinities. (e.g., L. korsoddensis Batten et al., 1994). These fossil-genera have been linked to the extant zygnemataceans Spirogyra (Worobiec and 3.5.3.3. Ecological implications. Early studies noted that this taxon Worobiec, 2010; Worobiec, 2014) and Transeauina (=Debarya; Head, occurred in very high relative abundances concurrent with, or 1992; Van Geel and Grenfell, 1996), respectively. Sporopollenin, a immediately following, the EPE (Visscher and Brugman, 1986; Eshet, taphonomically stable compound, has been identified within several 1990). These abundance ‘spikes’ have been recognised primarily at extant genera of Zygnemataceae (Blokker, 2000; de Leeuw et al., 2006), equatorial or northern latitudes (see Schneebeli-Hermann and Bucher, thus enhancing the preservational potential of this group in the 2015), and in both marine (Visscher and Brugman, 1986; Ouyang and geological record. Alternatively, it is similar to some rounded, single- Utting, 1990; Eshet et al., 1995; Spina et al., 2015) and non-marine walled dinoflagellate cysts with rugulate sculpture, such asPyxidinopsis (Steiner et al., 2003; Coney et al., 2007; Cao et al., 2008; Bercovici psilata (Wall and Dale in Wall et al., 1973) Head, 1994. Although P. et al., 2015; Kar and Ghosh, 2018) successions. The occurrence of psilata is typically smooth, some specimens feature coarse rugulae Reduviasporonites in non-marine strata suggests that this taxon similar to those of Rugaletes playfordii (e.g., Wall et al., 1973, pl. 3, proliferated in these conditions, and its marine occurrences were the Fig. 5; Mudie et al., 2017, pl.-fig. 22.14). A problem common to those result of transport into proximal marine basins (Rampino and Eshet, affinities is the absence of a consistent aperture (cf. partial or complete

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Fig. 7. Probable algal fossil-genus, Rugaletes, from the Permian–Triassic of the Sydney Basin, Australia; all scales = 20 μm, England Finder coordinates in parentheses below. A, B) Rugaletes playfordii Foster, 1979; A) arrow indicates possible irregular excyst­ ment rupture, S014131-2 (M22[3]), PHKB-1: 383.48 m, ?Spathian; B) S014120-2 (M36[2]), PHKB-1: 699.07 m, Smithian. C, D) Rugaletes awa­ kinoensis Raine in de Jersey and Raine, 1990; C) S014131-2 (M22[3]), PHKB-1: 362 m, Spathian; D) S014120-2 (M36[2]), PHKB-1: 362 m, Spathian.

rupture for a zygnematacean affinity, archeopyle for a dinoflagellate and a fossil (e.g., Traverse, 1955; Glikson et al., 1989) hydrocarbon affinity); however, some fossil specimens may possess irregular source. Extant braunii Kützing, 1849 has a global dis­ excystment ruptures (Fig. 7A). The occurrence of Rugaletes in non- tribution, a preference for fresh and brackish waters, and can endure marine sedimentary successions (see below) favours a freshwater algal extreme shifts in temperature (−20° to +40 °C; Demura et al., 2014). affinity (e.g., Zygnemataceae), but because the above interpretations Lecaniella Cookson and Eisenack, 1962b has a similar structure to Pel­ are based almost entirely on comparative morphology, we must regard tacystia and has a probable affinity to zygnematacean charophytes, these as tentative. being consistently compared to extant Transeauina or Zygogonium (Van Geel and Van der Hammen, 1978; Zippi, 1998). It occurs rarely in 3.5.4.3. Ecological implications. Although this genus was originally Gondwana during the Triassic (e.g., Zavattieri and Prámparo, 2006; described from non-marine strata of eastern Australia (Foster, 1979), Zavattieri et al., 2020) but is increasingly common and diverse around it has since been reported from a range of marine (e.g., Playford and the globe in upper Mesozoic and Cenozoic non-marine deposits (e.g., Dring, 1981; McLoughlin, 1988; de Jersey and Raine, 1990; Campbell Cookson and Eisenack, 1962b; Head, 1992; , 1997). Grebespora et al., 2001; Cirilli et al., 2005) and non-marine (McLoughlin, 1990; Jansonius, 1962 has close morphological similarity to extant and fossil Pole and Raine, 1994; this study) strata. representatives of Zygnemataceae (Grenfell, 1995; Zavattieri et al., 2017), e.g., Transeauina and Lecaniella, respectively. It has been widely reported from Triassic strata, particularly from non-marine successions 3.5.4.4. Sydney Basin occurrences. Rugaletes occurs, thus far, only of Gondwana (e.g., de Jersey, 1972, 1979; Hankel, 1992; Zavattieri and within the post-EPE strata of the Sydney Basin: R. playfordii ranges Batten, 1996; Murthy and Sarate, 2015). from the ?upper Changhsingian to Smithian stages (?uppermost Permian–Lower Triassic; P. crenulata–lower A. tenuispinosus zones), whereas R. awakinoensis occurs in Griesbachian to Spathian strata 3.6.2. Rare or stratigraphically/geographically restricted non-marine algae (Lower Triassic; Protohaploxypinus microcorpus–A. tenuispinosus zones; These tend to be exceptionally rare, have narrow geographic or Fig. 2). stratigraphic ranges, or restricted environmental tolerances. One of the more important, Bartenia Helby, 1987, has served as a key index taxon 3.6. Other taxa not recorded in samples from the Sydney Basin for the Late Triassic, and can be locally common primarily in Western Australia (Helby et al., 1987; Backhouse et al., 2002), and less com­ 3.6.1. Common non-marine algae monly, within disparate Gondwanan localities (e.g., Antarctica, Botryococcus Kützing, 1849, belonging to the chlorophyte order McLoughlin et al., 1997; Saudi Arabia, Issautier et al., 2019). Ulani­ Trebouxiales, has been reported from non-marine deposits throughout sphaeridium McMinn, 1982, is employed for two-walled, ellipsoidal to the (see Batten and Grenfell, 1996), including Permian–­ spherical cysts with a circular pylome and short solid fibrous spines Triassic strata of Gondwana (Dulhunty, 1944; Guy-Ohlson and connected basally by low ridges (McMinn, 1982, 1985). This genus has Lindström, 1994; Wheeler et al., 2020). It has been utilised as a pa­ at least superficial similarities in morphology to various other algae/ laeoenvironmental indicator for brackish or freshwater conditions with acritarch genera, such as Portalites Hemer and Nygreen, 1967 and low sediment input (Guy-Ohlson, 1992; Clausing, 1999) or regions of Micrhystridium, hence its affinities remain uncertain. The type species, fluvial input into marine settings (Slater et al., 2017). Botryococcus has U. berryense McMinn, 1982 has been reported from paralic to fully also received wide attention as both a modern (e.g., Weiss et al., 2010) continental Guadalupian to Lower Triassic strata of the Sydney Basin

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(McMinn, 1982) and the Gloucester Basin—a northern outlier of the from the (Hemer and Nygreen, 1967) and Permian (e.g., Sydney Basin (McMinn, 1987). However, representatives have also Foster et al., 1985; Banerjee and D'Rozario, 1990), respectively. How­ been reported from marginal to fully marine Cisuralian strata of Oman ever, their affinities remain highly uncertain and may be congeneric (Stephenson and Osterloff, 2002; Angiolini et al., 2006). The coenobial (see discussions by Tappan, 1980, Colbath and Grenfell, 1995 and chlorophyte fossil-genera Plaesiodictyon Wille, 1970 (Scenedesmaceae; Souza et al., 2016). Brenner and Foster, 1994) and Syndesmorion Foster and Afonin, 2006 (Hydrodictyaceae or Scenedesmaceae; Foster and Afonin, 2006) are 4. Taphonomic biases in the fossil record of microscopic algae considered to be closely related to Pediastrum Meyen, 1829 or Scene­ desmus Meyen, 1829, both of which are extant cosmopolitan freshwater The Permian–Triassic non-marine strata of Gondwana host abundant (or brackish; see Cook et al., 2011) algae and produce chemically-stable and diverse green algal assemblages, but the greatest diversity is among algaenans (Versteegh and Blokker, 2004). Although rare, Syndesmorion Zygnematophyceae, a clade of freshwater charophytes (e.g., Segroves, remains have been reported globally from both Permian and Triassic 1967; Brenner and Foster, 1994; Grenfell, 1995; Zavattieri and Prámparo, strata (e.g., Australia, Brenner and Foster, 1994; East Asia, Foster and 2006; Lindström and McLoughlin, 2007; Zavattieri et al., 2017, 2020; this Afonin, 2006; Europe, Fijałkowska, 1995; South America, Zavattieri study). Sporopollenin in the spore/pollen wall has been considered a sy­ et al., 2017). In contrast, Plaesiodictyon has only been reported from the napomorphy of land plants (Embryophyta), among which it is nearly Triassic (Anisian–Norian stages; Middle–Upper Triassic) and, thus, has ubiquitous, except in rare cases where it has been secondarily lost (e.g., served as a useful index taxon, particularly in the Northern Hemisphere aquatic angiosperms; Wellman, 2004). In contrast, the occurrence of (e.g., Batten, 1996a and references therein; Wood and Benson, 2000; sporopollenin among green algae tends to be more common in groups that Lindström et al., 2017; Paterson et al., 2019). However, it occurs less are closely related to land plants, such as Zygnematophyceae, a likely commonly in Gondwana (e.g., Brenner and Foster, 1994; Zavattieri and sister group to (Leliaert et al., 2012; Del Cortona et al., Prámparo, 2006). 2020). A wide range of extant zygnematophycean algae has long been known to use sporopollenin-like compounds in their zygospore walls (de 3.6.3. Algae typical of marine deposits but with rare non-marine reports Vries et al., 1983; Versteegh and Blokker, 2004; see de Leeuw et al., 2006), The environmental tolerances of the prasinophyte Tasmanites which likely serves to prevent bacterial decay or desiccation in soils or Newton, 1875 (; Wall, 1962; Guy-Ohlson and ephemeral lakes (Graham and Gray, 2001). This factor would have sig­ Boalch, 1992) have been well studied in relation to their contribution to nificantly enhanced the preservational potential of Zygnematophyceae, oil shale resources (Revill et al., 1994; Vigran et al., 2008). Long-spined and contributed to their relatively strong representation in deep-time fossil acritarch taxa, such as Veryhachium Deunff, 1954 and Baltisphaeridium assemblages. Eisenack, 1958a, have ambiguous (possibly dinophycean stem-group) The occurrence of chemically resistant polymers has been noted in affinities and are widely considered to be indicators of open marine more distantly related Palaeozoic–Mesozoic algae, but is less common. conditions (Stancliffe and Sarjeant, 1994; Lei et al., 2012; van Soelen Sporopollenin-like, acid-resistant biopolymers occur in some groups of and Kürschner, 2018), but may occur in paralic and tidal settings (Vajda chlorophytes; for example, ‘algaenan’ is produced by cells of extant et al., 2013), and even in freshwater environments in association with Botryococcus Kützing, 1849 (Trebouxiophyceae; Burczyk and Botryococcus (Peng et al., 2018). They are common in Permian and Dworzanski, 1988; Nguyen et al., 2003; Baudelet et al., 2017), with Triassic marine successions of Gondwana and have high relative fossil representatives of Botryococcus extending back at least to the abundances in the aftermath of the EPE (Balme, 1963, 1970; Dolby and and perhaps the Proterozoic (Colbath and Grenfell, 1995; Balme, 1976; Haig et al., 2015). Martín-Closas, 2003). The extant relatives of other probable treboux­ iophycean algal groups (Leiosphaeridia, Quadrisporites) have also de­ 3.6.4. Fossils with putative algal affinities monstrated algaenan and/or acid-resistant walls (Brenner and Foster, Some taxa found commonly in non-marine strata have been con­ 1994; de Leeuw et al., 2006; Steemans et al., 2010), whereas ‘spor­ sidered algae, but do not have well-resolved affinities. Although in­ opollenin-like’ compounds have been reported from extant pyr­ itially compared to algae, Pyramidosporites Segroves, 1967 has a pro­ amimonadalean prasinophytes that have close morphological similarity blematic affinity (see Balme, 1970), and at least one species formerly to Leiosphaeridia (e.g., Halosphaera, Parke and den Hartog-Adams, 1965; attributed to it (Froelichsporites traversei [Dunay and Fisher, 1979] , Aken and Pienaar, 1985). Litwin et al., 1993) probably represents the tetrads of gymnosperms Recent phylogenetic divergence age estimates for the green plant (Baranyi et al., 2018). Similarly, Portalites Hemer and Nygreen, 1967 is clade () suggest that all extant classes of green algae had a common non-marine acritarch in Gondwanan Permian and Triassic evolved by the Neoproterozoic–early Palaeozoic (Del Cortona et al., strata (e.g., Fielding and McLoughlin, 1992; Zavattieri et al., 2020), but 2020; Fig. 8); thus, the absence of many groups in Permian and Triassic a recent review of the genus suggested that at least some re­ strata, particularly among chlorophytes, can be largely attributed to presentatives have fungal affinities (Souza et al., 2016). Schizosporis preservational biases related to the physical and chemical durability of Cookson and Dettmann, 1959 emend. Pierce, 1976 is a common taxon cell and cyst walls. Such biases likely explain, in part, why there are in Mesozoic (particularly Cretaceous) freshwater deposits and has been relatively large numbers of Zygnematophyceae fossil-genera in ancient generally compared to extant green algae (e.g., Chlorophyceae, strata, and why this group is disproportionately well-represented in the Brenner, 1963; Zygnematophyceae, Grenfell, 1995). However, the Permian and Triassic fossil records of Gondwana (Fig. 8). As a result of Schizosporis type species, S. reticulatus Cookson and Dettmann, 1959, these biases, we hypothesise: has also been likened to the eggs of (Van Geel, 1998). Spheripollenites Couper, 1958 is probably polyphyletic (Batten and 1) ecological or palaeodiversity inferences based solely on algal paly­ Dutta, 1997); the original diagnosis describes simple cells with putative nomorph assemblages will be inherently constrained compared to pores, and this genus has been ascribed to several disparate groups, those derived from land plant palynomorphs (e.g., spores/pollen) such as gymnosperms (e.g., Couper, 1958) and fungi (e.g., Gutiérrez among which chemically-stable polymers are near-universal; and et al., 2010). In cases where dehiscence splits have been identified, 2) fossil-based evolutionary and extinction trends of green algae will species of Schizosporis (e.g., ‘S. gondwanensis’ Hart, 1963; ‘S. spriggii’ be most reliable for groups that typically incorporate chemically Cookson and Dettmann, 1959) and Spheripollenites and have been resistant biopolymers, such as Zygnematophyceae. transferred to taxa of zygnematophycean affinity (e.g.,Ovoidites scissus; Pierce, 1976; Grenfell, 1995). Arabisphaera Hemer and Nygreen, 1967 A way forward in detecting the representation in the fossil record of and Haplocystia Segroves, 1967 are rare palynomorphs in Gondwana algal and other microbial groups with poor cellular preservation may be

17 C. Mays, et al. Earth-Science Reviews 212 (2021) 103382

Fig. 8. Habitat preferences and phylogenetic tree with tentative placements of each of the Permian–Triassic fossil group identified herein, based on their present consensus affinities (Table 1). ‘?’ next to taxon name indicates placement with high degree of uncertainty, or more than one plausible affinity. Phylogeny and age correlation of extant green plants (Viridiplantae) from Del Cortona et al. (2020); Chromista (sensu Cavalier-Smith, 2018) phylogeny adapted from Janouškovec et al. (2017); fossil stratigraphic ranges (dotted lines) for Micrhystridium from Fensome et al. (1990) and dinoflagellates from Tappan and Loeblich (1973). Habitat preferences for each group indicate the relative proportion of species in a given habitat category; minimum increment indicates ≤10% of known species (from Fensome et al., 1990; Mangot et al., 2011; Zonneveld et al., 2013; Del Cortona et al., 2020; Jobard et al., 2020). Cam. = , Carb. = Carboniferous, Ce. = Cenozoic, Creta. = Cretaceous, Cryo. = , Dev. = , Ediac. = , Jur. = Jurassic, Mesoprot. = Mesoproterozoic, N = Neogene, Ord. = Ordovician, P = , Per. = Permian, S. = , Tri. = Triassic. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) the identification of group-specific biomarkers in the sedimentary ­re global primary productivity (Field et al., 1998), with similarly high cord (e.g., Radke et al., 1998; Brocks and Summons, 2004; Brocks and proportions likely for most of the Phanerozoic (Berner, 2009). As such, Pearson, 2005; Brocks et al., 2005; Grice et al., 2005, 2007; Schwark establishing the true biological productivity of algae on a global scale and Empt, 2006). However, there are likely to be ongoing problems will be of critical importance in constraining carbon cycle changes with the quantification of organic contributions from these groups during the EPE. owing to differential breakdown and loss of biopolymers during diag­ Continental records of fossil algae across the Permian–Triassic have enesis (Hebting et al., 2006). received less attention than those of the marine realm. One marker for the end-Permian ecosystem collapse has been the ‘abundance spike’ of 5. The fossil algal record of the Permian–Triassic biotic crises in the possible non-marine alga, Reduviasporonites, particularly in Gondwana Northern Hemisphere successions (Visscher and Brugman, 1986; Eshet, 1990; Bercovici et al., 2015; Schneebeli-Hermann and Bucher, 2015). 5.1. The Permian-Triassic transition and the end-Permian event (EPE) Since the affinity of this fossil-genus has not been resolved, its ecolo­ gical significance is equivocal (seeReduviasporonites section above). The Algae underwent dramatic changes in diversity and abundance continental successions of the Sydney Basin and adjacent Gloucester during the Permian and Triassic periods, most notably in the immediate Basin yield high relative abundances of freshwater algae, particularly aftermath of the EPE. Nearly all marine successions around the globe Circulisporites, Leiosphaeridia and Quadrisporites, especially at the top of have recorded elevated proportions of Leiosphaeridia (van Soelen and the Permian and in the Lower Triassic succession (Hennelly, 1958; Kürschner, 2018; Lei et al., 2019) and/or short-spined Micrhystridium Grebe, 1970; Helby, 1973; McMinn, 1987; Vajda et al., 2020; Mays and Veryhachium (Thomas et al., 2004; Schneebeli-Hermann and et al., 2020). Coeval increases of Botryococcus, Micrhystridium and Bucher, 2015; Peng et al., 2018; Lei et al., 2019). These changes signal a Quadrisporites have been observed within the Galilee and/or Bowen major turnover in marine primary producers (van de Schootbrugge and basins (Evans, 1966; de Jersey, 1979; Wheeler et al., 2020). Collec­ Gollner, 2013). Despite the proportional increases of algae and acri­ tively, the increases in relative abundances from eastern Australia are tarchs in many palynological successions, their absolute concentrations suggestive of freshwater algal proliferation in the wake of the EPE. only increase immediately after the EPE in south China (Shen et al., However, studies of absolute algal abundance changes have not yet 2013) and the Finnmark Platform (van Soelen and Kürschner, 2018), been conducted. but exhibit a long-term overall reduction in algal concentrations in both In the absence of high-resolution studies of continental algal as­ of these regions. Few studies from other regions have assessed the ab­ semblages from other parts of Gondwana, it is difficult to generalize solute concentrations of algae/acritarchs in palynoassemblages from about the patterns of turnover within this group through the Permian- this interval. Today, marine algae contribute approximately 50% of Triassic transition in the Southern Hemisphere. However, we note some

18 C. Mays, et al. Earth-Science Reviews 212 (2021) 103382 anecdotal evidence for increased relative abundances of freshwater 249 Ma; Mays et al., 2020). This event signifies a global cooling from algae in several sections across the Southern Hemisphere. Balme extreme greenhouse conditions of the late Smithian Stage (Romano (1963), Dolby and Balme (1976) and Peyrot et al. (2019) have noted et al., 2013), with a concurrent marine mass extinction (Brayard et al., vast quantities of leoispherids and spinose acritarchs in shallow marine 2009; Stanley, 2009) and restructuring of terrestrial plant communities deposits of the marginal basins of Western Australia. Some of these are (e.g., Hochuli and Vigran, 2010; Hermann et al., 2011; Lindström et al., likely to derive from continental or brackish-water algal populations 2019; Mays et al., 2020). The marine palynological record of the Smi­ based on the mixed terrestrial-marine biotas preserved in these strata thian–Spathian reveals a major increase in short-spined acritarchs in­ and the enclosed nature of these basins at that time (Haig et al., 2015). cluding Micrhystridium (Lindström et al., 2019), but very little is known In the Basin, South Africa, Steiner et al. (2003) noted a spike of the impact of this event on non-marine algae at present. in Reduviasporonites in beds now considered to slightly post-date the Other Permian–Triassic biotic disruption events have been recorded EPE, but other putative algae were not detected. Gastaldo et al. (2020) among marine and land plant ecosystems (e.g., end-Guadalupian event, noted an assemblage rich in Brazilea (=Ovoidites), Leiosphaeridia sp., Retallack et al., 2006, Rampino and Shen, 2019; Griesbachian–Die­ Micrhystridium and simple spores from a level close to the EPE horizon nerian event, Stanley, 2009, Hochuli et al., 2016). However, the algal (base of the Zone). Another sample, 10.5 m higher strati­ fossil records of these events have not yet been well studied. At least graphically, contained a more diverse palynological asssemblage but some of these events may have been only regional in scope and relate was also dominated by algal remains: Brazilea (=Ovoidites) sp., Leio­ primarily to specific palaeogeographic and palaeoenvironmental influ­ sphaeridia, Mehlisphaeridium, Micrhystridium, Quadrisporites horridus and ences. For example, the M. evansii Abundance Zone (Price, 1983), Rugaletes. These assemblages are consistent with the diverse algal suites constituting a widely recognised biostratigraphic marker event in the recorded above the EPE in eastern Australian successions (Vajda et al., Bowen and Gunnedah basins of eastern Australia, probably represents a 2020; Mays et al., 2020). Investigations of the mid-Zambezi Basin proliferation of algae during increasingly stressed conditions as de­ succession in Zambia identified a spike of algae (mostly Ovoidites, positional environments in those basins transitioned from open marine ?Mehlisphaeridium and Tetraporina) in the middle Madumabisa Forma­ to brackish-water settings as the widespread late Wuchiapingian (early tion (Barbolini et al., 2016). This assemblage pre-dates the EPE and late Permian) regression occluded the sea from this region (Fielding may be similar in age to the end-Guadalupian extinction or Micrhy­ et al., 2001; Phillips et al., 2018). stridium evansii Abundance Zone in eastern Australia. Elsewhere in southern Africa, palynological analyses of the Permian-Triassic transi­ 5.3. Implications of fossil algae during global environmental changes tion have been hindered by poor preservation of assemblages caused by thermal alteration from Jurassic intrusions (Coney et al., 2007; Prevec Algal proliferation events may play a role in explaining the dis­ et al., 2009, 2010; Gastaldo et al., 2020). Pereira et al. (2016) noted a tribution of mercury (Hg) in organic-rich strata through the Permian- marked increase in the representation of freshwater algae in the upper Triassic transition. Peaks in sedimentary mercury (up to a 100-fold Matinde Formation (‘Assemblage 3’) of the Moatize-Minjove Basin, increase above background levels), assumed to be derived from the Mozambique, compared to underlying (Permian) parts of the succes­ large igneous province or other regional volcanism, have sion. This zone contained rare to abundant forms of Cymatiosphaera, been recorded in several mass-extinction intervals through mid- Leiosphaeridia, Peltacystia and Reduviasporonites, and was correlated Permian to Lower Triassic successions in various parts of the world with (basal Triassic) assemblages elsewhere in Gondwana. (Grasby et al., 2016; Shen et al., 2019; Dal Corso et al., 2020). These Lower Triassic strata of the Sakamena Group, Morondava Basin, peaks have been implicated by some authors as a significant con­ Madagascar, have yielded palynoassemblages with very high abun­ tributing factor to ecosystem deterioration on land and in the oceans dances (21–52%) of Leiosphaeridia and acanthomorph acritarchs (Grasby et al., 2020). However, we note that heavy metal scavenging by (Hankel, 1993). Peltacystia, Schizosporis and Tetraporina also constitute certain algae (Stern et al., 2009; Outridge et al., 2019) may be partly relatively high abundances of these assemblages (4–10%) denoting a responsible for concentrating Hg during their proliferation following significant contribution of freshwater algae to these Lower Triassic as­ mass extinctions. Rather than indicating an excess of Hg distributed semblages, but the exact stratigraphic relationships of the sampled beds globally by volcanic emissions, high algal productivity might be re­ to the EPE in this basin are poorly constrained. The Sakamena Group sponsible for concentrating Hg markedly above background levels, and assemblages correlate broadly with the Kraeuselisporites saeptatus Zone sequestering this and other heavy metals in the sedimentary column. of Western Australia (Smithian Stage, Lower Triassic; Hankel, 1993). We contend that advances in understanding the patterns of turnover Further north, palynological assemblages of Kenya that correlate with in continental aquatic ecosystems through the Permian-Triassic transi­ the Protohaploxypinus microcorpus to P. samoilovichii zones of eastern tion will require extensive high-resolution palynostratigraphic sampling Australia (Greisbachian–Smithian stages, Lower Triassic), contain coupled with precise taxonomic identification of microfossils. Several average frequencies of 4.1% algal remains (mostly Grebespora and previous studies of Gondwanan Permian and/or Triassic palynology Maculatasporites) that confirm the persistence of significant quantities have simply grouped freshwater microfossils as ‘algal remains’ or ‘ac­ of freshwater algae through the later part of the Early Triassic (Hankel, ritarchs’ without recognizing the habitat-specific preferences of in­ 1991, 1992). dividual taxa outlined above. A more concerted effort targeting con­ Immediate post-EPE strata from the interior basins of central tinental algal microfossils ought to be capable of elucidating the India have not yet yielded evidence of algal proliferation (Tiwari and regional signals of nutrient loading and eutrophication in the aftermath Ram-Awatar, 1990; Srivastava et al., 1997) but studies in those areas of the end-Permian event, and the onset of salinification in lake systems have focused primarily on spore-pollen distributions for biostratigraphy as hothouse climates and continental interior aridification became more and have mostly identified taxa to only generic or higher levels. A re­ pronounced in the Early Triassic. latively protracted and subdued peak in algal abundance was detected above the EPE horizon in the Lambert Graben of East Antarctica by 6. Biogeography of Permian and Triassic Gondwanan non-marine Lindström and McLoughlin (2007), but they also noted at least one algae spike of algae in Lopingian strata well below the EPE. The Permian-Triassic transition was marked by profound changes in 5.2. Other biotic crises of the Permian and Triassic the distributions of non-marine algae. During the Permian, relatively homogenous non-marine algal assemblages have been reported across The Australian records of continental microfossils also suggest a southern and eastern Gondwana (including Australia, Antarctica, India major ecological disruption during the Smithian-Spathian event (ca and southern Africa). Collectively, these assemblages constitute a

19 C. Mays, et al. Earth-Science Reviews 212 (2021) 103382

Fig. 9. Permian palaeogeographic maps (ca 260 Ma) A illustrating the change in geographic ranges from the Permian to Triassic of three common Gondwanan Europe 60° algal groups. Pre-EPE = all Permian records until the end-Permian event (EPE); post-EPE = all Triassic and post-EPE Permian records. Based on 30°N Supplementary Figs. 1 and 2, from data compiled in Peltacystia North America Supplementary Table 2. Green sectors = Gondwana; Palaeo-Tethys blue sectors = /; brown Post-EPE Cathaysia/ Equator areas = mountains; yellow areas = lowlands; light range East Asia blue areas = continental shelf; other blue Pre-EPE areas = oceanic basins. Map adapted from Scotese range 30°S Africa (1997). A, Peltacystia (Zygnemataceae) which de­ Peltacystia lineates the Peltacystia Microalgal Province; B, Tet­ South America Greater Province India raporina (Zygnemataceae); and C, Quadrisporites 60° (Trebouxiophyceae). (For interpretation of the re­ ferences to colour in this figure legend, the reader is Antarctica Australasia referred to the web version of this article.) B

60°

30°N Tetraporina

Post-EPE Equator range Pre-EPE range 30°S

60°

C

60°

30°N Quadrisporites

Post-EPE range Equator Pre-EPE range 30°S

60°

widespread biogeographic province, here named the Peltacystia , Glossopteris. The high precipitation during the Microalgal Province (Fig. 9A). The province is named for the distinctive intervals (Poulsen et al., 2007) and relatively consistent cool moist zygnematacean genus Peltacystia, which, during the Permian and climatic conditions across the mid- to high latitudes of Gondwana Triassic periods, has been found only within Gondwana. Its Permian (Kiehl and Shields, 2005) would have maintained these broad floral and distribution delineates the boundaries of the province. In addition to algal provinces for much of the Permian. Peltacystia, these assemblages are characterised by another freshwater When the glossopterid biome collapsed during the EPE (latest charophyte Tetraporina, the chlorophyte Quadrisporites, and, less com­ Permian, ca 252 Ma), the Peltacystia Microalgal Province also came to monly, Mehlisphaeridium, an alga of uncertain affinity. The temporal an end. Although all of the characteristic algal genera persisted into the and geographic ranges of this province are similar to those of the Triassic, their distributions generally contracted to isolated populations ‘Glossopteris flora’ in the Permian (Chaloner and Lacey, 1973; Cúneo, (Fig. 9). Zygnematophyceae was near-cosmopolitan during the Per­ 1996; McLoughlin, 2001, fig. 6)—one of the most enduring and wide­ mian, and was particularly abundant and diverse across Gondwana, spread terrestrial biomes in Earth history (McLoughlin, 2011a). This which represented about 60% of Earth's land surface at that time. Most biome dominated the lowlands of the southern palaeotemperate zone members of this group, including those typical of the Permian Pelta­ (> 35°S), and was characterised by the hygrophilous, broad-leafed cystia Microalgal Province (e.g., Peltacystia and Tetraporina; Fig. 9A, B)

20 C. Mays, et al. Earth-Science Reviews 212 (2021) 103382 suffered a severe contraction in geographic distribution following the polyphyletic. In cases where close extant relatives were identified, the EPE. Similarly, some other typically ‘Gondwanan’ groups (e.g., Mehli­ modern groups are invariably prominent in freshwater, brackish or sphaeridium and Quadrisporites) were reduced in distribution across the terrestrial environments, consistent with their common occurrence in Southern Hemisphere (Fig. 9C). This suggests a relictual distribution of strata interpreted to have been deposited in non-marine settings based some ‘typical Permian’ taxa in the Triassic, perhaps confined to mark­ on sedimentological criteria. edly restricted ever-humid regions within an intensely monsoonal cli­ The affinities are reinforced by the presence of chemically-stable, mate regime that developed over much of Pangea after the EPE acid-resistant (e.g., sporopollenin or sporopollenin-like) walls among (Parrish, 1993; Preto et al., 2010). This may reflect the increase in their probable extant relatives; thus, fossil representatives of these provincialisation expressed by terrestrial faunas (Sidor et al., 2013); groups are expected to be proportionally more common in however, the global reorganization was attended by an expansion in Palaeozoic–Mesozoic fossil assemblages. Preservational biases: 1, range by other groups (e.g., Maculatasporites and Rugaletes). Despite the played a larger role for algal microfossils than for land plants, because proliferation of Reduviasporonites soon after the EPE, this event may not of the relative scarcity of durable biopolymers among algae; and 2, have had a major impact on the geographic range of this genus, as its contributed to the relatively high diversity of charophyte algae in the apparent distributions before and after the EPE are similar. fossil record, owing to their common utilisation of chemically-stable We are mindful, however, that different sampling strategies employed compounds. in previous studies and the uneven geographic distribution of past in­ The Permian–Triassic was an interval of numerous biotic crises, and vestigations might have strongly influenced these results. The specific en­ these are reflected in major abundance changes in the global records of vironmental factors that might have provided the dominant controls on fossil algae. Most attention has been given to the EPE (ca 252 Ma), the both the temporal and geographic expansion and decline of specific Permo- marine records of which have revealed a relative increase in leiospheres Triassic algal groups remain equivocal. In part, this is because the phylo­ (e.g., Leiosphaeridia) and short-spined acritarchs (e.g., Micrhystridium), genetic affinities of some taxa (e.g., Leiosphaeridia and Reduviasporonites) signalling a major turnover in marine primary producers. However, a remain poorly constrained. Even in examples where a strong case can be reduction in marine algal concentrations suggests a drop in marine made for a close relationship to an extant genus, the environmental toler­ primary productivity, at least regionally. An abundance ‘spike’ of ances of the Permo-Triassic forms can be difficult to categorize. For ex­ Reduviasporonites, an ambiguous fossil with a plausible affinity to ample, although Quadrisporites is now firmly considered to represent the freshwater algae, has been linked to the EPE from numerous marine and coenobia of Crucigenioideae (Trebouxiophyceae) based on both morpho­ non-marine successions, but this was not a global phenomenon. logical criteria and cell wall chemistry (Brenner and Foster, 1994; Batten, Although continental records are sparse, recent fossil records from 1996a; Bock et al., 2013), the precise environmental tolerances of its extant eastern Australia have demonstrated proportional increases in some relative Tetrastrum are poorly constrained beyond an affinity for nutrient- non-marine algae immediately following the EPE (Circulisporites, rich freshwaters (Naselli-Flores and Barone, 2010; Shubert and Gärtner, Leiosphaeridia and Quadrisporites). These increases suggest that wide­ 2015). spread floodbasin ponding, coupled with high nutrient supplies fol­ Clearly much more work is needed to clarify the tolerances of extant lowing deforestation of the landscape, occurred soon after the collapse algal taxa to a range of environmental parameters before these can be ex­ of terrestrial ecosystems, and flushing via fluvial systems may have trapolated to their Permian and/or Triassic relatives. However, a more solid partly contributed to the relatively high abundances of leiosphaerids understanding of the sedimentological context of palynological sampling and Reduviasporonites in the marine realm. may advance interpretation of the palaeoenvironmental signatures of fossil The EPE also inflicted significant changes to the geographic dis­ algae. In the context of Gondwanan Permian–Triassic successions, a long- tributions of non-marine algae. Although in most cases representing a term trend towards warming and drying (MacLeod et al., 2017) and an small proportion of the total palynomorph abundances, the constituents increase in seasonality (Fielding et al., 2019) from the late Permian to the of the Permian non-marine algal assemblages were relatively consistent late Early Triassic is marked in many areas by a loss of , increase in red- across most of eastern and southern Gondwana until the EPE. We bed sedimentation and more prominent representation of seasonal drying or propose the Peltacystia Microalgal Province, a distinctive, but wide­ semi-arid landscapes. Evidence for these include the development of cal­ spread and enduring suite of freshwater algal assemblages that were crete nodules, widespread desiccation cracks, calcified or ferruginized rhi­ typical of the Permian Period. This province is considered an algal zoliths, sedimentary structures associated with episodic flooding, and fossil counterpart to the coeval and geographically similar Glossopteris flora, plants with scleromorphic and xeromorphic characters (Waugh, 1971; which dominated the terrestrial palaeotemperate realm of Gondwana. McLoughlin and Drinnan, 1997a, 1997b; Catuneanu et al., 2005; Retallack, While all of the constituent genera persisted into the Triassic, the onset 2013). Tying the representation of algae to the sedimentological indices for of the EPE resulted in a severe range contraction of the algal taxa that the stages of advancement in aridification across central Gondwana should comprised the Peltacystia Province. Instead, the freshwater ecosystems provide a measure of confidence for interpreting the palaeoenvironmental following the EPE were likely characterised by sporadic, localised, signatures of these taxa that can be applied to other regions and strati­ short-duration increases in relative abundances, generally represented graphic intervals. by nearly monospecific assemblages of various algae. Of the other mass extinction intervals within the Permian and 7. Conclusions Triassic periods, only the Smithian-Spathian climatic event (ca 249 Ma) has been linked to a significant shift in algal abundances, and only Our review provides an updated framework for the affinities, eco­ within the marine realm. Aside from the EPE, very little attention has logical preferences, and geographic distributions of the most common been given to the impact of Permian and Triassic biotic crises on non- Permian and Triassic genera of putative algal microfossils from marine algae. Future investigations employing higher-resolution sam­ Gondwana. Suggested affinities for fossil taxa are based on a consensus pling coupled with well-resolved taxonomic assignments of fossil algae of morphological, biochemical and palaeoenvironmental data. When will ultimately be needed to draw a clear picture of the degree of dis­ placed into the most recent phylogenies of extant algae, the fossils re­ ruption to freshwater and terrestrial ecosystems caused by major global ported from the Sydney Basin represent a diverse range of green algae climatic shifts through the Palaeozoic–Mesozoic transition. (both charophytes and chlorophytes), together with possible dino­ Supplementary data to this article can be found online at https:// flagellate stem groups. At least two taxa of ‘acritarch’ Leiosphaeridia( , doi.org/10.1016/j.earscirev.2020.103382. Micrhystridium, and possibly Cymatiosphaera) are considered

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Declaration of Competing Interest Algarum. Ex officina Berlingiana, Lund (135 pp.). Agardh, C.A., 1824. Systema Algarum. Literis Berlingianis, Lund (312 pp.). Aken, M.E., Pienaar, R.N., 1985. Preliminary investigations on the chemical composition None. of the scale-boundary and cyst wall of Pyramimonas pseudoparkeae (Prasinophyceae). S. Afr. J. Bot. 51, 408–416. Andersen, T.F., Stalpers, J.A., 1994. A checklist of Rhizoctonia epithets. Mycotaxon 51, Acknowledgements 437–457. Anderson, J.M., 1977. The biostratigraphy of the Permian and Triassic, part 3: a review of We thank Chris Carter, Robin Raine and Karl Bruun for the photo­ Gondwana Permian palynology with particular reference to the northern Karoo micrographs of extant algae, and Joseph Bevitt for the Greek transla­ Basin, South Africa. Memoirs Bot. Surv. South Africa 41, 1–67. Angiolini, L., Stephenson, M.H., Leven, E.J., 2006. Correlation of the Lower Permian tion. Chris Fielding and Tracy Frank (University of Nebraska) and Bob surface Saiwan Formation and subsurface Haushi limestone, Central Oman. Nicoll (formerly of Geoscience Australia) are thanked for discussions on Geoarabia 11, 17–38. the depositional setting, palaeoclimate, and geochronology of the Ayaz, S.A., Esterle, J.S., Martin, M.A., 2015. Spatial variation in the stratigraphic archi­ tecture of the Fort Cooper and equivalent coal measures, Bowen Basin, Queensland. Permian–Triassic succession of the Sydney Basin. We thank Ana M. Aust. J. Earth Sci. 62, 547–562. Zavattieri, two anonymous reviewers and the Editor Karsten Pedersen Backhouse, J., 1991. Permian palynostratigraphy of the Collie Basin, Western Australia. for their helpful comments, which greatly enhanced the manuscript. Rev. Palaeobot. Palynol. 67, 237–314. Backhouse, J., Balme, B.E., Helby, R., Marshall, N.G., Morgan, R., 2002. Palynological The authors acknowledge the support of research grant EAR-1636625 zonation and correlation of the latest Triassic, Northern Carnarvon Basin. In: Keep, from the National Science Foundation, and the Swedish Research M., , S.J. (Eds.), The Sedimentary Basins of Western Australia 3: Proceedings of Council (VR) grants 2018-04527 to SM, and 2015-4264 and 2019- the Petroleum Exploration Society of Australia Symposium, Perth, WA. Petroleum Exploration Society of Australia, Perth, pp. 179–201. 04061 to VV. Balme, B.E., 1963. Plant microfossils from the Lower Triassic of Western Australia. Palaeontology 6, 12–40. Appendix A. Locality details, imaging specifications and algal Balme, B.E., 1969. The Permian-Triassic boundary in Australia. Geol. Soc. Australia Spec. Publ. 2, 99–112. nomenclature Balme, B.E., 1970. Palynology of Permian and Triassic strata in the Salt Range and Surghar Range, West Pakistan. In: Kummel, B., Teichert, C. (Eds.), Stratigraphic All fossil palynomorphs reported here were from previously pub­ Boundary Problems—Permian and Triassic of West Pakistan, Special Publications 4. lished samples, and collected from the following four localities University of , Lawrence, pp. 305–453. Balme, B.E., 1980. Palynology of Permian–Triassic boundary beds at Kap Stosch, East (Fig. 1B): 1, Frazer Beach outcrop, northern Sydney Basin (33° 11′ Greenland. Meddelelser om Grønland, udgivne af Kommissionnen for Videnskabelige 37.21″S, 151° 37′ 22.34″E; Vajda et al., 2020); 2, Coalcliff outcrop, Undersøgelser i Grønland 200, 1–37. southern Sydney Basin (34° 15′ 18.90″S, 150° 58′ 22.20″E; Fielding Balme, B.E., 1995. Fossil in situ spores and pollen grains: an annotated catalogue. Rev. Palaeobot. Palynol. 87, 81–323. et al., 2020); 3, Coal Cliff Colliery DDH 27 well core (CCC-27), southern Balme, B.E., Hennelly, J.P.F., 1956. Monolete, monocolpate, and alete sporomorphs from Sydney Basin (34° 13′ 25.28″S, 150° 56′ 50.67″E; Mays et al., 2020), Australian Permian sediments. Aust. J. Bot. 4, 54–67. and 4, Pacific Power Hawkesbury Bunnerong DDH 1 (PHKB-1), central Balme, B.E., Segroves, K.L., 1966. Peltacystia gen. nov.: a of uncertain affinities from the Permian of Western Australia. J. R. Soc. West. Aust. 49, 26–31. Sydney Basin (33° 58′ 17.61″S, 151° 13′ 43.52″E; Mays et al., 2020). Banerjee, M., D’Rozario, A., 1990. Palynostratigraphic correlation of Lower Gondwana Light microscopy and photomicrography of fossil specimens were sediments in the Chuparbhita and Hura Basins, Rajmahal Hills, eastern India. Rev. conducted using either a Zeiss Axioskop 2 Plus transmitted light mi­ Palaeobot. Palynol. 65, 239–255. Banks, M.R., 1978. Correlation Chart for the Triassic System of Australia. Department of croscope equipped with a Zeiss AxioCam MRc camera, or an Olympus National Development, Bureau of Mineral Resources, and Geophysics BX51 transmitted light microscope equipped with a Lumenera Infinity 2 Bulletin. Australian Government Publishing Service, Canberra, pp. 1–39. digital camera. Scanning electron microscopy images of gold-coated Baranyi, V., Wellman, C.H., Kürschner, W.M., 2018. Ultrastructure and probable bota­ nical affinity of the enigmatic sporomorph Froelichsporites traversei from the Norian palynomorph strew mounts on aluminium stubs were obtained at (Late Triassic) of North America. Int. J. Plant Sci. 179, 100–114. Stockholm University using a Philips XL30 ESEM-FEG. Composite Barbolini, N., Bamford, M.K., 2014. Palynology of an Early Permian coal seam from the photomicrographs consist of image compilations taken at different of Botswana. J. Afr. Earth Sci. 100, 136–144. stage heights, each with different focal points (following Mays, 2015), Barbolini, N., Smith, R.M.H., Tabor, N.J., Sidor, C.A., Angielczyk, K.D., 2016. Resolving the age of Madumabisa fossil : palynological evidence from the mid- and processed digitally with the ‘Auto-Blend Layers’ function in Adobe Zambezi Basin of Zambia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 457, 117–128. Photoshop CC 2019. Palynological samples are provided with prefix ‘S’, Barbolini, N., Rubidge, B., Bamford, M.K., 2018. A new approach to biostratigraphy in the slides are indicated by number suffixes; all samples and slides are Karoo retroarc foreland system: utilising restricted-range palynomorphs and their first appearance datums for correlation. J. Afr. Earth Sci. 140, 114–133. housed at the Department of Palaeobiology, Naturhistoriska riksmu­ Barone-Nugent, E.D., McLoughlin, S., Drinnan, A.N., 2003. New species of Rochipteris seet, Stockholm, Sweden. from the Upper Triassic of Australia. Rev. Palaeobot. Palynol. 123, 273–287. Algae are an informal, polyphyletic group encompassing a broad Batten, D.J., 1968. Probable dispersed spores of Cretaceous Equisetites. Palaeontology 11, 633–642. range of photosynthetic lineages. Algae sensu lato includes Batten, D.J., 1996a. Chapter 7C. Green and blue-green algae - colonial chlorococcales. In: evolutionarily disparate groups, such as Chromista (e.g., dino­ Jansonius, J., McGregor, D.C. (Eds.), Palynology: Principles and Applications. flagellates) and the clade Viridiplantae (land plants + ‘green algae’). In American Association of Stratigraphic Palynologists Foundation, Los Angeles, pp. 191–203. the fossil record, small organic-walled fossils of unknown affinity are Batten, D.J., 1996b. Chapter 26A. Palynofacies and palaeonvironmental interpretation. typically termed ‘acritarchs’ (Greek: ‘uncertain/mixed origins’); the In: Jansonius, J., McGregor, D.C. (Eds.), Palynology: Principles and Applications. definition of acritarch outlined byEvitt (1963) is followed here. Junior American Association of Stratigraphic Palynologists Foundation, Los Angeles, pp. 1011–1064. synonyms of fossil genera, and fossil-taxon authorities not mentioned in Batten, D.J., Dutta, R.J., 1997. Ultrastructure of exine of gymnospermous pollen grains the text are provided in Supplementary Table 1. Higher systematic from Jurassic and basal Cretaceous deposits in Northwest Europe and implications for classifications of extant green plants (Viridiplantae) followDel Cortona botanical relationships. Rev. Palaeobot. Palynol. 99, 25–54. et al. (2020); all other extant algal designations follow AlgaeBase Batten, D.J., Grenfell, H.R., 1996. Chapter 7D. Green and blue-green algae - Botryococcus. In: Jansonius, J., McGregor, D.C. (Eds.), Palynology: Principles and Applications. (Guiry et al., 2014; https://www.algaebase.org/), unless otherwise American Association of Stratigraphic Palynologists Foundation, Los Angeles, pp. stated. The terminology for excystment features is that of Colbath and 205–214. Grenfell (1995). Batten, D.J., Koppelhus, E.B., Nielsen, L.H., 1994. Uppermost Triassic to palynofacies and palynomiscellanea in the Danish Basin and Fennoscandian Border Zone. Cah. Micropaleontol. 9, 21–54. References Baudelet, P.-H., Ricochon, G., Linder, M., Muniglia, L., 2017. A new insight into cell walls of Chlorophyta. Algal Res. 25, 333–371. Bercovici, A., Cui, Y., Forel, M.-B., Yu, J., Vajda, V., 2015. Terrestrial paleoenvironment Afonin, S.A., Barinova, S.S., Krassilov, V.A., 2001. A bloom of Tympanicysta Balme (green characterization across the Permian–Triassic boundary in South China. J. Asian Earth algae of zygnematalean affinities) at the Permian-Triassic boundary. 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