New High‐Resolution Age Data from the Ediacaran–Cambrian Boundary

Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch

Year: 2019

New high-resolution age data from the Ediacaran-Cambrian boundary indicate rapid, ecologically driven onset of the Cambrian explosion

Linnemann, Ulf ; Ovtcharova, Maria ; Schaltegger, Urs ; Gärtner, Andreas ; Hautmann, Michael ; Geyer, Gerd ; Vickers-Rich, Patricia ; Rich, Tom ; Plessen, Birgit ; Hofmann, Mandy ; Zieger, Johannes ; Krause, Rita ; Kriesfeld, Les ; Smith, Jeff

Abstract: The replacement of the late Precambrian Ediacaran biota by morphologically disparate animals at the beginning of the Phanerozoic was a key event in the history of life on Earth, the mechanisms and the timescales of which are not entirely understood. A composite section in Namibia providing biostratigraphic and chemostratigraphic data bracketed by radiometric dating constrains the Ediacaran– Cambrian boundary to 538.6–538.8 Ma, more than 2 Ma younger than previously assumed. The U– Pb-CA-ID TIMS zircon ages demonstrate an ultrashort time frame for the LAD of the Ediacaran biota to the FAD of a complex, burrowing Phanerozoic biota represented by trace fossils to a 410 ka time window of 538.99±0.21 Ma to 538.58±0.19 Ma. The extremely short duration of the faunal transition from Ediacaran to Cambrian biota within less than 410 ka supports models of ecological cascades that followed the evolutionary breakthrough of increased mobility at the beginning of the Phanerozoic.

DOI: https://doi.org/10.1111/ter.12368

Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-158482 Journal Article Accepted Version

Originally published at: Linnemann, Ulf; Ovtcharova, Maria; Schaltegger, Urs; Gärtner, Andreas; Hautmann, Michael; Geyer, Gerd; Vickers-Rich, Patricia; Rich, Tom; Plessen, Birgit; Hofmann, Mandy; Zieger, Johannes; Krause, Rita; Kriesfeld, Les; Smith, Jeff (2019). New high-resolution age data from the Ediacaran-Cambrian boundary indicate rapid, ecologically driven onset of the Cambrian explosion. Terra Nova, 31(1):49-58. DOI: https://doi.org/10.1111/ter.12368 Ulf Linnemann driven onset of the Cambrian explosion This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. 10.1111/ter.12368 doi: lead article this todifferences as version between this cite Please of andthe Record. Version been and typesetting, through which may proofreading thecopyediting, process, pagination This article undergone has for buthas and accepted been not review publication full peer high-resolutionNew age datathe from Ediacaran typeArticle : Paper ULFDR LINNEMANN (Orcid : ID 0000-0003-0970-0233) Geyer Krause Australia. 8 Potsdam, Germany. 7 6 (Hawthorne), Victoria, Australia. 5 Geomaterialforschung,Hubland,-97074 Am Würzburg, D Germany. 4 3 Switzerland. 2 Königsbrücker Landstraße 159, Dresden, 01109, Germany. 1 School Atmosphere ofEarth, and Environment, Monash University, Melbourne (Clayton),Victoria, Helmholtz-Zentrum Potsdam,Deutsches GeoForschungsZentrum GFZ, Telegrafenberg, 14473 Victoria,Museums Melbourne, Australia. Department ofChemistry and Biotechnology, Swinburne University ofTechnology, Melbourne Paläontologisches undInstitut Museum, Schmid-Strasse Karl 8006 4, Zürich, Switzerland. Départementdes Sciences de Terre, la University ofGeneva, rue des Maraîchers 13, 1205 Genève, Senckenberg Collectionsof Natural History Dresden, Museum of Mineralogy and Geology, AcceptedBayerischeJulius-Maximilians-Universität, Geodynamikund für Lehrstuhl Article 4 , Patricia Vickers-Rich 1 , LesKriesfeld

1, *, Maria OvtcharovaMaria *, 8 , and JeffSmith 5,6, 8 5,6, , Tom Rich , Tom 2 , UrsSchaltegger 8

6 , Birgit Plessen – Cambrian boundaryindicate rapid,ecologically 2 , Andreas Gärtner 7 , Mandy Hofmann, Mandy 1 , Michael Hautmann 1 , JohannesZieger 3 , Gerd 1 , Rita previously assumed. The U This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. constrains the Ediacaran Namibia providing biostratigraphic and chemostratigraphic databracketedradiometric by dating mechanisms and the timescales of notwhich are entirely understood.A composite section in atanimals the beginningof the Phanerozoic was a key event the in history of life Earth, on ABSTRACT boundary,evolution of metazoans keywords: Ediacaran, Cambrian explosion, high-precision U-Pb zircon ages, Precambrian-Cam *corresponding author: [email protected] models duration of the faunal transition from Ediacaran to Cambrian biotawithin less than ka 410 supp fossilstrace to a 410 ka timewindow of 538.99±0.21 to Ma 538.58±0.19Theextre Ma. LAD of the Ediacaran biota to the FAD ofcomplex, a burrowing Phanerozoic biota represented by major taphonomic bias (e.g., Laflammeet al., 2013; Darroch etal., 2015; Schiffbaueret been explained by environmental, evolutionary or ecological factors,superimp possibly (metazoans) at the beginning the of Phanerozoic was a key event thehistory in of life, which has AcceptedINTRODUCTION the beginning of the Phanerozoic. Article of The replacementThe of the latePrecambrian Ediacaran by biota morphologically disparate The replacementThe of the enigmatic Ediacaran biotaby morphologically disparate animals ecological cascadesfollowedthat the evolutionary breakthrough increasedof mobility

– Cambrian boundary to 538.6 – Pb - CA -ID TIMS zircon ages demonstrate anultrashortframe time the for –

538.8 Ma, morethan 2 Ma youngerthan mely short al., 2016; osedby a the the brian orts

at 1996) combine rich palaeontological data (Darroch et withal.presence 2015) the of sections Swartpunt the on and Swartkloofberg farms in Southern Namibia (Saylor and Grotzinger, This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. agedata sufficientwith timeresolution have been lacking date. to Ediacaran Muscenteet al., 2018). Thesehypotheses predict different timescales for this turnover; work dating in these tuffs, using multigrain air-abrasion U high-precision allow radio-isotopic age determination. Grotzinger et (1995) al. publ metazoans. Here presentwe new high-precision U analytical precision was insufficient to quantifythe timescale necessaryfor establishing new DEFINITION AND TIMEFRAME OF THE EDIACARAN trace makers. thefor evolutionary transition from the Ediacaran biota to the existence of complex Phan that providea much refined agedatum for the beginning the of Cambrian and theabsolutefirst ages definedthe by lower boundaryof the Eumetazoa Bilateria). (i.e., Evidencethe is rather rapid appearance of complex tracefossils, for (Buatois and Mángano, 2016, Buatois etal., 2018) Landing, 2016), which is otherwise recognizable by thepronouncedfirst bioturbation i Head, Newfoundland.There, Oman. ThisOman. ash occurs just belowsequence a that recordsnegative a δ al., 2003; Bowring al.,et 2007), based a on U undermat miners fossilstrace the in Ediacaran Chen (e.g., al., et albeit2018), considered subhorizontal traces of hosting the biomineralized tubular fossil AcceptedBasal the Cambrian Carbon Isotope Excursion (BACE)(Zhu al.,and et immediately2004) ab Article The EdiacaranThe . This boundaryThis was previously noted to occur around 541.00±0.81 Ma (Amthor et – Cambrian boundary is characterized by the appearance of advanced T. pedum Treptichnuspedum appears for thefirst (Brasiertime al., et 1994; Geyerand Cloudina – Pb zirconPb ageofsample ash an from theAra Group of . However,biostratigraphic datacompletely are . – This conceptappears conflict to with bilaterian – Pb CAMBRIAN BOUNDARY - CA Assemblage Zone the in GSSP Fortune at – -ID TIMS-ID zircon agesfrom thesetuff layers Pb Pb zirconon ID-TIMS technique 13 C isotopeexcursion termed – Cambrian boundary ished pioneering tuff layerstha n earth history however, erozoic . ove strataove Their Their mally t This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. lacking from the strataabove the ashlayer.GSSP The section for the Ediacaran un 536.3±5.5 Ma(Chen Ash al., et 2015). beds related to this boundary are yet Swartpuntsection into units A biostratigraphic analysis. Recentfield studies of these outcrops haveresulted the in divisio sequencealso includestrace fossils indicative bilaterianof metazoansare that significant for imprints soft-bodiedof and biomineralized remains of the Ediacaran biota(Fig. 3). beds suitablefor radiometriccarbonates dating, useful stable for isotope chemostratigraphy, and China sequence, the Ediacaran (Brasier al.,et 1994; Geyer and Landing, 2016). From theboundary sections of the Yangtze/Sou in Avalonian Newfoundlandthe lacks soft-bodied Ediacaran biota as aswell dateableash beds complex lifecomplex during the Ediacaran Saylor(Fig. 2, and Grotzinger,1996). These sectionsare invaluable for studyingthe d the Nama Basin(Fig. and 1) exposed Swartpunton and Swartkloofberg farms in southern Namibia andlower the Cambrian NomtsasFormation (Nama are Group) preserved in theWitputs Sub NAMIBIAN KEYSECTIONS AND NEW ZIRCON AGES 2000) or the MountDunfee section (Nevada) (Smith etal., 2016). of theof Nomtsas Formation (Saylor and Grotzinger, 1996). by sandstone of the upperSpitskop Member. Rapid regional upliftledhiatus to a incaus deposition (Brasier (Brasier al.,et 1994), the WhiteInyo relevantsections globally, such asthosein the Flinders Ranges(Australia), Siberia,Ukraine the incision of canyons into the Spitskop SedimentaryMember. infilling of these val Accepted(Figs G it Article Sections ofupper the Ediacaran Spitskop Member(Urusis Formation, Schwarzrand Group) . 2and 3). Units A – F – – F, whereasnearby the Swartkloofberg section representsterminal a comprisea 139 thickm intercalation limestone, of and shale Cambrian boundary wasdated between 542.6±3.7 Ma and – Cambrian transitionas they containunique a association ashof – Death ValleyDeath – Mojaveregions (California) (Hagadorn et al., un known fromknown other – Cambrian boundary Importantly, this leys forms unitleys G evelopment of n of the basin of th ed for thefor base of the Nomtsas Formation(Schmitz, 2012). Spitskop Member, 540.61±0.67Ma for the upperpart theof Spitskop Memberand Bowring al., et 2007). Theseageswere recalculated to 542.68±2.8 forMa the middle part the of this paper)and 539.4±1 Ma (Nomtsasunit Formation, G part(middle of the Spitskop Member, upperEdiacaran), 543.3±1 Ma (Spitskop unitMember, This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. germsi metr 1997, 2012), occur siliciclastic, in storm-dominated shelf deposits of unit butareD above absent Treptichnus includingbranched forms such as limestone (unit E).Metres 125 to 128 unit F of contain anassociation of diverse f trace (Fig.4 Cambrian- bulldozersin part this of thesection, which Ediacaran taxa such as 2007). The trace fossil interval is overlain byblack, a thin-bedded micrite biomineralizedwith successivereduction the in extent of microbial above mats a 547.36±0.23 Ma old ash(Bowring complex organisms, peakedthe by adventof complex and burrowing metazoans responsible for the (Darroch etal., 2016; Smithal., et 2017). These fossil assemblagesindicate a progressive represented by AcceptedNudaus Formation, as are the poorlynon- or mineralized body fossils Article e – 107. The107. Ediacaran J).A recent studyalsoemphasizes presence the traceof fossils produced sedimby and The EdiacaranThe rangeomorph/erniettomorph biota, including such forms as Ash bedsin the Swartpunt and Swartkloofberg sectionshavedated been at 545.1±1 Ma

style bioturbation” (Buatois al.,et 2018 Pteridinium simplex cf. pedum Helminthopsis (Figs Cloudina – Cambrian transition interval Fig. (ECTI, is 3) represented18 an by m thick . 3 and 3 4B , which arealso known from olderstrata theof Huns Member and the (Figs. 3 and Streptichnus narbonnei Namacalathus – D), and D), other ichnofossils of Fortunian and Phanerozoic aspect , 4A 4A and6) (Saylor and Grotzinger, 1996; Narbonneet al., “may in“may factberegarded asrepresentative a of , p. 3 .

). Simple, Ediacaran-type tracesare of (Jensen and Runnegar, and2005) this paper) (Grotzinger al., et 1995, Gaojiashania and Swartpuntia 538.18±1.11Ma ossils, ossils, Shaanxilithes rise of more ent A of at al.,

emergence of Cambrian (and Phanerozoic-type This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. narbonnei inNamibian the sections (Fig. 4E and Landing, 2016),therefore, matchessimilar a appearance suchof traces with Phanerozoic aspect over severalover decametr and hasbeenripped into metre-sized fragments. Dueto thewide distributionrelated of fragments Formation, the 25 cm thick ash6 (538.58±0.19 Ma) exhibits features similar to those Ma, 539.52±0.14 Ma, 539.64±0.19 andMa 538.99±0.21 InMa. unitlower G of the section unit in in C ascending stratigraphic ashes order, 2 to 5 havedepositional ofages 539 and4D complex traces the in Ediacaran Uchman, 1995)show a transition betweentheichnospecies. two rather The suddenappearance of pedum results areresults presented in http://www.earthtime.org) (for methods and data seetableSupplementary Data,Table SD 1; the applying splintery, silicified and weathering-resistant layers. U F, because no additional ash bedexistsbetween ash 5 andCambrian the fossil assemblageat metr producer, which corresponds that displayed to by Acceptedyounger than ash (538.99±0.215 Ma) thefor base of the Cambrian.if Even ash6occurred primary theSpitskop in Member, it must be maximum depositional age of the NomtsasFormation. Incase, any this ageprovidesa minimum age reworked material from theunderlying SpitskopMember. Ifso, its age of 538.58±0.19 pr Ma been fragmented during sedimentdeposition. Alternatively and less probable, ash could 6 be Article from the younger, Terreneuvian,Rosenhof Member of the Fish River Subgroup (Geyer and ). The traceThe fossil assemblage the in 3 thickm unit Fin the Swartpunt section marks the InSwartpunt the section (Fig. ashbeds 3), crop as out to 8 80 cmwhitish-greeni thick,

CA and - ID Treptichnus -TIMStozircon grains, usingthe EARTHTIME es Fig , we, assume ash is 6 a primary ash bed . 5) . cf. pedum . Ash located 1, in unit A,has yieldedage an of 540.095±0.099Up- Ma. – – Cambrian boundarysection at the GSSP Newfoundland in (Geyer J), wherethe lowest occurrence of . an Streptichnusnarbonnei d also youngerthan the Cambrian fossil-bearingin bed unit ) advancedbilaterians, represented by Treptichnuspedum – Pb agedeterminations Pb wereperformed 205 reflects the complexbehaviour itsof Pb in – the Nomtsas Formation, whichhas 233 U T. . Specimens assigned to – 235 cf. U tracer solutionU tracer (ET 535, pedum inis unit Nomtsas of of older ashes Streptichnus F .58±0.34 (Figs ovides a sh, T. . 3 3 e Isotope Plateau (EPIP)and seeminglybelow BACE, the according to Zhu et al. (2017).The biostratigraphic constraints,units place A section, faris below the BACE not innot occur the section(Fig. 3) This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. 2012). reported fromin unit G the NomtsasFormation (Grotzinger al.,et 1995, recalculatedSchmitz, by 127the of Swartpunt section.It should noted be that ashanother bed aged 538.18±1.11 isMa BACE is possibly BACEis not global, (iii) or the Ediacaran abovethe strong Similarly, assemblagesthat are believed to beindicative bilaterians, in alloccur known sections above the BACE,but reliable changesin tracefossil rangeomorph (538.99±0.21 Ma) predatestermination the erniettomorphof the Acceptedturnoverduring the Ediacaran leastat locally. demonstratesthat Ediacaran biomineralized taxaextended forshort a time beyond key this event, anderniettomorphs rapidlywas followed by the advent of complex bilaterian trace-ma IMPLICATIONS FOR THE AND TIMING NATURE OF BIOTIC CHANGES FortuneHead section theandsections presented here. Article Our new agedata providefor the first timea precise, absolute evolutionarythis timing for Slightpositiveuniform δ The stratigraphicThe sequence Swartpunt at confirms thatthe disappearance rangeomorphsof S. narbonneiS. Swartpuntia germsi positiveδ and T. pedum 13 C excursion detectedC excursion in theAra Group of Oman (Amthor etal., 2003) . – However, the age determinations suggestunits that A . Cambrian transition (Fig. Accordingly,6). the age ash of 5 Reasons could(i) be a shallow bathymetry of the(ii) section, that the 13 C ratios around SD +1 3, (Fig. Table 3), combined with in unit atD metre 104. firstThe appearance of Cambrian-type , indicative for Cambrianas age produced by advanced – F into therange of the lateEdiacaran PositiveCarbon of – phylogenetic changes are only fromknown the Cambrian boundary, at leastin the Swartpunt Pteridiniumsimplex – and F kers, and lie well BACEdo

. es

This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. agedifference the betw andbeginning the of the Cambrian radiation occurredshort within a period ± of 410400 (ashMa 5) and 538.58±0.19 Ma (ash 6). Thus, the extinction theof rangeomorphs/erniettomorp ecosystem indicators, including because replacement, during which the CTF expanded atexpensethe theof ETB (Fig. Benton’s metaphoric ‘double wedge’(Benton, 1987; comparable to that priapulidof (Vannier worms et al., 2010). The second model, whi the morphological complexity Cambrianof trace-makers its with advanced grade of org duration of the ECTI,benchmarked as by newour agewas sufficient data, for a predates the firstappearance of hypothesized changesin environmental conditions (Fig. Acceptedvitalthe microbial matground food source byor direct interference (e.g. predation). acquisition newof feeding strategies the in negatively CTF, affecting the bytheETB destruction mass extinction reflectsthe tipping at point which thedevelopment of mobility all endpointlong-term a of demisedueto competition with the expanding CTF; (3 environmental changes thatsupposedlycaused this extinction; (2)the extinction theof ET increased ecological opportunitiesafter extinction of the ETB and/or in response to the significantly the in timescale they predict. Theseinclude: theCTF (1) expanded in responseto 2015; Smith etal., 2016; Muscente al.,et herein 2018).We discuss three models, whi ArticleEdiacaran-type biota (ETB) the by Cambrian-typefauna (CTF) (Laflamme al.,et 2014; Darroch et ca. 538.8be Ma, thus aboutca. 2.4 Ma younger than previously suggested. thereforesuggest the age theof Ediacaran The firstThe predicts model thatthe expansion of the CTF began newThe timeframe allows different testing of evolutionary models for the replacement theof it includes an erosional unconformity the in basal Cambrian(Fig. 3) een ashes It and5 6. should noted be thatduration this is overestimated Streptichnusnarbonnei Treptichnuspedum – Cambrian boundarybetween ash and5 needs ash6 to , part of Sepkoski, 1996), predicts an extended period of , cannow, be datedat between 538.99±0.21 7a ). However, isit unlikelythat the short

a moderately diverse assemblage. after the onset theof . Furthermore, ash6 7b ) theend-Ediacaran de novo ). diversityThe owed the ch conforms to ch differ anization evolution of ka, givenka, by B was the We al., al., of of hs , situation situation that is herein referred to as the process ofreplacement clade from theevolutionary toecological the timescale, suggest thatadaptive an breakthrough, such as the evolution of advanced mobility, coul present-day ecosystemsthe followingintroduction invasive of species (Lowe et al., 20 appeargeologically suddenly, analogous ata larger scale the to profound alterations s of adaptations that enhanced competitiveness, predatory skillsto or ability the alter the This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. Seilacherand Pflüger, 1994; Schiffbauer al., et 2016). Ecological effects competition ecologicallywith moresuccessful animals, predation or (Bengtson and Yue, 1992; destruction of the matground environment newlyby evolved sediment-mixing metazoan existencein Namibia, globally.or trace-makers,and thereis evidenceno forsuccessive a decline during anextended period of co- an exception. Generally, rangeomorphs arenot found abovethe lowestoccurrence Cambrianof rangeomorphsof into the Cambrianquestionable is (Laflammeet al., 2013) andb at represents rangeomorphs from theCambrian (Jensen et 1998; al., Hagadorn al.,et 2000). However,surviv in light this (Darroch et al., 2015; Muscenteet al., 2018),haveasthe sporadic re declinefrom the older White Sea assemblages to the Namayounger assemblages hasbeendepicte accentuated the abruptness of th model.Apossible preservation bias againstETB in the Cambrian (Gehling,may 1999) the shortinterval of finaltheir disappearancebenchmarked bynew the agedata,predicted is by this progressivedecline theof rangeomorphs/erniettomorphs duringlate the Ediacaran, con this replacement by orders of magnitude,leading to thetruncation theof shrinking ‘wedge’. The progressively response in to the expansion anotherof until an adaptivebreakthrough accelerates al., 2013). Acceptedrangeomorphs/erniettomorphs, casts the empirical evidencefor this model into doubt basal Cambrian,and uncertainties in the taxonomic identity of potential Cambrian Article It hasfrequently been proposed that theextinction of the ETB was ecologicallydriven, e.g. by is transition. However,persistence the of microbial mats into the truncated double wedge model of (Fig. newly evolved key 7c ports ports of ): one cladedeclines leading a to have 04). We habitat would (Laflamme et d shift the trasted by ome s, orship est est d Foundation.Further, w geochronologyfacilitythe Universityat of throughGeneva the Swis support fieldworkof in southern Namibia since 2004. particular Namibia, for supportduring fieldwork. our Sincere thanks go to the Geological Survey of acknowledged.greatly We further thank andL. B.Roemer, Gressert L. and B. Boehm-Ernie from Aus, including important suggestions byB. Saylor (Case Western Reserve University, Cleveland, Introduction to the field area by K.H. Hoffmann (Windhoek, Namibia)and fruitful discussion unknownThree reviewers are thankedfor helpful their comments, discussionsand corrections. ACKNOWLEDGEMENTS transition. and IGCP587 IGCP493. Forschungsgemeinschaft.part is ofproject This UNESCOInternational Geosciences contributionwas GG of madepossibleby ofresearch grant549/22-1 GE Senckenberg NaturforschendeandGesellschaft the Deutsche Forschungsgemeinschaft.The environmental and evolutionaryaspects worked in concertduring the Ediaca environmental changescurrently is which weak, alsodetracts frompossible a scenario which in represented by the erosionalunconformity short.was However, evidence for possible (1) if the maximum duration within the the errorof agedata is assumed(2) and thegeologi althoughdata our are not completely incompatible with anenvironmentallyd This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. Accepted Article Summarized,we found the best model- ly to G. Schneider, facilitating for work,our and theNational to Geographic Society for e appreciatelong-term funding theGeoPlasmaLab of Dresden bythe to -data fit for thetruncated double wedgemodel, Weacknowledge long-term funding the of s National s Science the Deutsche ran riven scenario, at least – Cambrian biotic Program Namibia, USA) areUSA) c time s This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. Amthor, J.E., Grotzinger,J.P., Schröder, S., Bowring, S.A., Ramezani, J., Martin, M.W., and Matter, A., REFERENCES CITED Bengtson, S.,and Yue, Z., 1992, Predatorial borings in PrecambrianLate mineralized exoskel Benton, M.J., 1987, Progress and competition in macroevolution: Biological Revi Brasier, Cowie,M., J., and Taylor, J., 1994, Decision on the Precambrian-Cambrian boundary Buatois, L.A., and Mángano, M.G., 2016,Ediacaran ecosystems anddawn the animals, of Bowring, S.A., Grotzinger, Condon, J.P., D.J., Ramezani, J., Newall, M.J., and Allen, P.A., 2007, Chen, D., Chen, D., Zhou, Fu,X., Y., andWang,Yan, J., D., 2015, New zirconU-Pb ages of theEdiacaran- Buatois, Almond, L.A., J., Mángano, M.G., Jensen, S., and Germs, G.J.B., 2018, Sedimentdisturbance AcceptedChen, Zh., Chen, Zhou,X., Ch.,and Yuan, X., Xiao, Sh., 2018, LateEdiacaran trackways produced by Article 2003, Extinction of Oman:Geology, v. Science, v. 257, p. 367 stratotype: Episodes, v. Supergroup, Sultanate of AmericanOman: Journal Science,of p.v. 307, 1097 Geochronologic constraints the on chronostratigraphic framework of the Neoproterozoic Huqf 338. Cambrian boundarystrata in China: South Terra 2018, 8:4514, doi:10.1038/s41598-018-22859-9, 9 pp. Ediacaranby bulldozersand roots the theof CambrianScientific explosion: Nature Reports bilaterian animals with paired appendages:Science Advances 2018, 4:eaao6691, pp. 8 Vol. 1,Precambrian and Paleozoic: Topics Geobiology, in v. Mángano, andBuatois,M.G., L.A., eds., The trace-fossil record of major evolutionarychan

31 Cloudina , p. 431 – 369. 17 , p. 3 and – 434. – 8. Namacalathus

at theat Precambrian-Cambrian boundaryin

Nova, v. 27 39 , p. 62 , p. 27 – 68. – 72 . Springer, Berlin. ews, v. 62, p. 305 – 1145. in

etons: ges, – Jensen, S., Gehling, J.G., andDroser, M.L., 1998, Ediacara-typefossils Cambrian in sediments: Gehling, J.G., 1999, Microbial mats terminal in Proterozoic siliciclastics; Ediacaran death Hagadorn, J.W,Fedo, C.M., and Waggoner, B.M., 2000, Early Cambrianfossils Ediacaran-type from Grotzinger,J.P., Bowring, S.A., Saylor, B.Z.,and Kaufman, A.J., 1995, Biostratigraphic and This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. Geyer, G.,and Uchman, A., 1995, Ichnofossil assemblagesfrom Group the Nama (Neoproterozoic- Erwin, D.H., 2001, Lessons from thebiotic past:recoveries from mass extinction:Proceedi Darroch, S.A.F., Boag, T.H., R.A., Racicot, Tweedt,S., Mason, S.J., Erwin, D.H., and Laflamme, M., Darroch,S.A., Sperling, E.A., Boag, T.H., Racicot,R.A., Mason, S.J., Morgan, A.S., and Laflamme, M., AcceptedGeyer, G.,and Landing, E., 2016, The Precambrian Article Publications, boundaries: a historical approach to a dilemma: Geological Society (London)Special Nature,v. 393, p. 567 Palaios, v California: JournalCalifornia: of Paleontology, v geochronologicconstraints early on animal evolution: Science, v. 270, p. 598 Beringeria, Special Issue 2, p. 175 Cambrian)Lower in Namibia and the Proterozoic-Cambrian boundaryproblem revisi Palaeogeography, Palaeoclimatology, Palaeoecology, v. 459, p. 198 2016, A mixed Ediacaran-metazoan assemblagefrom theZaris Subbasin, Namibia: Society, B, v. 282, p. 20151003. 2015, Bioticreplacement and mass extinction of the Ediacara biota: Proceedings the of Ro National Academy Sciences,of v. . 14, 40

v. 448, p. 311 – 57 (1999). – 569. – 349.

– 98 202. , p. 5399 .

47 , p. 731 – – Phanerozoicand Ediacaran 5403. – 740. – 208. – Cambrian – 604. masks: ngs of ngs of the ted: yal yal Muscente,A.D., Boag, T.H., Bykova, N., and Schiffbauer, J.D., 2018, Environmental disturbance, S.,Lowe, Browne, Boudjelas,M., S.,and De Poorter, M., 2004, 100 of the World’s WorstInvasive Narbonne,G.M., Saylor, B.Z., and Grotzinger,J.P., 1997, The youngest Ediacaran fromfossils Laflamme, Darroch,M., S.A., Tweedt, S.M., Peterson, K.J., and Erwin, D.H., 2013, endThe theof Landing, 1994, E., Precambrian Narbonne,G.M., Xiao, S., and Shields, G.,2012, EdiacaranThe Period, This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. Jensen, S., and Runnegar, B.N., A 2005, complex trace fromfossil the Spitskop Member (terminal Peng, S.C., Babcock, andL.E., Cooper,R.A., 2012, The period,Cambrian AcceptedSaylor, B.Z.,and Grotzinger, 1996, J.P., Reconstruction important of Proterozoic-Cambrian Article v. 177,v. p. 248 resourceavailability, and biologic turnover the at dawn animal of life: Earth-Science version). Species SpecialistGroup, IUCN, University of Auckland, 12 pp. (updated and reprinted Alien A Species. Selection from Invasive the Global Species Database. Vol. 12: TheInvasive of Cambrianof time: Geology, p. v. 22, 179 Southern Africa:Journal of Paleontology, v. 558 Ediacara biota: Extinction, replacement, biotic or CheshireCat?: Gondwana Research, v. 23, p. Ediacaran Schmitz, M.D., and Ogg, G.M., eds., Geologic Timescale. Elsevier, Amsterdam, p. 413 Namibia: CommunicationsNamibia: theof Geological Survey of Namibia, exposuresthrough recognition the deformationof thrust the in Nama Group of so Schmitz, M.D., and Ogg, G.M., The Geologic Timescale 2012, p.437 – 573. – ? LowerCambrian) of southern Namibia:Geological Magazine,142, v. p. 561 – 264. – Cambrian boundaryglobal stratotype ratified andnew a perspective – 184. 71 , p. 953 – 967.

in v. in Gradstein, F.M.,Ogg, J.G.,

11 – Gradstein, F.M., Ogg, J.G., 488. , p. 1 – 12.

uthern boundary – Reviews, 435. – 569. This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. Seilacher,A., and Pflüger, F.,1994, From biomats to benthicagriculture: biohistoric a revolution, Schiffbauer,J.D., Huntley, J.W., O’Neil, G.R., Darroch, S.A., Laflamme, andM., Cai, Y., 2016, The Sepkoski Jr,J.J., 1996, Competition in macroevolution:double The wedgerevisited, Schmitz, M.D., 2012, Radiometricages usedin GTS 2012, Smith, E.F.,Smith, Nelson, L.L., Strange,M.A., Eyster, A.E., Rowland, S.M.,Schrag, D.P., and Macdonald, Va E.F.,Smith, Nelson, L.L., Tweedt,S.M., Zeng, H., and Workman, J.B., 2017, Acosmopolitan late Zhu, Zhuravlev, M., A.Yu., Wood, R.A., Zhao, F., and Sukhov, S.S., 2017,A deep rootfor the Cambrian

Acceptednnier, J., Calandra, I., Gaillard, C.,and Żylińska,A., 2010, Priapulid worms: Pioneer horizontal Article GSA Today, 26, p. v. 4 latest Ediacaran Wormworld setting fauna: the ecological stage forCambrian the Explosion: und Informationssystem der von Carl Ossietzky UniversitätOldenburg, p.97 Krumbein, W.E., Peterson, andD.M., Stal, L.J., eds., Biostabilization of Sediments: Bibliotheks- Chicago, London, p.211 Erwin, D.H., and Lipps, J.H., Evolutionary eds., Paleobiology: University of Chicago assemblagesfrom Mount Dunfee, Nevada,Geology, USA: v. F.A., 1996, The end of the Ediacaran: Two new exceptionally preserved body fossil and Ogg, G.M., GeologicThe Timescale 2012: Elsevier, p. 1045 biostratigraphic link: Proceedings of the Royal Society,v.284, B, 201709340. Ediacaran bioticassemblage: newfossils from Nevada and Namibia supportglobal a Geology, v. explosion: Implications newof and bio- chemostratigraphy from the Siberian Platform burrowers at the Precambrian 45 , p.459 – – 462. 11. – 255.

– Cambrian boundary: Geology, v. 38, p. 711 in Gradstein, F.M., Ogg, J.G., Schmitz, M.D., 44 – , p. 911 1082. – 914. – 714. –

105. in Jablonski, D, Press, : :

This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. Zhu, Zhang, M.Y., J.M., Li, G.X., and Yang, A.H., 2004, Evolution Cof isotopesin the Cambrian o Spitskop Member, unit F, metre 126. Figure4 grey-green sandstone, 4 1930; Spitskop Member, unit D, metre 104. Figure3 Grotzinger, 1996). ages obtainedages by micrite; 7 Swartpuntsection (units A Figure Geological2. map offarms the Swartkloof, Swartpuntand Nord-Witpütz. locatioNote FigureGeological 1. map of southern Namibia and the Nama basin (Grotzingerand Miller, 20 FIGURE CAPTIONS Ediacaran Acceptedandvalues fossil horizons. 1 Article China: implications Cambrian for subdivision and trilobite mass extinctions:Geo 287 . . Fossils from theand Swartpunt Swartkloofberg sections. Geologic sections Swartpuntat (units A – – – Cambrian boundaryinterval in the Swartpuntand Swartkloofberg sections. PreciseU black thick-bedded micrite; 8 301. CA

- ID -TIMStechniques with uncertaintiesgiven at sigma 2 level, carbon isotope – greenish shale; 5 – F) and the Swartkloofberg section (unit (modifiedG) from Saylor and – debris flow, shale, olistoliths; 2 C – Unusually small specimen assigned to – black thin-bedded micrite; 9 – B grey thick-bedded micrite; 6 –

Streptichnusnarbonnei – F) and Swartkloofberg (unit G)indicating the – shale, sandstone, conglomerate; 3 A –

Pteridiniumsimplex Jensen and Runnegar, 2005; – ash bed. – grey thin-bedded Streptichnus bios, v. Gürich, n of the 08). 08). 37 f – , p. Pb Pb –

Ediacaran geochronological data(this in study) a time windowranging 540.1 from to 53 Figure Range6. of forms life and suggested biological developments versusincluding age Figs.see and3 6). Figure Concordia5. diagrams theof CA- environmental disturbances (a). in fauna type red);(CTF, x-axis representsdiversity; shaded interval indicateshypothetical Figure Three7. models for the displacementof the Ediacara-type biota(ETB, blue) theby Cam equal 5 mm, blackscale bars C, F) (in 5 mm. Coin diameter 22.6(inA, mm trace subregularwith constrictions; Nomtsas Formation,G. Whitescale unit bars (in pedum unit F,metre 127. burrows differentwith typesof annulations (arrows) suggestingspiral a burrow; Spitskop Member, (arrow nearright margin); NomtsasFormation, unit GJ ash above 6. pelletedtype or trace(arrow in lower left corner)and delicate traces composed of elongatepr This article is protected by copyright. All rights reserved. This article isprotected rights by All copyright. reserved. tentatively assigned to traces secondarywith weakmineralization of outersurface (arrows point to branching points), narbonnei with simplewith Accepted ArticleIncompletely preserved vertical burrowsresembling (Seilacher, 1955), garlands crossing each other; Spitskop Member,unit F, meter 127. – Jensen and Runnegar, 2005; Spitskop Member,unit F meter 127. D Cambrian boundaryinterval in the Swartpuntand Swartkloofbergsections. Planolites H –

-type horizontal tracescrossing each other, associated withstring- a Cochlichnus Olenichnus isp.;from Nomtsas Formation, unit G. ; Spitskop; Member, unit F, metre127. ID -TIMS U-Pb zircon data (for position of inashes the section Bergaueria ; unit F meter 127. – Irregularly sinuous pelleted G I I) – – Trace fossil assemblage . Shallow horizontalShallow 8.3 indicatingMa the –

Treptichnus F B, – Branched D,E, G, H, J new of cf. -pearl- E brian- – obes obes

) This article isprotected rights by All copyright. reserved. Accepted Article

This article isprotected rights by All copyright. reserved. Accepted Article