1 A Chronostratigraphic Framework for the Rise of the Ediacaran Macrobiota: New

2 Constraints from Mistaken Point Ecological Reserve, Newfoundland

3 Jack J. Matthews1, 2*, Alexander G. Liu3, Chuan Yang4, Duncan McIlroy2, 5, Bruce Levell6, 4 Daniel J. Condon4

5 1: Oxford University Museum of Natural History, Parks Road, Oxford, OX1 3PW, U.K.

6 2: Department of Earth Sciences, Memorial University of Newfoundland, 300 Prince Philip 7 Drive, St. John’s, NL, A1C 3X5, Canada.

8 3: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 9 3EQ, U.K.

10 4: British Geological Survey, Keyworth, NG12 5GG, U.K.

11 5: Bonne Bay Marine Station, Norris Point, NL, A0K 3V0, Canada

12 6: Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, 13 U.K.

14 *Corresponding author: [email protected]

15

16 ABSTRACT

17 The Conception and St. John’s Groups of southeastern Newfoundland contain some of the oldest

18 known fossils of the Ediacaran macrobiota. Mistaken Point Ecological Reserve (MPER)

19 UNESCO World Heritage Site is an internationally recognised locality for such fossils, and hosts

20 early evidence for both total-group metazoan body fossils, and metazoan-style locomotion. The

21 MPER sedimentary succession includes ~1500m of fossil-bearing strata containing numerous

22 dateable volcanogenic horizons, and therefore offers a crucial window into the rise and

23 diversification of early animals. Here we present six stratigraphically-coherent radio-isotopic

24 ages derived from zircons from volcanic tuffites of the Conception and St. John’s Groups at

25 MPER. The oldest architecturally complex macrofossils, from the upper Drook Formation, have

1

26 an age of 574.17 ± 0.66 Ma (including tracer calibration and decay constant uncertainties). The

27 youngest rangeomorph fossils from MPER, in the Fermeuse Formation, have a maximum age of

28 564.13 ± 0.65 Ma. Fossils of the famous ‘E’ Surface are confirmed to be 565.00 ± 0.64 Ma,

29 while exceptionally preserved specimens on the ‘Brasier’ Surface in the Briscal Formation are

30 dated at 567.63 ± 0.66 Ma. We use our new ages to construct an age-depth model for the

31 sedimentary succession, constrain sedimentary accumulation rates, and convert stratigraphic

32 fossil ranges into the time domain to facilitate integration with time calibrated data from other

33 successions. Combining this age model with compiled stratigraphic ranges for all named

34 macrofossils within the MPER succession, spanning 76 discrete fossil-bearing horizons, enables

35 recognition and interrogation of potential evolutionary signals. Peak taxonomic diversity is

36 recognised within the Mistaken Point and Trepassey Formations, and uniterminal rangeomorphs

37 with undisplayed branching architecture appear several million years before multiterminal,

38 displayed forms. Together, our combined stratigraphic, palaeontological, and geochronological

39 approach offers a holistic time-calibrated record of evolution during the mid-late Ediacaran

40 Period, and a framework within which to consider other geochemical, environmental, and

41 evolutionary datasets.

42 Keywords: Ediacaran, Geochronology, Rangeomorph, Evolution, Palaeobiology

43

44 1. INTRODUCTION

45 The Avalon Peninsula of Newfoundland, Canada, has long been recognised as one of the world’s

46 leading localities for Ediacaran macrofossils. It hosts a >7.5 km thick late Neoproterozoic

47 volcano-sedimentary succession, with a broadly shallowing-upwards trend encompassing basin,

48 slope, shoreface and fluvial palaeoenvironments (Williams and King, 1979; Gardiner and

49 Hiscott, 1988; Wood et al., 2003; Canfield et al., 2007). Macrofossils of Ediacaran age occur

2

50 within siliciclastic deposits of the Conception and St. John’s Groups, which have been

51 interpreted as deep-marine and slope depositional environments close to a volcanic arc (Wood et

52 al., 2003). The Mistaken Point Ecological Reserve (MPER), located on the southeastern portion

53 of the Avalon Peninsula (Fig. 1), contains some of the most abundant and well-preserved fossil

54 assemblages of Ediacaran taxa in the region (Narbonne in Fedonkin et al., 2007; Liu and

55 Matthews, 2017; Fig. 2). Discovered in the late 1960s (Misra, 1969), this locality has thousands

56 of fossil specimens on bedding planes spanning ~1.5 km of stratigraphic thickness. Fossils are

57 preserved as impressions of external morphology beneath tuffites (Narbonne, 2005; Liu, 2016),

58 which undergo preferential weathering and erosion (Matthews et al., 2017) to reveal the

59 underlying ancient seafloors for scientific study.

60 Fossils of the Ediacaran macrobiota have received multiple phylogenetic interpretations

61 (summarised Dunn and Liu, 2019), but recent ichnological, palaeontological, developmental and

62 biomarker studies together demonstrate that at least some Ediacaran taxa represent early

63 metazoans (Ivantsov and Malakhovskaya, 2002; Gold et al., 2015; Bobrovskiy et al., 2018; Dunn

64 et al., 2018, 2019; Evans et al., 2019). The Avalonian localities in Newfoundland are considered

65 to be amongst the oldest Ediacaran macrofossil-bearing sites (Boag et al., 2016; Pu et al., 2016),

66 and include body and trace fossils that have been interpreted as evidence for the presence of

67 early metazoans (Liu et al., 2010, 2014, 2015; Menon et al., 2013; Dunn et al., 2018). However,

68 the precise phylogenetic positions of many Newfoundland taxa, and their relationships to one

69 another (Dececchi et al., 2017), remain to be resolved.

70 Understanding the causes of the emergence, evolution, and extinction of the Ediacaran

71 macrobiota, and the relationship of these events to environmental change, requires the

72 construction of an accurate, highly-resolved chronostratigraphic framework within which

73 biostratigraphic, taphonomic, sedimentological, geochemical, and environmental data can be

74 integrated. This must be achieved region by region, with the ultimate goal being the integration

3

75 of worldwide geochemical, palaeobiological, and stratigraphic data into a common time domain,

76 facilitating objective comparison and integration (Condon et al., 2015).

77 Despite the obvious potential of Newfoundland’s Ediacaran volcaniclastic successions for

78 geochronological studies, relatively few peer-reviewed dates have been published from these

79 sections (e.g. Pu et al., 2016; Canfield et al., 2020). Similarly, although the extensive succession

80 of fossil-bearing horizons within MPER holds substantial potential for revealing evolutionary

81 patterns within mid-late Ediacaran marine ecosystems, no comprehensive review of the

82 stratigraphic ranges of taxa has previously been published. We here present stratigraphic ranges

83 for all formally described macrofossil taxa throughout the Conception and St. John’s Groups in

84 MPER, in addition to six new U-Pb (zircon) chemical abrasion – isotope dilution – thermal

85 ionization mass spectrometry (CA-ID-TIMS) dates from MPER tuffites spanning the majority of

86 the fossil-bearing section. We use these dates to develop and evaluate an age-depth model for the

87 succession, with the aim of facilitating regional and global integration and comparisons. Our

88 ages also permit development of an age model for sediment deposition through the Drook to

89 Fermeuse Formations, and provide temporal constraint for the evolutionary patterns identified in

90 our stratigraphic range charts.

91

92 2. SEDIMENTARY CONTEXT OF GEOCHRONOLOGICAL SAMPLES

93 The radio-isotopic dating in this study is based on analysis of zircons from tuffite horizons

94 within the siliciclastic sedimentary succession. The mechanism by which this tuffaceous material

95 was introduced to the depositional setting is debated, with some workers considering it to have

96 been introduced by turbidite or contourite currents (Benus, 1988). However, others have

97 assumed that tuffaceous material was deposited onto the sea surface by a volcanic event, before

98 settling to the seafloor from suspension (Anderson and Conway-Morris, 1982; Jenkins, 1992;

4

99 Wood et al., 2003; Bamforth et al., 2008; Brasier et al., 2011). These competing scenarios have

100 implications both for taphonomy, and for the interpretation of radio-isotopic dates obtained from

101 tuffites.

102 We analysed tuffite samples from six stratigraphic horizons within MPER for high-precision U-

103 Pb (zircon) radio-isotopic dating (SI1, Fig. S1). The locations and stratigraphic levels of these

104 samples are presented in Figure 1. Stratigraphic levels and distances stated herein are based on

105 new mapping of the MPER succession conducted between 2011 and 2014 (Matthews, 2015).

106 DRK-10. Sample DRK-10 was collected from the so-called ‘Pizza Disc Bed’ at Pigeon Cove.

107 This locality lies ~25 m below the top of the Drook Formation, and is notable for its preservation

108 of large lobate ‘pizza discs’, also known as ivesheadiomorphs (Liu et al., 2011), as well as

109 numerous small frondose fossils (Liu et al., 2012). The fossil-bearing horizon is directly overlain

110 by ~35 cm of green-buff, highly cleaved volcaniclastic sediment (SI1, Fig. S1a). The analysed

111 zircons come from an integrated sample of this ~35 cm-thick tuffite.

112 A slabbed and polished section through the lower ~25 cm of the tuffite reveals possible

113 convolute bedding and diffuse patches of carbonate, probably of secondary origin, at the base

114 (SI1, Fig. S2). This basal 7.5 cm is darker in colour than the surrounding light green-buff

115 material and consists of normally-graded, fine-grained sandstone to siltstone with extensive

116 chlorite-rich cement. Above this lies a poorly-sorted siltstone with local sand-size clasts, and

117 several laminae with ~25º apparent dip to bedding (i.e. the interpreted palaeo-horizontal plane of

118 section). The bed continues to grade normally into a mudstone at the top. At the very top of the

119 bed (above the analysed sample in SI1, Fig. S2), mm-scale interbeds of the tuffite with the

120 overlying grey siltstone suggest post-depositional reworking of the tuffite.

121 DRK-1. This sample was collected from the lower Briscal Formation at Daley’s Cove, ~50 m

122 above the top of the Drook Formation, within a succession of thin to medium bedded grey

5

123 sandstones that fine upwards to siltstones (SI1, Fig. S1b). It comprises a discrete ~5 cm thick

124 buff-green, silt-grade tuffite (SI1, Fig. S3), which does not overlie a known fossil-bearing

125 surface. The basal ~1 cm of the sampled horizon is dark grey in colour, and contains shale clasts

126 ~3 mm in diameter and a number of light-grey parallel laminae. This lowest layer grades into ~8

127 mm of light-buff siltstone dominated by irregularly-shaped “clots”, ~1 mm diameter, getting

128 smaller-upwards and composed of authigenic chlorite crystals (interpreted to be replacing

129 unstable volcanic minerals). The remainder of the bed comprises normally-graded, light-buff to

130 green siltstone, with prominent parallel laminae throughout, and some evidence of cross-

131 lamination in the middle of the bed. The sample collected was of the entire ~5 cm thickness of

132 the tuffite.

133 BRS-1. Sample BRS-1 is from a tuffaceous bed directly overlying the recently described

134 ‘Brasier’ Surface in the lower Briscal Formation, which yields exceptionally preserved

135 macrofossils including Fractofusus and Charniodiscus (Liu, 2016; Liu and Matthews, 2017).

136 The sampled bed, lying ~110 m above the base of the Formation, comprises a ~30 cm thick,

137 normally-graded medium sandstone, which is noticeably greener at the base. This buff-green

138 colour commonly indicates the presence of tuffaceous material elsewhere in MPER, and so our

139 sample was preferentially collected from the basal 10 cm of the bed. This bed is the lowest of

140 several thickly-bedded buff-green tuffaceous beds that create a noticeable, metres-thick marker

141 horizon that contrasts with the dark grey deposits of the rest of the local section (SI1, Fig. S1c).

142 It was not possible to collect a sample suitable for slabbing from this bed.

143 MP-14. This sample is from the tuff that directly overlies the ‘E’ Surface at Mistaken Point

144 (SI1, Fig. S1d), and lies within the upper Mistaken Point Formation, ~60 m below its boundary

145 with the Trepassey Formation. The sample was collected from above the ‘E’ Surface ‘Yale’

146 outcrop (sensu Clapham et al., 2003), and is the same horizon sampled by Pu et al. (2016). The

147 tuffite overlying the fossil surface comprises a ~5 mm thick crystal tuff horizon dominated by

6

148 feldspar and polycrystalline lithic fragments in a chlorite matrix, overlain by 10 cm of buff,

149 highly cleaved tuffite, grading from medium sand-grade material at the base to mud-grade at the

150 top. There is a marked transition from sand- to silt-grade material 2 cm from the base of the slab

151 (SI1, Fig. S4). The tuffite is capped by ~15 mm of black chlorite and pink carbonate, both of

152 which are interpreted to have been emplaced some time after the deposition of the tuffite. This

153 chlorite-carbonate horizon is only seen above the Mistaken Point ‘Yale’ and ‘Queens’ outcrops,

154 and is not observed above other outcrops of the ‘E’ Surface at Cape Race, Watern Cove, or the

155 Stumps (Matthews et al., 2017). Overlying this enigmatic horizon are 24 cm of normally graded,

156 green to grey siltstone. The basal thin, ~5 mm-thick crystal tuff horizon could not be sampled in

157 volumes necessary for geochronological analysis due to restrictions on collection, so the

158 analysed material comes from the overlying 10 cm-thick tuffite, but below the chlorite-carbonate

159 horizon.

160 LC-1. This sample is a ~4 cm-thick buff-coloured tuffite from the western edge of Long Cove,

161 and lies directly on top of a fossil surface within the Trepassey Formation informally referred to

162 as the ‘Pizzeria’ on account of its abundant ivesheadiomorph specimens (formerly “pizza discs”)

163 (SI1, Fig. S1e). The recognisable non-ivesheadiomorph taxa at this locality include Charnia,

164 Charniodiscus, and Pectinifrons. The tuffite comprises green to light-grey siltstone, with faint

165 sub-parallel laminae in places (SI1, Fig. S5). Further analysis of internal structure within the

166 tuffite is hampered by weathering and associated iron oxyhydroxide and dendritic manganese

167 mineralisation. The full thickness of this tuffite bed was sampled.

168 SH-2. SH-2 samples a ~30 cm tuffaceous deposit from within the lower Fermeuse Formation

169 (SI1, Fig. S1f), located adjacent to the well-documented Shingle Head fossil horizon (Clapham et

170 al., 2003). The Shingle Head surface documents the stratigraphically highest published

171 rangeomorph assemblage in the MPER succession. The basal surface of the bed is

172 topographically uneven, which may be associated with the widespread slumping within this part

7

173 of the succession (Wood et al., 2003). The sampled tuffite unit includes convolute laminae, and

174 is inferred to have acted as the décollement for the overlying slumped beds. As such this tuffite

175 would have been previously deposited upslope.

176 The basal 8 cm of the tuffite is a fining-upwards sandstone capped by weakly convolute mm-

177 scale laminae of green ash and black mudstone (SI1, Fig. S6). These grade into a ~20 cm thick

178 zone of intense convolute lamination, with recumbently folded sediment. The uppermost 8 cm of

179 the sample is cemented by ferroan calcite (identified by staining with Alizarin Red-S and

180 Potassium Ferricyanide, following Dickson, 1965).

181 Tuffite Deposition

182 None of the sampled tuffites have the characteristics of simple water-lain ash fall events. Several

183 of the sampled tuffites exhibit evidence for subaqueous, down-slope deposition, including graded

184 beds with features also found in classical Bouma sequence deposits; ripple cross-lamination;

185 intraclasts; and gradational or interbedded upper boundaries that transition into often finer-

186 grained tuffite-free siliciclastic siltstones and mudstones (Bouma, 1962). The basal coarse-

187 grained crystal tuff unit within the MP-14 sample is here interpreted parsimoniously as a coarser

188 deposit below an upward-fining turbidite. Comparable flow-head deposits of lithic/crystal tuffs

189 with little fine-grained matrix, overlain by normally-graded tuffaceous turbidites, are known

190 from recent ash-rich turbidites, such as those originating from the Minoan eruption of Santorini

191 (Sparks and Wilson, 1983). We therefore propose that at least some of the MPER tuffites were

192 deposited by ash-laden turbidity currents rather than water-lain ash falls. This ashy turbidite

193 model implies a hiatus between initial tuff deposition, its reworking downslope, and its eventual

194 re-deposition. Our interpretation is similar to that made for U-Pb (zircon) dating of similar

195 tuffites in other basins where a priori constraints allow for a test of the U-Pb (zircon) dating (e.g.

196 Schmitz and Davydov, 2012). Such studies suggest that any lag between magmatic zircon ages

8

197 and sedimentation is not significant at the level of interpretation made in this study. Although our

198 dates (and those of most previous studies) do not account for re-sedimentation and erosional

199 mixing (cf. Pu et al., 2016), this need not hinder construction of a MPER age-depth model.

200 Moreover, the bulk rock geochemistry of the MPER tuffites, upon which inferences of tectonic

201 setting have been made (Retallack, 2014, 2016), is called into question by the incorporation into

202 the beds of non-volcaniclastic material during re-sedimentation. Our ashy-turbidite hypothesis

203 infers that the alignment of frondose taxa directly beneath such tuffites may record flow direction

204 of turbidity currents themselves, rather than inter-depositional contour currents as has been

205 suggested previously (e.g. Wood et al., 2003; Flude and Narbonne, 2008).

206

207 3. STRATIGRAPHIC RANGE CHART CONSTRUCTION

208 A total of 22 distinct Ediacaran species have to date been formally reported within MPER (Liu

209 and Matthews, 2017), along with several as-yet unnamed taxa (e.g., ‘ostrich feathers’, Clapham

210 and Narbonne, 2002). Some previously described taxa (e.g. Aspidella and Hiemalora) have been

211 re-interpreted as the holdfast discs of frondose taxa (Serezhnikova, 2007; Burzynski and

212 Narbonne, 2015), and others such as ivesheadiomorphs are now regarded as taphomorphs (Liu et

213 al., 2011). The combined stratigraphic ranges and temporal distributions of these fossils through

214 the MPER section offer opportunities to identify and critically assess hypothesised evolutionary

215 relationships between Ediacaran macro-organisms (e.g. Brasier and Antcliffe, 2009; Laflamme et

216 al., 2013; Dececchi et al., 2017), and to recognise possible ecological or environmental factors

217 that may have influenced such relationships through time (e.g. Darroch et al., 2013; Mitchell and

218 Kenchington, 2018).

219 Biostratigraphic ranges can also be used in palaeogeographic reconstruction, and to define

220 regional or global stratigraphic units. The Ediacaran System spans a time interval of over 90

9

221 million years, but its formal division is yet to be achieved (Xiao et al., 2016). Determining

222 whether Ediacaran macrofossils are suitable for use in biostratigraphic correlation (possessing

223 distinct stratigraphic ranges, broad geographic ranges, high abundance, and independence from

224 facies) would be an important step towards developing a global Ediacaran stratigraphic

225 framework (e.g. Narbonne et al., 2012; Xiao et al., 2016), but requires detailed records of species

226 occurrence in space and time. Although stratigraphic ranges cannot be taken as accurate

227 indicators of the exact first and last appearances of taxa, owing to the incompleteness of the

228 fossil record (e.g. Jenkins, 1995; Sadler, 2004), they can constrain evolutionary hypotheses by

229 enabling rejection of implausible/unsupported options.

230 Previous compilations of Avalonian stratigraphic ranges have largely focused on single taxa

231 (typically presented in publications where a taxon is described for the first time; e.g., Gehling

232 and Narbonne, 2007, p. 20), or ‘representative’ taxa (Brasier and Antcliffe, 2004; Liu et al.,

233 2012). Particularly on the Avalon Peninsula, many fossils have only been described from a

234 handful of well-preserved bedding planes, with other fossiliferous surfaces receiving little

235 attention in the literature. In this study, data regarding the stratigraphic occurrence of individual

236 Ediacaran macrofossil taxa within MPER were collated between 2007 and 2018. Fossils were

237 identified by one of us (AGL) for consistency in taxonomic identification, and the occurrence of

238 taxa was noted on individual studied horizons. Geological mapping and measuring of section (by

239 JJM) throughout MPER enabled construction of a stratigraphic column onto which individual

240 surfaces could be plotted. Where the same surface was found to crop out in multiple locations

241 (e.g. the ‘D’ and ‘E’ Surfaces at the Stumps, Watern Cove and Mistaken Point; Matthews et al.,

242 2017), fossil data from each of those locations is thus plotted as coming from a single

243 stratigraphic level.

244 Taxonomic nomenclature follows previously published systematic descriptions or widely used

245 informal names. Organisms were identified to species level where possible, and data were

10

246 additionally cross-checked against literature records (see Supplementary Information 2) to ensure

247 that the observations were as complete as possible. Taxa were only included where we are

248 certain that the taxon under consideration is present: possible occurrences of a specific organism,

249 where identification is uncertain due to taphonomic factors, have been omitted from the final

250 figures to facilitate more robust interpretation of patterns in the dataset. Frondose fossils are

251 grouped into the higher-level taxonomic groupings Rangeomorpha and Arboreomorpha (Erwin

252 et al., 2011; Laflamme et al., 2013; though see Grazhdankin, 2014). Within the rangeomorphs,

253 taxa were divided into uniterminal and multiterminal taxa (terminology cf. Dunn et al., 2018).

254 Non-frondose impressions were assigned to discoidal specimens, taphomorphs, or non-frondose

255 taxa/impressions.

256 The stratigraphic ranges here are not presented as definitive records for individual taxa. They

257 simply summarise the current state of knowledge in the region, and are subject to revision

258 following future discoveries. Despite this caveat, the observed patterns represent a marked

259 advance in published documentation of the stratigraphic ranges of the Ediacaran macrobiota in

260 Newfoundland, and permit formulation of preliminary hypotheses regarding Ediacaran

261 evolutionary patterns and processes, which can be compared to other regional or global records

262 such as those from the Bonavista Peninsula of Newfoundland (e.g. Hofmann et al., 2008), or

263 Charnwood, UK (e.g. Noble et al., 2015).

264

265 4. U-Pb GEOCHRONOLOGY ANALYTICAL METHODS

266 U-Pb dating of zircons from six volcanic tuffs intercalated in the Conception and St. John’s

267 Groups in MPER was carried out at the National Environmental Isotope Facility, British

268 Geological Survey, via CA-ID-TIMS analyses. Detailed analytical methods are outlined in

269 Supplementary Information 3, and complete Pb and U isotopic data are presented in

11

270 Supplementary Information 4. Age results are illustrated in Figure 3 and reported in SI3, Figure

271 S7. The sample age is calculated based on the weighted mean 206Pb/238U date of the youngest

272 population analyses that overlap within 2σ analytical uncertainty, and is reported with its error at

273 95% confidence level in the ±X/Y/Z Ma format, where X is the analytical uncertainty in the

274 absence of all external errors, Y includes X and the tracer calibration uncertainty, and Z includes

275 Y and the 238U decay constant uncertainty of Jaffey et al. (1971).

276

277 5. U-Pb RESULTS AND AGE INTERPRETATIONS

278 In this section we outline the U-Pb (zircon) dataset obtained for the six MPER ash samples. As

279 is typical with high-precision U-Pb (zircon) datasets produced by CA-ID-TIMS, there is texture

280 within the data that requires discussion in order to support age interpretations and age

281 assignment. We follow the conventional interpretative approach, assigning ages using the

282 youngest coherent population (e.g. Schmitz and Davydov, 2012), due to the need to be able to

283 reproduce the dates that sample ages are based upon (i.e., significant Pb-loss is not likely to

284 result in reproducible U-Pb dates). Dates older than the 'youngest population' are interpreted to

285 reflect the analyses of xenocrystic material incorporated either prior/during eruption or during

286 final emplacement. Additional complicating factors (i.e., Pb-loss, post-depositional reworking)

287 are discussed below.

288 DRK-10. Zircon 206Pb/238U dates from the DRK-10 tuffite range from 573.36 – 577.38 Ma (n =

289 9) and the four youngest dates give a weighted mean age of 574.17 ± 0.19/0.24/0.66, with a

290 Mean Square Weighted Deviation (MSWD) of 2.8. The weighted mean 207Pb/206Pb date is 573.4

291 ± 1.9/2.1/5.0 Ma (n = 4, MSWD = 0.32).

12

292 DRK-1. Zircon 206Pb/238U dates from tuffite DRK-1 in the basal Briscal Formation range from

293 571.02 – 580.06 Ma (n = 19), and the 8 youngest dates give a weighted mean age of 571.38 ±

294 0.16/0.25/0.66 Ma, with an MSWD of 2.0. The weighted mean 207Pb/206Pb date is 573.0 ±

295 1.6/1.7/4.9 Ma (n = 8/19, MSWD = 2.9).

296 BRS-1. BRS-1 in the middle Briscal Formation yielded zircon 206Pb/238U dates ranging from

297 566.33 – 570.63 Ma (n = 8). The youngest date (z3) is excluded due to it being significantly

298 younger than the remaining population of data and is not reproduced. The five youngest

299 analyses, excluding z3, give a weighted mean age of 567.63 ± 0.21/0.26/0.66 Ma, with an

300 MSWD of 2.1. The weighted mean 207Pb/206Pb date is 566.8 ± 2.9/3.1/5.5 Ma (n = 5/8, MSWD =

301 0.52).

302 MP-14. Sample MP-14 is interpreted as an ashy turbidite, and the data obtained are interpreted

303 to provide a depositional age. In this study, zircon 206Pb/238U dates from the MP-14 tuffite range

304 from 563.81 – 567.48 Ma (n=11). The youngest age (z16) is interpreted as having undergone

305 post-crystallisation Pb-loss. The four youngest analyses, excluding z16, give a weighted mean

306 age of 565.00 ± 0.16/0.22/0.64 Ma, with an MSWD of 1.2. The weighted mean 207Pb/206Pb date

307 is 567.2 ± 2.5/2.7/5.3 Ma (n = 5/11, MSWD = 0.47).

308 LC-1. Zircon 206Pb/238U dates from sample LC-1 in the Trepassey Formation range from 564.68

309 – 567.41 Ma (n = 11). The two youngest dates give a weighted mean age of 564.71±

310 0.63/0.65/0.88, and their weighted mean 207Pb/206Pb date is 564.9 ± 2.1/2.1/5.0 Ma (n = 2/11,

311 MSWD = 0.69).

312 SH-2. The SH-2 sample, from the Fermeuse Formation, shows significant signs of slumping and

313 redeposition, and is thus interpreted as an eruptive age providing a maximum age constraint for

314 this level in the section. Zircon 206Pb/238U dates from this sample range from 563.67 – 569.01

315 Ma (n = 11). The six youngest dates gave a weighted mean age of 564.13 ± 0.20/0.25/0.65, with

13

316 an MSWD of 1.5. The weighted mean 207Pb/206Pb date is 563.6 ± 0.9/1.0/4.7 Ma (n = 6/11,

317 MSWD = 0.96).

318 All data are compiled in Supplementary Information 4 and interpreted dates are summarised in

319 Table 1.

320 6. COMPARISON WITH PRIOR DATING OF THE MPER SUCCESSION AND

321 DEVELOPING THE MPER AGE MODEL

322 The overarching aim of this study was to develop an age-depth model for the MPER succession,

323 in order to provide estimates for the ages of key fossil horizons and age-ranges for fossil

324 assemblages. Our age interpretations for each sample U-Pb dataset are now considered together

325 in a stratigraphic framework to construct an age-depth model. We then compare our age

326 interpretations to previously published radio-isotopic dates from ash layers in the same section.

327 Our study builds upon a legacy of geochronology investigations on the MPER succession.

328 Following the early work of Benus (1988), Bowring et al. (2003) reported a coherent U-Pb

329 (zircon) data set from ash layers in the top of the Mall Bay Formation; midway through the

330 Gaskiers Formation; in the basal Drook Formation; and a final ash from within the fossiliferous

331 Drook Formation, from above the Pizza Disc surface (Table 2). These unpublished dates were

332 presented in abstract form, and it is not reported whether they are 238U-206Pb or 207Pb/206Pb dates.

333 The U/Pb tracer calibration is also unknown. Nevertheless, these samples were used to conclude

334 a short duration (~3.3 Myr) between the termination of the short-lived Gaskiers glaciation and

335 the fossiliferous strata of the Drook Formation (e.g. Narbonne and Gehling, 2003). However it is

336 known that these determinations pre-dated the advent of chemical abrasion for U-Pb ID-TIMS

337 analyses. Subsequently, Pu et al. (2016) published a full U-Pb chemical abrasion ID-TIMS data

338 set for the samples analysed in the Bowring et al. (2003) study, augmented by another Avalon

339 Peninsula date from the ‘E’ Surface, and ash beds associated with glacial deposits across

14

340 Newfoundland. Pu et al. (2016) employed a number of methodological developments made since

341 the Bowring et al (2003) study (e.g., use of zone refined Re with reduced Tl blank, improved

342 UO2 correction). That study increased the duration of the interval between the base of the Drook

343 Formation and the ash overlying the fossiliferous Pizza Disc Surface from 3.3 to 8.9 Myr (Table

344 2). However, although the Pu et al. (2016) dates are younger than those in Bowring et al. (2003),

345 the observed differences across the samples are not systematic (see Table 2 and below for further

346 discussion).

347 This study shares two sampled horizons in common with the Pu et al. (2016) study, but the ages

348 do not agree within the stated analytical uncertainties/laboratory specific calibration uncertainties

349 (Table 2 and SI3 Figures S8 and S9). The first pair of dates we consider are for samples

350 MPMP33.56 (Pu et al., 2016) and MP-14 (this study), which both sample the ash overlying the

351 ‘E’ Surface. The Pu et al. U-Pb data largely overlap (SI3, Fig. S8), but the weighted mean dates

352 differ by 1.3 ± 0.4 Myr. We note that the MPMP33.56 data are discordant, yielding a weighted

353 mean 207Pb/206Pb date of 585.8 ± 8.4 Ma, indicating a component with an ‘inherited’

354 composition. This discordance is not observed in our U-Pb data from the same horizon (SI3,

355 Fig. S8). The MPMP33.56 sample’s 566.25 ± 0.35 Ma date does not violate the principle of

356 stratigraphic superposition, but the fact that the U-Pb data are discordant leads us to favour the

357 MP-14 date (this study) to constrain the age of the ‘E’ Surface and the MPER age-depth model.

358 The second pair of dates (samples DRK-10, this study, and Drook-2, Pu et al., 2016) come from

359 two samples taken from the same horizon above the Pizza Disc surface at Pigeon Cove, based

360 upon sample description and location data. The interpreted 206Pb/238U dates differ by 3.3 ± 0.4

361 Myr (Figure 3 and SI3, Figure S9). Importantly, the 570.94 ± 0.38 Ma date (Pu et al., 2016) is

362 younger than our date of 571.53 ± 0.19 Ma from an ash bed 43 m above the Pizza Disc Surface

363 (DRK-1). Including the 570.94 ± 0.38 Ma age in our age-depth model would require that both

364 our DRK-1 and DRK-10 dates do not reflect deposition, and instead reflect dating of older

15

365 zircons and/or open system behaviour. Both DRK-1 and DRK-10 ages from this study obey

366 stratigraphic superposition. An alternative is that the Drook-2 (Pu et al., 2016) date is too young,

367 possibly due to post-depositional Pb-loss, although the coherence of the U-Pb data would argue

368 against this. This apparent bias highlights additional sources of uncertainty that require further

369 investigation.

370 A third point of comparison can be made between the constraint we have for the lower part of the

371 Fermeuse Formation (SH-2, 564.13 +/- 0.20 Ma) and a U-Pb CA-ID-TIMS date of 562.5 +/- 1.1

372 Ma from an ash bed (N10-SH6B, see Figure 3) that is ~17 m below the SH-2 ash (Canfield et al.,

373 2020). Those authors regard N10-SH6B to be within the Trepassey Formation, however our

374 geological mapping put this locality within the Fermeuse Formation. The slumping associated

375 with SH-2 has led us to consider this as a maximum deposition age. Assuming the N10-SH6B

376 ash is not also slumped it may be a more accurate age estimate for the lower part of the Fermeuse

377 Formation. However the U-Pb data (Canfield et al., 2020) differs from this study and Pu et al.

378 (2016) in a number of ways: (i) it uses a U/Pb tracer without a stated calibration (this study and

379 Pu et al., 2016) use the EARTHTIME U-Pb tracers (Condon et al., 2015); (ii) the individual

380 analyses are based upon multi-grain fractions; (iii) the leaching step lasted 'a few hours'; and (iv)

381 the single dates are considerably less precise (Figure 3). Combined, these points make it difficult

382 to assess the accuracy of this date and whether the difference between the Canfield et al. (2020)

383 depositional age and our maximum age is geological, or reflects bias between the two datasets,

384 or most likely, a combination of both. As such we have not included the N10-SH6B date in our

385 age model, however it is worth noting that our MPER age model does overlap with these data

386 when the 95% confidence interval is considered.

387 In this study, the age-depth model of the middle-upper Ediacaran in MPER was developed using

388 the Bayesian Markov Chain Monte Carlo model incorporated in Chron.jl by C. Brenhin Keller.

389 Because of potential non-resolved lead loss of analysed zircons, StratMetropolis function was

16

390 used with inputs of weighted mean 206Pb/238U dates. The input data are shown in Figure 3A, and

391 the age-depth model is plotted in Figure 3B (see also Supplementary Information 5). Based upon

392 the discussion above relating to the prior dating, we have based our age-model on dates from this

393 study, with the exception of including the date of 579.88 ± 0.44 Ma (sample NoP-0.9; Pu et al.,

394 2016) that comes from the base of the Drook Formation at ‘North Point’, St. Mary’s Bay,

395 Newfoundland (Fig. 1B) to provide a lower age limit on the base of the Formation. Given this

396 does not come from our measured MPER succession, and we do not know how this basal Drook

397 age constraint projects into our measured section, except that it will either be at the base of our

398 succession, or at a lower level, we use 579.88 ± 0.44 Ma as a maximum age for the lowermost

399 Drook Formation in the MPER measured succession (SI3, Fig. S10). The MP12+5m and CR2

400 fossil surfaces in the Fermeuse Formation lie in the c.200 m of stratigraphy above the dated

401 section, and so ages for these surfaces within the age model were cautiously ascribed by

402 assuming a constant sedimentation rate through the Formation.

403 The age-depth model reveals (1) stratigraphic superposition is upheld, and (2) there is an

404 apparent depositional rate change in the middle of the Briscal Formation, separating broadly

405 constant, relatively slow depositional rates in the lower section from more rapid depositional

406 rates in the upper section. The change to more rapid deposition and a greater number of tuffites

407 from the middle of the Briscal Formation onwards is consistent with the Carey and Sigurdsson

408 (1984) model for deposition within a back-arc basin, and could, for example, represent the

409 transition to back-arc spreading and island arc volcanism following the initial rifting and

410 development of an inter-arc basin (Carey and Sigurdsson, 1984).

411

412 7. STRATIGRAPHIC RANGES OF EDIACARAN MACROFOSSILS IN MPER

17

413 Previous plots of Ediacaran species occurrences against time vary significantly in their scope.

414 They range from treatment of individual taxa in local sections (e.g. Bamforth and Narbonne,

415 2009), through summaries of distributions within individual regions (e.g., the East European

416 Platform; Grazhdankin, 2014, fig. 6), to discussion of selected iconic taxa on a global scale (e.g.

417 Brasier and Antcliffe, 2004; updated by Xiao and Laflamme, 2009; Narbonne et al., 2012).

418 Global studies (e.g. Laflamme et al., 2013; Grazhdankin, 2014, fig. 7) reveal a broad increase in

419 generic and higher order diversity through the late Ediacaran Avalon and White Sea assemblages

420 (sensu Waggoner, 2003), followed by a decline in the Nama assemblage, but fossil occurrences

421 are grouped at a coarse formational scale, and the taxonomic groupings are dictated to varying

422 degrees by the competing influences of taphonomy, depth, environment, age and

423 palaeogeography (Boag et al., 2016). If we are to interpret evolutionary trajectories from

424 Ediacaran macrofossils, link these to geological events and phenomena, or use macrofossils for

425 biostratigraphic correlation, we require finer-scale resolution of biostratigraphic patterns.

426 Previous work in Newfoundland suffers from either a lack of geochronological constraint (the

427 Catalina Dome; Hofmann et al., 2008), and/or uncertainty surrounding regional correlation. A

428 compilation of MPER and Catalina Dome data presented by Liu et al. (2012, fig. 8) combined

429 fossil occurrences from sites separated by over 200 km, but the published lithostratigraphic

430 correlations on which those correlations were based are now considered by us to be inaccurate

431 (Matthews, 2015). The present MPER study provides a detailed local, time-calibrated dataset

432 with which to assess fine scale, taxon-specific patterns in taxonomic distribution through time.

433 Separating the MPER data from those of the Catalina Dome offers the opportunity to then

434 independently compare the two sections to test observed patterns in the stratigraphic distribution

435 of taxa.

436 Our data considerably extend the known stratigraphic ranges for Vinlandia antecedens,

437 Fractofusus species, Charniodiscus sp., Culmofrons, Frondophyllas, Pectinifrons,

18

438 Primocandelabrum sp., Hiemalora and filamentous impressions in MPER relative to previous

439 studies (Fig. 4). Hadryniscala avalonica (Hofmann et al., 2008) is recognised in MPER for the

440 first time. The stratigraphic range of holdfast discs spans the entire range of frondose macrofossil

441 taxa, while the range for Hiemalora closely matches that of Primocandelabrum specimens, as

442 might be expected given their interpretation as component parts of those frondose organisms

443 (Serezhnikova, 2007; Burzynski and Narbonne, 2015). Ivesheadiomorphs have the longest range

444 of any non-discoidal impression, and are also the oldest impressions seen in MPER.

445

446 The oldest non-ivesheadiomorph fossil-bearing surface encountered also contains some of the

447 largest macrofossils in the MPER succession (Trepassia at locality DRK3CW), potentially

448 implying an older, as yet unsampled ancestry to these taxa. Uniterminal rangeomorphs with

449 undisplayed first and second order branching architecture (sensu Brasier et al., 2012), namely

450 Charnia, Vinlandia, and Trepassia, are the oldest frondose taxa, and these are joined by

451 Thectardis and Charniodiscus sp. in the Drook Formation (Fig. 4). Multiterminal rangeomorphs,

452 and rangeomorphs with displayed first and second order branches, are not observed until the

453 lower Briscal Formation. When translated to time (Fig. 5), this appearance of new rangeomorph

454 constructions occurs at about 568 Ma, and correlates with a marked increase in the occurrence of

455 fossil-bearing surfaces, and broader taxonomic diversity. Although we recognise that this pattern

456 may result from the smaller number of sampled horizons prior to 568 Ma, the data could be

457 interpreted to point to an extended ~7 Myr interval of gradual diversification of the

458 Rangeomorpha prior to a more rapid radiation in the Briscal Formation. We also note that the

459 turbiditic depositional environments in our study area reflect a mixture of infrequent event-bed

460 deposition and more gradual background sedimentation, but that even the background

461 sedimentation is likely to include breaks in sedimentation of unknown duration (Miall, 2016;

462 Davies and Shillito, 2018). Both the constant sedimentation rates implied by our age model, and

19

463 the durations represented by each individual ‘snapshot’ of a community preserved on each

464 observed bedding plane, will be affected by the incompleteness of the rock record.

465

466 Peak taxonomic diversity is observed in the upper Mistaken Point and lower Trepassey

467 Formations, around 565 Ma (Fig. 5), but this also corresponds to the part of the succession with

468 the most tuffites, and it is therefore entirely possible that this reflects a preservation bias, with

469 increasing numbers of available fossilisation opportunities offering a wider sample of taxonomic

470 diversity.

471

472 The sequence of apparent disappearances of taxa through the upper levels of the succession is

473 not considered to be evolutionarily significant, since many of these taxa are known in much

474 younger strata elsewhere (e.g. Charnia in Siberia; Grazhdankin et al., 2008). The absence of

475 fossils in the upper St. John’s Group at MPER is thus likely to be a

476 palaeoenvironmental/taphonomic artefact (cf. Narbonne, 2005).

477

478 There is considerable variation in the frequency of occurrence of taxa on fossil-bearing bedding

479 planes within MPER. Some taxa (e.g., Charnia, Pectinifrons, and the various Charniodiscus and

480 Fractofusus species) are relatively common, whereas others (e.g. Avalofractus, Broccoliforma,

481 Plumeropriscum, and Primocandelabrum hiemaloranum) are rare. Taphonomy may play a role

482 in explaining some of these patterns, for example some rare taxa are small, and so are more

483 difficult to identify on poorly preserved surfaces. The rarity of these taxa, both on and between

484 surfaces, is notable and worthy of future investigation. If corroborated at other sites, this

485 observation may imply a tendency towards ecological dominance in certain taxa. As noted at

486 other sites worldwide (e.g. Finnegan et al., 2019), beta diversity can be high amongst Ediacaran

487 bedding plane palaeocommunities, with adjacent surfaces often containing markedly different

20

488 species diversities and compositions. We note however that there is considerable variability in

489 the areal extent of the studied bedding planes, with some being 100s of m2 in area, and others

490 limited to small ledges. Where assessment of variation across individual surfaces is possible

491 (Matthews et al., 2017), variation in alpha diversity is moderate. Given that our record essentially

492 compiles random snapshots in time of variably populated ecosystems that have undergone

493 variable degrees of taphonomic filtering, we urge caution in interpreting the stratigraphic ranges

494 we present in isolation as evolutionary trends. Future cross-checking of our results with those

495 from other Avalonian localities (for which we are in the process of compiling palaeontological

496 and geochronological data) will permit testing of apparent patterns. It is worth noting that the

497 observation that uniterminal, undisplayed rangeomorph taxa appear before other forms is

498 consistent with the only currently available compilation of stratigraphic ranges from the

499 Bonavista Peninsula (Hofmann et al., 2008, fig. 4).

500

501 8. DISCUSSION

502 The geochronological ages presented here confirm the Mistaken Point biota as the oldest known

503 assemblage of the Ediacaran macrobiota (spanning at least the interval ~574–564 Ma).

504 Notwithstanding the issue of two different dates for the ‘Pizza Disc’ surface at the top of the

505 Drook Formation, comparison of our data with those of Pu et al. (2016) suggests that the first in

506 situ macrofossils in the MPER succession appear ~5 Myrs after the Gaskiers glaciation. This is a

507 shorter duration than was presented by those authors, but we support their suggestions that

508 macrofossils existed prior to this date (both in MPER and elsewhere in Newfoundland), and that

509 there is no clear link between fossil appearance and a post-Gaskiers oxygenation event (Pu et al.,

510 2016; see also Sperling et al., 2015).

21

511 In this paper we attempt to integrate our geochronological data from MPER with data published

512 in other studies (Bowring et al., 2003, Pu et al., 2016 and Canfield et al., 2020). This includes

513 three levels where dates from this study can be compared with previous dates from identical or

514 nearby beds, and we discuss the geological and analytical issues surrounding variance between

515 these ages. Combined, these datasets highlight additional and non-quantified sources of

516 geochronological uncertainty; however our approach of considering these within a stratigraphic

517 framework can aid the development of an age-thickness model.

518 There is a temporal overlap between the MPER fossil-bearing section and that of Charnwood

519 Forest, U.K. (bracketed to 569–556 Ma; Noble et al., 2015), and some sections in the Central

520 Urals (Maslov et al., 2013), but even the youngest MPER fossils predate macrofossil-bearing

521 strata in Siberia, China, Brazil and Namibia (Grotzinger et al., 1995; Parry et al., 2017; Yang et

522 al., 2017). Detailed studies from the ~558–550 Ma White Sea region of Russia (Martin et al.,

523 2000; Grazhdankin, 2004, 2014), and the as yet undated Ediacara Member of South Australia

524 (Gehling and Droser, 2013; Reid et al., 2018), have demonstrated that facies exert a significant

525 control on the distribution of taxa in those shelf and shallow marine settings, with particular

526 groups of organisms commonly found together in specific palaeoenvironments, while others are

527 excluded. Disentangling evolutionary and palaeoenvironmental controls on the distribution of

528 Ediacaran macrofossils requires temporal integration of the Ediacaran stratigraphic record. On

529 the basis of available evidence, the deep marine MPER succession and its related biota appear to

530 have been older than many other Ediacaran fossil-bearing successions: demonstrably time

531 equivalent shallow marine successions for direct comparison remain to be confirmed.

532 The new ages importantly provide tighter constraint on the age of horizontal surface traces that

533 have been described from the MPER succession (Liu et al., 2010, 2014). These impressions lie

534 on a surface in the upper Mistaken Point Formation that sits stratigraphically between our MP-14

535 and LC-1 dated horizons. Our age model predicts that the age of this horizon is ~564.8 Ma,

22

536 confirming these traces as the oldest known candidate metazoan surface traces in the rock record.

537 The age model also provides a chronostratigraphic framework within which to consider other

538 datasets, such as geochemical trends within the Conception and St John’s Groups (e.g., Canfield

539 et al., 2007), can be combined, offering the potential to test hypotheses linking environmental

540 and evolutionary events.

541

542 9. CONCLUSIONS

543 A series of new radio-isotopic dates for the Ediacaran successions of the Mistaken Point

544 Ecological Reserve confirm that the MPER fossils represent the world’s oldest examples of the

545 classic Ediacaran macrobiota. Two of the six dated levels have been dated in other studies, and

546 the ages from the two studies differ with respect to the oldest fossiliferous levels. This

547 disagreement requires further investigation. Our new radio-isotopic dates are stratigraphically

548 coherent, and have been used to develop an age-depth model for the succession.

549 Renewed mapping of the MPER and its surroundings allows for an improved lithostratigraphic

550 record of the succession, and the extension of stratigraphic ranges for several key Ediacaran taxa.

551 This integrated litho- and chrono-stratigraphic framework for south-eastern Newfoundland,

552 enmeshed with palaeontological stratigraphic occurrence data, provides a blueprint for future

553 work to constrain the temporal ranges of many key Neoproterozoic taxa.

554

555 Our age-depth model has then been used as a transfer function to propel the fossil ranges from

556 the ‘depth domain’ into the ‘time domain’. As additional Ediacaran successions, both

557 fossiliferous and non-fossiliferous, become similarly temporally calibrated, we hope it will be

558 possible to establish temporal and environmental controls on the distribution of Ediacaran taxa

559 across their entire temporal range. Finally, age models such as this offer opportunities to

23

560 combine palaeomagnetic, geochemical, microfossil, and other datasets to temporally correlate

561 distantly located global successions, and will prove invaluable for ongoing efforts by the ICS to

562 subdivide the Ediacaran System.

563

564 10. ACKNOWLEDGEMENTS

565 This research was supported by the Natural Environment Research Council (grant numbers

566 NE/J5000045/1 to JJM, and NE/L011409/2 to AGL), an NSERC DG award to DM, and a

567 NIGFSC award to JJM. We are grateful to Mike Eddy and one other reviewer for their

568 constructive comments that greatly improved this paper. We are indebted to R. Thomas for

569 support in the field and years of helpful discussions. T. Hearing and J. Stewart are thanked for

570 assistance in data collection. P.J. Matthews and A. Wood are thanked for support with sample

571 preparation. The people of Portugal Cove South and Trepassey are thanked for their hospitality.

572 The Department of Fisheries and Land Resources, Government of Newfoundland and Labrador,

573 provided permits to conduct research within the Mistaken Point Ecological Reserve between

574 2007 and 2018. Access to fossil localities within the Mistaken Point Ecological Reserve for

575 research is by permit only. Readers are advised that fossils outside the boundaries of MPER are

576 protected by the Paleontological Resource Regulations 67/11, under the Historic Resources Act,

577 1990. The early stages of this research project were guided and developed by M. Brasier, to

578 whom we dedicate this contribution.

579

580 11. REFERENCES

581 Anderson, M.M., and Conway-Morris, S., 1982, A review with descriptions of four unusual 582 forms of the soh-bodied fauna of the Conception and St. John’s groups, Avalon 583 Peninsula, Newfoundland, in Proceedings, Third North American Paleontological 584 Convention,.

24

585 Bamforth, E.L., and Narbonne, G.M., 2009, New Ediacaran Rangeomorphs from Mistaken 586 Point, Newfoundland, Canada: Journal of Paleontology, v. 83, p. 897–913.

587 Bamforth, E.L., Narbonne, G.M., and Anderson, M.M., 2008, Growth and ecology of a multi- 588 branched Ediacaran rangeomorph from the Mistaken Point assemblage, Newfoundland: 589 Journal of Paleontology, v. 82, p. 763–777.

590 Benus, A.P., 1988, Sedimentological context of a deep-water Ediacaran fauna (Mistaken Point, 591 Avalon Zone, eastern Newfoundland): Trace Fossils, Small Shelly Fossils and the 592 Precambrian Cambrian Boundary: Proceedings, 1987, Memorial University (New York 593 State Museum and Geological Survey Bulletin), p. 8–9.

594 Boag, T.H., Darroch, S.A.F., and Laflamme, M., 2016, Ediacaran distributions in space and time: 595 testing assemblage concepts of earliest macroscopic body fossils: Paleobiology, v. 42, p. 596 574–594, doi:10.1017/pab.2016.20.

597 Bobrovskiy, I., Hope, J.M., Ivantsov, A., Nettersheim, B.J., Hallmann, C., and Brocks, J.J., 2018, 598 Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals: 599 Science (New York, N.Y.), v. 361, p. 1246–1249, doi:10.1126/science.aat7228.

600 Bouma, A.H., 1962, Sedimentology of some flysch deposits: Agraphic approach to facies 601 interpretation, v. 168.

602 Bowring, S.A., Myrow, P.M., Landing, E., and Ramezani, J., 2003, Geochronological constraints 603 on terminal Neoproterozoic events and the rise of metazoans: Geophysical Research 604 Abstracts, v. 5, 13219, p. 219. 605 Brasier, M., and Antcliffe, J., 2004, Decoding the Ediacaran enigma: Science, v. 305, p. 1115– 606 1117, doi:10.1126/science.1102673.

607 Brasier, M.D., and Antcliffe, J.B., 2009, Evolutionary relationships within the Avalonian 608 Ediacara biota: new insights from laser analysis: Journal of the Geological Society, v. 609 166, p. 363–384.

610 Brasier, M.D., Antcliffe, J.B., and Callow, R.H.T., 2011, Evolutionary trends in remarkable 611 fossil preservation across the Ediacaran–Cambrian transition and the impact of metazoan 612 mixing: Taphonomy, p. 519–567.

613 Brasier, M.D., Antcliffe, J.B., and Liu, A.G., 2012, The architecture of Ediacaran Fronds: 614 Palaeontology, v. 55, p. 1105–1124, doi:10.1111/j.1475-4983.2012.01164.x.

615 Burzynski, G., and Narbonne, G.M., 2015, The discs of Avalon: Relating discoid fossils to 616 frondose organisms in the Ediacaran of Newfoundland, Canada: Palaeogeography 617 Palaeoclimatology Palaeoecology, v. 434, p. 34–45, doi:10.1016/j.palaeo.2015.01.014.

618 Canfield, D.E., Poulton, S.W., and Narbonne, G.M., 2007, Late-Neoproterozoic deep-ocean 619 oxygenation and the rise of animal life: Science, v. 315, p. 92–95.

620 Canfield, D.E., Knoll, A.H., Poulton, S.W., Narbonne, G.M., and Dunning, G.R., 2020, Carbon 621 isotopes in clastic rocks and the Neoproterozoic carbon cycle: American Journal of 622 Science, v. 320 (2), p. 97–124.

25

623 Carey, S., and Sigurdsson, H., 1984, A model of volcanogenic sedimentation in marginal basins: 624 Geological Society, London, Special Publications, v. 16, p. 37–58, 625 doi:10.1144/GSL.SP.1984.016.01.04.

626 Clapham, M.E., and Narbonne, G.M., 2002, Ediacaran epifaunal tiering: Geology, v. 30, p. 627– 627 630, doi:10.1130/0091-7613(2002)030<0627:EET>2.0.CO;2.

628 Clapham, M.E., Narbonne, G.M., and Gehling, J.G., 2003, Paleoecology of the oldest known 629 animal communities: Ediacaran assemblages at Mistaken Point, Newfoundland: 630 Paleobiology, v. 29, p. 527–544, doi:10.1666/0094- 631 8373(2003)029<0527:POTOKA>2.0.CO;2.

632 Condon, D.J., Boggiani, P., Fike, D., Halverson, G.P., Kasemann, S., Knoll, A.H., Macdonald, 633 F.A., Prave, A.R., and Zhu, M., 2015, Accelerating Neoproterozoic research through 634 scientific drilling: Scientific Drilling, v. 19, p. 17–25, doi:https://doi.org/10.5194/sd-19- 635 17-2015.

636 Condon, D.J., Schoene, B., McLean, N.M., Bowring, S.A., and Parrish, R.R., 2015, Metrology 637 and traceability of U–Pb isotope dilution geochronology (EARTHTIME Tracer 638 Calibration Part I): Geochimica et Cosmochimica Acta, v.164, p.464-480. 639 Darroch, S.A.F., Laflamme, M., and Clapham, M.E., 2013, Population structure of the oldest 640 known macroscopic communities from Mistaken Point, Newfoundland: Paleobiology, v. 641 39, p. 591–608, doi:10.1666/12051.

642 Davies, N.S., and Shillito, A.P., 2018, Incomplete but intricately detailed: The inevitable 643 preservation of true substrates in a time-deficient stratigraphic record: Geology, v. 46, p. 644 679–682, doi:10.1130/G45206.1.

645 Dececchi, T.A., Narbonne, G.M., Greentree, C., and Laflamme, M., 2017, Relating Ediacaran 646 Fronds: Paleobiology, v. 43, p. 171–180, doi:10.1017/pab.2016.54.

647 Dickson, J. a. D., 1965, A Modified Staining Technique for Carbonates in Thin Section: Nature, 648 v. 205, p. 587–587, doi:10.1038/205587a0.

649 Dunn, F.S., and Liu, A.G., 2019, Viewing the Ediacaran biota as a failed experiment is 650 unhelpful: Nature Ecology & Evolution, v. 3, p. 512–514, doi:10.1038/s41559-019-0815- 651 4.

652 Dunn, F.S., Liu, A.G., and Donoghue, P.C.J., 2018, Ediacaran developmental biology: 653 Biological Reviews, v. 93, p. 914–932, doi:10.1111/brv.12379.

654 Dunn, F.S., Liu, A.G., and Gehling, J.G., 2019, Anatomical and ontogenetic reassessment of the 655 Ediacaran frond Arborea arborea and its placement within total group Eumetazoa: 656 Palaeontology, v. 62, p. 851–865, doi:10.1111/pala.12431.

657 Erwin, D.H., Laflamme, M., Tweedt, S.M., Sperling, E.A., Pisani, D., and Peterson, K.J., 2011, 658 The Cambrian Conundrum: Early Divergence and Later Ecological Success in the Early 659 History of Animals: Science, v. 334, p. 1091–1097, doi:10.1126/science.1206375.

26

660 Evans, S.D., Gehling, J.G., and Droser, M.L., 2019, Slime travelers: Early evidence of animal 661 mobility and feeding in an organic mat world: Geobiology, v. 17, p. 490–509, 662 doi:10.1111/gbi.12351.

663 Fedonkin, M.A., Gehling, J.G., Grey, K., Narbonne, G.M., and Vickers-Rich, P., 2007, The Rise 664 of Animals: Evolution and Diversification of the Kingdom Animalia: The Johns Hopkins 665 University Press, 344 p.

666 Finnegan, S., Gehling, J.G., and Droser, M.L., 2019, Unusually variable paleocommunity 667 composition in the oldest metazoan fossil assemblagesSETH FINNEGAN ET 668 AL.EDIACARAN PALEOCOMMUNITY VARIABILITY: Paleobiology, v. 45, p. 235– 669 245, doi:10.1017/pab.2019.1.

670 Flude, L.I., and Narbonne, G.M., 2008, Taphonomy and ontogeny of a multibranched Ediacaran 671 fossil: Bradgatia from the Avalon Peninsula of Newfoundland: Canadian Journal of Earth 672 Sciences, v. 45, p. 1095–1109.

673 Gardiner, S., and Hiscott, R.N., 1988, Deep-water facies and depositional setting of the lower 674 Conception Group (Hadrynian), southern Avalon Peninsula, Newfoundland: Canadian 675 Journal of Earth Sciences, v. 25, p. 1579–1594, doi:10.1139/e88-151.

676 Gehling, J.G., and Droser, M.L., 2013, How well do fossil assemblages of the Ediacara Biota tell 677 time? Geology, v. 41, p. 447–450, doi:10.1130/G33881.1.

678 Gehling, J.G., and Narbonne, G.M., 2007, Spindle-shaped Ediacara fossils from the Mistaken 679 Point assemblage, Avalon Zone, Newfoundland: Canadian Journal of Earth Sciences, v. 680 44, p. 367–387, doi:10.1139/E07-003.

681 Gold, D.A., Runnegar, B., Gehling, J.G., and Jacobs, D.K., 2015, Ancestral state reconstruction 682 of ontogeny supports a bilaterian affinity for Dickinsonia: Evolution & Development, v. 683 17, p. 315–324, doi:10.1111/ede.12168.

684 Grazhdankin, D., 2004, Patterns of distribution in the Ediacaran biotas: facies versus 685 biogeography and evolution: Paleobiology, v. 30, p. 203–221.

686 Grazhdankin, D., 2014, Patterns of Evolution of the Ediacaran Soft-Bodied Biota: Journal of 687 Paleontology, v. 88, p. 269–283, doi:10.1666/13-072.

688 Grazhdankin, D.V., Balthasar, U., Nagovitsin, K.E., and Kochnev, B.B., 2008, Carbonate-hosted 689 Avalon-type fossils in arctic Siberia: Geology, v. 36, p. 803–806.

690 Grotzinger, J.P., Bowring, S.A., Saylor, B.Z., and Kaufman, A.J., 1995, Biostratigraphic and 691 Geochronological Constraints on Early Animal Evolution: Science, v. 270, p. 598–604.

692 Hofmann, H.J., O’Brien, S.J., and King, A.E., 2008, Ediacaran biota on Bonavista Peninsula, 693 Newfoundland, Canada: Journal of Paleontology, v. 82, p. 1–36, doi:10.1666/06-087.1.

694 Ivantsov, A.Y., and Malakhovskaya, Y.E., 2002, Giant traces of Vendian animals: Doklady 695 Earth Sciences, v. 385, p. 618–622.

27

696 Jaffey, A.H., Flynn, K.F., Glendenin, L.E., Bentley, W.C., and Essling, A.M., 1971, Precision 697 Measurement of Half-Lives and Specific Activities of 235U and 238U: Physical Review 698 C, v. 4, p. 1889–1906, doi:10.1103/PhysRevC.4.1889.

699 Jenkins, R.J.F., 1992, Functional and Ecological Aspects of Ediacaran Assemblages, in Lipps, 700 J.H. and Signor, P.W. eds., Origin and Early Evolution of the Metazoa, Springer US, 701 Topics in Geobiology 10, p. 131–176, http://link.springer.com/chapter/10.1007/978-1- 702 4899-2427-8_5 (accessed September 2015).

703 Jenkins, R.J.F., 1995, The Problems and Potential of Using Animal Fossils and Trace Fossils in 704 Terminal Proterozoic Biostratigraphy: Precambrian Research, v. 73, p. 51–69.

705 Laflamme, M., Darroch, S.A.F., Tweedt, S.M., Peterson, K.J., and Erwin, D.H., 2013, The end 706 of the Ediacara biota: Extinction, biotic replacement, or Cheshire Cat? Gondwana 707 Research, v. 23, p. 558–573, doi:10.1016/j.gr.2012.11.004.

708 Liu, A.G., 2016, Framboidal pyrite shroud confirms the ‘death mask’model for moldic 709 preservation of Ediacaran soft-bodied organisms: Palaios, v. 31, p. 259–274.

710 Liu, A.G., Kenchington, C.G., and Mitchell, E.G., 2015, Remarkable insights into the 711 paleoecology of the Avalonian Ediacaran macrobiota: Gondwana Research, v. 27, p. 712 1355–1380, doi:10.1016/j.gr.2014.11.002.

713 Liu, A.G., and Matthews, J.J., 2017, Great Canadian Lagerstätten 6. Mistaken Point Ecological 714 Reserve, Southeast Newfoundland: Geoscience Canada, v. 44, p. 63–76, 715 doi:10.12789/geocanj.2017.44.117.

716 Liu, A.G., Mcilroy, D., Antcliffe, J.B., and Brasier, M.D., 2011, Effaced preservation in the 717 Ediacara biota and its implications for the early macrofossil record: Palaeontology, v. 54, 718 p. 607–630, doi:10.1111/j.1475-4983.2010.01024.x.

719 Liu, A.G., McIlroy, D., and Brasier, M.D., 2010, First evidence for locomotion in the Ediacara 720 biota from the 565 Ma Mistaken Point Formation, Newfoundland: Geology, v. 38, p. 721 123–126.

722 Liu, A.G., McIlroy, D., Matthews, J.J., and Brasier, M.D., 2012, A new assemblage of juvenile 723 Ediacaran fronds from the Drook Formation, Newfoundland: Journal of the Geological 724 Society, v. 169, p. 395–403, doi:10.1144/0016-76492011-094.

725 Liu, A.G., Mcilroy, D., Matthews, J.J., and Brasier, M.D., 2014, Confirming the Metazoan 726 Character of a 565 Ma Trace-Fossil Assemblage from Mistaken Point, Newfoundland: 727 PALAIOS, v. 29, p. 420–430, doi:10.2110/palo.2014.011.

728 Martin, M.W., Grazhdankin, D.V., Bowring, S.A., Evans, D.A.D., Fedonkin, M.A. and 729 Kirschvink, J.L., 2000. Age of Neoproterozoic bilatarian body and trace fossils, White 730 Sea, Russia: Implications for metazoan evolution: Science, 288 (5467), p. 841–845. 731 732 Maslov, A.V., Meert, J., Levashova, N.M., Ronkin, Yu.L., Grazhdankin, D.V., Kuznetsov, N.B., 733 Krupenin, M.T., Fedorova, N.M., and Ipat’eva, I.S., 2013, New constraints for the age of 734 Vendian glacial deposits (Central Urals): Doklady Earth Sciences, v. 449, p. 303–308, 735 doi:10.1134/S1028334X13030203.

28

736 Matthews, J.J., 2015, The stratigraphical context of the Ediacaran Biota of eastern 737 Newfoundland: Unpublished Doctoral Thesis, University of Oxford,.

738 Matthews, J.J., Liu, A.G., and McIlroy, D., 2017, Post-fossilization processes and their 739 implications for understanding Ediacaran macrofossil assemblages: Geological Society, 740 London, Special Publications, v. 448, p. SP448.20, doi:10.1144/SP448.20.

741 Menon, L.R., McIlroy, D., and Brasier, M.D., 2013, Evidence for Cnidaria-like behavior in ca. 742 560 Ma Ediacaran Aspidella: Geology, v. 41, p. 895–898, doi:10.1130/G34424.1.

743 Miall, A.D., 2016, The valuation of unconformities: Earth-Science Reviews, v. 163, p. 22–71, 744 doi:10.1016/j.earscirev.2016.09.011.

745 Misra, S.B., 1969, Late Precambrian (?) fossils from southeastern Newfoundland: Geological 746 Society of America Bulletin, v. 80, p. 2133.

747 Mitchell, E.G., and Kenchington, C.G., 2018, The utility of height for the Ediacaran organisms 748 of Mistaken Point: Nature Ecology & Evolution, v. 2, p. 1218–1222, 749 doi:10.1038/s41559-018-0591-6.

750 Narbonne, G.M., 2005, THE EDIACARA BIOTA: Neoproterozoic Origin of Animals and Their 751 Ecosystems: Annual Review of Earth and Planetary Sciences, v. 33, p. 421–442, 752 doi:10.1146/annurev.earth.33.092203.122519.

753 Narbonne, G.M., and Gehling, J.G., 2003, Life after snowball: The oldest complex Ediacaran 754 fossils: Geology, v. 31, p. 27–30, doi:10.1130/0091- 755 7613(2003)031<0027:LASTOC>2.0.CO;2.

756 Narbonne, G.M., Xiao, S., Shields, G., Gradstein, F., Ogg, J., Schmitz, M.D., and Ogg, G., 2012, 757 The Ediacaran Period: Geologic Timescale, p. 427–449.

758 Noble, S.R., Condon, D.J., Carney, J.N., Wilby, P.R., Pharaoh, T.C., and Ford, T.D., 2015, U-Pb 759 geochronology and global context of the Charnian Supergroup, UK: Constraints on the 760 age of key Ediacaran fossil assemblages: Geological Society of America Bulletin, v. 127, 761 p. 250–265, doi:10.1130/B31013.1.

762 Parry, L.A. et al., 2017, Ichnological evidence for meiofaunal bilaterians from the terminal 763 Ediacaran and earliest Cambrian of Brazil: Nature Ecology & Evolution, v. 1, p. 1455– 764 1464, doi:10.1038/s41559-017-0301-9.

765 Pu, J.P., Bowring, S.A., Ramezani, J., Myrow, P., Raub, T.D., Landing, E., Mills, A., Hodgin, E., 766 and Macdonald, F.A., 2016, Dodging snowballs: Geochronology of the Gaskiers 767 glaciation and the first appearance of the Ediacaran biota: Geology, v. 44, p. 955–958, 768 doi:10.1130/G38284.1.

769 Reid, L.M., Holmes, J.D., Payne, J.L., García-Bellido, D.C., and Jago., J.B., 2018, Taxa, 770 turnover and taphofacies: a preliminary analysis of facies-assemblage relationships in the 771 Ediacara Member (Flinders Ranges, South Australia): Australian Journal of Earth 772 Sciences, DOI:10.1080/08120099.2018.1488767 773 Retallack, G.J., 2016, Ediacaran sedimentology and paleoecology of Newfoundland 774 reconsidered: Sedimentary Geology, v. 333, p. 15–31, doi:10.1016/j.sedgeo.2015.12.001.

29

775 Retallack, G.J., 2014, Volcanosedimentary paleoenvironments of Ediacaran fossils in 776 Newfoundland: Geological Society of America Bulletin, v. 126, p. 619–638, 777 doi:10.1130/B30892.1.

778 Sadler, P.M., 2004, Quantitative Biostratigraphy—Achieving Finer Resolution in Global 779 Correlation: Annual Review of Earth and Planetary Sciences, v. 32, p. 187–213, 780 doi:10.1146/annurev.earth.32.101802.120428.

781 Schmitz, M.D., and Davydov, V.I., 2012, Quantitative radiometric and biostratigraphic 782 calibration of the Pennsylvanian–Early Permian (Cisuralian) time scale and pan- 783 Euramerican chronostratigraphic correlation: Geological Society of America Bulletin, v. 784 124, p. 549–577, doi:10.1130/B30385.1.

785 Serezhnikova, E.A., 2007, Palaeophragmodictya spinosa sp nov., a bilateral benthic organism 786 from the Vendian of the Southeastern White Sea region: Paleontological Journal, v. 41, p. 787 360–369.

788 Sparks, R.S.J., and Wilson, C.J.N., 1983, Flow-head deposits in ash turbidites: Geology, v. 11, p. 789 348–351, doi:10.1130/0091-7613(1983)11<348:FDIAT>2.0.CO;2.

790 Sperling, E.A., Wolock, C.J., Morgan, A.S., Gill, B.C., Kunzmann, M., Halverson, G.P., 791 Macdonald, F.A., Knoll, A.H., and Johnston, D.T., 2015, Statistical analysis of iron 792 geochemical data suggests limited late Proterozoic oxygenation: Nature, v. 523, p. 451– 793 454, doi:10.1038/nature14589.

794 Waggoner, B., 2003, The Ediacaran biotas in space and time: Integrative and Comparative 795 Biology, v. 43, p. 104–113, doi:10.1093/icb/43.1.104.

796 Williams, H., and King, A.F., 1979, Trepassey map area, Newfoundland: Geological Survey of 797 Canada, Energy, Mines, and Resources Canada.

798 Wood, D.A., Dalrymple, R.W., Narbonne, G.M., Gehling, J.G., and Clapham, M.E., 2003, 799 Paleoenvironmental analysis of the late Neoproterozoic Mistaken Point and Trepassey 800 formations, southeastern Newfoundland: Canadian Journal of Earth Sciences, v. 40, p. 801 1375–1391.

802 Xiao, S.H., and Laflamme, M., 2009, On the eve of animal radiation: phylogeny, ecology and 803 evolution of the Ediacara biota: Trends in Ecology & Evolution, v. 24, p. 31–40.

804 Xiao, S., Narbonne, G.M., Zhou, C., Laflamme, M., Grazhdankin, D.V., Moczydlowska-Vidal, 805 M., and Cui, H., 2016, Towards an Ediacaran Time Scale: Problems, Protocols, and 806 Prospects: Episodes, v. 39, p. 540–555, doi:10.18814/epiiugs/2016/v39i4/103886.

807 Yang, C., Li, X.-H., Zhu, M., and Condon, D.J., 2017, SIMS U–Pb zircon geochronological 808 constraints on upper Ediacaran stratigraphic correlations, South China: Geological 809 Magazine, v. 154, p. 1202–1216, doi:10.1017/S0016756816001102.

810

811

30

812

813

814

815 FIGURES

816 Figure 1. Map and stratigraphic column for the Mistaken Point Ecological Reserve (MPER). A: 817 Map of Newfoundland. B: Map of the Avalon Peninsula. C: Geological map of the MPER 818 region, with the Reserve highlighted in red. Geological units coloured as in D. Sample localities 819 marked with red stars. D: Stratigraphic column for MPER, showing the levels of the sampled 820 horizons. 821 Figure 2. Representative fossils from surfaces within MPER. A: Trepassia wardae, bed DRK1T, 822 Drook Fm., Daley’s Cove. B: Charnia masoni, bed MP7, Mistaken Point Fm. C: Charniodiscus 823 procerus, bed MP7. D: Charniodiscus spinosus, bed MP N (see Bamforth & Narbonne, 2008). 824 E: Hapsidophyllas flexibilis, bed ‘B’ of Landing et al., 1988, Mistaken Point Fm. F: Pectinifrons 825 abyssalis, bed MP16, Trepassey Fm. Best seen when wet. G: Ivesheadiomorphs and frondose 826 taxa on the ‘Pizzeria’ surface (the surface directly below dated sample LC-1), Long Cove, 827 Trepassey Fm. H: Fractofusus misrai and holdfast disc, ‘D’ Surface at the Stumps (see 828 Matthews et al., 2017), Mistaken Point Fm. I: Fractofusus misrai (the largest specimen we have 829 observed anywhere), bed BR6, Briscal Fm. Scale bars = 50 mm except in C = 10 mm. 830 Figure 3. A: Ranked 206Pb/238U date plots for the data generated in this study, and two samples 831 also dated as part of the Pu et al (2016) study. B: Age-depth model based upon the interpreted 832 206Pb/238U ages. 833 Figure 4. Stratigraphic range chart for published Ediacaran macrofossils from Mistaken Point 834 Ecological Reserve, Newfoundland. Each black horizontal bar indicates occurrences of that 835 taxon on a specific bedding plane horizon at a known level within the measured section. 836 Stratigraphic thickness is based on measurements made as part of this study. Fossil occurrence 837 data combine information from the literature (see Supplementary Information 2 for a full list of 838 literature references) with primary observations made by us between 2007–2018. 839 Figure 5. Chronostratigraphic range chart for published Ediacaran macrofossils from Mistaken 840 Point Ecological Reserve, Newfoundland. Depth to time conversions were performed using the 841 age model in Fig. 3B. Age model uncertainties are not included. Note that multiple surfaces may 842 have been given the same age, and so plot together.

31

A C REVISED GEOLOGICAL MAP OF D REVISED STRATIGRAPHY OF NEWFOUNDLAND MISTAKEN POINT ECOLOGICAL RESERVE MISTAKEN POINT ECOLOGICAL RESERVE DRK-1

DRK-10

Mistaken Point Ecological Reserve 2000 m Fermeuse Formation (720 m)

B SH-2

ST. JOHN’S GROUP ST.

Trepassey 1500 m Formation 250 km (240 m) LC-1

B MP-14 Mistaken Point

Formation (290 m)

BRS-1 1000 m Briscal Formation (310 m) BRS-1

St. John’s DRK-1 DRK-10

AVALON PENINSULA Mistaken Point

MP-14 500 m ‘North Point’ Drook N Watern Cove CONCEPTION GROUP Formation LC-1 (770 m) Long Cove Mistaken Point Shingle Head

0 50 100 km SH-2 0

562.5 565.0 567.5 570.0 572.5 575.0 577.5

SH-2

Plot of 206Pb/238U date for N10-SH6B (Canfield et al. 2020, 2s) N10-SH6B Plot of 206Pb/238U dates for each of samples (Pu et al. 2016, 2s)

206 238 LC-1 Pb/ U dates (this study, 2s) included in WM calculation 206Pb/238U dates (this study, 2s) excluded from WM calculation MPMP33.56

MP-14

Bris-1 DRK-1 Drook-2

206 238 Pb/ U date (Ma) DRK-10

SH-2 Fermeuse N10-SH6B 95% C.I. of age model based on weighted mean 206Pb/238U dates (this study) 1600 Weighted mean 206Pb/238U dates (Canfield et al. 2020, 2s)

Weighted mean 206Pb/238U dates (Pu et al. 2016, 2s) repassey 206 238 T LC-1 Weighted mean Pb/ U dates (this study, 2s) 1400

MP-14 MPMP33.56 Point 1200 Mistaken

Briscal Height (m) Bris-1

DRK-1 800 Drook-2 DRK-10 Drook 562.5 Age (Ma) 565.0 567.5 570.0 572.5 575.0 577.5

2000 m

sp.

Holdfast

sp.

sp. sp.

Fermeuse Formation

Beothukis mistakensis Beothukis abyssalis Pectinifrons spinosus Charniodiscus arborea Arborea avalonica Hadryniscala Ivesheadiomorphs

Vinlandia antecedens Vinlandia abaculus Avalofractus feather’ ‘ostrich misrai Fractofusus procerus Charniodiscus Charniodiscus catalinensis Hadrynichorde

Charnia masoni Charnia plumosa Culmofrons hofmanni Plumeropriscum organism’ ‘string Primocandelabrum flexibilis Hapsidophyllas alta Broccoliforma

Hiemalora wardae Trepassia grandis Frondophyllas avalonensis Thectardis

Primocandelabrum hiemalorum Primocandelabrum Bradgatia

Filaments Fractofusus andersoni Fractofusus  SH-2  ‘Shingle Head’ (MP12)

1500 m Trepassey Formation  LC-1  ‘Pizzeria’ (MP 9)

 MP-14  ‘E’ Surface Mistaken (MP E) Point Formation

1000 m

Metres through MPER Stratigraphy MPER through Metres Briscal Formation  BRS-1  ‘Brasier’ (BR 5)

 DRK-1  DRK-10  ‘Pizza Disc’ Discs Multiterminal rangeomorphs Arboreomorphs (DRK2PC) Drook Non-frondose taxa Uniterminal rangeomorphs Formation Ivesheadiomorphs

500 m  Dated Tuffite  Significant Fossil Surface

sp.

sp.

sp. Fermeuse

562 Formation

Holdfast

Pectinifrons abyssalis Pectinifrons procerus Charniodiscus

Vinlandia antecedens Vinlandia hofmanni Plumeropriscum

Hiemalora masoni Charnia grandis Frondophyllas feather’ ‘ostrich Bradgatia spinosus Charniodiscus arborea Arborea alta Broccoliforma avalonica Hadryniscala

Beothukis mistakensis Beothukis plumosa Culmofrons abaculus Avalofractus organism’ ‘string misrai Fractofusus andersoni Fractofusus hiemalorum Primocandelabrum Primocandelabrum flexibilis Hapsidophyllas Charniodiscus Ivesheadiomorphs

Trepassia wardae Trepassia avalonensis Thectardis

Filaments

Hadrynichorde catalinensis Hadrynichorde  SH-2  ‘Shingle Head (MP12) 564 Trepassey Formation  LC-1  ‘Pizzeria’ (MP 9)  MP-14 Mistaken  ‘E’ Surface Point (MP E) 566 Formation

 BRS-1 568  ‘Brasier’ (BR 5)

Ma Briscal Formation 570

 DRK-1

572 Multiterminal rangeomorphs

Drook Formation  DRK-10 574  ‘Pizza Disc’ (DRK2PC) Discs Arboreomorphs Non-frondose taxa Uniterminal rangeomorphs Ivesheadiomorphs 576  Dated Tuffite  Significant Fossil Surface TABLE 1. Summary of interpreted U-Pb (zircon) dates from MPER. X – internal or analytical uncertainty (Myr). Y – quadratic addition of tracer calibration error. Z – quadratic addition of both tracer calibration and 238U decay constant uncertainty. MSWD - Mean Square Weighted Deviation. Stratigraphic Height Weighted Mean

Sample Position (m) 206Pb/238U date ±X ±Y ±Z N MSWD Interpretation

(Formation) (Ma)

SH-2 Fermeuse 1685 564.13 0.20 0.25 0.65 6/11 1.5 Maximum age

LC-1 Trepassey 1413 564.71 0.63 0.65 0.88 2/11 N.A. Eruption/Deposition

MP-14 Mistaken Point 1315 565.00 0.16 0.22 0.64 4/11 1.2 Eruption/Deposition

BRS-1 Briscal 880 567.63 0.21 0.26 0.66 5/8 2.1 Eruption/Deposition

DRK-1 Briscal 790 571.38 0.16 0.25 0.66 8/19 2.0 Eruption/Deposition

DRK-10 Drook 747 574.17 0.19 0.24 0.66 4/9 2.8 Eruption/Deposition

1

Table 2. Summary of U-Pb ages for key ash layers in the Conception Group and how these, and the time difference estimated between levels, has varied as a function of the different studies.

Bowring et al (2003) Pu et al. Benus Bowring et al vs. Pu et (2016) vs Dated (1996) (2003) Pu et al (2016) This study al (2016) this study ash 'U-Pb' 'U-Pb' 206Pb/23 206Pb/238 layer age ± age ± 8U age ± U age ± Δt ± Δt ± E 565 3 566.25 0.35 565.00 0.16 1.3 0.4 Pizza Disc 578.8 0.5 570.94 0.38 574.17 0.19 7.9 0.6 3.2 0.4 Basal Drook 582.1 0.5 579.88 0.44 2.2 0.7 Mall Bay 583.7 0.5 580.34 0.52 3.4 0.7 Δt betwee n Glacial 4.9 Myr 0.7 9.4 Myr 0.6 6.2 Myr 0.6 and Pizza Disc

2

SUPPLEMENTARY INFORMATION 1 (SI1): SAMPLED TUFFITES

FIGURE S1. Field locality photographs for the sampled tuffites within MPER. A: DRK-10 above the Pizza Disc surface, Pigeon Cove, Drook Fm. B: DRK-1, near Drook, in the lower Briscal Fm. C: BRS-1, above the Brasier Surface in the Briscal Fm. D: MP-14 above the ‘E’ Surface, Mistaken Point, Mistaken Point Fm. E: LC-1 above the ‘Pizzeria’, Trepassey Fm. F: SH-2, Fermeuse Fm. at Shingle Head.

FIGURE S2. Slabbed and polished sample of the DRK-10 tuffite. A: True colour scan. B: False colour image to emphasise internal structures within the unit. Scale bar is 1 cm. Sampled housed in the Oxford University Museum of Natural History, accession number OUM XXXXX.

FIGURE S3. Slabbed and polished sample of the DRK-1 tuffite. A: True colour scan. B: False colour image to emphasise internal structures within the unit. Scale bar is 1 cm. Sampled housed in the Oxford University Museum of Natural History, accession number OUM XXXXX.

FIGURE S4. Slabbed and polished sample of the MP-14 tuffite. A: True colour scan. B: False colour image to emphasise internal structures within the unit. Scale bar is 1 cm. Sampled housed in the Oxford University Museum of Natural History, accession number OUM XXXXX.

FIGURE S5. Slabbed and polished sample of the LC-1 tuffite. A: True colour scan. B: False colour image to emphasise internal structures within the unit. Scale bar is 1 cm. Sampled housed in the Oxford University Museum of Natural History, accession number OUM XXXXX.

FIGURE S6. True colour image of a slabbed and polished sample of the SH-2 tuffite. The top section of the slab has been stained for carbonate using Alizarin Red-S and Potassium Ferricyanide. Scale bar is 1 cm. Sampled housed in the Oxford University Museum of Natural History, accession number OUM XXXXX.

SUPPLEMENTARY INFORMATION 2 (SI2): Information used in compiling macrofossil stratigraphic ranges

The occurrence of fossils on bedding planes within MPER was documented over the course of multiple years by AGL. Field notes on the presence of individual taxa were cross-checked against photographic records of each surface, and only taxa that could be confidently identified were included in this study. Information on relative abundance of taxa on individual surfaces was not collected for all surfaces, and therefore is not included here. Since the weather and lighting conditions under which a surface is viewed can substantially impact an observer’s ability to recognise fossils, we endeavoured to search for specimens in the MPER at least twice over the period of study. However, we know that there are some previously documented levels at which we did not observe fossils, and so we accept that this compilation is not 100% complete. Every effort was made to access and assess all available bedding plane surfaces where it was safe to do so, but certain sections of the stratigraphy (notably in the middle of the Mistaken Point

Formation, and in the upper Trepassey Formation) were too inaccessible or poorly exposed for data to be gathered.

Taxa were identified to species level wherever possible. Specimens of Primocandelabrum in

Newfoundland have historically only been divided into Primocandelabrum hiemaloranum

(showing a clear Hiemalora-type holdfast structure), and Primocandelabrum sp. This latter grouping could include specimens of P. boyntoni, P. aethelflaedia, and P. aethelwynnia documented from Charnwood Forest, UK (Kenchington et al., 2017), but since the

Newfoundland taxa are yet to be subjected to detailed morphological analysis, we have not distinguished between those taxa in this study. We recognised a number of undocumented taxa or ancilliary impressions occurring as rare components of the palaeocommunities, but apart from filaments (see Liu and Dunn, 2020) and the ‘string organism’, we have not included these within the main figures. Lobate discs, previously noted as distinct impressions (Clapham et al., 2003), have been grouped with ivesheadiomorphs in this study, although we recognise that they may be discrete structures.

Lobate discs were only identified at two horizons within MPER, on the ‘E’ and ‘G’ surfaces.

In addition to our primary field surveys, we also collated fossil occurrence data from the available literature (see the following list of publications). Data from publications were only included if we could be confident of the position of the studied horizon within our stratigraphic column, and if we were confident that the fossil would have been correctly identified. In some instances a paper mentions the presence of a taxon, but because we couldn’t verify precisely which surface was being referred to, those occurrences have not been included (e.g. some

Charnia and Trepassia in Narbonne and Gehling 2003; some Vinlandia and Trepassia in

Laflamme et al., 2007; and some Ivesheadiomorphs in Laflamme et al., 2012). We were also unable to include data from several field guides in which fossil-bearing surfaces are documented, but assemblage composition is not presented (e.g. Narbonne et al., 2005). The presence of

Arborea arborea within MPER follows synonymisation of Charniodiscus arboreus within that taxon by Laflamme et al. (2018).

References used in compiling the stratigraphic ranges, or cited in this section

Anderson, M.M., and Conway Morris, S., 1982, A review, with descriptions of four unusual

forms, of the soft-bodied fauna of the Conception and St. John's Groups (Late Precambrian), Avalon Peninsula, Newfoundland: Proceedings of the third North American

paleontological convention, v. 1, p. 1–8.

Bamforth, E.L., and Narbonne, G.M., 2009, New Ediacaran rangeomorphs from Mistaken Point,

Newfoundland, Canada: Journal of Paleontology, v. 83, p. 897–913.

Bamforth, E.L., Narbonne, G.M., and Anderson, M.M., 2008, Growth and ecology of a multi-

branched Ediacaran rangeomorph from the Mistaken Point assemblage, Newfoundland:

Journal of Paleontology, v. 82, p. 763–777.

Brasier, M.D., and Antcliffe, J.B., 2009, Evolutionary relationships within the Avalonian

Ediacara biota: new insights from laser analysis: Journal of the Geological Society, v. 166,

p. 363–384.

Brasier, M.D., Antcliffe, J.B., and Liu, A.G., 2012, The architecture of Ediacaran fronds:

Palaeontology, v. 55, p. 1105–1124.

Clapham, M.E., Narbonne, G.M., and Gehling, J.G., 2003, Paleoecology of the oldest known

animal communities: Ediacaran assemblages at Mistaken Point, Newfoundland:

Paleobiology, v. 29, p. 527–544.

Darroch, S.A., Laflamme, M., and Wagner, P.J., 2018, High ecological complexity in benthic

Ediacaran communities: Nature Ecology & Evolution, v. 2, p. 1541–1547.

Dunn, F.S., Wilby, P.R., Kenchington, C.G., Grazhdankin, D.V., Donoghue, P.C., and Liu, A.G.,

2019, Anatomy of the Ediacaran rangeomorph Charnia masoni: Papers in Palaeontology,

v. 5, p. 157–176. Flude, L.I., and Narbonne, G.M., 2008, Taphonomy and ontogeny of a multibranched Ediacaran

fossil: Bradgatia from the Avalon Peninsula of Newfoundland: Canadian Journal of Earth

Sciences, v. 45, p. 1095–1109.

Gehling, J.G., and Narbonne, G.M., 2007, Spindle-shaped Ediacara fossils from the Mistaken

Point assemblage, Avalon zone, Newfoundland: Canadian Journal of Earth Sciences, v. 44,

p. 367–387.

Hofmann, H.J., O'Brien, S.J., and King, A.F., 2008, Ediacaran biota on bonavista peninsula,

Newfoundland, Canada: Journal of Paleontology, v. 82, p. 1–36.

Kenchington, C.G., and Wilby, P.R., 2017, Rangeomorph classification schemes and intra-

specific variation: are all characters created equal?: Geological Society, London, Special

Publications, v. 448, p. 221-250.

Laflamme, M., and Narbonne, G.M., 2008, Competition in a Precambrian world: palaeoecology

of Ediacaran fronds: Geology Today, v. 24, p. 182–187.

Laflamme, M., Narbonne, G.M., and Anderson, M.M., 2004, Morphometric analysis of the

Ediacaran frond Charniodiscus from the Mistaken Point Formation, Newfoundland:

Journal of Paleontology, v. 78, p. 827–837.

Laflamme, M., Narbonne, G.M., Greentree, C., and Anderson, M.M., 2007, Morphology and

taphonomy of an Ediacaran frond: Charnia from the Avalon Peninsula of Newfoundland:

Geological Society, London, Special Publications, v. 286, p. 237–257. Laflamme, M., Flude, L.I., and Narbonne, G.M., 2012, Ecological tiering and the evolution of a

stem: the oldest stemmed frond from the Ediacaran of Newfoundland, Canada: Journal of

Paleontology, v. 86, p. 193–200.

Laflamme, M., Gehling, J.G., and Droser, M.L., 2018, Deconstructing an Ediacaran frond: three-

dimensional preservation of Arborea from Ediacara, South Australia: Journal of

Paleontology, v. 92, p. 323–335.

Landing, E., Narbonne, G.M., Myrow, P., Benus, A.P., and Anderson, M.M., 1988, Faunas and

depositional environments of the Upper Precambrian through Lower Cambrian,

southeastern Newfoundland: New York State Museum Bulletin, v. 463, p. 8–52.

Liu, A.G., and Matthews, J.J., 2017, Great Canadian Lagerstätten 6. Mistaken Point Ecological

Reserve, Southeast Newfoundland: Geoscience Canada, v. 44, p. 63–76.

Liu, A.G., and Dunn, F.S., 2020, Filamentous connections between Ediacaran fronds: Current

Biology, v. 30, p. 1322–1328.

Liu, A.G., Mcllroy, D., and Brasier, M.D., 2010, First evidence for locomotion in the Ediacara

biota from the 565 Ma Mistaken Point Formation, Newfoundland: Geology, v. 38, p. 123–

126.

Liu, A.G., McIlroy, D., Antcliffe, J.B., and Brasier, M.D., 2011, Effaced preservation in the

Ediacara biota and its implications for the early macrofossil record: Palaeontology, v. 54,

p. 607–630. Liu, A.G., McIlroy, D., Matthews, J.J., and Brasier, M.D., 2012, A new assemblage of juvenile

Ediacaran fronds from the Drook Formation, Newfoundland: Journal of the Geological

Society, v. 169, p. 395–403.

Liu, A.G., Kenchington, C.G., and Mitchell, E.G., 2015, Remarkable insights into the

paleoecology of the Avalonian Ediacaran macrobiota: Gondwana Research, v. 27, p. 1355–

1380.

Mason, S.J., and Narbonne, G.M., 2016, Two new Ediacaran small fronds from Mistaken Point,

Newfoundland: Journal of Paleontology, v. 90, p. 183–194.

Matthews, J.J., Liu, A.G., and McIlroy, D., 2017, Post-fossilization processes and their

implications for understanding Ediacaran macrofossil assemblages: Geological Society,

London, Special Publications, v. 448, p. 251–269.

Mitchell, E.G., and Kenchington, C.G., 2018, The utility of height for the Ediacaran organisms

of Mistaken Point: Nature Ecology and Evolution, v. 2, p. 1218–1222.

Narbonne, G.M., and Gehling, J.G., 2003, Life after snowball: the oldest complex Ediacaran

fossils: Geology, v. 31, p. 27–30.

Narbonne, G.M., Dalrymple, R.W., Laflamme, M., Gehling, J.G., and Boyce, W.D., 2005, Life

after snowball: Mistaken Point Biota and the Cambrian of the Avalon: North American

paleontological convention field trip guidebook, 98 pp.

Narbonne, G.M., Laflamme, M., Greentree, C., and Trusler, P., 2009, Reconstructing a lost

world: Ediacaran rangeomorphs from Spaniard's Bay, Newfoundland: Journal of

Paleontology, v. 83, p. 503–523. SUPPLEMENTARY INFORMATION 3 (SI3): U-Pb CA-ID-TIMS methods

Zircons were separated from each sample using conventional mineral separation techniques.

They were pretreated by a chemical abrasion technique after Mattinson (2005), which involved thermal annealing in a furnace at 900°C for 60 hours, followed by partial dissolution in 29M HF at 180°C in high-pressure vessels for 12 hours. The chemically abraded grains were fluxed in/rinsed with several hundred microliters of dilute HNO3 and 6M HCl to remove the leachates.

All zircon fragments were spiked with the EARTHTIME ET535 (or ET2535) mixed 205Pb-

233U-235U (±202Pb) isotopic tracer(s) (Condon et al. 2015; McLean et al. 2015) prior to complete dissolution in 29M HF at 220°C for 60 hours and subsequent Pb and U purification by an HCl-based anion-exchange column chemistry (Krogh, 1973). Pb and U were loaded together onto single outgassed Re filaments along with a silica-gel emitter solution and their isotopic ratios were measured on a Thermo-Electron Triton instrument equipped with an ion- counting SEM system. Pb was measured in dynamic mode on a MassCom secondary electron multiplier (SEM) and was corrected for mass bias using a fractionation factor of 0.14 ± 0.02

%/amu (1σ) for samples prepared using the ET535 spike, and in real-time, based on measured

202Pb/205Pb ratios, for samples spiked with the ET2535 tracer. U isotopes were measured as dioxide ions either in static mode, on Faraday detectors equipped with 1012 Ω resistors for intensities greater than 4 mV, or in dynamic mode for lower intensities. U mass fractionation was calculated in real-time based on the isotopic composition of the ET535 and ET2535 tracers. Oxide correction was based on an 18O/16O ratio of 0.00205 ± 0.00004, and the sample

238U/235U ratio was assumed 137.818 ± 0.045 (Hiess et al., 2012).

Data reduction, calculation of dates and propagation of uncertainties used the Tripoli and

ET_Redux applications and algorithms (McLean et al. 2011).

Figure S7. Conventional U-Pb concordia plots for the six samples analysed in this study. Blue ellipses are those analyses used in the weighted mean calculations, dashed ellipses are interpreted as reflecting post-depositional Pb-loss, other older analyses reflecting ‘inheritance’.

Figure S8. U-Pb Concordia plot for U-Pb (zircon) data from the ‘E’ Surface ash layer, sample MP-14 (this study) and sample MPMP33.56 (Pu et al., 2016).

Figure S9. U-Pb Concordia plot for U-Pb (zircon) data from the ‘Pizza Disc’ ash layer, sample DRK-10 (this study) and sample Drook-2 (Pu et al., 2016). Also plotted is the U-Pb (zircon) data from sample DRK-1 (this study) that lie ~43 metres up section of the ‘Pizza Disc’ ash layer which we interpret as being similar in age to the zircon from Drook-2.

Figure S10. Extended age-depth model the Conception and St John’s Groups using the approach outlined in the manuscript using dates from the Drook, Briscal and Mistaken Point, Trepassey and Fermeuse Formations (this study), combined with data from the base of the Drook Formation (NoP-0.9) from Pu et al (2016). This age model combines dates from the measured section at MPER, importing the basal Drook Formation age from St Marys Bay (~70 km away) and as such the position of the NoP-0.9 date in the MPER section is not known. This age model assumes that the measured thickness of the Drook Formation, where the base of the Formation is not exposed, in the MPER is a minimum thickness and as such the NoP-0.9 date is treated as a maximum age constraint.

SUPPLEMENTARY INFORMATION 4 (SI4): U-Pb Compositional and Isotopic Data

Dates (Ma) Composition Isotopic Ratios 206Pb/ 207Pb/ 206Pb/ 207Pb/ Sample 238U ±2σ 207Pb/ ±2σ 206Pb ±2σ Corr. mass Th/ Pb* Pbc Pb*/ 206Pb/ 208Pb/ 238U 207Pb/ 206Pb Fraction a abs 235U b abs a abs coef. % disc c U(pg) U d (pg) e (pg) f Pbc g 204Pb h 206Pb i ia ±2σ % 235U i ±2σ % ia ±2σ %

DRK-10 z12 573.36 0.69 573.13 0.90 572.23 3.43 0.64 -0.16 114.1 1.65 14.4 0.17 86.7 4027.4 0.511 0.09302 0.126 0.7585 0.21 0.0592 0.15 z2 574.11 0.26 573.90 0.99 573.07 4.76 0.24 -0.14 224.0 1.36 26.6 0.59 45.2 2233.7 0.423 0.09314 0.047 0.7598 0.23 0.0592 0.22 z7 574.35 2.56 574.40 2.39 574.59 3.41 0.96 0.09 204.5 1.31 24.1 0.35 69.2 3445.5 0.408 0.09319 0.466 0.7607 0.55 0.0592 0.15 z10 574.43 0.32 574.23 1.01 573.43 4.39 0.57 -0.13 272.9 1.37 32.5 0.62 52.7 2598.8 0.425 0.09320 0.059 0.7604 0.23 0.0592 0.20 z3 575.54 0.27 575.45 0.85 575.08 3.78 0.50 -0.04 180.1 1.41 21.7 0.34 63.4 3092.5 0.439 0.09339 0.049 0.7625 0.19 0.0592 0.17 z8 575.75 0.42 574.69 1.91 570.53 9.35 0.16 -0.87 231.5 1.42 28.0 1.15 24.2 1192.7 0.441 0.09342 0.076 0.7612 0.44 0.0591 0.43 z4 576.48 1.11 575.91 2.22 573.66 10.36 0.34 -0.46 110.4 1.77 14.3 0.54 26.4 1207.9 0.550 0.09355 0.201 0.7633 0.51 0.0592 0.48 z1 576.65 1.27 575.92 1.15 573.05 2.64 0.89 -0.58 231.4 1.41 27.9 0.29 95.0 4625.1 0.439 0.09358 0.231 0.7633 0.26 0.0592 0.12 z9 577.38 0.67 576.28 1.33 571.94 5.71 0.50 -0.90 147.8 1.24 17.2 0.46 37.8 1922.6 0.385 0.09370 0.122 0.7639 0.30 0.0592 0.26

DRK-1 z20A 571.02 0.31 571.38 1.17 572.81 5.55 0.33 0.37 126.8 0.77 13.1 0.31 43.0 2426.0 0.240 0.09262 0.057 0.7554 0.27 0.0592 0.25 z15 571.12 0.78 568.33 3.62 557.15 17.57 0.27 -2.46 64.2 1.19 7.3 0.60 12.2 638.3 0.370 0.09264 0.143 0.7502 0.83 0.0588 0.80 z19 571.31 0.37 572.27 0.64 576.07 2.48 0.65 0.89 910.1 0.69 92.5 0.70 132.1 7566.4 0.215 0.09267 0.068 0.7570 0.15 0.0593 0.11 z13 571.34 0.35 570.32 0.96 566.24 4.52 0.32 -0.84 299.3 0.74 30.8 0.62 49.5 2808.6 0.231 0.09268 0.064 0.7536 0.22 0.0590 0.21 z7 571.49 1.20 574.48 6.91 586.32 33.56 0.20 2.60 189.0 0.55 18.5 3.69 5.0 315.1 0.170 0.09270 0.220 0.7608 1.57 0.0596 1.55 z8 571.76 0.58 572.48 2.00 575.37 9.36 0.35 0.67 125.9 1.34 14.8 0.63 23.6 1180.9 0.415 0.09275 0.105 0.7574 0.46 0.0593 0.43 z1 571.76 0.35 571.74 0.71 571.66 2.91 0.60 0.05 770.2 0.68 78.1 1.04 74.8 4301.9 0.212 0.09275 0.063 0.7561 0.16 0.0592 0.13 z11 571.98 1.11 573.53 6.15 579.64 29.82 0.22 1.38 65.1 0.99 7.1 1.11 6.4 359.6 0.308 0.09278 0.202 0.7592 1.40 0.0594 1.37 z14 572.03 0.34 564.63 2.52 534.95 14.53 -1.32 -6.87 122.7 1.04 13.5 0.68 19.9 1066.7 0.323 0.09279 0.063 0.7438 0.58 0.0582 0.66 z18 572.04 0.23 572.06 0.65 572.12 2.86 0.51 0.07 157.6 0.88 16.8 0.21 79.5 4357.7 0.273 0.09279 0.042 0.7566 0.15 0.0592 0.13 z18A 572.34 0.51 573.85 2.66 579.81 12.96 0.18 1.34 45.2 0.98 4.9 0.29 17.0 924.3 0.303 0.09285 0.093 0.7597 0.61 0.0594 0.60 z4 572.44 1.14 572.26 4.50 571.52 19.29 0.74 -0.09 459.4 0.63 46.1 2.25 20.4 1202.8 0.197 0.09286 0.208 0.7570 1.03 0.0591 0.89 z16 572.60 0.43 572.25 1.54 570.87 7.41 0.26 -0.23 149.0 0.55 14.7 0.56 26.1 1560.6 0.172 0.09289 0.079 0.7569 0.35 0.0591 0.34 z17 572.64 0.40 572.13 1.67 570.10 7.82 0.41 -0.38 108.9 0.86 11.6 0.47 24.8 1377.8 0.267 0.09290 0.073 0.7567 0.38 0.0591 0.36 z3 574.11 0.54 573.75 1.97 572.34 9.25 0.36 -0.25 195.6 0.73 20.1 0.96 20.9 1201.3 0.226 0.09314 0.099 0.7596 0.45 0.0592 0.42 z5 575.03 0.83 574.69 2.35 573.32 10.74 0.41 -0.26 167.9 1.45 20.4 0.99 20.5 1006.4 0.449 0.09330 0.150 0.7612 0.54 0.0592 0.49 z9 577.03 0.61 577.91 1.04 581.37 4.16 0.60 0.81 551.6 0.62 55.6 1.03 53.9 3153.8 0.191 0.09364 0.110 0.7668 0.24 0.0594 0.19 z2 579.80 1.56 581.09 9.42 586.12 45.40 0.20 1.12 38.0 1.44 4.6 1.01 4.6 240.6 0.446 0.09411 0.281 0.7723 2.13 0.0595 2.09 z6 580.06 0.80 578.04 2.39 570.09 11.03 0.37 -1.70 93.0 1.23 10.9 0.52 20.8 1067.7 0.383 0.09415 0.145 0.7670 0.54 0.0591 0.51

BRS-1 z3 566.33 0.29 566.34 0.55 566.39 2.45 0.48 0.07 337.3 0.94 36.0 0.19 190.5 10279.9 0.292 0.09183 0.053 0.7468 0.13 0.0590 0.11 z6 567.03 0.77 567.13 3.96 567.55 19.42 0.21 0.14 86.6 1.39 10.2 0.92 11.1 559.8 0.432 0.09194 0.141 0.7481 0.91 0.0590 0.89 z5 567.33 0.55 568.37 2.59 572.53 12.67 0.20 0.96 71.4 0.98 7.7 0.48 16.0 870.9 0.304 0.09200 0.101 0.7502 0.59 0.0592 0.58 z9 567.51 0.34 567.20 0.83 565.94 3.92 0.34 -0.21 221.0 0.77 22.8 0.43 53.3 3002.9 0.241 0.09203 0.062 0.7482 0.19 0.0590 0.18 z4 567.96 0.50 566.74 2.41 561.85 11.81 0.22 -1.02 54.4 0.84 5.7 0.32 18.0 1008.7 0.260 0.09210 0.093 0.7474 0.55 0.0589 0.54 z2 568.02 0.49 568.10 1.15 568.39 5.32 0.38 0.13 137.9 0.83 14.4 0.39 36.6 2040.0 0.258 0.09211 0.090 0.7498 0.26 0.0591 0.24 z8 569.60 0.88 571.65 2.96 579.78 14.16 0.27 1.81 81.8 0.88 8.7 0.65 13.4 749.1 0.275 0.09238 0.162 0.7559 0.68 0.0594 0.65 z7 570.63 0.54 572.39 2.85 579.39 13.89 0.19 1.57 61.6 0.88 6.5 0.48 13.7 764.3 0.272 0.09256 0.098 0.7572 0.65 0.0594 0.64

MP-14 z16 563.81 0.62 564.38 1.29 566.67 5.24 0.64 0.57 78.7 0.63 7.8 0.20 38.1 2227.9 0.197 0.09140 0.115 0.7434 0.30 0.0590 0.24 z15 564.74 0.50 565.76 1.26 569.85 5.58 0.52 0.96 91.7 0.65 9.1 0.20 45.2 2630.1 0.202 0.09156 0.093 0.7458 0.29 0.0591 0.25 z2 564.95 0.21 565.31 0.74 566.75 3.66 0.19 0.38 144.4 0.88 15.2 0.26 59.4 3256.7 0.274 0.09159 0.039 0.7450 0.17 0.0590 0.16 z12 565.10 0.37 565.50 1.60 567.11 7.54 0.41 0.42 274.7 0.54 26.6 1.14 23.3 1399.5 0.169 0.09162 0.068 0.7453 0.37 0.0590 0.34 z4 565.37 0.53 564.39 2.98 560.43 14.60 0.25 -0.81 174.3 0.71 17.6 1.10 16.0 930.4 0.220 0.09166 0.097 0.7434 0.69 0.0588 0.67 z1 566.05 0.31 566.21 0.73 566.87 3.40 0.37 0.22 198.6 0.58 19.4 0.30 64.7 3823.3 0.179 0.09178 0.057 0.7465 0.17 0.0590 0.15 z14 566.18 0.33 566.91 1.59 569.84 7.82 0.19 0.72 117.5 0.49 11.2 0.50 22.6 1378.2 0.151 0.09180 0.061 0.7477 0.37 0.0591 0.36 z13 566.26 0.34 566.42 0.90 567.06 3.92 0.56 0.21 154.8 0.59 15.2 0.28 54.2 3195.0 0.184 0.09181 0.063 0.7469 0.21 0.0590 0.18 z9 566.96 0.42 566.78 1.88 566.07 9.12 0.27 -0.09 189.5 0.68 19.0 0.94 20.3 1178.8 0.212 0.09193 0.078 0.7475 0.43 0.0590 0.42 z5 567.19 1.01 566.50 1.40 563.74 4.79 0.75 -0.54 169.1 0.55 16.5 0.21 77.8 4619.7 0.172 0.09197 0.186 0.7470 0.32 0.0589 0.22 z6 567.48 0.32 567.24 0.67 566.26 3.21 0.31 -0.15 816.3 0.78 84.2 1.14 73.7 4135.5 0.243 0.09202 0.058 0.7483 0.15 0.0590 0.14

LC-1 z6B 564.68 1.23 565.22 1.62 567.40 6.44 0.61 0.55 918.5 0.55 88.9 3.30 27.0 1615.8 0.170 0.09155 0.228 0.7448 0.37 0.0590 0.29 z10 564.72 0.73 564.69 0.72 564.57 2.19 0.80 0.04 1805.2 0.62 178.0 0.92 193.2 11248.5 0.193 0.09155 0.136 0.7439 0.17 0.0590 0.10 z6A 565.53 0.61 565.77 0.80 566.75 3.10 0.64 0.29 757.3 0.58 74.1 1.24 59.7 3524.7 0.180 0.09169 0.112 0.7458 0.19 0.0590 0.14 z8 565.92 0.31 565.73 0.42 564.99 1.56 0.68 -0.10 1279.2 0.66 127.7 0.62 207.0 11937.3 0.205 0.09176 0.057 0.7457 0.10 0.0590 0.06 z2 565.92 0.19 565.92 0.42 565.91 1.76 0.62 0.07 1058.8 0.58 103.7 0.92 112.1 6596.7 0.181 0.09176 0.035 0.7460 0.10 0.0590 0.07 z3 566.30 0.29 566.24 0.47 566.00 1.90 0.61 0.01 2229.1 0.65 222.1 1.81 122.6 7094.2 0.202 0.09182 0.054 0.7466 0.11 0.0590 0.08 z5 566.32 0.22 566.38 0.63 566.63 2.99 0.31 0.12 1286.9 0.61 126.8 2.05 61.9 3628.4 0.188 0.09183 0.040 0.7468 0.14 0.0590 0.13 z11 566.48 0.30 566.28 0.41 565.48 1.49 0.69 -0.11 1599.5 0.62 158.4 0.74 212.8 12376.7 0.194 0.09185 0.056 0.7467 0.09 0.0590 0.06 z7 566.64 0.33 566.39 0.39 565.37 1.47 0.66 -0.16 615.7 0.69 62.0 0.34 181.2 10368.5 0.215 0.09188 0.060 0.7468 0.09 0.0590 0.06 z12 567.24 0.43 566.93 0.56 565.66 2.19 0.62 -0.21 1228.8 0.56 119.8 1.25 95.6 5662.5 0.173 0.09198 0.078 0.7478 0.13 0.0590 0.10 z13 567.41 2.98 567.26 2.47 566.64 3.96 0.96 -0.07 2474.0 0.59 243.6 2.51 97.1 5700.1 0.185 0.09201 0.549 0.7483 0.57 0.0590 0.18

SH-2 z15 563.67 0.43 563.51 0.22 562.84 1.74 0.32 -0.08 464.9 0.61 45.6 0.21 219.1 12786.4 0.190 0.09138 0.080 0.7419 0.05 0.0589 0.07 z16 563.95 0.70 563.64 0.84 562.40 3.12 0.68 -0.20 278.2 0.51 26.7 0.24 110.4 6614.3 0.160 0.09142 0.130 0.7421 0.19 0.0589 0.14 z9 564.03 0.63 564.02 0.72 563.95 2.56 0.71 0.06 496.4 0.55 48.0 0.38 125.3 7431.2 0.171 0.09144 0.116 0.7428 0.17 0.0589 0.11 z14 564.24 0.73 563.75 0.84 561.76 3.50 0.58 -0.37 495.3 0.55 48.0 0.61 78.8 4677.2 0.172 0.09147 0.135 0.7423 0.19 0.0589 0.16 z19 564.31 0.39 564.40 0.46 564.79 1.63 0.71 0.16 612.9 0.50 58.6 0.21 283.7 17022.7 0.155 0.09148 0.071 0.7434 0.11 0.0590 0.07 z12 564.39 0.40 564.32 0.63 564.03 2.66 0.56 0.01 226.0 0.48 21.5 0.23 92.6 5594.3 0.150 0.09150 0.074 0.7433 0.15 0.0589 0.12 z3 564.66 0.22 564.68 0.42 564.72 1.64 0.69 0.08 652.5 0.54 63.0 0.43 146.9 8738.5 0.167 0.09154 0.040 0.7439 0.10 0.0590 0.07 z5 564.85 0.21 564.70 0.57 564.13 2.56 0.48 -0.05 813.0 0.44 76.5 1.04 73.5 4493.2 0.136 0.09158 0.039 0.7439 0.13 0.0589 0.11 z1 565.55 0.19 565.55 0.38 565.54 1.65 0.53 0.07 812.2 0.55 78.9 0.57 138.4 8199.2 0.172 0.09169 0.035 0.7454 0.09 0.0590 0.07 z2 568.16 0.56 567.65 0.68 565.58 2.50 0.68 -0.39 687.8 0.57 67.4 0.77 88.1 5205.2 0.178 0.09214 0.103 0.7490 0.16 0.0590 0.11 z7 569.01 0.68 568.15 0.71 564.74 2.23 0.78 -0.68 504.8 0.47 48.3 0.48 100.3 6079.4 0.146 0.09228 0.125 0.7499 0.16 0.0590 0.10

a Corrected for initial Th/U disequilibrium using radiogenic 208Pb and Th/U[magma] = 2.8 ± 1.0 (2σ). b Isotopic dates calculated using λ238 = 1.55125E-10 (Jaffey et al. 1971) and λ235 = 9.8485E-10 (Jaffey et al. 1971). c % discordance = 100 - (100 * (206Pb/238U date) / (207Pb/206Pb date)) d Th contents calculated from radiogenic 208Pb and 230Th-corrected 206Pb/238U date of the sample, assuming concordance between U-Pb Th-Pb systems. e Total mass of radiogenic Pb. f Total mass of common Pb. g Ratio of radiogenic Pb (including 208Pb) to common Pb. h Measured ratio corrected for fractionation and spike contribution only. i Measured ratios corrected for fractionation, tracer and blank. All common Pb assumed to be laboratory blank. Total procedural blank 0.05 ± 0.02 (2σ) pg for U. Blank isotopic composition: 206Pb/204Pb = 18.10 ± 0.27, 207Pb/204Pb =15.55 ± 0.14, 208Pb/204Pb = 37.82 ± 0.41 (1σ).

SUPPLEMENTARY INFORMATION 5 (SI5) A Chronostratigraphic Framework for the Rise of the Ediacaran Macrobiota: New Constraints Jack Matthews (University of Oxford), Alexander Liu (University of Cambridge), Chuan Yang Dataset of stratigraphic occurences of published Ediacaran macrofossils from Mistaken Poin

FOSSILIFEROUS SURFACES

Metres from Formation (as described Base of Fm (see Metres through Site/Surface herein) notes) Section

CR2 Fermeuse 283 1893 MP12 + 5m Fermeuse 80 1690 SH-2 TUFFITE SAMPLE Fermeuse 75 1685 MP 12 (Shingle Head) Fermeuse 75 1685 MP20 Fermeuse 45 1655 Fermeuse/Trepassey boundary 1610 MP17 Trepassey 53 1423 LC-1 TUFFITE SAMPLE Trepassey 43 1413 MP 9 Trepassey 43 1413 MP13 Trepassey 31 1401 MP 8 Trepassey 15 1385 MP North Trepassey 7.5 1377.5 Trepassey/Mistaken Point boundary 1370 MP 4 + 1m Mistaken Point 286 1366 MP 4 Mistaken Point 285 1365 MP 4 - 1.4m Mistaken Point 283.6 1363.6 MP 3 Mistaken Point 273.67 1353.67 MP J +2m Mistaken Point 272.67 1352.67 MP 6 Mistaken Point 272.17 1352.17 MP18 Mistaken Point 272 1352 MP3 - 2.5m Mistaken Point 271.17 1351.17 MP J Mistaken Point 270.67 1350.67 MP 10 (MP I) Mistaken Point 268.55 1348.55 MP15 Mistaken Point 267 1347 MP 7 Mistaken Point 267 1347 MP16 Mistaken Point 262 1342 MP H Mistaken Point 260.58 1340.58 MP G Mistaken Point 244.8 1324.8 MP G (WC) -10cm Mistaken Point 244.7 1324.7 MP2 F +1.1m Mistaken Point 237.88 1317.88 MP2 F Mistaken Point 236.78 1316.78 MP-14 TUFFITE SAMPLE Mistaken Point 235 1315 MP E Mistaken Point 235 1315 WC Between D and E Mistaken Point 234.28 1314.28 CR1 D + 1m Mistaken Point 233.56 1313.56 MP D Mistaken Point 232.56 1312.56 MP2 D -2m (28.5m level in Lan Mistaken Point 230.56 1310.56 MP C-D Mistaken Point 223.055 1303.055 MP C Mistaken Point 213.55 1293.55 MP B Mistaken Point 212.81 1292.81 MP B - 55cm Mistaken Point 209.81 1289.81 LMP + 1 m Mistaken Point 56 1136 LMP Mistaken Point 55 1135 Mistaken Point/Briscal boundary 1080 CR4 Briscal 296 1066 BR9 Briscal 255 1025 SWIM Briscal 250 1020 BR2 Briscal 224 994 BC+3m Briscal 213 983 BR3 + 16cm Briscal 210.16 980.16 Bristy C (X-ray) Briscal 210 980 BR3 Briscal 210 980 BR3 - 1.5m Briscal 208.5 978.5 PCS2 + 3m Briscal 205 975 PCS2 Briscal 202 972 BR4a Briscal 178.5 948.5 BR4b Briscal 178.5 948.5 BR4c Briscal 178.5 948.5 BR5 + 6m Briscal 116 886 BRS-1 TUFFITE SAMPLE Briscal 110 880 BR5 Briscal 110 880 BR5 - 60 cm Briscal 109.4 879.4 BR5 - 2.6m Briscal 107.4 877.4 BR5 - 9.6m (arches_ Briscal 100.4 870.4 BR5 - 10.2 m Briscal 99.8 869.8 BR6 Briscal 34 804 DRK1T Briscal 33 803 BR6 - 5.7m Briscal 28.3 798.3 BR6 - 7m Briscal 27 797 BR7 + 2m Briscal 27 797 BR7 Briscal 25 795 CW 1 Briscal 22 792 DRK-1 TUFFITE SAMPLE Briscal 20 790 Briscal/Drook boundary 770 BR8 Drook 763 763 DRK2PC + 1m Drook 748 748 DRK-10 TUFFITE SAMPLE Drook 747 747 DRK2PC Drook 747 747 DRK2PC - 31cm Drook 746.69 746.69 DRK2PC -3m Drook 744 744 CANT + 70cm Drook 711.7 711.7 CANT Drook 711 711 CANT -11m Drook 700 700 CANT -17m Drook 694 694 DRK3CW Drook 691 691 DRK 4 Drook 623 623 NOTES Taxon Range: The presence of a taxon on a particular surface is indicated by t Age Model - Ages in Red: N.B. Ages in red have been extrapolated outside the range of th Age Model - Ages in Orange: N.B Ages in orange have been calculated using a stratigraphic a Metres from Base of Fm: As the base of the Drook Formation is not exposed in MPER, all Metres through Section: The stratigraphic position of surfaces was calculated from a mix Formation Boundaries These are highlighted in yellow Position of Sampled Tuffites These are highlighted in Green (Note that the age model age is Fossil Identification All taxonomic occurences in this dataset are based on fossil ide s from Mistaken Point Ecological Reserve, Newfoundland (British Geological Survey), Duncan McIlroy (Memorial University of Newfoundland), Bruce Levell (U t Ecological Reserve, Newfoundland

95% C.I. of age model 95% C.I. of age model Age of Surface in based on weighted mean based on weighted mean

Age Model 206Pb/238U dates (+) 206Pb/238U dates (-) Holdfast Hiemalora 1 2 562.6 N/A N/A 1893 563.4 N/A N/A 1690 563.4 0.6 0.6 563.4 0.6 0.6 1685 563.5 0.6 0.6 1655 563.7 0.6 0.6 564.6 0.4 0.4 1423 1423 564.6 0.4 0.4 564.6 0.4 0.4 1413 1413 564.7 0.3 0.4 1401 564.8 0.3 0.4 1385 1385 564.8 0.3 0.4 1377.5 1377.5 564.8 0.3 0.4 564.8 0.3 0.4 564.8 0.3 0.4 1365 564.8 0.3 0.4 1363.6 1363.6 564.9 0.3 0.4 1353.67 564.9 0.3 0.4 1352.67 564.9 0.3 0.4 1352.17 1352.17 564.9 0.3 0.4 1352 564.9 0.2 0.3 1351.17 564.9 0.2 0.3 1350.67 564.9 0.2 0.3 1348.55 564.9 0.2 0.3 1347 1347 564.9 0.2 0.3 1347 564.9 0.2 0.3 1342 1342 564.9 0.2 0.3 565.0 0.2 0.3 1324.8 565.0 0.2 0.2 1324.7 565.0 0.2 0.2 1317.88 565.0 0.2 0.2 1316.78 565.0 0.2 0.2 565.0 0.2 0.2 1315 1315 565.0 0.2 0.2 1314.28 565.0 0.2 0.2 565.0 0.2 0.2 1312.56 565.1 0.2 0.2 1310.56 565.1 0.3 0.2 1303.055 1303.055 565.2 0.4 0.3 1293.55 565.2 0.4 0.3 1292.81 565.2 0.4 0.3 566.2 0.7 0.7 1136 566.2 0.7 0.7 1135 1135 566.5 0.7 0.7 566.6 0.7 0.7 1066 566.9 0.7 0.7 1025 1025 566.9 0.7 0.7 1020 567.1 0.6 0.7 994 994 567.1 0.6 0.7 567.2 0.6 0.7 567.2 0.6 0.7 980 567.2 0.6 0.7 980 567.2 0.6 0.7 978.5 567.2 0.6 0.7 975 567.2 0.6 0.7 567.4 0.5 0.6 948.5 567.4 0.5 0.6 948.5 567.4 0.5 0.6 948.5 567.8 0.3 0.3 886 567.8 0.3 0.3 567.8 0.3 0.3 880 880 567.8 0.3 0.3 879.4 567.9 0.4 0.3 877.4 568.2 0.7 0.5 870.4 568.2 0.7 0.5 869.8 570.8 0.5 0.7 570.9 0.5 0.7 571.1 0.4 0.6 798.3 571.1 0.4 0.6 571.1 0.4 0.6 797 571.2 0.3 0.5 571.3 0.2 0.4 571.4 0.2 0.2 572.6 0.8 0.8 573.1 0.7 0.8 763 763 574.0 0.3 0.4 748 574.0 0.2 0.2 574.0 0.2 0.2 747 574.0 0.2 0.2 574.0 0.3 0.2 574.3 0.6 0.4 574.3 0.6 0.4 574.4 0.6 0.5 574.4 0.6 0.5 574.5 0.7 0.5 575.0 0.9 0.7

the stratigraphic position of that surface, expressed in the appropriate taxon column he original age model nd chronological constraint from outside this study, from the Gaskiers Fm l measurements for this Fm are taken from the lowest horizon within the Reserve xture of the use of geological cross-sections, and measured stratigraphic sections. In large parts of MP provided, not that yielded from the individual sample analyses themselves) ntification by AGL, for consistency of interpretation University of Oxford), and Daniel Condon (British Geological Survey) Trepassia wardae Vinlandia antecedens Charnia masoni Beothukis mistakensis Culmofrons plumosa Avalofractus abaculus Plumeropriscum hofmanni organism' String Frondophyllas grandis 3 4 5 6 7 8 9 10 11

1685

1413 1413 1413 1413

1385 1377.5

1352

1350.67 1348.55 1347 1347 1347 1342 1340.58 1324.8 1324.8 1324.8 1324.8 1324.8 1324.8

1315 1315 1315 1315 1315 1312.56 1312.56 1312.56

1303.055 1293.55

1135 1135 1135 1135 1135 1135 1135

994 983

980 980 980

972

880 880 880 880 880

877.4 870.4 870.4

804 803

795 792

747 747

711.7 711 700 694 691 ER, the succession cannot be directly logged due to access issues 1347 1315 12 Ostrich feather' 1352.17 1377.5 1685 1413 1352 1342 1315 13 Pectinifrons abyssalis 1348.55 1314.28 1324.8 1347 1315 14 Fractofusus misrai 1313.56 1347 1315 15 Fractofusus andersoni 1377.5 1385 1413 16 Primocandelabrum hiem. 1348.55 1350.67 1352.17 1340.58 1324.8 1413 1347 1352 1342 1315 17 Primocandelabrum sp. 1353.67 1348.55 1350.67 1352.17 1340.58 1324.8 1685 1413 1347 1342 1315 18 Bradgatia sp. 1353.67 1317.88 1377.5 1413 1315 19 Hapsidophyllas flexibilis 1340.58 1377.5 1324.8 1685 1413 1347 1352 1342 1315 20 Charniodiscus procerus 1312.56 1312.56 1312.56 1312.56 1312.56 1312.56

1303.055 1293.55 1293.55 1293.55 1292.81 1292.81 1292.81 1292.81 1289.81

1135 1135 1135

994 994

980.16 980 980

886

880 880 880 879.4 877.4 870.4

804 804 804

797

795 795

1350.67 1352.17 1377.5 1324.8 1413 1315 21 Charniodiscus spinosus 1377.5 1342 1385 22 Arborea arborea 1348.55 1353.67 1377.5 1324.8 1655 1685 1347 1352 1401 1366 23 Charniodiscus sp. 1377.5 1413 1342 1315 24 Thectardis avalonensis 1413 1315 25 Broccoliforma alta 1413 1352 1315 26 Hadryniscala avalonica 1324.8

27 Hadrynichorde catalinensis 1352.17 1655 1347 1385 1352 28 Filaments 1348.55 1351.17 1313.56 1377.5 1324.8 1685 1423 1347 1347 1385 1413 1401 1342 1352 1315 29 Ivesheadiomorphs 1312.56 1312.56 1312.56

1303.055 1293.55 1292.81

1136 1135 1135 1135 1135

1020 1020 994

980 980

972 972

886

880 880 880 880 880

870.4 870.4 869.8 804 803

797

795

748

747 747 747 747 746.69 744

711 711

694 691 623