ACTAUNIVERSITATIS

UPSALIENSISUPPSALA

2012

Digital Comprehensive Summaries of Uppsala Dissertationsfrom the Faculty of Science and Technology 967

Early Cambrian ProblematicLophotrochozoans andDilemmas of ScleritomeReconstructions

CECILIA M LARSSON

ISSN 1651-6214ISBN 978-91-554-8462-0urn:nbn:se:uu:diva-180195

Dissertation presented at Uppsala University to be publicly examined in Hambergsalen,Geocentrum, Villavägen 16, Uppsala, Friday, October 19, 2012 at 09:00 for the degree ofDoctor of Philosophy. The examination will be conducted in English.

AbstractLarsson, C. M. 2012. Early Cambrian Problematic Lophotrochozoans and Dilemmasof Scleritome Reconstructions. Acta Universitatis Upsaliensis. Digital ComprehensiveSummaries of Uppsala Dissertations from the Faculty of Science and Technology 967. 47 pp.Uppsala. ISBN 978-91-554-8462-0.

The emergence and radiation of metazoan body plans around the Precambrian/Cambrianboundary, some 500-600 million years ago, seems to be concordant with the appearanceand diversification of preservable hard parts. Several Precambrian soft-bodied, multicellularorganisms most likely represent stem-group bilaterians, but their fossil record is rather sparse. In contrast, the Cambrian fossil record is comparably rich – comprising hard part, tracefossil and delicate soft tissue preservation – and most animal phyla that we know of todayhad evolved by the end of the Cambrian. Consequently, this time represents an importantperiod in the early evolution of metazoan life forms. Most skeletal remnants of invertebrateorganisms from this period are preserved in incomplete, disarticulated sclerite assemblages, andthe true architecture of the original skeletal structure, the scleritome, may therefore be hard todiscern. Many scleritomous taxa have been suggested to be members of the lophotrochozoanclade, while their exact position within this group remains unclear. Such taxa are often referredto as Problematica. This thesis deals with some problematic scleritomous early Cambrianlophotrochozoans, and as such also addresses the dilemmas of scleritome reconstructions.In the first part, completely disarticulated calcareous sclerites from the lower Cambrian ofNorth Greenland are described as Trachyplax arctica. Hypothetical scleritome reconstructionalternatives and comparisons to other scleritome-bearing taxa are discussed, but the lack ofarticulated material obscures any satisfactory conclusions regarding phylogenetic affinities andthe original morphology of the organism. The other part of the thesis focuses on some minute,organophosphatic scleritomous metazoans, tommotiids, found in lower Cambrian limestonesuccessions in South Australia – Paterimitra pyramidalis and Kulparina rostrata – theirscleritome architecture and their phylogenetic relationship with paterinid brachiopods. Theoldest brachiopod from South Australia, Askepasma saproconcha, and the slightly youngerAskepasma toddense are also described and discussed. Based on articulated specimens, recentlydescribed partial scleritomes of the tommotiid Eccentrotheca helenia and similarities in shellultrastructure with both Eccentrotheca and Askepasma, Paterimitra is interpreted as a stem-group brachiopod and reconstructed as a bilaterally symmetrical, sessile, filter feeder with atubular/conical scleritome. The morphological similarities with Paterimitra point in the samedirection for the slightly older Kulparina.

Keywords: Problematica, scleritome, Trachyplax, tommotiid, Cambrian, South Australia,North Greenland

Cecilia M Larsson, Uppsala University, Department of Earth Sciences, Palaeobiology, Villav.16, SE-752 36 Uppsala, Sweden.

© Cecilia M Larsson 2012

ISSN 1651-6214ISBN 978-91-554-8462-0urn:nbn:se:uu:diva-180195 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-180195)

Jocke

Selma

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List of Papers

This thesis is based on the following papers, referred to in the text by their Roman numerals.

I Larsson, C.M., Peel, J.S., Högström, A.E.S. (2009)

Trachyplax arctica, a new multiplated problematic fossil from the lower Cambrian of North Greenland. Acta Palaeontologica Polonica, 54(3):513–523 doi: http://dx.doi.org/10.4202/app.2009.0026

II Skovsted, C.B., Holmer, L.E., Larsson, C.M., Högström, A.E.S., Brock, G.A., Topper, T.P., Balthasar, U., Pettersson Stolk, S., Paterson, J.R. (2009) The scleritome of Paterimitra: an Early Cambrian stem group brachiopod from South Australia. Proceedings of the Royal Society of London B, 276 (1662):1651-1656

III Holmer, L.E., Skovsted, C.B., Larsson, C.M., Brock, G.A., Zhang, Z. (2011) First record of a bivalved larval shell in early Cambrian tommotiids and its phylogenetic significance. Palaeontology, 54 (2):235-239

IV Topper, T.P., Holmer, L.E., Skovsted, C.B., Brock, G.A., Balthasar, U., Larsson, C.M., Pettersson Stolk, S., Harper, D.A.T. (in press). The oldest brachiopods from the lower Cambrian of South Australia. Acta Palaeontologica Polonica. doi: http://dx.doi.org/10.4202/app.2011.0146

V Larsson, C.M., Skovsted, C.B., Brock, G.A., Balthasar, U., Holmer, L.E., Topper, T.P. (manuscript submitted to Palaeontology) Paterimitra pyramidalis from South Australia; Scleritome, shell structure and evolution of a lower Cambrian stem group brachiopod.

VI Larsson, C.M. (manuscript prepared for submission to Journal of Paleontology) Revision of the tommotiid Kulparina rostrata (Conway Morris & Bengtson in Bengtson et al., 1990) from South Australia.

Articles are reproduced with permission from the respective copyright holders.

Papers I and IV © Institute of Palaeontology, Polish Academy of Sciences Paper II, V and VI © The authors Paper III © Palaeontological Association/Wiley-Blackwell Publishing Ldt

Statement of authorship

Paper I: C.M.L. photographed the material and produced the tables and Figs 2-7, participated in the analysis and wrote the main part of the manuscript.

Paper II: C.M.L. took part in recent field work, processing of material and SEM work, contributed to analysis and manuscript preparation.

Paper III: C.M.L. took part in recent field work, processing of material and SEM work, contributed to interpretations and preparation of the final version of the manuscript.

Paper IV: C.M.L. assisted in field work and participated in manuscript preparation.

Paper V: C.M.L. took part in recent field work, processing of samples and picking of residues, conducted the majority of SEM work, completed the analysis and scleritome reconstruction, wrote the main part of the manuscript and produced all tables as well as Figs 2-17 and 21.

Paper VI: C.M.L. participated in picking of residues, conducted SEM work, produced all figures, and wrote the manuscript.

Disclaimer

The papers and manuscripts presented herein are for the purpose of public examination as a doctoral thesis only. They are not deemed valid for taxonomic or nomenclatural purposes [see article 8.2 in the International Code of Zoological Nomenclature]. Accordingly, all new taxonomic names and emendations are void, and authority for taxonomic work is retained by the original publications.

Contents

1. Introduction ................................................................................................. 9 The 'Cambrian Explosion' – early evolution of animals ............................. 9 Sclerites, scleritomes and reconstructions ................................................ 10 Building a house without a blueprint ....................................................... 12 'Problematica' and problematic lophotrochozoans ................................... 15 Aims of this PhD thesis ............................................................................ 17

2. Multiplated enigmas from North Greenland ............................................. 18 Trachyplax arctica Larsson, Peel & Högström, 2009 .............................. 18

3. South Australian tommotiids and the evolution of paterinid brachiopod shell structures .............................................................................................. 22

Tommotiids from South Australia ............................................................ 24 Paterimitra pyramidalis – a stem-group brachiopod ............................... 26 Askepasma, Paterimitra and the evolution of the paterinid brachiopod shell structure ........................................................................................... 28 Kulparina rostrata: 1+1=1 ....................................................................... 30

4. Svensk sammanfattning ............................................................................ 33 Den kambriska explosionen – djurlivets tidiga evolution .................... 33 Skleriter, skleritom och rekonstruktioner – att bygga ett hus utan ritningar ............................................................................................... 34 'Problematica' och lofotrochozoer ....................................................... 35 Avhandlingens syfte ............................................................................ 36 Trachyplax arctica från Nordgrönland ................................................ 36 Tommotiider från södra Australien och evolutionen av skalstrukturen hos paterinida brachiopoder ......................................... 37

5. Acknowledgements ................................................................................... 39

6. References ................................................................................................. 40

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1. Introduction

The 'Cambrian Explosion' – early evolution of animals The early evolution and diversification of metazoan life-forms has been the subject of countless scientific studies and controversies and, to this day, continue to befuddle palaeontologists, palaeobiologists and evolutionary biologists around the world. The 'Cambrian explosion' tells the story of the seemingly rapid appearance and radiation of metazoan body plans, as well as the evolution of preservable mineralized or chitinous hard parts (e.g. tubes, shells, sclerites, spicules and teeth) some 500-600 million years ago (see for example Fortey et al. 1997; Budd & Jensen 2000; Conway Morris 2000, 2003; Budd 2003, 2008; Shu 2008; Nielsen & Parker 2010; Peters & Gaines 2012). Most modern scientists agree that most of the animal phyla that we know of today had evolved by the end of the Cambrian. The soft-bodied multicellular organisms of the Ediacara fauna (late Precambrian) are enigmatic in that they mostly lacked any preservable hard parts (but see Germs 1972 and Clites et al. 2012 for some interesting exceptions). Thus, fossils from this period are difficult to compare to known phyla (Nielsen & Parker 2010). However, the sparse fossil record indicates that some of the Ediacara fossils most likely represent stem-group1 bilaterians. For example, Fedonkin & Waggoner (1997), described the enigmatic Ediacaran Kimberella Glaessner, 1959 as ‘a mollusc-like bilaterian organism’, and trace and possible body fossils of undisputed bilaterians are also known (Jensen 2003; Rogov et al. 2012). In contrast, the Cambrian fossil record worldwide is rich, containing abundant fossilized hard parts, trace fossils as well as fossils preserving delicate soft tissues.

Consequently, while many stem-group bilaterians may have been present already in the late Precambrian, the emergence of modern phyla appears to have occurred during the Cambrian period and seems to be concordant with the appearance and diversification of preservable hard parts. The question is how and why these soft bodied metazoans so abruptly evolved forms bearing hard parts and/or teeth? What caused this seemingly sudden turnover and diversification of metazoan body plans and the evolution of hard parts is far 1 a crown group represents the last common ancestor of all living forms in the phylum and all of its descendants; a stem group represents a series of entirely extinct organisms leading up to the crown group away from the last common ancestor of this phylum and the most closely related phylum – sensu Budd & Jensen (2000)

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from clear. Nielsen & Parker (2010), among others, argued that the 'Cambrian explosion' was triggered by morphological novelties – the evolution of the bilaterian body plan with bilateral symmetry, an anterior mouth, through-gut, and posterior anus; the evolution of vision; and the evolution of a brain fully capable of acting on the visual input; all of which in turn triggered continued evolution and diversification in a predator/prey call and response-like manner (see also Conway Morris 1993, 2000; Bengtson 2002; Parker 2003; Murdock & Donoghue 2011). It has also been suggested that the Cambrian biodiversification event coincides with a unique increase in genome size (Li & Zhang 2010). Environmental factors such as raised levels of free oxygen, changes in sea level and water chemistry, tectonic processes, and a meteorite impact event have also been suggested as possible triggers (Knoll & Carroll 1999; Conway Morris 2002; Grey et al. 2003; Fike et al. 2006; Canfield et al. 2007; Yin et al. 2007; Shu 2008; Peters & Gaines 2012). But no evolutionary event is an island; hence, the explanation is most likely complex and is consequently subject to multidisciplinary studies. Despite immense amounts of data cumulated over the past century, the nature of the origin of metazoan phyla remains an area of discussion and speculation (Seilacher et al. 1998; Budd & Jensen 2000; Conway Morris 2000, 2003; Budd 2003; Cohen & Weydman 2005; Graur & Martin 2004; Conway Morris 2006; Raff 2008; Shu 2008; Nielsen & Parker 2010; Telford 2011).

Sclerites, scleritomes and reconstructions Scleritomes are mineralized or chitinous multicomponent skeletal structures of invertebrate animals2 (Bengtson 1985). The individual elements of a scleritome, usually termed sclerites3 (Bengtson 1970), may be numerous, as in echinoderms, or few, as in polyplacophorans. A scleritome comprises one or several sclerite morphotypes; these may or may not display gradual morphological transitions, be irregular or symmetrical, and occur in right- and left-mirrored morphologies (Figure 1).

While preserved complete articulated scleritomes are rare, disarticulated sclerites are common constituents throughout the fossil record of all geological systems, the Cambrian being no exception; it is part of a palaeontologist’s mission to put them back together as accurately as possible. However, reconstructing a scleritome from assemblages of individual sclerites poses a challenge fraught with optional solutions and potential traps (Bengtson 1985). After/while determining which sclerites

2 such as the skeletons of polyplacophorans, echinoderms, arthropods, armoured annelids, sponges, brachiopods, bivalves, and halwaxiids. 3 e.g. plates, cones, spines, scales, and valves, microscopic-macroscopic in size.

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actually belong to the same kind of organism4, it may be possible to distinguish different sclerite morphotypes. But unless there is a complete articulated specimen to refer to, the number of identified sclerite morphologies may not represent the true number of sclerites morphologies present in the scleritome.5 Next, it has to be determined how many sclerites of each type that belong to one specimen. How many sclerites of type x correspond to one sclerite of type y etc? In this phase any specimens representing two or more naturally articulated sclerites will prove very useful. This eventually leads to a puzzle phase, where the scleritome of the organism is to be reconstructed. This is accomplished using comparisons to known morphologies of extinct and extant taxa, observations from functional morphology and palaeoecology etc.

Figure 1. Line drawing illustrating morphology transitional series for an assemblage of hypothetical sclerites, dashed lines with arrows indicating symmetry planes and morphology transition paths. A, transitional series of bilaterally symmetrical sclerites. B, transitional series of asymmetrical sclerites occurring in enantiomorphic (left- and right-mirrored) symmetry pairs, as indicated by solid lines.

4 by means of mineralogy, gross morphology, size, mode of growth, external and internal surface features such as micro- and macro-ornamentation and shell structure. 5 The observed number of sclerite morphotypes may also vary, depending on whether close morphologies are regarded as variations within the same morphotype or as separate morphotypes.

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Building a house without a blueprint The reconstruction of a fossil organism is always more or less speculative. Limiting factors that may affect the outcome are preservation, amount of available material, and the presence of model organisms and blueprints. Taphonomy, the study of the decompositional processes through which remains of an organism pass post mortem – including purely biological processes like scavenging and decay of soft tissue, chemical processes such as dissolution and recrystallization of mineralised hard parts, and mechanical processes like bioturbation and large-scale reworking of sediments – is also an important factor. As some materials are more resistant to degrading processes than others, this may result in bias in the fossil record. At the same time, partial dissolution or recrystallization and mechanical wear of hard parts may cause preservational artefacts in the fossil itself. Hence, well-preserved material is easier to discriminate than poorly-preserved, and in situ preservation is preferable to reworked material. Exceptional preservation, such as in Cambrian fossil lagerstätten6 like the Burgess Shale, the Kinnekulle Orsten or the Chengjiang biota, where even unmineralized and fragile features may be preserved, represent the dream scenario for every palaeontologist (see for example Müller & Walossek 1985; Briggs et al. 1994; Gabbott 2006; Gabbott et al. 2004; Hou et al. 2004).

Well-preserved, articulated specimens may serve as models or blueprints for the reconstruction of related, poorly-preserved and/or disarticulated material (see for example the discussions of the history of conodonts and of Halkieria Poulsen, 1967 below). In the absence of blueprints, the most valuable help would be naturally articulated specimens, indicating the true nature of the original skeleton. Poorly-preserved, reworked and small assemblages increase the risk for miscalculations and erroneous conclusions. There is also the intermediate alternative, where the reconstruction into complete scleritomes and identification of taxa may be difficult, even though the affinities of the individual sclerites are clear, as is the case, for example, with many sponges and echinoderms.

Following this, reconstructions of scleritomous fossil organisms could be categorized into three major groupings, each one indicating how close to or far from the true architecture of the original scleritome the reconstruction is likely to be (Table 1), relatively speaking.

Category 1: Reconstructions of organisms of known affinities, i.e. where described findings of complete specimens can serve as a blueprint to follow when reconstructing the scleritome of disarticulated specimens, e.g. trilobites and polyplacophorans. These reconstructions are fairly reliable.

6 sedimentary deposit exhibiting extraordinary fossil richness (konzentrat or concentration lagerstätte) or exceptional fossil preservation (konservat or conservation lagerstätte).

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Category 2: Reconstructions of scleritomes of organisms of known taxonomic affinity, but with an obscure or complex sclerite arrangement, e.g. echinoderm plates and sponge spicules that may be comparatively easy to identify taxonomically but still hard to reconstruct correctly owing to the complexity or plasticity of the scleritome structure.

Category 3: Reconstructions of scleritomes of more or less unknown organisms where the very affinity of individual sclerites or associations of sclerites may be problematic in itself. In such cases the reconstruction of the scleritome may be a morphological jig-saw puzzle open for speculation. This is the case for the fossil organisms dealt with in this thesis, Trachyplax (I) and tommotiids (II-V).

Table 1. Scleritome reconstruction categories 1-3.

Model organisms/blueprints available

Sclerite/scleritome affinities

Expected scleritome reconstruction accuracy (relative)

Category 1 yes Known high-medium

Category 2 yes, or at least partial known, at least to a certain extent, but reconstruction may be obstructed owing to scleritome complexity

medium-low

Category 3 no Unknown low, reconstruction highly speculative

This kind of categorization is not only applicable to reconstructions of scleritomous taxa, but to any organism with a multi-component skeleton, also those with internal hard parts, such as vertebrates. The first reconstruction of a fossil organism is almost always of speculative nature. Hence, most multi-component fossils of which we know the true architecture today were first described according to the criteria of Category 3 and have advanced to Category 1, sometimes via Category 2, as more detailed data and better preserved specimens have become available.

The extinct conodont animal provides a good example. Conodonts, originally described as spiny tooth-like phosphatic microfossils, were first discovered by Pander in 1856, and for about one century they were exclusively known as individual elements unlike other known fossil – Category 3. About 80 years later, Schmidt (1934) and Scott (1934) reported naturally-occurring conodont assemblages, showing that the individual tooth-like fossils belonged to a multicomponent apparatus, usually comprising several different morphologies. Because of their geographic distribution and excellent fossil record conodonts make good index fossils and are widely used for stratigraphic correlations, not least within the oil

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industry. Partly because of their economic value in connection with oil exploration, conodonts have formed the subject of thousands of scientific studies and publications; they have been proposed to be remains of e.g. plants, rotifer teeth, molluscan radulae, arthropod organs, lophophorates elements, annelid jaws and chordates – Category 2. Almost another half century would pass, however, before the true nature of conodonts was discovered. Briggs et al. (1983) described the unique finding of a small, well preserved, elongate soft-bodied animal from lower Carboniferous deposits in the Edinburgh district, Scotland. The animal comprised a head with a pair of lobate structures, behind which a conodont apparatus was located (seemingly in situ), followed by a stretched slender body with posterior and caudal fins, and it was suggested that the conodont apparatus served as teeth rather than internal support (Briggs et al. 1983) – Category 1. Conodonts are now regarded as chordates, but their exact relationship to other taxa and biological affinities remains to be resolved.

The concept of scleritomes has received increasing attention as the number of described taxa with various types of sclerites and scleritomes have increased both in numbers and in morphological diversity (Bengtson 1985, 2004; Conway Morris 2006). Fossils from the Cambrian period have been of particular interest in this context, not only because they represent early metazoan life forms, but also because many fossils from around this time exhibit complex multi-component skeletal structures. One thing that many of them have in common is that they are often interpreted as bilaterally symmetrical “slug”-shaped organisms, which may well reflect the limits of human fantasy. However, we can only use the tools and models at hand when reconstructing these organisms, and many of the described animals and trace fossils from this period are bilaterally symmetrical. A familiar example is provided by Halkieria, originally described as isolated sclerites from the Cambrian of Denmark (Poulsen 1967) (Category 3). Based on the isolated blade-like sclerites, one single natural sclerite association comprising three sclerites (Bengtson & Missarzhevsky 1981), and using the Cambrian Wiwaxia Matthew, 1899 as a model, it was reconstructed by Bengtson & Conway Morris (1984) as a slug-like bilaterian (Category 2). Discovery of articulated specimens of Halkieria evangelista Conway Morris & Peel, 1995, from the lower Cambrian Sirius Passet fossil lagerstätte of North Greenland, not only served to test the reconstruction but, surprisingly, also introduced additional skeletal elements in the form of prominent anterior and posterior shields not foreseen by the model (Category 1). Vinther & Nielsen (2005) suggested assignment of Halkieria to a new class within the Mollusca, the Diplacophora, mainly based on morphological and structural similarities with polyplacophorans. Based on the Burgess Shale fossil Orthrozanclus reburrus Conway Morris & Caron, 2007, the halkieriids and the wiwaxiids were joined in the proposed monophyletic group Halwaxida, which was

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suggested to form part of the stem group of the Mollusca, or a larger group of lophotrochozoan phyla (Conway Morris & Caron 2007).

'Problematica' and problematic lophotrochozoans A key aspect of modern biology and palaeontology is the subject of phylogenetics which strives to contribute to the understanding of how different metazoan taxa are related to each other through their evolutionary history (phylogeny). Such taxonomic classification of organisms relies on the quality and quantity of available information on biological affinities, morphology and age of fossils, as well as molecular data from studies of extant metazoans (phylogenetic signal). As inferred in previous sections, the recognition and assignment of organisms to known phylogenetic groupings (extinct or extant) can be difficult, when phylogenetic signals, for some reason, are weak. Such taxa are often referred to as 'Problematica' (see for example Bengtson 1986; Conway Morris 1991; Yochelson 1991; Jenner & Littlewood 2008).

Jenner & Littlewood (2008) listed three major biological reasons for which phylogenetic signals may be absent or insufficient: (i) rapid succession of lineage splitting events may limit the phylogenetic signal, such that there is not enough time for distinctive features useful for grouping descendant species to evolve; (ii) extinction of organisms may hinder conclusions concerning homology/homoplasy between clades, or even completely obliterate phylogenetic signal should the organisms not be discovered; and (iii) evolution of non-phylogenetic signal, such as characters resulting from convergent evolution, hybridization and parallelism, may strongly distort or completely conceal true phylogenetic signals (especially when it comes to clades with short stems and long terminal branches).

These categories are applicable to both living and fossil organisms. When it comes to fossils, however, there are several additional factors that may complicate the interpretation and obstruct the signals. These, also listed in the section on scleritome reconstruction above, include taphonomy, preservational artefacts, incomplete specimens and assemblages, typological thinking7, and the fact that our interpretations of fossil remnants inescapably are based on our knowledge of extant organisms and that this might impede innovative solutions.

The older the fossils, the more likely it is that phylogenetic signal is obstructed or lost. Problematic metazoan fossils are comparably common

7 when the body plan of a fossil does not fit that of any living phylum, it is not uncommonly classified as Problematica, although this kind of reasoning does not meet the requirements of phylogenetic logic (Bengtson 1986; Briggs et al. 1992; Budd & Jensen 2000; Jenner 2006; Jenner & Littlewood 2008).

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from the time around the Precambrian-Cambrian boundary. This is to be expected, as it was a time of relatively rapid divergence of many animal lineages, and also the time when the first preservable hard parts evolved. As some of these fossils may look spectacular when compared to extant metazoans, they may attract a broad interest on a superficial plane in popular science media, as well as within the broader scientific community. But looks are not everything, and it cannot be stressed enough that these fossils, as well as less spectacular ones, may also provide invaluable information on the timing and evolution from stem to crown groups (Bengtson 1986; Budd & Jensen 2000; Budd 2003; Jenner & Littlewood 2008 among others). Studies of extant organisms may provide information on which group is related to which, but if we wish to trace the process and the timing of evolutionary events that resulted in our modern biota, the fossil record is perhaps our only source of information. Therefore, the study of Cambrian Problematica is a vital tool when untangling the branches of the tree of metazoan life. Advances within this field rely heavily on extensive fieldwork and discoveries of new, more informative, specimens, as well as detailed studies of morphological and ultrastructural features.

The three major clades of the Bilateria – the Deuterostomia8, the Ecdysozoa9, and the Lophotrochozoa10 (Halanych 2004) – are all represented in the fossil record from around the Precambrian-Cambrian boundary and onwards. The Lophotrochozoa was first defined by Halanych et al. (1995) and includes all lophophorate phyla11 and all phyla that have a trochophore larva12. Many extinct problematic scleritomous groups, e.g. halwaxiids, machaeridians, multiplacophorans and tommotiids, have been suggested to belong to different lophotrochozoan phyla (see for example Conway Morris & Peel 1995; Williams & Holmer 2002; Conway Morris & Carron 2005; Vinther & Nielsen 2005; Vinther et al. 2008). Using the stem and crown group concepts, palaeontologists strive to resolve the phylogenetic relationship within the Lophotrochozoa, through identification and comparison of stems of the included groups on various taxonomic levels. The exact phylogenetic relationships within the Lophotrochozoa are still the focus of ongoing debate and in order to resolve this problem, studying, describing and comparing extant and extinct organisms assigned to this clade are important, ongoing, processes (Passamaneck & Halanych 2006; Helmkampf et al. 2008; Yokobori et al. 2008; Paps et al. 2009; Sperling et al. 2011).

8 e.g. hemichordates and echinoderms 9 e.g. arthropods and priapulids 10 e.g. brachiopods and molluscs 11 i.e. organisms possessing the arm-like filter feeding apparatus called a lophophore, e.g. brachiopods, bryozoans and phoronids 12 e.g. molluscs, nemerteans and annelids

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Aims of this PhD thesis The time around the Precambrian-Cambrian boundary represent an important period in the history of metazoan evolution. The objective of this thesis is to critically examine the record of some early Cambrian phosphatic and calcareous sclerite assemblages with the aim of clarifying their phylogenetic relationships to the known record of Cambrian stem-group lophotrochozoans. The completely disarticulated calcareous sclerites of Trachyplax arctica Larsson, Peel & Högström, 2009, from the lower Cambrian of North Greenland were first described by Larsson et al. (2009), thus falling within Category 3 (Paper I; chapter 2). In contrast, the organophosphatic sclerites of the tommotiids Paterimitra pyramidalis Laurie, 1986 (Papers II, III, V) and Kulparina rostrata (Conway Morris & Bengtson in Bengtson et al., 1990) (Paper VI) from the lower Cambrian of South Australian, are perhaps more accurately placed somewhere in between Categories 2 and 3, since articulated sclerite composites indicating the original scleritome structure are known; additionally, they can be referred to each other and paterinid brachiopods based on their shell structure (chapter 3). Together with the paterinid brachiopod Askepasma Laurie, 1986 (Paper IV; chapter 3) they serve to illustrate the connection between stem- and crown-group taxa. Through these studies, the thesis also addresses different aspects of scleritome reconstruction, as the nature of the different sclerite assemblages offers different starting points for the reconstruction of their respective scleritomes.

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2. Multiplated enigmas from North Greenland

Fossiliferous Cambrian deposits exist on every continent around the globe. Since Koch's (1923) initial report of a series of unfossiliferous white limestones on the northern side of the Jørgen Brønlund Fjord in south east Peary Land, the Cambrian deposits of central North Greenland, have been closely studied and mapped (summarised by Peel & Sønderholm 1991; Ineson & Peel 1997; Henriksen et al. 2009; see Figure 2). Perhaps the most famous of these Cambrian deposits is the lower Cambrian Sirius Passet (konservat) lagerstätte derived from the Buen Formation on the eastern shore of J P Koch Fjord (Figure 2). A rich fauna of exceptionally-preserved fossils has been described subsequently (summarized by Peel 2010; Ineson & Peel 2011; Peel & Ineson 2011a, b; Vinther et al. 2011a, b), prominent amongst which is the scleritomous Halkieria evangelista, noted above.

A second lower Cambrian lagerstätte from North Greenland has been discovered in calcareous deposits of the Paralleldal Formation that, as part of the Brønlund Fjord Group (BFG), overlie the Buen Formation in southern Peary Land (Ineson & Peel 1997; see Figure 2). The silicified limestones in the lower part of the formation have yielded a rich silicified fauna including brachiopods (Popov et al. 1997), helcionellid and stenothecid molluscs, trilobites and operculate corals (Blaker & Peel 1997; Atkins & Peel 2004, 2008; Stein & Peel 2008; Peel 2011). The fauna also includes the enigmatic scleritomous Trachyplax arctica described in Paper I of this thesis.

Trachyplax arctica Larsson, Peel & Högström, 2009

The sclerites assigned to Trachyplax arctica (Paper I) include at least eight morphotypes (A-H, Figure 3; Paper I: figs 2-5), of which at least five (B-D and G-H) occur in enantiomorphic symmetry pairs, and two (A – by far the most common and therefore chosen as taxonomic defining element – and E) which show obvious bilateral symmetry, whereas the nature of sclerite type F is less clear. The recognition of the eight sclerite types as belonging to the same taxa is based on their size and roughness (several millimetres and rather thick and robust); composition (silicified, originally calcareous); mode of growth (marginal accretionary, reflected by external concentric growth lines); and the presence of radial ridges originating from the apex (spreading

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over parts of or the entire external surface). In addition, the different sclerite morphologies can be derived from each other and placed in a transitional series.

Figure 2. North Greenland locality map and stratigraphy. A, Box indicating area enlarged in B. B, locality map of Peary Land, central North Greenland, indicating position of Sirius Passet Lagerstätte (stared), Paralleldal (filled circle), Buen, Jørgen Brønlund Fjord, and J P Koch Fjord. C, stratigraphy of Paralleldal, indicating sampling horizon (filled circle). Modified from Larsson et al. 2009.

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As the material consists exclusively of isolated sclerites, without preserved internal shell structures, and as there are no previous descriptions of similar sclerites, Trachyplax represents a case with an apparent lack of model organisms. Only few other clues exist to aid scleritome reconstruction and analysis of phylogenetic relationship to other taxa. Consequently, the scleritome reconstructions discussed for T. arctica are highly speculative (Paper I: fig. 7), being mainly based on: sclerite type abundance; hypothetical sclerite type transitions (Paper I: fig. 6); and assumed functional morphology. They also reflect the inferred shallow marine top-of-mound environment that the animal probably inhabited, the roughness of the sclerites, as well as comparisons with a wide range of other multiplated taxa including molluscs (aplacophorans, polyplacophorans, multiplacophorans), halwaxiids and machaeridians. As such, Trachyplax arctica represents a prime example of the fossil scleritome Category 3 (as described in chapter 1 above) and the phylogeny of this fossil so far remains an enigma.

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Figure 3. A-T, Sclerite types A-H of Trachyplax arctica, all except B are external views. A-D, sclerite type A: A, dorsal, B, internal, and C, lateral views of average sized specimen (MGUH 29087, holotype); D, dorsal view of large specimen (MGUH 29090). E-F, sclerite type B: E, dorsal, and F, lateral views (MGUH 29091). G-H, sclerite type C: G, dorsal, and H, lateral views (MGUH 29094). I-K, sclerite type D: I, dorsal, J and K, lateral views (MGUH 29095). L-N, sclerite type E: L, dorsal, M and N, lateral views (MGUH 29097). O-P, sclerite type F: O, dorsal, and P, lateral views (MGUH 29098). Q-R, sclerite type G: Q, dorsal, and R, lateral views (MGUH 29101). S-T, sclerite type H: S, dorsal, and T, lateral views (MGUH 29102). Institutional abbreviation MGUH refers to the type collection of the Geological Museum, Copenhagen, part of the Natural History Museum of Denmark. All specimens are derived from Geological Survey of Greenland collection 274907.

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3. South Australian tommotiids and the evolution of paterinid brachiopod shell structures

Cambrian fossiliferous deposits have been known from South Australia for more than 130 years, and were first reported by Tepper (1879) from the Parara Limestone close to Ardrossan, Yorke Peninsula, which is part of the Stansbury basin (Figure 4). Over the years, the Cambrian stratigraphy and faunas of South Australia have been the subject of numerous studies (e.g. Tate 1892; Daily 1956; Dalgarno 1964; Debrenne 1970; Gravestock 1984; Bengtson et al. 1990; Gravestock et al. 2001; Jago et al. 2006, 2012, to mention a few). The Flinders Ranges stretch through the Arrowie basin (Figure 4), which contains the famous (Precambrian) Ediacara konservat lagerstätte with moulds and casts of early multicellular life forms preserved on the surface of sandstone slabs, the Ediacara biota. All specimens described and discussed in Papers II-VI are derived from spot samples and systematic sampling of measured sections cutting through thick carbonate-dominated lower Cambrian successions, representing shallow-water, carbonate platform (Ajax, Wilkawillina and Wirrapowie limestones) to outer shelf environments (lowermost Mernmerna Formation). For detailed descriptions of these sections see for example Paterson & Brock (2007); Skovsted et al. (2011a); Topper et al. (2011a, b).

The trilobite and small shelly faunas of the South Australian Cambrian sequences are commonly used for biostratigraphic zonation of these strata. In recent years, the early Cambrian small shelly fauna of South Australia has gained increasing attention as new and previously collected material have yielded partly articulated specimens shedding light on the nature of original scleritomes (Papers II-III,V-VI; Holmer et al. 2008; Skovsted et al. 2008, 2009b, 2011a, b; Topper et al. 2010, 2011b).

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Figure 4. Locality map. A, overview map of Australia, marking South Australia and Northern Territory, AB=Amadeus Basin. B, South Australia, dark shaded areas indicating Arrowie and Stansbury basins respectively, 1-7 indicating approximate positions of sampled sections and spot samples. 1 represents Horse Gully section (Bengtson et al. 1990; Gravestock et al. 2001). 2 area includes Mount Scott Range sections AJX-M and AJX-N. 3 represent Bunyeroo Gorge. 4 represents MMF. 5 represents Wilkawillina Gorge and includes Wilkawillina Limestone type section (WILK) and 10MS section. 6 area includes Elder Range (ER), Chase Range (CR1) and Druid Range spot locality. 7 represents spot locality close to Kanyaka ruins. YP= Yorke Peninsula. Modified from Papers II-V; Bengtson et al. (1990); Gravestock et al. (2001); and Jago et al. (2006).

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Tommotiids from South Australia Tommotiids, an extinct group of scleritome-bearing metazoans, are represented by minute organophosphatic sclerites of various shapes and uncertain affinity that occur in lower Cambrian deposits around the world (Rozanov et al. 1969; Landing 1984; Missarzhevsky 1989; Conway Morris & Chen 1990; Esakova & Zhegallo 1996); they are also well known from Australia (Laurie 1986; Bengtson et al. 1990; Gravestock et al. 2001). Historically, they were first recorded by Tate (1892) in his report on Cambrian fossils from South Australia, but were only proposed as a unique fossil group about 40 years ago (Fonin & Smirnova 1967; Rozanov et al. 1969; Bengtson 1970). Over the years, several early Cambrian genera of enigmatic, phosphatic small shelly fossils have been assigned to this group, e.g. Dailyatia Bischoff, 1976, Camenella Missarzhevsky in Rozanov et al., 1969, Eccentrotheca Landing, Nowlan & Fletcher, 1980, Lapworthella Cobbold, 1921, Micrina Laurie, 1986, and Porcauricula Qian & Bengtson, 1989.

Although tommotiid sclerites generally occur in distinct sclerite morphs, they are almost exclusively known from assemblages of disassociated sclerites, and have therefore commonly been regarded as a problematic group (but ontogenetically fused elements do occur, for relevant examples see Papers II, V and VI; Landing 1984, 1995; Li & Xiao 2004; Demidenko 2004; Skovsted et al. 2008, 2011a). The rarity of fused sclerite elements and partial scleritomes has undoubtedly hindered the formation of any firm conclusions regarding scleritome organization, biology, systematic position and ecology. Although tommotiids are generally considered to be members of the lophotrochozoan clade (Williams & Holmer 2002; Ushatinskaya 2002; Skovsted et al. 2008; Kouchinsky et al. 2012; Murdock et al. 2012), the group cannot be confidently assigned to any extant crown-group taxon.

As is the case for many scleritomous groups, early attempts to reconstruct tommotiids were restricted to bilaterally symmetrical, vagrant slug-like designs (see for example Bengtson 1970, 1977; Landing 1984; Evans & Rowell 1990; Williams & Holmer 2002; Demidenko 2004; Li & Xiao 2004), with the early Cambrian Halkieria evangelista serving as a model (see Bischoff 1976 for an alternative view). Skovsted et al. (2008), however, documented the very first finding of more complete tommotiid specimens in the form of partially articulated specimens of Eccentrotheca Landing, Nowlan & Fletcher, 1980, from the Arrowie basin. These specimens were later described as the new species Eccentrotheca helenia Skovsted, Brock, Topper, Paterson & Holmer, 2011(a). The material revealed a tubular scleritome comprising an unresolved number of low, cap-shaped sclerites forming a basal ring surrounding an apical aperture, and high, laterally compressed sclerites arranged in oblique rings forming an upper tubular structure (Figure 5 A-B; Skovsted et al. 2008, 2011a). The form of the

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organism suggests a sessile, filter feeder with a pedicle-like attachment structure emerging through the basal opening and the tube housing the main body and lophophore of the organism (Skovsted et al. 2008, 2011a).

Figure 5. A-B, articulated specimen of Eccentrotheca helenia, holotype SAMP 42537, lateral views, picture courtesy of Christian B. Skovsted. C, artificially produced specimen of Micrina etheridgei with conjoined sellate (s; CPC 39703) and mitral (m; CPC 39704) sclerites, lateral view, picture courtesy of Lars E. Holmer. All scale bars represent 500µm. Institutional abbreviations: SAMP, South Australian Museum, Palaeontological collection, Adelaide, Australia; CPC, Commonwealth Palaeontological Collections, Canberra, Australia.

Following the reinterpretation of Eccentrotheca, Skovsted et al. (2009b) suggested a high level-grouping of the Order Tommotiida Landing, 1984 into one 'camenellan' clade (comprising the families Lapworthellidae, Kennardiidae and Tommotiidae) and one clade comprising the Tannuolinidae and the 'eccentrothecimorph tommotiids' (Eccentrotheca, Paterimitra Laurie, 1986, Kulparina Conway Morris & Bengtson in Bengtson et al., 1990, Porcauricula Missarzhevsky in Rozanov et al., 1969 and Sunnaginia Missarzhevsky in Rozanov et al., 1969). Eccentrothecimorph tommotiids have been reconsidered as members of the stem group of the lophophorate phyla (i.e. Brachiopoda and Phoronida) and it has been hypothesized that the brachiopod body plan, with its two bilaterally symmetrical shells, evolved through a stepwise specialisation and reduction in the number of sclerites in eccentrothecimorph tommotiids (Papers II-IV; Skovsted et al. 2008, 2009b, 2011a; Balthasar et al. 2009; Kouchinsky et al. 2010; Murdock et al. 2012). This model was adopted by Holmer et al. (2008) who constructed a hypothetical scleritome of the tannuolinid Micrina etheridgei (Tate, 1892) consisting of one sellate and one mitral sclerite (Figure 5 C).

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Paterimitra pyramidalis – a stem-group brachiopod Until a few years ago, the tommotiid Paterimitra pyramidalis, originally

described from the Todd River Dolomite in the Amadeus Basin (Northern Territory; Figure 4 A), was known only from one sclerite type (Laurie & Shergold 1985; Laurie 1986; Bengtson et al. 1990; Gravestock et al. 2001). In papers II (Skovsted et al. 2009a), III (Holmer et al. 2011) and V (Larsson et al. submitted) of this thesis, the scleritome of Paterimitra is reconstructed, interpreted and discussed in the light of new findings of two additional sclerite types, partially articulated specimens, new data on shell micro- structure and in the context of biological and phylogenetic affinities of eccentrothecimorph tommotiids and paterinid brachiopods discussed in recent publications (Skovsted et al. 2008; Balthasar et al. 2009; Holmer et al. 2009; Skovsted et al. 2011a). The new material comprises over 1400 specimens derived from several stratigraphic sections measured through the Wilkawillina, Wirrapowie and Ajax limestones in the Arrowie Basin (AJX-M, AJX-N, MMF, 10MS, CR1, WILK, Bunyeroo Gorge, Druid Range spot locality; see Figure 4 B). Additionally, Bengtson et al. (1990) recorded Paterimitra from the Ajax Limestone in Mount Scott Range, Arrowie Basin, and Gravestock et al. (2001) from three sections in the Stansbury Basin (Horse Gully – HG00, CD-2, SYC-101; see Figure 4 B). Paterimitra pyramidalis mainly occur in the Abadiella huoi and Parara tatei trilobite zones (Paper V). The new material reveals that P. pyramidalis possessed at least three sclerite types (Papers II and V):

S1: the formerly known bilaterally symmetrical, pyramidal sclerite type, exhibiting

an open posterior side forming a triangular notch with a protruding subapical flange; laterally flanked by long lateral plates and an anterior plate, the edge of which forms a semi-circular anterior sinus together with the anterior-facing edges of the lateral plates (Figure 6 A-D).

S2: a bilaterally symmetrical triangular to saddle-shaped sclerite with a posteriorly upturned flange (Figure 6 E-H).

L: laterally compressed, highly variable, triangular to semi-circular, asymmetrical sclerites with a more or less pronounced apical twist and basal curvature (Figure 6 I-Q, U), sometimes confusingly similar to the laterally compressed sclerites of Eccentrotheca.

All three sclerite types share the same mode of internal accretionary growth and a characteristic polygonal micro-ornament (Figure 6 R). Most importantly, articulated specimens (n12) comprising S1 and S2 sclerites as well as S1 and L sclerites, occur in several samples. The articulated specimens exhibit one S2 sclerite nested within the triangular notch of one S1 sclerite resulting in a posterior opening, formed by the subapical flange and the upturned flange, and a shallow posterior sinus (Figure 6 S-T); and L sclerites lining the anterior sinus of the S1 sclerite (Figure 6 V).

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Figure 6. Paterimitra pyramidalis from the Flinders Ranges, South Australia. A-D, S1 sclerites: A, apical view (SAMP 46315); B, posterior view (SAMP 47840); C, lateral view (SAMP 47841); D, anterior view (SAMP 47842). E-H, S2 sclerites: E, apical view (SAMP 43306); F, lateral view (SAMP 47847); G, posterior view (SAMP 43305); H, apical view (SAMP 46316). I-Q, L sclerites: I, lateral, and K, apical views (SAMP 43311); J, lateral view (SAMP 47852); L, lateral view (SAMP 43312); M, oblique lateral view (SAMP 47853); N, oblique lateral view (SAMP 47854); O, oblique lateral view (SAMP 47855); P, apical view (SAMP 47858); Q, lateral view (SAMP 47859). R, external micro-ornament. S-T, articulated S1 and S2 sclerites: S, posterior, and T, lateral views (SAMP 43310). U, compound of articulated L sclerites (SAMP 47862). V, S1 sclerite L sclerites attached to the lateral plates, posterior view (SAMP 43314). Scale bar in R, 10µm; all other scale bars, 100µm. Institutional abbreviation SAMP, South Australian Museum, Palaeontological collection, Adelaide, Australia.

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Using Eccentrotheca helenia as a model, Paterimitra is reconstructed as a bilaterally symmetrical, tube- or cone-shaped, sessile filter feeder. One S1 and one S2 sclerite form a bowl-shaped base, corresponding to the basal ring of low cap-shaped sclerites in Eccentrotheca, with a pedicle-like attachment structure emerging from the posterior opening. Although no ring-like elements like those of Eccentrotheca are found for Paterimitra, L sclerites attached to S1 sclerites in several different ways indicate a similar arrangement. Consequently, the L sclerites in the reconstruction are arranged in oblique rings fitting the anterior sinus, forming a slightly expanding tube as the rings are stacked onto each other (Paper V, fig. 21). In this aspect, Paterimitra pyramidalis can be said to represent an early stage of Category 2 in the reconstruction phases described in chapter 1, as the better known scleritome of Eccentrotheca may represent a partial blueprint for the reconstruction. Following the findings of additional sclerite types, articulated specimens and inferred scleritome construction, Paper V also contains an emended diagnosis for the genus and sole species of Paterimitra.

Paper III describes the protegula and larval shells of Paterimitra and Micrina. Both are described as having posteriorly located protegula – on the sellate and the mitral sclerites of Micrina and on the S1 and S2 sclerites of Paterimitra. The interpretation for Paterimitra is slightly revised in Paper V, as it is shown that the protegulum of S2 sclerites is rarely preserved and the nature of it therefore remains questionable. Paper III also points to the similarity between the larval shell of Paterimitra S1 sclerites and the ventral larval shell of the stem-group rhynchonelliform Salanygolina Ushatinskaya, 1987, which possess a colleplax very similar to the anterior plate of S1 sclerites (Holmer et al. 2009). The larval shells of Micrina and Paterimitra are homologized with the valves of brachiopods, and the bivalved brachiopod shell is proposed to represent paedomorphic retention of the larval condition in tommotiids.

Askepasma, Paterimitra and the evolution of the paterinid brachiopod shell structure Paterinids are the oldest known organophosphatic brachiopods (Williams et al. 1996; Laurie 2000). Paper IV (Topper et al. in press) reports on the oldest brachiopods from the lower Cambrian Ajax, Wilkawillina and Wirrapowie limestones and the Mernmerna Formation in the Arrowie Basin, South Australia. Askepasma toddense Laurie, 1986, (Figure 7 A-H) mainly occurs within the Abadiella huoi Zone (in sections AJX-M, AJX-N, 10MS, Bunyeroo Gorge, WILK, MMF, ER-9, and Druid Range spot locality; see Figure 4 B). A new species, Askepasma saproconcha (Figure 7 I-O), is older, occurring in pretrilobitic strata (sections CR1, WILK, and Kanyaka

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ruins spot locality; see Figure 4 B). The genus Askepasma was erected by Laurie (1986), who recorded specimens from the lower Cambrian Todd River Dolostone in the eastern Amadeus Basin, Northern Territory (Figure 4 A). Specimens of Askepasma have been reported previously also from the southern Arrowie Basin by Holmer et al. (2006) and from the Stansbury Basin by Gravestock et al. (2001: Horse Gully and SYC-101; see Figure 4 B).

Figure 7. Cambrian paterinid brachiopods Askepasma toddense and Askepasma saproconcha, from South Australia. A-H, Askepasma toddense. A-D, ventral valves. A, plan view of ventral exterior (SAMP 47069). B, lateral, and C, posterior views of ventral exterior (SAMP 47072). D, plan view of ventral interior (SAMP 47073). E-G, dorsal valves. E, plan, and F, lateral views of dorsal exterior (SAMP 41668). G, plan view of dorsal interior (SAMP 41667). H, close up of external micro-ornament (SAMP 47071). I-Q, Askepasma saproconcha. I-M, ventral valves. I, plan, and K, posterior views of ventral exterior (SAMP 41646). J, oblique lateral view of ventral exterior (SAMP 47085). L, close up of external micro-ornament (SAMP 47121). M, plan view of ventral interior (SAMP 47089). N-P, dorsal valve. N, plan, O, oblique lateral, and P, posterior views of dorsal exterior (SAMP 47095). Q, anterior view of articulated valves (SAMP 47088). Scale bar in H, 50µm; scale bar in L, 10µm; all other scale bars, 1mm. Institutional abbreviation SAMP, South Australian Museum, Palaeontological collection, Adelaide, Australia.

Eccentrothecimorph tommotiids show many similarities to early paterinid brachiopods, including morphological (Papers II and V; Skovsted et al.

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2011a) and ontogenetic characters (Paper III). Yet another aspect which strengthens the suggested close phylogenetic relationship between eccentrothecimorph tommotiids and paterinid brachiopods, is their strikingly similar microstructure (Papers IV-V; Balthasar et al. 2009). Both Paterimitra pyramidalis and Askepasma toddense exhibit a first and second order lamination of the shell, and a shell-permeating network of polygonal compartments, which is also reflected in a characteristic external reticulate micro-ornament. In fact, the similarities are so strong that they are virtually indistinguishable when studied in polished cross sections. Eccentrotheca possess the same shell micro-structure, but lacks the external polygonal ornament. It is further suggested that the shell-permeating organic framework in Paterimitra might represent a precursor of organic envelopes defining the shape of calcite fibres in rhynchonelliform brachiopods (Papers IV-V).

Even the name Paterimitra strives to reflect the similarity in structure and ornament between the sclerites and the shells of the paterinid brachiopods Paterina Beecher, 1891 and Micromitra Meek, 1873 (Laurie 1986). Since Paterimitra combines so many specific tommotiid (especially Eccentrotheca) and paterinid brachiopod features, it is proposed that it represents a transitional stage in the stepwise evolution of paterinid brachiopod from an Eccentrotheca-like ancestor. Therefore it is a stem-group brachiopod.

Kulparina rostrata: 1+1=1 The tommotiid species Kulparina rostrata Bengtson in Bengtson et al., 1990, and ‘Eccentrotheca guano’ Conway Morris & Bengtson in Bengtson et al. 1990, were originally reported as disassociated sclerites from the Kulpara and lower Parara limestones of Horse Gully section in the Stansbury Basin (Figure 4 B), where they co-occur at three sample horizons (Bengtson et al. 1990). Both species have been recorded subsequently in several sections, spot locality samples and drill cores in the Stansbury (Gravestock et al., 2001) and Arrowie basins (Skovsted et al., 2011a) (Figure 4 B). In Paper VI (Larsson et al. manuscript) these two species are united and re-described as the single species Kulparina rostrata (Conway Morris & Bengtson in Bengtson et al. 1990) with a revised diagnosis. The main reason for this interpretation (briefly inferred by Skovsted et al. 2009 and 2011a) is the discovery of articulated specimens comprising sclerites of both K. rostrata and ‘E. guano’ from the Wilkawillina Limestone type section, Bunyeroo Gorge, in the Arrowie Basin (Figure 4 B). Sclerites of ‘E. guano’ occur at a total of nine sample horizons, five of which also contain sclerites of K. rostrata.

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Figure 8. Sclerites of Kulparina rostrata, from Wilkawillina Limestone type section, Wilkawillina Gorge, Bunkers Graben, South Australia. A-J, S1 sclerites of Kulparina rostrata: A, posterior, and B, apical views (SAMP 44786); C, posterior view (SAMP eeeee); D, posterior view (SAMP xxxxx); E, posterior view of large pyramidal sclerite with two fused accessory sclerites (SAMP 44787); F, posterior, and G, anterior views (SAMP zzzzz); H, oblique apical view of pyramidal sclerite fused with three accessory sclerites (SAMP 44785); I, posterior view (SAMP 44788); J, oblique apical/anterior view (SAMP ggggg). K-S, L sclerites of Kulparina rostrata: K, lateral view (SAMP ttttt); L, lateral view (SAMP 44780); M, lateral view (SAMP mmmmm); N, oblique lateral view (SAMP ooooo); O, lateral view (SAMP 44781); P, lateral view of ontogenetically fused sclerites (SAMP rrrrr); Q, lateral view of ontogenetically fused sclerites (SAMP wwwww); R, lateral view of ontogenetically fused sclerites (SAMP 44775); S, lateral view of ontogenetically fused sclerites (SAMP äääää). All scale bars represent 200µm. Institutional abbreviation SAMP, South Australian Museum, Palaeontological collection, Adelaide, Australia.

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In the original description, the sclerites referred to as Kulparina rostrata were considered to be asymmetrical, occurring in dextral and sinistral morphologies, and the terminology introduced for the tommotiid Sunnaginia, describing the relationship between the different sides (‘S1, S2, S3’) and lobes (‘L1, L2, L3’) of the sclerite (Landing et al. 1980; Bengtson et al. 1990) was used. The new material (Paper VI) proves that these sclerites are actually close to bilaterally symmetrical (Figure 8 A-J). The sclerite morphology closely resembles that of the S1 sclerites of Paterimitra pyramidalis and consequently the terminology used to describe Paterimitra S1 sclerites has been adopted, despite the risk of confusion with the old Sunnaginia ‘S’ and ‘L’ terminology which is no longer applicable for Kulparina.

As previously pointed out (Papers II and V; Skovsted et al. 2008, 2011a), the laterally compressed sclerites of Eccentrotheca are very similar to the L sclerites of Paterimitra. This is also true for sclerites described as ‘E. guano’ (Figure 8 K-S). Although these are considerably more irregular and unpredictable when it comes to growth, their gross shape and the way they are attached to S1 sclerites of Kulparina and the complex structures they form when attached to each other are strongly reminiscent of Paterimitra (Paper VI; Figure 8 S). Consequently, sclerites previously described as ‘Eccentrotheca guano’ are suggested as being termed L sclerites of Kulparina rostrata, the terminology for Paterimitra L sclerites being applied when convenient.

Finding a suitable equivalent to the S2 sclerites of Paterimitra proves considerably harder, but several possible explanations are discussed in Paper VI, based on the broad variability in the S1 sclerites of Kulparina rostrata and possible bias factors, including quality and sorting of the material. Like Paterimitra, Kulparina is considered to be a sessile filter feeder possessing a modified tubular scleritome, and it qualifies for reconstruction in Category 2, slightly below Paterimitra. Even this remains uncertain, however, as at least one sclerite type is believed to be awaiting discovery. ‘Eccentrotheca guano’ + Kulparina rostrata = Kulparina rostrata.

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4. Svensk sammanfattning

Den kambriska explosionen – djurlivets tidiga evolution Omständigheterna kring metazoernas13 tidiga evolution och diversifiering gäckar än idag paleontologer, paleobiologer och evolutionsbiologer världen över. Begreppet den kambriska explosionen syftar både på den tillsynes plötsliga uppkomsten och snabba spridningen av metazoiska kroppsorganisationer (body plans), som på utvecklingen av fossiliserbara mineraliserade eller kitinösa hårddelar (t ex skal, tuber, skleriter och tänder), som ägde rum för omkring 500-600 miljoner år sedan. Att de flesta av de djurfyla som vi känner till idag hade utvecklats redan vid slutet av kambrium råder det stor enighet om inom den moderna forskarvärlden. Men flercelliga djurliknande organismer existerade redan under prekambrisk tid, även om fossil av dessa är relativt ovanliga. Ett välkänt exempel är Ediacara-faunan, som utgörs av flercelliga, senprekambriska organismer bevarade som avgjutningar och avtryck i sandsten. Men då nästan samtliga av dessa organismer saknade fossilliserbara hårddelar är fossilen synnerligen svårtolkade och deras släktförhållande till de efterkommande kambriska metazoerna är än så länge höljt i dunkel. Det verkar dock troligt att en del ediacarafossil representerar stambilaterier 14 15. Kambriska fossila lämningar finns däremot världen över och är förhållandevis rika på såväl fossiliserade hårddelar och spårfossil, som detaljrik mjukdelsbevaring.

Även om många stambilaterier kan ha existerat redan under senprekambrisk tid, verkar det alltså som att uppkomsten av moderna fyla sammanfaller med utvecklingen och diversifieringen av mineraliserade hårddelar i början av kambrium. Detta leder osökt till frågor om hur och varför de helt mjukvävnadsbaserade metazoerna, inom en geologiskt sett väldigt kort tidsrymd, utvecklade en mängd varierande kroppsorganisationer med skal och/eller tänder. Var det en ömsesidig kapprustning hos rovdjur och bytesdjur orsakad av evolutionen av bilateralsymmetri, syn och ett komplext nervsystem? Hade det något samband med den anmärkningsvärda 13 Metazoa – vetenskaplig samlingsterm för flercelliga djur. 14 Bilateria – vetenskaplig samlingsterm för metazoer med en bilateralsymmetrisk kroppsorganisation. 15 en krongrupp representerar den sista gemensamma anfadern till alla levande former i ett fylum och alla dess ättlingar; en stamgrupp representerar en evolutionär serie helt utdöda organismer vilken leder fram till krongruppen, bort från den sista gemensamma anfadern för det aktuella fylumet och det närmast besläktade fylumet.

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ökningen av genomets storlek som inträffade under samma tid? Eller var det så att den kambriska explosionen triggades igång av miljöfaktorer såsom ökad tillgång till fritt syre, förändringar i havsnivån och havets kemiska sammansättning, tektoniska processer eller kanske meteoritnedslag? Förklaringen är rimligtvis komplex och de föreslagna omständigheterna kring metazoernas ursprung och diversifiering är än idag högst diskutabla.

Skleriter, skleritom och rekonstruktioner – att bygga ett hus utan ritningar Skleritom är mineraliserade eller kitinösa yttre (eller inre) skelett hos ryggradslösa djur, bestående av multipla komponenter (Bengtson 1985). De enskilda komponenterna i ett skleritom, skleriter, kan vara många (som hos tagghudingar) eller få (som hos polyplakoforer); förekomma i en eller flera morfotyper/sklerittyper, vilka ibland går att placera i gradvisa morfologiska övergångsserier; och vara asymmetriska, symetriska eller uppträda i höger- och vänsterorienterade (enantiomorfa/speglade) symmetripar (Figur 1). Fossil av kompletta artikulerade skleritom är tämligen sällsynta, medan disartikulerade skleriter ofta är vanliga komponenter i fossila lämningar från samtliga geologiska perioder, även kambrium. Paleontologens uppgift består bl a i att rekonstruera skleritom från samlingar av enskilda skleriter. En uppgift vars svårighetgrad varierar beroende på materialets beskaffenhet. Vilka skleriter härrör från samma sorts djur? Hur många sklerittyper finns det? Hur många skleriter av varje typ kan det rimligtvis ha funnits i det ursprungliga skleritomet? Är organismen känd sedan tidigare? Finns det en modell att utgå från? Alla dessa frågor måste besvaras i möjligaste mån. Sedan tar pusslandet vid…

Rekonstruktionen av en fossil organism begränsas av materialets bevaringsstatus och mängd. Dåligt bevarat, omarbetat material bestående av få komponenter ökar risken för felaktiga slutsatser. Exceptionellt välbevarade kompletta fossil, som de från kambriska lagerstätten16, där till och med ömtåliga och omineraliserade delar finns bevarade, utgör en ovärderlig informationskälla, då de kan tjäna som ritningar att gå efter vid rekonstruktion av disartikulerat material. I avsaknad av modellorganismer kan förekomsten av artikulerade fragment ge en fingervisning om skleritomets ursprungliga uppbyggnad. Många kambriska djur var av bilateralsymmetrisk, ”snigelliknande” natur och i brist på alternativa modellorganismer har många rekonstruktioner av kambriska skleritom tagit sin utgångspunkt i dessa. Något som i flera fall behövt omprövas och revideras. Rekonstruktioner av fossila skleritom kan delas in i tre kategorier, där varje kategori ger en relativ indikation om hur nära eller långt ifrån 16 sedimentära avlagringar vilka uppvisar extraordinär fossilrikedom (konzentrat lagerstätte [ty]) eller exceptionellt välbevarade fossil (konservat lagerstätte [ty]).

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originalskleritomets verkliga uppbyggnad rekonstruktionen skulle kunna ligga (Table 1). Kategori 1: Rekonstruktioner av skleritom av organismer av känd biologisk

affinitet17, där beskrivna kompletta exemplar kan tjäna som ritningar att följa, t ex trilobiter och polyplakoforer. Dessa rekonstruktioner är relativt tillförlitliga.

Kategori 2: Rekonstruktioner av skleritom av organismer där de individuella skleriternas affinitet är relativt klar, men där rekonstruktionsarbetet och den taxonomiska identifieringen av organismen försvåras av själva skleritomets komplexitet (t ex svampdjur och tagghudingar). Organismer kan vara relativt enkla att identifiera men ändå tämligen komplicerade att rekonstruera.

Kategori 3: Rekonstruktioner av skleritom av okända organismer, där skleriternas affinitet i sig kan vara problematisk. Hör skleriterna ens ihop egentligen? I dessa fall är hela rekonstruktionsarbetet som att bygga ett hus utan tillgång till ritningarna – man får lita till sin erfarenhet och yrkesskicklighet.

Den första rekonstruktionen av en fossil organism är alltid mer eller mindre spekulativ. De flesta fossil med multipla komponenter vars verkliga uppbyggnad vi känner idag, beskrevs ursprungligen enligt kriterierna för Kategori 3 och har sedan avancerat till Kategori 1, inte sällan via Kategori 2, i takt med att nya data har blivit tillgängliga. Ett typexempel är Halkieria, som ursprungligen beskrevs som isolerade skleriter från kambriska avlagringar i Danmark (Poulsen 1967; Kategori 3). Baserat enbart på dess bladlika skleriter, en enhet bestående av tre naturligt artikulerade skleriter och med den kambriska Wiwaxia som utgångsmodell rekonstruerades Halkieria senare som en snigelliknande bilaterie (Bengtson & Conway Morris 1984; Kategori 2). Upptäckten av välbevarade kompletta exemplar av Halkieria evangelista i underkambriska Sirius Passet lagerstätte på norra Grönland, stödde den föreslagna rekonstruktionen, men visade också att organismen hade en främre och en bakre sköld, vilket modellen som använts inte kunnat ge någon indikation om (Conway Morris & Peel 1995; Kategori 1).

'Problematica' och lofotrochozoer En central gren inom modern biologi och paleontologi är fylogenetik. Den studerar hur olika organismer är besläktade med varandra, baserat på deras evolutionära historia (fylogeni). En sådan taxonomisk indelning av fossila organismer är helt beroende av kvalitén på och mängden tillgängliga data rörande biologisk affinitet, morfologi och fossilets ålder, liksom molekylära data från studier av nu levande metazoer (fylogenetisk signal). Identifieringen av fossila organismer och placeringen av dem i kända fylogenetiska grupperingar (utdöda eller nu existerande) kan försvåras avsevärt om den fylogenetiska signalen av någon anledning är svag. Sådana

17 släktskap, tillhörighet, samhörighet.

36

taxa benämns ofta Problematica (se t ex Bengtson 1986; Conway Morris 1991; Yochelson 1991; Jenner & Littlewood 2008). Sannolikheten för att den fylogenetiska signalen ska vara försvagad eller rent av gått förlorad, ökar med fossilets ålder. Det är därför inte en slump att fossil av problematiska metazoer är relativt vanliga från tiden kring den prekambriska/kambriska gränsen. Problematiska kambriska organismer utgör en viktig informationskälla i studier rörande utvecklingen av stam- och krongrupper, samt i arbetet med rekonstruktionen av de metazoiska livsformernas evolutionära träd (Bengtson 1986; Jenner & Littlewood 2008, m fl).

Bilateria delas in i tre övergripande grupperingar – Deuterostomia18, Ecdysozoa19 och Lofotrochozoa20 (Halanych 2004) – vilka alla är välrepresenterade i fossila lämningar från omkring den prekambriska/kambriska gränsen och framåt. Lophotrochozoa definierades av Halanych m fl (1995) som en grupp bestående av samtliga lofoforata fyla21 och alla fyla som har en trochofor-larv22. Halwaxiider, machaeridier, multiplakoforer och tommotiider är exempel på några av de många utdöda problematiska skleritom-bärande grupper som har föreslagits tillhöra olika lofotrochozo-fyla eller deras stamgrupper.

Avhandlingens syfte Tiden kring den prekambriska/kambriska gränsen utgör en mycket viktig period i djurlivets evolutionära historia. Målsättningen med denna avhandling är att kritiskt granska och beskriva förekomsten av ett antal samlingar av tidigkambriaska kalcitiska och organofosfatiska skleriter från problematiska lofotrochozoer, samt att bidra till att klarlägga deras fylogenetiska placering i förhållande till redan kända grupper av stamlophotrochozoer. Studierna tjänar också till att exemplifiera och illustrera några av de olika aspekterna av skleritomrekonstruktioner beskrivna i föregående textavsnitt.

Trachyplax arctica från Nordgrönland I artikel I i denna avhandling beskrivs den tidigare helt okända Trachyplax arctica utifrån en samling uteslutande disartikulerade kalcitiska (sekundärt förkislade) skleriter från den underkambriska Paralelldal-formationen i Peary

18 t ex hemichordater och tagghudingar 19 t ex leddjur och priapulidmaskar 20 t ex brachiopoder (armfotingar) och mollusker/blötdjur (bl a musslor, snäckor, bläckfiskar, polyplakoforer) 21 organismer med en lofofor, en armliknande vattenfiltreringsmekanism för födoinsamling, t ex brachiopoder (armfotingar), bryozoer (mossdjur) och phoronider (hästskomaskar) 22 t ex blötdjur, nemertiner (slem-/snörmaskar) och annelider (ringmaskar)

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Land, Nordgrönland (se kapitel 2, Figur 2-3). Antaganden om skleriternas affinitet grundas här på deras mineralogi, bevaringstillstånd, förekomst i samma prover, gemensamma morfologiska och ytstrukturella egenskaper, samt möjligheten att identifiera en morfologisk övergångsserie inkluderande samtliga sklerittyper. Utifrån detta diskuteras olika rekonstruktionsalternativ baserade på såväl relativ förekomst av olika sklerittyper, som på jämförelser med andra sklerit-bärande organismer från samma tid. Trachyplax fylogenetiska tillhörighet diskuteras också i ljuset av de likheter med andra organismer som kan observeras i det studerade materialet. Alla försök till rekonstruktioner och fylogenetisk tillhörighet måste i detta fall betraktas som högst spekulativa, då den information som är möjlig att extrahera ur materialet är tämligen vag och sparsmakad. Skulle materialet kategoriseras enligt ovan bestämda kriterier, skulle det utan tvekan hamna i Kategori 3.

Tommotiider från södra Australien och evolutionen av skalstrukturen hos paterinida brachiopoder Artikel II-VI (kapitel 3) behandlar den evolutionära kopplingen mellan tidigkambriska paterinider23 och tommotiider sett ur ett antal aspekter. Tommotiider är en utdöd grupp bestående av skleritom-bärande metazoer representerade av små, organofosfatiska skleriter av varierande former och oklar affinitet i underkambriska avsättningar över hela världen (Rozanov m fl 1969; Landing 1984; Missarzhevsky 1989; Bengtson m fl 1990; Conway Morris & Chen 1990; Esakova & Zhegallo 1996). Fram till väldigt nyligen var de nästa uteslutande beskrivna som disartikulerade skleriter och av denna anledning har tommotiider som regel betraktats som problematica. De flesta rekonstruktioner har begränsats till snigelliknande, frilevande konstruktioner, inte sällan med den kambriska Halkieria evangelista som utgångsmodell. Men 2008 beskrev Skovsted m fl. fynd av artikulerade exemplar av tommotiiden Eccentrotheca (senare beskriven som Eccentrotheca helenia av Skovsted m fl. 2011; Figur 5 A-B) från Australien (Figur 4). Dessa exemplar visar att skleritomet hade en tubformad arkitektur, uppbyggd av en basenhet bestående av ett fåtal låga breda plattor som omgärdar en apikal öppning; samt av på varandra staplade, lätt lutande ringar bestående av höga, lateralt tillplattade skleriter. Eccentrotheca tolkas nu som en sessil (fastsittande) vattenfilterande organism, med en fästanordning liknande brachiopoders pedikel som stack ut genom den apikala öppningen och en lofoforliknande konstruktion som rymdes tillsammans med större delen av djurets kropp i själva tuben – stamlofoforat.

Kort därefter rapporterades i Artikel II om de första fynden av artikulerade exemplar av den underkambriska tommotiiden Paterimitra 23 en utdöd grupp fosfatskaliga brachiopoder som existerade från tidig kambrium till mellersta ordovicium.

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pyramidalis (Figur 6), även den från Australien. Tidigare var endast en pyramidformad, bilateralsymmetrisk sklerittyp känd från denna organism. Vårt nya material innehåller ytterligare en bilateralsymmetrisk sklerittyp, en asymmetrisk sklerittyp (som morfologiskt sett är väldigt lik de höga, tillplattade Eccentrotheca-skleriterna), samt flera delvis artikulerade exemplar som ger en fingervisning om hur de olika sklerittyperna var placerade i förhållande till varandra i skleritomet. Ett tydligt signum för Paterimitra är dess karaktäristiska polygonala ornamentering. I Artikel III diskuteras förekomsten av protegula (embryonala skal) och larvalskal under tidiga ontogenetiska stadier24 hos tommotiiderna Paterimitra och Micrina (Figur 5 C), och indikationer dessa ger för släktskap med tidiga brachiopoder. Artikel IV i denna avhandling innehåller en beskrivning av den äldsta pateriniden från södra Australien, Askepasma saproconcha, och en reviderad beskrivning av den något yngre Askepasma toddense (Figur 7). Artikeln behandlar också skalultrastrukturen hos A. toddense, vilken är förvirrande lik skalultrastrukturen hos P. pyramidalis.

Alla dessa rön kokas i Artikel V ner till en grundligt reviderad beskrivning av Paterimitra pyramidalis, vars skleritom här rekonstrueras som en kon- eller tubformad, bilateralsymmetrisk struktur, med en bakre öppning motsvarande den apikala öppningen hos Eccentrotheca. Paterimitra tolkas som en sessil, vattenfiltrerande organism. Med stöd både i morfologi och i skalstruktur föreslås den representera ett övergångsstadium som introducerar en bilateralsymmetrisk kroppsorganisation i en utvecklingslinje från Eccentrotheca-liknande anfäder till paterinider – en stambrachiopod.

I Artikel VI revideras tommotiidarterna ’Eccentrotheca guano’ och Kulparina rostrata vilka befunnits representera en och samma art, Kulparina rostrata (Figur 8). Bevis för detta är bland annat fynd som tydligt visar skleriter av de båda typerna artikulerade med varandra. Med stöd i morfologiska likheter med såväl Eccentrotheca helenia (höga, lateralt tillplattade skleriter) som Paterimitra (bilateralsymmetriska, pyramidala skleriter) föreslås en liknande skleritomkonstruktion för Kulparina.

De rekonstruktioner som presenteras och/eller diskuteras i artiklarna om Paterimitra och Kulparina skulle om de kategoriserades enligt ovan angivna kriterier, hamna något närmare Kategori 2 än Kategori 3. Detta eftersom det i båda fallen finns artikulerat material och en partiell modellorganism, Eccentrotheca. Men så länge de kompletta skleritomen förblir okända måste även dessa rekonstruktioner betraktas som spekulativa, om än ett steg närmare målet.

24 ontogeni betecknar utvecklingsperioden av en organism från befruktning till könsmogen individ, i detta fall är det frågan om från embryo, via larv och så småningom till färdigutvecklad individ.

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5. Acknowledgements

First of all I would like to acknowledge all my supervisors for their support during my time as a PhD student. Their invaluable scientific knowledge, skills and experience, which they have never hesitated to share with me, is greatly appreciated. Anette Högström, my first main supervisor – thank you for initiating the project, for choosing me to be your first PhD student, and for supporting me and standing by my side in times of professional doubts as well as of personal losses. John Peel – thank you for getting me started when Anette was unavailable. Lars Holmer – thank you for introducing me to the South Australia SSF group in Sydney, bringing me to the field there and making sure I finished this. Glenn Brock – thank you for letting me join you for fieldwork in the Flinders Ranges, use the facilities in Sydney, fixing practical issues and bringing me and my family to Heron Island. Christian Skovsted – you stepped in when Anette moved on to new employment, thank you for taking over her role, for letting me use your office and for being so understanding and helpful. Anette, Christian! We were all completely inexperienced in our respective roles. I wish to emphasize that I have learned a lot from you, and, hopefully, you have learned something from me. Thank you for your time and good luck with you future students!

Thanks are due also to Uppsala University (Dept of Earth Sciences) for funding my PhD studies and to the Royal Swedish Academy of Sciences (KVA) for additional financial support.

Colleagues Åsa, Sandra, Sofia, Sebastian, Linda and Tim – without you I would not have lasted long as a PhD student. All other colleagues that have been in and out of the Palaeobiology Programme in Uppsala during my time here are also greatly acknowledged. Also many thanks to Stefan Bengtson at the Swedish Natural History Museum (NRM) for letting me use NRM facilities and, in so doing, saving me from many hours of commuting.

My deepest and sincerest thanks go to my family and friends. You have had to put up with much more than any of you deserve and without your support this thesis project would never have been possible.

Especially warm thanks and lots of love to Jocke, Selma and Fanny. Words cannot express how deeply thankful I am to you for letting me do this and for supporting me all the way through. Now it is done, now I am yours. Jag har snakat er!

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