Ediacaran Macrofossils Prior to the ~580 Ma Gaskiers Glaciation in Newfoundland, Canada

Ediacaran macrofossils prior to the ~580 Ma Gaskiers glaciation in Newfoundland, Canada

ALEXANDER G. LIU AND BENJAMIN H. TINDAL

Liu, A. G., & Tindal, B. H. 2020: Ediacaran macrofossils prior to the ~580 Ma Gaskiers glaciation in Newfoundland, Canada. Lethaia, https://doi.org/10.1111/let.12401.

Macrofossils of the inferred protist‐grade organism Palaeopascichnus linearis occur stratigraphically beneath glacial diamictites of the ~580 Ma, Gaskiers‐equivalent, Trin- ity ‘facies’ of the Rocky Harbour Formation on the Bonavista Peninsula of Newfound- land, Canada. These fossils significantly pre‐date previously reported macrofossils from Avalonia and extend the taphonomic window for moldic preservation of macroscopic organisms beyond the Gaskiers glacial event into the middle Ediacaran Period. This finding confirms the long stratigraphical range of palaeopascichnid fossils worldwide and informs discussions surrounding both the age of poorly time‐constrained stratigraphical units in Norway and Australia, and formal sub‐division of the Ediacaran Sys- tem. □ Bonavista Peninsula, Ediacara biota, Palaeopascichnus, protist, stratigraphy.

Alexander G. Liu ✉ [[email protected]], and Benjamin H. Tindal [[email protected]], Department of Earth Sciences, University of Cambridge, Downing Street Cambridge CB2 3EQ, UK; manuscript received on 10/04/2020; manuscript accepted on 26/07/2020.

The island of Newfoundland in eastern Canada hosts 2011). Both of these units have been dated to ~580– several globally significant localities for late Edi- 579 million years (Bowring et al. 2003; Pu et al. acaran age fossils of the Ediacaran Macrobiota. Such 2016), and along with other glacial deposits of this localities record benthic palaeocommunities of age (e.g. the Mortensnes Formation of Finnmark, diverse soft‐bodied organisms and include Mistaken Norway; Rice et al. 2011) are considered to record an Point Ecological Reserve UNESCO World Heritage important regional glacial event: the Gaskiers glacia- Site and Spaniard's Bay on the Avalon Peninsula, tion (e.g. Halverson et al. 2005; Fairchild & Kennedy and the Catalina Dome (within the Discovery Global 2007). Iron speciation data from Newfoundland indi- Geopark) on the Bonavista Peninsula (Fig. 1B; Nar- cate at least local oxygenation of the deep ocean fol- bonne 2004; Narbonne in Fedonkin et al. 2007; Hof- lowing the Gaskiers glaciation (Canfield et al. 2007), mann et al. 2008; Liu & Matthews 2017). These fossil encouraging proposed links between the Gaskiers assemblages are dated to between ~574 and 562 Ma event and the evolution of diverse macroscopic com- (Canfield et al. 2020; Matthews et al. 2020) and lie plexity and large body size (as represented by the rise within siliciclastic strata deposited in deep‐marine to and diversification of the classic Ediacara‐type biota; marine‐slope settings (Wood et al. 2003). Over 30 e.g. Narbonne & Gehling 2003). However, such phys- distinct taxa have been described to date (Liu et al. iological links remain unproven at present (Sperling 2015), and in addition to non‐metazoan and prob- et al. 2015; Pu et al. 2016). lematic taxa, the assemblages include some of the Globally, the Lantian Formation of South China oldest reported body (e.g. Liu et al. 2014; Dunn et al. provides the most compelling evidence for complex 2018) and trace (Liu et al. 2010; Menon et al. 2013) macroscopic Ediacaran life prior to 580 Ma (Yuan fossil evidence for total group metazoans. Fossils of et al. 2011; Wan et al. 2016), but its precise age is yet the Ediacaran Macrobiota from Newfoundland rep- to be ascertained, and the vast majority of its taxa are resent some of the oldest known examples of the not observed in later Ediacaran fossil assemblages. classic Ediacara‐type biota anywhere in the world Older reports of complex macroscopic eukaryotes (alongside Charnwood Forest, England, and the remain contentious (e.g. El Albani et al. 2010), reflect Wernecke and Mackenzie Mountains of Canada; problematic taxa (Fedonkin & Yochelson 2002) or Noble et al. 2015; Rooney et al. 2020). comprise simple algal‐like (Ye et al. 2015; Zhu et al. All previously documented Ediacaran macrofossils 2016) or discoidal impressions (e.g. Burzynski et al. in Newfoundland stratigraphically and radiometri- 2020). cally post‐date glacigenic diamictites of the Gaskiers This study presents specimens of the probable Formation (Eyles & Eyles 1989), or its northern protozoan Palaeopascichnus linearis from marine equivalent on the Bonavista Peninsula, the Trinity strata within the Rocky Harbour Formation of New- ‘facies’ of the Rocky Harbour Formation (Normore foundland. These specimens demonstrably pre‐date

DOI 10.1111/let.12401 © 2020 Lethaia published by John Wiley & Sons Ltd on behalf of Lethaia Foundation This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 2 A. G. Liu and B. H. Tindal LETHAIA 10.1111/let.12401

Fig. 1. Map of the ﬁeld locality and regional stratigraphical context. A, Newfoundland, Canada. B, the Avalon and Bonavista peninsulas, showing key Ediacaran fossil localities (orange), and the location of Trinity East area (yellow). C, towns of the Trinity area, showing the location of Trinity East, and the Freshwater Trestle (yellow star) and Herring Cove (green star) fossil localities. Inset: photograph of the logged section taken from across Freshwater Trestle. D, regional stratigraphy at formation scale (following Normore 2011). The radiometric date originates from a volcanic horizon 11.1 m below the base of the Trinity ‘facies’ diamictite at Old Bonaventure (orange star in C; stated error indicates only internal [analytical] uncertainty, Pu et al. 2016).

~580 Ma diamictites of the Trinity ‘facies’ and there- logged at a 10‐cm resolution as part of an ongoing fore represent the oldest documented macrofossils study into Ediacaran glacial sedimentology in New- from the Ediacaran successions of Newfoundland. foundland. The stratigraphical and sedimentological discussions below draw upon observations made during that regional study, and are additionally Materials and methods informed by the ﬁndings of a team of six undergrad- uates from the University of Cambridge who mapped Fossil‐bearing horizons are situated on the western the wider region around the town of Trinity at shoreline of an inlet known locally as Freshwater 1:10,000 scale in the summer of 2018. Trestle, just a few hundred metres to the west of the town of Trinity East on the Bonavista Peninsula, Geological context Newfoundland (Fig. 1). Continuous exposure through the middle of the Rocky Harbour Formation Two distinct Ediacaran age stratigraphical succes- (Musgravetown Group) is observed along a disused sions on the Bonavista Peninsula are separated by railway cutting that runs parallel to the shoreline. the Spillars Cove–English Harbour fault (O'Brien & Fossil‐bearing surfaces from two discrete horizons King 2002, 2004; Normore 2011). To the east of the were sampled (Fig. 2), yielding 32 distinct fossil spec- fault lies the St. John's Basin, with a succession com- imens, which were studied in the laboratory. Studied prising shallowing‐upwards deep‐marine to ﬂuvial specimens are accessioned in the collections of the units of the Conception, St. John's and Signal Hill Sedgwick Museum, University of Cambridge under Groups. The Conception and St. John's Groups host specimen numbers CAMSM X 50348.1 to CAMSM almost all previous reports of fossils of the Ediacaran X 50348.7 in Appendix S1. The sedimentary section Macrobiota in Newfoundland (e.g. Hofmann et al. along the western side of Freshwater Trestle was 2008; Mason et al. 2013; Liu et al. 2015). To the west,

Fig. 2. Sedimentary log through the Rocky Harbour Formation section on the western shoreline of Freshwater Trestle, near Trinity East, Bonavista Peninsula, Newfoundland. Facies names to the right follow the lithostratigraphical nomenclature of Normore (2011), but their order in our section is not consistent across all other nearby sections (e.g. Supplementary Material of Pu et al. 2016). The two fossil horizons lie 7 and 35 m below the base of the Trinity ‘facies’. MISS = microbially induced sedimentary structures. LETHAIA 10.1111/let.12401 Pre‐Gaskiers Ediacaran macrofossils 3 4 A. G. Liu and B. H. Tindal LETHAIA 10.1111/let.12401 the Bonavista Basin hosts sedimentary rocks of the Bonaventure (Fig. 1C) indicate a short duration for Musgravetown Group, which reflect sedimentation deposition of the diamictite, contemporaneous in shallow marine depositional environments, within error with deposition of the Gaskiers Forma- beneath non‐marine sedimentary rocks of the Crown tion on the Avalon Peninsula (Pu et al. 2016, see dis- Hill Formation (O'Brien & King 2002; Normore cussion below). 2011). This western basin has not previously yielded reports of Ediacaran age macrofossils. Freshwater Trestle fossil locality The Rocky Harbour Formation lies within the Musgravetown Group and comprises siliciclastic and The studied section in Freshwater Trestle comprises volcanogenic lithologies that have been divided into approximately 200 m of largely continuous stratigra- seven mappable ‘facies’ by Normore (2011, following phy. Beds dip at 80–90° to the northeast. With the pos- O'Brien & King 2002, 2004, 2005) during regional sible exception of the base of the diamictite, the mapping for the Geological Survey of Newfoundland observed succession appears to be conformable (Fig. 2). and Labrador. These mapped ‘facies’ commonly con- The section begins with massive, polymictic, fine‐ tain several distinct sedimentary lithologies and to very coarse‐grained grey sandstones that match facies (sensu stricto), and they could therefore be bet- previous descriptions of the Cape Bonavista ‘facies’, ter described as facies assemblages. The Rocky Har- and pink to grey sandstones with occasional purple‐ bour Formation ‘facies’ are interpreted to reflect brown mudstone drapes assigned to the King's Cove marginal marine and glacially influenced deposi- Lighthouse ‘facies’. These two ‘facies’ are recognized tional environments (Normore 2010, 2011). to be laterally transitional elsewhere on the Bonavista The Trinity ‘facies’ lies towards the middle of the Peninsula (Normore 2011, fig. 2). Thin‐ to medium‐ Rocky Harbour Formation and is composed of beds comprising packages of laminated purple‐ matrix‐supported diamictite with dropstones, faceted brown mudrock, dark brown siltstone and discontin- and striated clasts (Normore 2011). Local relation- uous grey‐brown sandstone within the King's Cove ships between the Trinity ‘facies’ and other litholo- Lighthouse ‘facies’ exhibit rare symmetrical ripples, gies within the Rocky Harbour Formation are not synaeresis cracks and pebbles (Fig. 3). The mudrock straightforward, with considerable lateral facies vari- laminae host Palaeopascichnus specimens as hypo‐ ation (Normore 2011). However, diamictite deposits and epirelief surface impressions (Fig. 4). The sym- across the Bonavista Peninsula have been considered metrical ripples indicate oscillatory flow, which we broadly coeval (Normore 2011), and dates obtained attribute to wave action in a nearshore marine depo- from above and below this ‘facies’ at Old sitional environment. The polymictic nature of the

Fig. 3. A, outcrop of the King's Cove Lighthouse ‘facies’ (23.5 m in the Figure 2 log) along the Freshwater Trestle railway cutting, showing bedding planes with purple‐brown mudstone laminae on exposed surfaces. Scale bar is 50 cm long. B, close up of the region in the centre of (A), revealing thin, grey sandstone beds separated by mudstone laminae. C, hand sample from the King's Cove Lighthouse ‘facies’ showing alternations of discontinuous thin ﬁne sandstone to siltstone beds and mudstone laminae. Scale bar = 10 mm. D–E, stratiﬁed diamictite of the Trinity ‘facies’ (75 m in the Figure 2 log), showing dropstone clasts. LETHAIA 10.1111/let.12401 Pre‐Gaskiers Ediacaran macrofossils 5

Fig. 4. Palaeopascichnus linearis fossils from Freshwater Trestle, Trinity East. A, branching specimens (arrowed) of P. linearis, CAMSM X 50348.1.2c‐e. B, two specimens (arrowed) with chambers that gently expand along the length of the chain, CAMSM X 50348.1.2a‐b. C, straight palaeopascichnid specimen (arrowed), with globular chambers. This specimen could potentially be referred to Orbisiana (following Kolesnikov et al. 2018b, see discussion in the main text), CAMSM X 50348.2a. D, dense P. linearis assemblage, CAMSM X 50348.3c‐e, i. E, several discrete but irregular specimens of Palaeopascichnus, some of which (arrowed) could reflect aggregations of chambers that could be more correctly assigned to Orbisiana, CAMSM X 50348.4c‐e. Scale bars all = 5 mm. sands, grits and rare pebbles in the sandstone, com- The diamictite is overlain by 40 m of laminated bined with their sub‐rounded to rounded aspect and green‐grey siltstones, previously mapped within the wide size range, may result from fluvial or marine Herring Cove ‘facies’ of the Rocky Harbour Forma- reworking of nearby volcanogenic and glacial mate- tion (Normore 2011). Elsewhere in the region, Nor- rial. more described the Herring Cove ‘facies’ as a A pink, highly silicified siltstone at 56–59 m volcano‐sedimentary unit with sills, peperites, tuffs, (Fig. 2) is interpreted to be tuffaceous. This lithology mudstones and laminated siltstones, but we observed separates the sandstones below from 18 m of mostly only limited evidence for volcanogenic material in massive, silty, unstructured polymictic diamictites our measured section. We interpret the Herring Cove attributed to the Trinity ‘facies’ of the Rocky Har- ‘facies’ siltstones to reflect predominantly quiescent bour Formation (Normore 2011). The uppermost marine conditions following ice retreat. 3.6 m of this diamictite is stratified and contains No fossils were found above the diamictite in the dropstones that suggest deposition of material from Freshwater Trestle section, but we did observe several floating ice (Fig. 3D), favouring a glaciomarine/ Palaeopascichnus specimens in a section previously glaciolacustrine environment for this unit during gla- mapped as the Herring Cove ‘facies’ (Normore 2011) cial retreat, as opposed to a terrestrial till (following at Herring Cove, between Port Rexton and Champ- Eyles et al. 1983). The dropstones also provide way ney's West (~3km to the east of our measured sec- up indicators, which in addition to ripples in the tion; Figs 1C, 5D). Those specimens occur as positive underlying King's Cove Lighthouse ‘facies’, and epirelief impressions on the top of a green siltstone cross‐lamination in the Cape Bonavista ‘facies’, have and are found 70 cm above a prominent pink bed enabled us to orientate the stratigraphical succession. previously described as a volcanic tuff with tepee‐like 6 A. G. Liu and B. H. Tindal LETHAIA 10.1111/let.12401 structures (Normore 2011, pl. 9E), but which we Recent revision of palaeopascichnid taxonomy has interpret as a possible peperite. The Trinity ‘facies’ is seen multiple taxa assigned to this group, while other not observed to crop out at Herring Cove, preventing morphologically similar taxa have been distanced direct confirmation of the relative stratigraphical from it (e.g. Ivantsov 2017; Kolesnikov et al. 2018a, position of the specimens with respect to the diamic- 2018b). Comparison of material from different global tite at this location. localities has aided recognition of distinct morpho- Taken together, the Freshwater Trestle section types (e.g. Kolesnikov et al. 2018a, 2018b), but appears to document a transition from a proximal, detailed morphometric work on populations of speci- shallow marine environment, through glacigenic mens has revealed considerable morphological varia- diamictite deposition, to quiescent marine condi- tion in chamber shape, size and ability to branch tions, punctuated by influxes of volcanogenic mate- within individual populations, questioning the utility rial (which may be primary, or secondarily of such characters for differentiating taxa at a species reworked). This general history is consistent with our level (Hawco et al. 2020). Furthermore, several exam- observations elsewhere in the area. There is consider- ples of apparently transitional forms between taxa at able variation in the thickness of the Trinity ‘facies’ both generic and species level exist within individual at sites across the Trinity Bay region (ranging from populations (discussed in Jensen et al. 2018), and our 15 to >100 m; Normore 2011; Supplementary Infor- material appears consistent with this phenomenon. mation of Pu et al. 2016), but we interpret the At present, Orbisiana and Palaeopascichnus are diamictite to be a single marker horizon in the distinguished by Orbisiana typically having consis- region. tently sized, globular/circular chambers arranged in biserial or multiserial chains or aggregated clusters, whereas Palaeopascichnus specimens comprise only uniserial chains of relatively elongate chambers Fossil assemblage (commonly ellipsoidal to globular), which can change in width along the length of the organism fi Fossils were identi ed at two levels within the Fresh- (e.g. Jensen 2003; Jensen et al. 2018; Kolesnikov et al. ~ water Trestle section, at 7 and 35 m below the base 2018a). Specimens of both genera are capable of ‘ ’ of the Trinity facies diamictite (Fig. 2). The upper branching distally, but in Palaeopascichnus the level yielded fossils on a single bedding surface of chambers on subsequent branches are smaller in ‐ < purple brown mudstone, 1 mm thick, overlying a width than their predecessors, whereas in Orbisiana sandstone. The lower level consisted of several fossil- there is no change in width (Kolesnikov et al. 2018a). ‐ iferous horizons, with fossils all found on purple The majority of our specimens comprise uniserial ‐ fi ‐ brown mudstone surfaces, within a thin bedded ne chains possessing chambers with an elongate mor- ‐ to coarse grey sandstone succession (Fig. 3A). phology (Fig. 4A,B,D), and an ability for chambers The most common macrofossils are surface to sequentially expand, but some specimens exhibit impressions of linear chains of rounded, hollow chains of chambers that are more circular in shape chambers that can be assigned to P. linearis (Fedon- and which show no change in width (e.g. Fig. 4C). kin, 1976) Kolesnikov et al. 2018b, following the syn- We assume that the observed variation in shape in onymizations suggested by those authors. P. linearis our studied population is original, but note that we specimens are between 0.34 and 2.60 cm in length do not possess independent strain indicators for the = (n 32). The chambers either maintain constant outcrop. Our material is morphologically most simi- width along the length of a chain (maximum cham- lar to described and figured specimens from the late ber widths within individual specimens range Ediacaran Stáhpogieddi Formation of Arctic Norway, between 1.29 and 3.41 mm), or exhibit gentle widen- referred to Palaeopascichnus delicatus (Jensen et al. / ing and or branching into multiple chains (Fig. 4A, 2018, fig. 3). Our material differs from P. delicatus B). Some specimens appear to comprise globular Palij, 1976 in having relatively low expansion rates rather than elongate chambers (Fig. 4C) and could within individual chains of chambers, and reasonably potentially be assigned to Orbisiana, another consistent chamber size throughout individual chains palaeopascichnid taxon (see Kolesnikov et al. 2018a). (sensu Kolesnikov et al. 2018b). We therefore attri- Both Palaeopascichnus and Orbisiana are known to bute the majority of our specimens to P. linearis. be preserved as moldic impressions elsewhere, for example in the Fermeuse Formation of Newfound- land (Hawco et al. 2020, fig. 5), and the Verkhovka Microbially induced sedimentary structures Formation of the White Sea, Russia (Kolesnikov The mudstone horizons in the King's Cove Light- fi et al. 2018a, g. 4). house ‘facies’ also record several sedimentary surface LETHAIA 10.1111/let.12401 Pre‐Gaskiers Ediacaran macrofossils 7

Fig. 5. Sedimentary surface textures from the Freshwater Trestle section (A–C), and Palaeopascichnus specimens from Herring Cove (D), Bonavista Peninsula, Newfoundland. A, finely spaced ridges, potentially biogenic, on a mudstone surface, CAMSM X 50348.5. B, C, undu- lating bumps and pits, likely to reflect bubble impressions within a microbial biomat, CAMSM X 50348.4 and CAMSM X 50348.6, respec- tively. D, Palaeopascichnus specimens (arrowed) from the Herring Cove ‘facies’ of the Rocky Harbour Formation at Herring Cove, near Fox Island, CAMSM X 50348.7c‐h. Scale bars = 10 mm, except D = 5 mm. textures (sensu Davies et al. 2016; Fig. 5A–C), some synchronously with glacigenic diamictites of the of which closely resemble impressions that have been Gaskiers Formation on the Avalon Peninsula (which interpreted as biotic in origin in other late Neopro- were deposited between 580.90 ± 0.40 and terozoic successions. These include very fine, seem- 579.88 ± 0.44 Ma; all dates U‐Pb CA‐ID‐TIMS anal- ingly paired wavy ridges of <0.1 mm width, which yses on volcanogenic zircons; Pu et al. 2016). The age are similar to fabrics originally referred to as Areni- of the fossil‐bearing King's Cove Lighthouse ‘facies’ cola didyma from the Long Mynd of Shropshire (Sal- at Freshwater Trestle is therefore most likely ter 1856). Irregularly spaced positive hyporelief ≥579.63 ± 0.15 Ma (Fig. 1D). circular bumps, ≤1–3 mm in diameter, are inter- Due to structural deformation, lateral facies varia- preted as likely bubble or gas escape impressions tion and poor regional exposure, it is not possible to (Fig. 5B,C). Surface fabrics present on many of the conclusively demonstrate synchronicity in the onset Palaeopascichnus‐bearing surfaces are finely undulat- and termination of glacial sedimentation across the ing (e.g. Fig. 4A–C), and may or may not be biogenic 12‐km area separating the Freshwater Trestle fossil in origin. locality and the dated Old Bonaventure sections without further radiometric dating. Previously proposed stratigraphical relationships for the Trinity ‘fa- Discussion cies’ within the Rocky Harbour Formation (Normore 2011, fig. 4) raise the possibility that some sections Constraining the age of the fossil assemblage may contain two diamictite horizons, but we did not observe any evidence for this scenario within the Radiometric dating of volcanogenic deposits associ- study area. We follow Pu et al. (2016) in interpreting ated with the Trinity ‘facies’ near Old Bonaventure the Trinity ‘facies’ of the Rocky Harbour Formation (Fig. 1C) constrains the age of diamictite deposition as a singular regional event equivalent to the Gask- to between 579.63 ± 0.15 and 579.24 ± 0.17 Ma (Pu iers Formation. This interpretation requires that the et al. 2016, fig. DR2A). These dates imply that the Freshwater Trestle fossils pre‐date the Gaskiers Trinity diamictite was deposited broadly glaciation. 8 A. G. Liu and B. H. Tindal LETHAIA 10.1111/let.12401

The global age range of palaeopascichnids 1994) by Xiao & Dong, 2006; Yuan et al. 2011; see Kolesnikov et al. 2018a). Taxa assigned to the Palaeopascichnida (Grazh- Our discovery of P. linearis in pre‐Gaskiers (i.e. dankin 2014) are commonly found in shallow marine >580 Ma) sedimentary successions follows sugges- settings in the terminal Ediacaran, including just – tions that the Lantian Formation palaeopascichnids below the Ediacaran Cambrian boundary Global are early–middle Ediacaran in age (considered per- Standard Stratotype section and Point on the Burin haps as old as 600 Ma on the basis of litho‐ and Peninsula of Newfoundland (Gehling et al. 2001), chemostratigraphical correlation with Member II of and stratigraphically close to horizons bearing Cam- ‐ the Doushantuo Formation; Yuan et al. 2011; Wan brian type trace fossils in the Urals and Arctic Nor- et al. 2016 and references therein). Fossil material way (Kolesnikov et al. 2015; Jensen et al. 2018). The from the Kimberley region of Australia that likely genus Palaeopascichnus has also been reported from pre‐dates the Gaskiers (Lan & Chen 2012) might be several sites on the East European Platform in better described as Curviacus following the more Ukraine (Palij 1976), Poland (Paczesna 1986) and recent description of that genus (Shen et al. 2017), Russia (Fedonkin 1981; Kolesnikov et al. 2015; Gol- but reflects an additional example of a pre‐Gaskiers ubkova et al. 2018), the Yudoma Group of Siberia ‐ palaeopascichnid. Palaeopascichnids therefore (Ivantsov 2017), the Itajaí Basin of Brazil (Becker appear to have been globally distributed prior to the Kerber et al. 2020) and South Australia (Glaessner Gaskiers glaciation, seemingly providing a prelude to 1969; Haines 2000). In Newfoundland, it also fre- the larger and more complex organisms of the late quently occurs in marine slope deposits of the ~ Ediacaran Macrobiota. ( 560 Ma) Fermeuse Formation at Ferryland (Gehl- In the absence of radiometric dates, specimens ing et al. 2000; Liu & McIlroy 2015; Hawco et al. from the upper Wonoka Formation in the Flinders 2020). Notably, material originally referred to Orbisi- Ranges of South Australia (Haines 2000) have typi- ana linearis by Wan et al. (2014) from the Lantian cally been assumed to be of late Ediacaran age, on Formation of South China has recently been syn- the basis of their stratigraphical occurrence above a onymized within P. linearis (Kolesnikov et al. negative carbon isotope excursion (CIE) within the 2018b), on the basis of its morphological attributes Wonoka Fm. (correlated to the Shuram event; e.g. (Kolesnikov et al. 2018a). Bowring et al. 2007) and the suggestion that lone- Palaeopascichnus was originally interpreted as a stones, granule clusters and pellets associated with trace fossil (e.g. Glaessner 1969; Palij 1976), but is the Acraman impact ejecta layer in the underlying now widely recognized as the body fossil of a sessile, Bunyeroo Formation correlate to the Gaskiers event procumbent epibenthic organism (e.g. Haines 2000; (Gostin et al. 2010). That correlation with the Gask- Gehling et al. 2000; Jensen 2003; Antcliffe et al. 2011; iers is tenuous (Gostin et al. 2011). Recent dating of Hawco et al. 2020). Similarities have been drawn the Shuram CIE to between ~574 and 567 Ma in between Palaeopascichnus and certain Phaeophyta NW Canada and Oman (Rooney et al. 2020; see also (brown algae; Haines 2000; Jensen 2003), stratiform Canfield et al. 2020) would appear to confirm that, if stromatolites (Runnegar 1995), Textured Organic the Wonoka–Shuram correlation is reliable, the taxo- Surfaces (Gehling & Droser 2009) and xeno- nomically depauperate Palaeopascichnus assemblage phyophoran protists (e.g. Seilacher et al. 2003). How- in the Wonoka Fm. is of late Ediacaran age (i.e. ever, most recent studies have converged on a ~ – fi – fi 567 539 Ma). Con rmation of the Wonoka Shu- protistan phylogenetic af nity on the basis of devel- ram CIE correlation is necessary to rule out alterna- opmental analysis and possible evidence for aggluti- tive interpretations for the age of the Wonoka nated chamber walls (e.g. Antcliffe et al. 2011; Formation, some of which (e.g. a Wonoka–Gaskiers Kolesnikov et al. 2018b; Hawco et al. 2020). correlation, Halverson et al. 2005) find support from Orbisiana has previously been interpreted as a the recognition of pre‐Gaskiers palaeopascichnids in possible alga (e.g. Sokolov 1976), but its close similar- Newfoundland. ities in form and probable wall structure to The oldest occurrences of Palaeopascichnus on the Palaeopascichnus require consideration of a protistan Digermulen Peninsula of Norway closely overlie the phylogenetic placement (Kolesnikov et al. 2018a). glacigenic Mortensnes Formation, which has been Orbisiana is described almost entirely from the East correlated with the Gaskiers glaciation (Halverson European Platform (e.g. Sokolov 1976; Chistyakov et al. 2005; Rice et al. 2011). Palaeopascichnus at the et al. 1984; Golubkova et al. 2018; Kolesnikov et al. base of the Indreelva Member have been used to con- 2018a), but with important possible occurrences in strain the age of that unit to <565 Ma, therefore sup- the Lantian Formation of South China (originally porting a Gaskiers age for the underlying tillites of referred to Seirisphaera zhangii Chen (Chen et al. the Mortensnes Formation (Jensen et al. 2018). LETHAIA 10.1111/let.12401 Pre‐Gaskiers Ediacaran macrofossils 9

Although close association of those specimens with range of this taxon in Avalonia, and confirming a discoidal fossils just a few metres up section would long stratigraphical range for palaeopascichnids appear to support a late Ediacaran (post‐Gaskiers) throughout the entire late Ediacaran (see Grazh- age for that unit, recognition of palaeopascichnids in dankin 2014, and discussion in Jensen et al. 2018). Avalonian pre‐Gaskiers strata herein relaxes the age Since Palaeopascichnus is not considered to be a constraints provided by the presence of Palaeopasci- metazoan (e.g. Antcliffe et al. 2011; Kolesnikov et al. chnus alone, such that the base of the Indreelva 2018b; Hawco et al. 2020), this discovery does not Member could lie anywhere within the late Edi- change our current understanding of the timing of acaran. early animal diversification. However, in conjunction Palaeopascichnus has long been recognized as a with examples from the Lantian Formation of China, frequent component of Ediacaran macrofossil assem- it does expand the record of pre‐Gaskiers protistan blages, with some authors even considering diversity (see also Porter et al. 2003; Bosak et al. palaeopascichnids to be members of the Vendo- 2011, 2012; Riedman et al. 2014) and demonstrates bionta (Seilacher et al. 2003; Grazhdankin 2014). that a variant of the mouldic taphonomic window However, recognition that the Ediacaran Macrobiota extends prior to the Gaskiers glaciation in some envi- comprises a range of diverse, unrelated organisms, ronmental settings. A stratigraphical range spanning alongside questioning of the Vendobiont hypothesis the Lantian Fm. to the Ediacaran‐Cambrian bound- (e.g. Runnegar 1995; Dunn & Liu 2019) means that ary, coupled with morphological variation within consideration of the entire biota as a single entity is populations, suggests that palaeopascichnids are not no longer appropriate. This is particularly pertinent suitable candidates as index fossils for sub‐division of when discussing palaeopascichnids, which uniquely the Ediacaran System. amongst the original Ediacara biota are increasingly Acknowledgements. – We thank Andrea Mills of the Geological considered to be protists with agglutinated chamber Survey of Newfoundland and Labrador for helpful discussions walls. Our discovery of pre‐Gaskiers examples of an regarding the stratigraphy of the study area. The field mapping of iconic late Ediacaran macrofossil taxon is thus tem- S. Baldwin, P. Dakin, A. Sheat, D. Zhang, T. Spencer and E. Southern assisted in understanding the regional context. This pered by the fact that Palaeopascichnus is not partic- research was funded by the Natural Environment Research Coun- ularly representative of the soft‐bodied Ediacaran cil (grants NE/L011409/2 to AGL, and NE/R009457/1 to BHT). Macrobiota of younger localities. Not only was it The manuscript benefitted from constructive reviews from two anonymous reviewers. probably unrelated to most other late Ediacaran macrofossil taxa, but it is also possible that its preservation requires different taphonomic conditions. Sei- lacher et al. (2003) suggested that palaeopascichnids References lived embedded within microbial mats, which may Antcliffe, J.B., Gooday, A.J. & Brasier, M.D. 2011: Testing the explain their high preservation potential, and the protozoan hypothesis for Ediacaran fossils: a developmental analysis of Palaeopascichnus. 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