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TYPE DIVERSITY from the EARLY CAMBRIAN of BALTICA by BEN J

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TYPE DIVERSITY from the EARLY CAMBRIAN of BALTICA by BEN J [Palaeontology, Vol. 60, Part 1, 2017, pp. 117–140] A CRYPTIC RECORD OF BURGESS SHALE-TYPE DIVERSITY FROM THE EARLY CAMBRIAN OF BALTICA by BEN J. SLATER1,3,THOMASH.P.HARVEY2, ROMAIN GUILBAUD1 and NICHOLAS J. BUTTERFIELD1 1Department of Earth Sciences, University of Cambridge, Downing St, Cambridge CB2 3EQ, UK; [email protected] 2Department of Geology, University of Leicester, University Rd, Leicester LE1 7RH, UK 3Current address: Department of Earth Sciences, Uppsala University, Villav€agen 16, 752 36, Uppsala, Sweden Typescript received 11 September 2016; accepted in revised form 8 November 2016 Abstract: Exceptionally preserved ‘Burgess Shale-type’ fossil priapulids are the first recorded from the Cambrian of Bal- assemblages from the Cambrian of Laurentia, South China tica. The File Haidar SCF assemblage is broadly comparable and Australia record a diverse array of non-biomineralizing to those recovered from Cambrian basins in Laurentia and organisms. During this time, the palaeocontinent Baltica was South China, though differences at lower taxonomic levels geographically isolated from these regions, and is conspicu- point to possible environmental or palaeogeographical con- ously lacking in terms of comparable accessible early Cam- trols on taxon ranges. These data reveal a fundamentally brian Lagerst€atten. Here we report a diverse assemblage of expanded picture of early Cambrian diversity on Baltica, and small carbonaceous fossils (SCFs) from the early Cambrian provide key insights into high-latitude Cambrian faunas and (Stage 4) File Haidar Formation of southeast Sweden and patterns of SCF preservation. We establish three new taxa surrounding areas of the Baltoscandian Basin, including based on large populations of distinctive SCFs: Baltiscalida exceptionally preserved remains of Burgess Shale-type meta- njorda gen. et sp. nov. (a priapulid), Baltichaeta jormunganda zoans and other organisms. Recovered SCFs include taxo- gen. et sp. nov. (an annelid) and Baltinema rana gen. et sp. nomically resolvable ecdysozoan elements (priapulid and nov. (a filamentous problematicum). palaeoscolecid worms), lophotrochozoan elements (annelid chaetae and wiwaxiid sclerites), as well as ‘protoconodonts’, Key words: Cambrian explosion, small carbonaceous fos- denticulate feeding structures, and a background of filamen- sils, Burgess Shale-type preservation, priapulids, Wiwaxia, tous and spheroidal microbes. The annelids, wiwaxiids and annelids. L OWER Cambrian sediments of Sweden have long been from a deep drillcore of the Zawiszyn Formation, Poland known to contain a variety of shelly macrofossils (Ahman (Lendzion 1975; Dzik & Lendzion 1988; Daley & Legg & Martinsson 1965; Bergstrom€ 1968; Topper & Skovsted 2015). 2014), small shelly fossils (SSFs) (Bengtson 1968), ichno- There is, however, an alternative means of capturing a fossils (Linnarsson 1871; Jensen 1990, 1997; Jensen & measure of BST diversity, even in the absence of excep- Bergstrom€ 2000) and acritarchs (Vidal 1981; Hagenfeldt tional macrofossil preservation. The (mostly) disarticu- 1989, 1994; Eklund 1990; Hagenfeldt & Bjerkeus 1991). lated, taphonomically recalcitrant elements of these Body fossils of non-biomineralizing organisms, however, organisms are widely recovered as ‘small carbonaceous are limited to a handful of isolated euarthropods and fossils’ or SCFs (Butterfield & Harvey 2012). Like their lobopodians (Størmer 1956; Bergstrom€ 1971; Krumbiegel ‘small shelly’ counterparts, SCFs are deeply polyphyletic, et al. 1980; Dzik & Krumbiegel 1989), with no evidence united by little more than their size and a particular of the diverse Burgess Shale-type (BST) macrofossil search image, in this case organic-walled fossils that are assemblages that have revolutionized our understanding too small to be seen on bedding surfaces, but too large or of early Cambrian palaeobiology in Laurentia, South delicate to be reliably recovered via conventional palyno- China and Australia (Butterfield 2003). The only docu- logical processing. Despite their fragmentary nature, how- mented occurrence of Cambrian macroscopic BST preser- ever, many SCFs can nonetheless be resolved to a vation currently recorded from Baltica is three specimens taxonomically informative level. Importantly, what SCFs © 2016 The Authors. doi: 10.1111/pala.12273 117 Palaeontology published by John Wiley & Sons Ltd on behalf of The Palaeontological Association. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 118 PALAEONTOLOGY, VOLUME 60 lose from disarticulation they gain in abundance and dis- is gradational, and parts of the Borgholm Formation (e.g. tribution, offering a fundamentally enhanced account of the Grotlingbo€ Member) are recognized as latest early palaeobiogeographical and stratigraphical patterns. The Cambrian in age, with the diachronous boundary young- key to recovering these large-scale patterns, of course, is ing westwards (Nielsen & Schovsbo 2011). The subsurface global sampling, though most Cambrian SCF studies to portions of the File Haidar Formation are well known date have been centred on relatively few localities in west- from drillcore, and have been extensively studied both ern Canada and South China (Butterfield 1994; Butter- sedimentologically (e.g. Nielsen & Schovsbo 2007, 2011) field & Harvey 2012; Harvey et al. 2012a, b; but see and for acritarch biostratigraphy (Hagenfeldt 1989, 1994; Smith et al. 2015a). Here we expand this record to the Eklund 1990). palaeogeographically isolated palaeocontinent of Baltica. The early Cambrian age (Stage 4; c. 514–509 Ma) of Global palaeogeographical reconstructions of the early the File Haidar Formation, used here following the Cambrian vary considerably (e.g. McKerrow et al. 1992; scheme of Nielsen & Schovsbo (2011), is based on a com- Li et al. 2008; Meert & Lieberman 2008), but there is gen- bination of acritarch biostratigraphy (Heliosphaeridium eral agreement that the sedimentary depocentres of Scan- dissimilare – Skiagia cilosa, Volkovia dentifera – Liepaina dinavia/Baltoscandia and the East European Platform plana assemblage zones (Hagenfeldt 1989, 1994; Moczy- belonged to a coherent craton, Baltica, separated from dłowska & Vidal 1986; Moczydłowska 1991, 1998)) and other contemporary landmasses by substantial expanses of detailed sequence-stratigraphical correlation (Nielsen & ocean (Torsvik & Cocks 2005; Cawood & Pisarevsky Schovsbo 2007, 2011) to the Holmia kjerulfi and ‘Orna- 2006; Meert 2014). During the early Cambrian, present- mentaspis’ linnarssoni trilobite zones (Bergstrom€ & Ahl- day Scandinavia lay in an inverted position, facing the berg 1981; Ahlberg & Bergstrom€ 1993). Shelly fossils are South Pole (Hartz & Torsvik 2002; Cocks & Torsvik rare in the File Haidar Formation, confined to occasional 2005; Alvaro et al. 2016). Although once thought to fragmentary trilobite remains (Ahlberg 1984; Ahlberg oppose Laurentia across the Iapetus Ocean (see Hartz & et al. 1986) and rare brachiopods, though some surface Torsvik 2002, fig. 1), the Scandinavian margin is now exposures yield abundant SSFs including Mobergella considered to have faced Siberia on the margins of the (Ahman & Martinsson 1965); trace fossils typical of early Ægir Ocean (Nielsen & Schovsbo 2011). Moreover, Cambrian assemblages are also locally abundant (Jensen almost all palaeomagnetic data place Baltica in the mid to 1997). The underlying crystalline basement is substantially high temperate palaeolatitudes (35–60° S) during the older, with bounding age constraints of 1700 and 900 Ma early Cambrian (Torsvik & Rehnstrom€ 2001; Meert & (Welin et al. 1982). Lieberman 2004; Cocks & Torsvik 2005; Landing et al. Sediments of the File Haidar Formation record marine 2013). By contrast, all of the well-known Cambrian BST- deposition in a storm-influenced nearshore sand belt. Lagerst€atten fall within the palaeotropics. Proximal environments are sand-dominated, with distal regions of the inner-shelf grading into siltstones and shales (Nielsen & Schovsbo 2007). The formation is subdivided GEOLOGICAL SETTING into five members based on lithology and thin conglomer- atic marker beds (Figs 2, 3; Nielsen & Schovsbo 2007, The File Haidar Formation (early Cambrian, Stage 4) is 2011). Sediments of the lowermost Viklau Member consist locally exposed at the surface in and around southern of interbedded green-grey quartz sandstones, bioturbated Sweden, and subcrops extensively beneath the Baltic Sea siltstones and green shales. The overlying N€ar Shale Mem- (Figs 1, 2; Hagenfeldt 1989, 1994; Nielsen & Schovsbo ber is dominated by quartz sandstone in proximal settings 2007). Deposition took place in a shallow epicontinental (e.g. in the File Haidar-1 core; Fig. 3), grading distally into sea, broadly mirroring the architecture of the modern successions of heavily bioturbated green-grey siltstones Baltic and Bothnian seas, and separated from the Russian and shales with subordinate sandstones (e.g. in the margin by a substantial hinterland (Floden 1980; Lidmar- Grotlingbo-1€ core; Fig. 3). The N€ar Sandstone Member is Bergstrom€ 1988; Nielsen & Schovsbo 2011, figs 82–86). dominated by fine-medium grained quartz sandstones with The File Haidar Formation consists of fine-medium occasional subordinate siltstone beds. The proximal equiv- sandstones interspersed with recurrent mudstones and alents of these three members are the Mickwitzia Sand- siltstones,
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