Evolution and Taxonomy of Cambrian Arthropods from Greenland and Sweden

Home , Emeraldella, Godzilliidae, Holmiidae, Isoxys, Orsten, Ovatoryctocara

Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 558

Evolution and taxonomy of Cambrian arthropods from Greenland and Sweden

MARTIN STEIN

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I. Stein, M. 2008. Fritzolenellus lapworthi (Peach and Horne, 1892) from the lower Cambrian (Cambrian Series 2) Bastion Formation of North-East Greenland. Bulletin of the Geological Society of Denmark 56:1–10. II. Stein, M. & Peel, J. S. 2008. Perissopyge (Trilobita) from the lower Cambrian (Series 2, Stage 4) of North America and Greenland. GFF 130:71–78. III. Stein, M., Waloszek, D., Maas, A., Haug, J. T. & Müller, K. J. 2008. The stem crustacean Oelandocaris oelandica re-visited. Acta Palaeon- tologica Polonica 53:461–484. IV. Stein, M. (manuscript) A new arthropod from the Early Cambrian of North Greenland with a ‘great appendage’ like antennula. Submitted to Zoological Journal of the Linnean Society. V. Stein, M., Peel, J. S., Siveter, D. J. & Williams, M. (manuscript) Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland. VI. Lagebro, L., Stein, M. & Peel, J. S. (manuscript) A new arthropod from the early Cambrian Sirius Passet Fauna of North Greenland.

Reproduction of the published papers is made with kind permission from the copyright holders:

Paper I © Bulletin of the Geological Society of Denmark, Dansk Geologisk Forening Paper II © GFF, Geologiska Föreningen Paper III © Acta Palaeontologica Polonica, Instytut Paleobiologii PAN Statement of authorship Access to the material studied in papers I,–II, IV–VI was granted by J. S. Peel. Paper I: M. Stein performed the studies and wrote the manuscript. Paper II: M. Stein carried out the taxonomic studies and wrote the section on systematic palaeontology. J. S. Peel provided the introduction and the sections on material and stratigraphy. Paper III: M. Stein and D. Waloszek carried out most of the studies of the material. Initial reconstructions were created by M. Stein, D. Waloszek, and A. Maas. M. Stein created an early version of the three dimensional model of the largest stage and the animated sequence; J. T. Haug created the final version of the model of the largest stage and all models of the ontogenetic sequence. K. J. Müller collected the material. Manuscript mainly by M. Stein and D. Waloszek with contributions by the other authors. Paper IV: M. Stein performed the studies, created the reconstructions and wrote the manuscript. Paper V: Initial studies were carried out by M. Stein and J. S. Peel. Detailed studies were carried out by M. Stein, D. Siveter and M. Williams. Manuscript mainly by M. Stein with contributions by the other authors. Paper VI: L. Lagebro provided an initial study of the material. M. Stein performed detailed restudy and wrote the section on systematic palaeontology. J. S. Peel wrote the introduction.

Disclaimer The papers presented here are for the purpose of public examination as a doctoral thesis only. They are not considered publications according to the ICZN. Accordingly, all new taxonomic names and emendations in papers IV–VI are void. Authority for taxonomic work in papers I–III is by the original publications.

Front cover Reconstruction of Kiisortoqia avannaarsuensis from the early Cambrian Sir- ius Passet Lagerstätte of Greenland. Contents

Introduction ...... 7 Trilobite biostratigraphy ...... 9 Paper I ...... 10 Paper II ...... 12 Arthropod phylogeny ...... 14 The current status of euarthropod phylogeny from a neontological perspective ...... 15 The ground pattern and the importance of fossils ...... 16 The position of Trilobita ...... 19 Paper III ...... 21 Paper IV ...... 22 Paper V ...... 24 Paper VI ...... 25 Svensk sammanfattning ...... 27 Trilobit-stratigrafi på Grönland ...... 28 De tidiga leddjurens evolution ...... 29 Acknowledgments ...... 30 References ...... 31

Introduction

Arthropods are a diverse group of multicellular animals (metazoans), esti- mated to account for more than three quarters of the present-day metazoan diversity. They constitute an important element of many ecosystems, both marine and terrestrial. Four major groups are recognized among extant arthropods. The chelicerates include the familiar spiders, scorpions, mites, and ticks, and less familiar forms such as the horseshoe crabs. Crabs and lob- sters are grouped together as crustaceans, along with woodlice and krill, but also with smaller and less familiar forms such as brine-shrimps and the truly ubiquitous ostracodes and copepods, and even sessile forms such as barna- cles. Millipedes and centipedes comprise the myriapods, but the all but too familiar insects form the largest of all living arthropod groups. These four groups sharing a common ancestor constitute the Euarthropoda and are char- acterized by a unique body structure and movement apparatus where muscles do not act as antagonists to bones or fluid-filled pressure vessels lodged inside a ‘soft’ body. Rather, a firm cuticle, which is produced by the epider- mal cells surrounding the body, forms an ‘exoskeleton’ consisting of hard- ened (sclerotized) plates conjoined by soft membranous regions that allow for flexibility. Muscles, attached to the sclerotized parts, act against this ‘exoskeleton’. How the euarthropod groups are related to each other remains the subject of sometimes contentious debate. The nature of several small groups considered to be the closest relatives to the euarthropods is also debated. While there is consensus that the little known onychophorans (velvet worms) are arthropods in the wider sense, researchers still argue about if the minute tardigrades (water bears) belong to the group or are more closely related to roundworms. The pentastomids (tongue worms), a group of worm-like para- sites infesting the respiratory organs of land-living vertebrates (amphibians, ‘reptiles’, birds, and mammals) are widely accepted as arthropods. But are they the sister group to euarthropods or highly derived crustaceans, and thus euarthropods? Given their tremendous diversity, it is not surprising that arthropods have had a long evolutionary history, evident not least in a rich fossil record spanning the whole Phanerozoic. Most common in the fossil record are forms with well biomineralized (calcified) ‘exoskeletons’, such as trilobites or certain crustaceans, including ostracodes and malacostracans. Trilobites ap- peared early in the Cambrian and flourished through the whole Palaeozoic

7 prior to disappearing in the terminal Permian extinction. They are common and diverse components of Cambrian faunas and have been of paramount importance in biostratigraphic and palaeogeographic studies of that period for more than a century and a half. But the fossil record of arthropods is not just limited to forms with calcified ‘exoskeletons’. Throughout the Phanerozoic, examples of exceptional preservation of soft parts offer unique glimpses into past ecosystems. Arthro- pods form a surprisingly common element of these so-called lagerstätten, al- though taphonomic bias against various organism groups means that even these remarkable deposits do not necessarily mirror the true composition of the original ecosystems. In strata of the Cambrian system (542–488 Ma BP), the oldest period of the Phanerozoic, researchers have unearthed a number of fossil lagerstätten that have received particular public attention, notably the Burgess Shale of Canada, the Chengjiang Lagerstätte of China, or assem- blages of ‘Orsten’-type fossils from several places in the world. This attention is certainly largely due to our fascination with the apparent abrupt ap- pearance of fossil traces of multicellular life around the base of the Phanero- zoic. Many investigators believe that the earliest major diversification of metazoans took place as this era unfolded, a key event in the history of life. Whether this be true or not, Cambrian lagerstätten do provide the oldest available direct evidence of the early diversity of many metazoan groups. Arthropods are a very prominent element also in these ancient Cambrian biota, showing a striking diversity of form and life habits. At least to some extent, this dominance may be due to the relatively good preservation potential of their cuticle encasing the whole body. This not only yields large quan- tities of arthropod fossils, but also allows preservation of morphological detail in extremely high fidelity, including details of limb structure. Thus, a way has been opened for a more direct comparison of the anatomy of fossils with extant taxa than is possible for many other fossils. Not surprisingly, this wealth of detail has stimulated greater attention to fossil arthropods in phylogenetic studies of the group than fossils of most other invertebrate animal groups. This dissertation was originally conceived as a stratigraphic study of early to middle Cambrian trilobite faunas of North-East and North Greenland but the focus shifted gradually to more palaeobiological questions, inspired by emerging views on arthropod evolution and phylogeny, including also the question of the phylogenetic placement and significance of Trilobita. Thus, attention turned to exceptionally preserved arthropod fossils, with material derived from two renowned Cambrian lagerstätten: the early Cambrian Sir- ius Passet biota of North Greenland, and the late Cambrian (Furongian) ‘Orsten’ of Sweden, the type for a kind of exceptional preservation that is now found in strata spanning the early Cambrian to the early Ordovician in many localities world wide.

8 Trilobite biostratigraphy

Cambrian stratigraphy is currently undergoing a major revision aiming at a standardized global chronostratigraphic framework (Babcock et al. 2005, Babcock & Peng 2007). The traditional Early, Middle, and Late Cambrian, variously defined on different paleocontinents, are being replaced by four globally recognizable series, of which the first two very loosely correspond to the earliest traditional subdivision.

Figure 1: Subdivision of the Cambrian System according to the new chronostratigraphic framework. Series and stages with a grey background are yet to be defined.

9 So far, only the Furongian Series (Peng et al. 2004), which roughly corre- lates with the traditional Late Cambrian, and the Terreneuvian Series, which replaces the provisional series 1 (Landing et al. 2007) have been defined by Global Standard Stratotype-sections (GSSPs) (Figure 1). An informative example of some of the difficulties associated with the definition of these new series is provided by ongoing discussions concerning the boundary between series 2 and 3, corresponding to the traditional Early-Middle Cambrian boundary. The former Middle Cambrian was traditionally defined by the occurrence of paradoxidid trilobites in Baltica, Avalonia, and West Gondwana, but it has been shown that this first occurrence is diachronous. In the Early- Middle Cambrian boundary interval of Morocco paradoxidid trilobites occur together with holmiid trilobites which, as part of Olenelloidea, traditionally define the Early Cambrian (Geyer & Palmer, 1995; see Geyer 2005 for an extensive review). Geyer (2005) listed five trilobite horizons being discussed currently as a potential new boundary marker between the provisional series 2 and 3, but progress is hampered by the endemism of early Cambrian trilobite faunas, different litho- and biofacies distributions, and not least by the different state of knowledge and taxonomic practice in relevant geographical areas (Geyer 2005). Studies of Cambrian faunas in North Greenland have recognized rich trilobite faunas with considerable potential for intercontinental correlation (e.g. Robison 1988, 1994, Babcock 1994a, b, Blaker & Peel 1997). The stratigraphic sequence succession in North Greenland is relatively complete and encompasses inner craton and outer shelf facies in close juxtaposition. Thus, boreal faunas of Baltic aspect have been described from outer shelf facies in close proximity to warm water faunas of Laurentian aspect (Babcock 1994a, b). Recently, the diverse trilobite faunas of North Greenland described by Blaker and Peel (1997) has been recognized as particularly significant for resolution of the problem of the boundary interval between provisional series 2 and 3 (Fletcher 2003, Geyer 2005). As of yet, the trilobite faunas of North-East Greenland are not well known and correlation of the Cambrian provisional series 2 of this region with that of other areas of Laurentia has been advanced by the study of small shelly faunas (Skovsted 2006). Correlation with North Greenland remains impre- cise but the present studies offer the first prospect for elucidating similarities in the trilobite faunas of the two areas.

Paper I Stein, M. 2008. Fritzolenellus lapworthi (Peach and Horne, 1892) from the lower Cambrian (Cambrian Series 2) Bastion Formation of North-East Greenland. Bulletin of the Geological Society of Denmark 56:1–10.

10 Figure 2: A, Fritzolenellus lapworthi from the Bastion Formation of North-East Greenland; B, Reconstruction of F. lapworthi; C, Olenellus cf. hanseni from the Ella Island Formation of North-East Greenland.

This paper deals with olenellid trilobites from the Bastion and Ella Island formations (provisional Stage 4) of North-East Greenland, collected in the early 1950s. The focus is on material from the older Bastion Formation, from which the bulk of the material is derived. Collections from the overlying Ella Island Formation only yielded two immature cephala. The specimens of the material from the Bastion Formation are identified as Frit- zolenellus lapworthi (Peach & Horne, 1892), a species originally described from the 'Fucoid' Beds of the An t'Sron Formation of north-west Scotland. The Greenland material is considerably better preserved than that of the type region. This allowed a more detailed description, in particular of the post- cephalic morphology. The material also includes immature specimens, per- mitting a first, limited account of the ontogeny of the species. The occurrence of F. lapworthi in Greenland offers a first opportunity of a direct corre-

11 lation of the Cambrian Stage 4 strata of north-west Scotland with this part of Laurentia. So far, correlation between the areas rested largely on the occurrence of the problematic fossil Salterella, which, in Scotland, occurs in the ‘Fucoid’ Beds and the overlying ‘Salterella Grit’, in North-East Greenland in the Bastion, Ella Island, and Hyolithus Creek formations (Skovsted 2006, Poulsen 1932, Cowie & Adams 1957). Salterella also occurs in the Parallel- dal Formation of North-Greenland and in lower Cambrian strata of Inglefield Land, North-West Greenland (Peel & Yochelson 1892). So far, F. lapworthi has not been identified in any material from other regions of Greenland. The trilobites of the overlying Ella Island Formation may prove to be of utility for correlation with North Greenland, but further work is required. The two olenellid cephala from that formation are similar to Olenellus hanseni (Poulsen, 1932) described from this formation. This species was unfortunately based on immature cephala and fragmentary thoracic material only and may require revision. Similar material has been described from the Henson Gletscher and Kap Troedsson formations of North Greenland, described as Olenellus cf. truemani Walcott, 1913 (Blaker & Peel 1997). This material also includes immature specimens which lend them- selves for comparison with the type material of O. hanseni. If this material could be positively identified as O. hanseni, it could serve as a basis for an emendation of the species and would further provide a direct tie point between North Greenland and North-East Greenland.

Paper II Stein, M. & Peel, J. S. 2008. Perissopyge (Trilobita) from the lower Cambri- an (Series 2, Stage 4) of North America and Greenland. GFF 130:71–78.

Paper II deals with the distinctive trilobite Perissopyge Blaker, Nelson & Peel, 1997 and its occurrence in Laurentia. Two species have been described previously, both from the Cambrian Stage 4; P. triangulata Blaker, Nelson & Peel, 1997, occurring in the Harkless Formation of Nevada, and P. phenax, occurring in the Henson Gletscher Formation of North Greenland and reported from the Sekwi Formation of Yukon Territory, Canada (Blaker et al. 1997, Blaker & Peel 1997). This paper documents Canadian material for the first time and adds a further occurrence in the Paralleldal Formation of North Greenland, which is overlain by strata that can be correlated with Siberia (Debrenne & Peel 1986). The occurrence of P. phenax in the Paralleldal and Henson Gletscher formations thus further supports correlation of the Henson Gletscher Formation with Siberia and China, while the occurrence in Yukon Territory offers a tie point into that area of Laurentia.

12 Figure 3: A, Perissopyge triangulata, Harkless Formation, Nevada, USA; B, C, P. phenax, Sekwi Formation, Yukon Territory, Canada, D, E, Perissopyge sp. Ella Is- land Formation, North-East Greenland.

An indeterminate species of Perissopyge is reported also from the Ella Is- land Formation of North-East Greenland. This co-occurrence with Olenellus hanseni, which may also occur in the Henson Gletscher Formation of North Greenland, may hold potential for further correlation between North and North-East Greenland. The distinctive pygidial morphology of Perissopyge makes it also attrac- tive as a potential biostratigraphic marker, as it is easily identified among early Cambrian trilobite faunas. Unfortunately, it seems that the limited distribution as yet only grants regional utility.

13 Arthropod phylogeny

As noted above, it is not clear which taxon is the closest relative (sister taxon) to the Euarthropoda. The living Onychophora are representatives of the non-sclerotized forms among Arthropoda in the wider sense (Arthropoda sensu lato), but there is a considerable morphological gap between these and the euarthropods. Accordingly, there must have been a long evolutionary history between the last common ancestor (stem species) of both onychophorans and euarthropods and the stem species of Euarthropoda. Species do change over time, i.e. along their phylogenetic lineage, but, given the large morphological gap, it is less likely that all the morphological changes —from dorsal cuticular sclerotization to eye, limb, and head formation to name but a few—all occurred in the (anagenetic) lineage of a single species of Euarthropoda. More likely, there were several branching points along the way. All species that branched off along the evolutionary lineage toward Eu- arthropoda but became extinct, are stem lineage representatives or deriva- tives of the stem lineage of the Euarthropoda. The only way we may know of them directly is if they are preserved as fossils. Identified correctly, they can tell us in which order morphological changes occurred along the stem lineage. It is clear that the cuticular ‘exoskeleton’ of euarthropods must have been acquired as a novel feature somewhere along the euarthropod stem lineage. This must have occurred in several steps as it includes different novelties: formation of sclerotized dorsal areas (tergites) and soft membranous areas between the tergites to allow for flexibility; dissolution of the subepidermal muscle tube and formation of isolated muscle strands that develop tendon- like connectives into the cuticle; development of appendages that are subdi- vided into sclerotic rings and membranous connections; development of pivot joints on these limbs, limiting the flexure of the sclerotic rings to one axis of movement. A number of fossil taxa mainly known from Cambrian lager- stätten have these features, but lack other euarthropods autapomorphies. They are likely representatives of the euarthropod stem lineage and, together with euarthropds, constitute the Arthropoda sensu stricto. The ground pattern of the stem species of Arthropoda s. str. as promoted by Maas et al. (2004) and Waloszek et al. (2007) includes further features, e.g. a pair of antero- ventral compound eyes, a short head comprising two segments carrying the eyes and one pair of appendages (the antennulae) respectively, and the mouth in a ventral position, opening toward the posterior. All these changes

14 must have accumulated before the stem species of Arthropoda s. str. Addi- tional changes occurred later in the euarthropod stem lineage. Thus the evolutionary lineage toward Euarthropoda can be divided into at least two sections, divided by the node of Arthropoda s. str. Examples of the first section are the so-called lobopods, small to moderately long worm-shaped animals with long, tubular segmental appendages. The possibility that also the Tardigrada and the Pentastomida belong there is still debated. One hypothesis considers Pentastomida to be the closest living relatives to Euarthropoda, having pivot jointed limbs but lacking segmental subdivision of the cuticle in tergites and soft membranous areas (e.g. Maas et al. 2004). While this is supported by further morphological and developmental data, an alternative hypothesis based on sperm ultrastructure and molecular data suggests that pentastomids are highly derived crustaceans (Møller er al. 2008 and references therein; see also Waloszek et al. 2006 for a recent review of the competing hypotheses).

The current status of euarthropod phylogeny from a neontological perspective Euarthropod phylogeny has been in a state of flux for a long time, and the advent of molecular systematics during the last decade has added new con- troversial hypotheses about relationships rather than helping settle standing issues. One ongoing debate concerns the phylogenetic position of Pycnogo- nida; they are currently placed either within Chelicerata as the sister taxon of Euchelicerata (Xiphosura and Arachnida) or as the sister taxon of all other euarthropods (see Dunlop & Arrango 2005 for a review). The phylogenetic position of Myriapoda is another remaining problem. The traditional concept of Mandibulata comprising Myriapoda, Insecta, and Crustacea has recently been challenged by molecular studies that place myriapods as the sister taxon to Chelicerata (e.g. Hwang et al. 2001, Mallatt et al. 2004, Dunn et al. 2008). There is little morphological support for this hypothesis, other than some aspects of development of the nervous system. Analyses of morphological or combined data usually resolve myriapods together with Crustacea and Insecta as part of Mandibulata (e.g. Giribet et al. 2001, 2005, Edgecombe 2004). Finally, the phylogenetic position of insects remains disputed. Tradi- tionally considered to be the sister taxon of Myriapoda in the Atelocerata (= Tracheata) hypothesis, molecular or combined molecular and morphological (e.g. Giribet et al. 2001, 2005, Hwang et al. 2001, Mallatt et al. 2004) and neuro-anatomical (e.g. Fanenbruck et al. 2004, Harzsch 2006) studies often resolve them as more closely related to or even nested within Crustacea. The controversies about euarthropod phylogeny are largely beyond the scope of the present studies. Further, most of the competing hypotheses out-

15 lined above do not involve any fossil data. Nevertheless, the topology of the euarthropod phylogenetic tree has implications for the ground pattern of Eu- arthropoda and therefore needs to be considered.

The ground pattern and the importance of fossils Characterizing the ground pattern of Euarthropoda based on neontological data alone is hampered not least by the uncertainties of in-group relationships. Here, fossils provide an invaluable source of information, as the only direct evidence of morphology in the stem lineages of taxa which may bridge significant morphological gaps between terminal taxa. It is clear that an advanced cephalization with a head tagma incorporating several segments was part of the euarthropod ground pattern. The most anterior, protocerebral segment carries the eyes, and in certain crustacean taxa paired, so called frontal organs (Vilpoux & Waloszek 2003, Fanenbruck & Harzsch 2005, Semmler et al. 2008). The following, deutocerebral, segment carries a pre-oral appendage, the chelicera in Chelicerata or antennula in Crustacea, Insecta, and Myriapoda (traditionally called antenna in the latter two taxa). The third, tritocerebral segment carries the first postantennular limb, called pedipalp in Chelicerata or (second) antenna in (Eu-)Crustacea. In Myriapoda and Insecta this limb is absent, most likely reduced. The assumption of a tripartite brain incorporating neuromeres of the three most anterior segments as part of the euarthropod ground pattern is problematic (Walossek & Müller 1998), as even derived euarthropod taxa such as bran- chiopods and isopods still have separate ganglial knots. There is ample fossil evidence that such a head tagma, incorporating the protocerebral, deutocerebral, and three additional segments was present in the earliest representatives of the crustacean (and possibly mandibulatan) evolutionary lineage (Walossek & Müller, 1990, 1998). There is further evidence, that these early representatives hatched with a ‘head larva’, i.e. a larva with only the segmental composition of this head tagma (Walossek & Müller, 1990, 1998). The ‘short-head larva’ of Eucrustacea incorporates one segment less and is interpreted as an autapomorphy of that taxon. It is the body tagmosis of chelicerates that poses a pertinent problem. The anterior tagma in Euchelicerata, the prosoma, incorporates the proto- and deutocerebral segments plus five additional limb-bearing segments. Adult Pycnogonida have a cephalosoma that corresponds in segmental composition to the euarthropod head, but this is first acquired during ontogeny in extant representatives. The protonymph larvae appear to be ‘short-head larvae’ with only the proto-, deutocerebral, and two additional limb-bearing segments (Vilpoux & Waloszek 2003). The caudal outgrowths of the larva of the only Cambrian representative of Pycnogonida (Waloszek & Dunlop 2002) were subsequently interpreted as a fourth pair of limbs (Vilpoux &

16 Waloszek 2003). This would mean that the larva of the Cambrian species has one more pair than the protonymph larvae of extant species. Some investigators have taken the problem of chelicerate body tagmosis as support for rejecting a head with the eye segment and four limb-bearing segments as a ground pattern feature of Euarthropoda. They rather regard such a head tagma as a feature that evolved first in the mandibulatan stem lineage (Scholtz & Edgecombe 2005). The alternative hypothesis assumes that the euarthropod head became modified within Chelicerata (Waloszek & Maas 2005). This may gain support from so called ‘great appendage’ arthropods, that are considered to be chelicerate stem lineage representatives (Chen et al. 2004, Cotton & Braddy 2004) and have such a head tagma. This contrasts with reports of a head comprising only three appendage-bearing segments for some of the taxa (García-Bellido & Collins 2007), but recent detailed re-investigations of one species cast doubt on that assessment. They rather confirm a head incorporating no less than four appendage-bearing segments (Liu et al. 2007), as assumed already for the euarthropod ground pattern. Assignment of these taxa to the chelicerate stem lineage rests on the spe- cific morphology of the ‘great appendage’, a stout grasping appendage which is considered to be the first (deutocerebral) limb and homologous to the chelicera of Chelicerata (Chen et al. 2004, Cotton & Braddy 2004). This homology statement is particularly based on one species, Haikoucaris er- caiensis Chen, Waloszek & Maas, 2004, which is intermediate in the morphology of its grasping leg between that of the previously described taxa and the chelicerate chelicera. These new views on the chelicerate stem lineage mark a radical departure from previous assumptions of the evolution of chelicerae, which were traditionally considered to be the limbs of the tritocerebral segment. The deutocerebral segment, carrying the antennula of crustaceans, myriapods and insects, was considered to have been lost along the chelicerate stem lineage (e.g. Bitsch & Bitsch 2007). This view, first challenged by molecular data (e.g. Damen et al. 1998, Telford & Thomas 1998) was mainly based on a misinterpretation of the chelicerate nervous system (Mittmann & Scholtz 2003). According to the traditional view, it was trilobites and closely related fossil arthropods that were considered to be representatives of the chelicerate stem lineage in the ‘arachnomorph’ concept (Scholtz & Edgecombe 2005 for a review). Accepting homology between the chelicerae of Chelicerata and the deutocerebral antennula of the other euarthropod taxa forced reconsideration of the morphology of the deutocerebral limb in the ground pattern of Euarthro- poda. The traditional view assumed a sensorial flagelliform, i.e. multiannu- lated, limb, as was developed in trilobites and related fossil arthropods. This morphology was readily homologized with the sensorial antennulae of insects, myriapods and certain crustaceans. The limb was considered to be lost

17 together with the deutocerebral segment in the upper chelicerate stem lineage. The new view required that the chelicerae were derived from a flagelliform antennula, or, more likely, from a more limb-like deutocerebral appendage that must have had a feeding function already in the stem species of Euarthropoda. From a purely neontological perspective, the latter idea was nurtured by the potential placement of Pycnogonida as the sister taxon to the remaining Euarthropoda. In the case of a sensory antennula in the euarthropod ground pattern, this placement would require convergent transformation into a feeding limb in two taxa (Dunlop & Arrango 2005). Fossils provided additional support for a feeding function of the deutocerebral limb in the euarthropod ground pattern, independent of the position of Pycnogonida. Studies of crustacean (or possibly mandibulatan) stem lineage representatives have demonstrated that the stem species of Crustacea had an antennula adapted for feeding and locomotion rather than sensorial purposes (see Walossek 1999 for a summary). This was originally considered to be an autapomorphy, adopted from the traditional view of such an antennula in the ground pattern of Euarthropoda, but had to be reevaluated in the light of the new data. The flagellate antennula, often considered characteristic of the group is an autapomorphy of certain in-group taxa, foremost Malacostraca (e.g. Waloszek 2003). In the light of homology between the feeding and lo- comotory crustacean antennula and the feeding chelicera of chelicerates, it is apparent now that the adaptation of the antennula for feeding in the crustacean stem species was not an autapomorphy but a symplesiomorphy, retained from the last common ancestor of chelicerates and crustaceans (possibly mandibulates; e.g. Waloszek et al. 2007). A novelty developed in the crustacean (or mandibulate) stem lineage may be that the antennula works in concert with the postantennular limbs as part of the cephalic feeding apparatus. Studies of early members of Arthropoda s. str. yielded further support for this hypothesis, as they have revealed that these forms had a limb-like feeding antennula while lacking any other obvious structures for feeding (Maas et al. 2004, Waloszek et al. 2005, 2007). It should be noted that there are alternative interpretations of the head structure in at least one of these fossils, Fuxianhuia protensa Hou, 1987, which consider the most anterior limb to be protocerebral rather than deutocerebral (Scholtz & Edgecombe 2005, 2006). In this interpretation, another structure under a large, shield-like tergite is considered to be a jaw-like deutocerebral limb. The supposed protocerebral limb is considered to be a ‘primary antenna’ homologous to the ony- chophoran palp, either lost in the euarthropod stem lineage or retained in a vestigial form as the protocerebral frontal organs of certain eucrustacean taxa (Semmler et al. 2008). This interpretation suffers from several problems; firstly, the supposed jaw-like deutocerebral limb in F. protensa could be demonstrated to be an internal structure, most likely gut diverticula, and in other early Arthropoda s. str. the structure is clearly missing (Waloszek et

18 al. 2005). Further, the notion that Chelicerata rely on a ‘whole limb mouth- part’ for feeding, whereas Mandibulata rely on the gnathobasic parts of their postantennular limbs (Scholtz & Edgecombe 2005) is an over simplification. As discussed, there is ample evidence that the antennula was part of the cephalic feeding apparatus in the crustacean stem species, while Xiphosura as euchelicerates use the median edges of the limb bases (basipods) of their postcheliceral limbs for mastication. Finally, the assumption of a specialized deutocerebral jaw in the ground pattern of Euarthropoda is problematic be- cause a sensorial antennula is more likely to be derived from a generalized limb-like structure. The latter point needs to be considered in particular with respect to the various competing hypotheses of euarthropod relationships which may require sensory antennulae to be evolved convergently more than once. A further independent origin may be required to accommodate a group of fossil taxa, as will be discussed in the next section.

The position of Trilobita Trilobita is an entirely extinct group of euarthropods. Putative autapomorphies are the calcification of the cuticle and dorsal eyes with circumocular sutures. The trilobation of the trunk tergites with a raised axis and lowered tergopleurae often considered characteristic for the group is a symplesiomorphy retained from the ground pattern of Arthropoda s. str. In contrast to many other euathropod taxa, Trilobites and closely related fossil taxa have long flagelliform, probably sensory antennulae composed of a large number of short annulae. Traditionally regarded to be related to the Chelicerata, more recent work affiliates them with the mandibulate stem lineage based on their antennular morphology, which is considered to represent the ‘secondary antenna’ evolved in the stem lineage of Mandibulata according to Scholtz & Edgecombe (2005). This interpretation faces the dilemma that there is reason to assume a feeding antennula as part of the crustacean ground pattern, which would require multiple character reversals (once for the stem species of Crustacea, a second time for the stem species of Mala- costraca). Thus, caution should be exercised against using the mere presence of sensory antennulae as an argument for placement of fossil taxa along the stem lineage of Mandibulata. Even more so, in the light of a possibly convergent evolution of sensory antennulae in various euarthropod taxa discussed above. Based on details of limb morphology and development of the cephalic feeding apparatus, trilobites and related fossil arthropods with a flagelliform antennula must have branched off prior to early representatives of the crustacean (or possibly mandibulatan) stem lineage. Rather, a flagelliform antennula in these taxa may represent a possible synapomorphy of a group of these ‘trilobitomorphs’ (the classical ‘Trilobitomorpha’ originally comprised

19 also the ‘great appendage’ arthropods now regarded as chelicerate stem lineage representatives). Monophyly of a group of Trilobita and e.g. naraoiids, hemeltiids, tegopeltids, and xandarellids, all with a flagelliform antennula, might also be supported by aspects of limb morphology. All have a bipartite exopod with a proximal portion carrying lamellar setae and a distal lobe-like portion with a setal fringe (Edgecombe & Ramsköld 1999, Bergström & Hou 2003, Cotton & Braddy 2004, Scholtz & Edgecombe 2005) which is a now widely noted autapomorphy. Inside this grouping, xandarellids are often regarded as the sister taxon to the remainder, due to the absence of a pygidium, defined as a point at which tergites ceased being released anteriorly in ontogeny (Ram- sköld et al. 1997, ‘subterminal generative zone’ of Hughes et al. 2008). There are additional ‘trilobitomorph’ taxa with flagelliform antennualae; apart from the undisputed presence of lamellar setae, the exopod structure of Emeraldella brocki Walcott, 1912 has been debated (Bruton & Whittington 1983, Hou & Bergström 1997, Edgecombe & Ramsköld 1999), with the latter authors arguing for a bipartite exopod as in the other taxa. Retifacies ab- normalis Hou, Chen & Lu, 1989 and Sidneya inexpectans Walcott, 1911 have lamellar setae but apparently no subdivision of the exopod. The latter species is also considered to have had a ‘head’ that only incorporates the protocerebral and deutocerebral segments (Bruton 1981). A putatively closely related species, Sidneya sinica Zhang, Han & Shu, 2002 has a relatively longer head shield than S. inexpectans with setae protruding from underneath it, indicating incorporation of postantennular limbs. However, unless Bru- ton’s (1981) assessment of the head in S. inexpectans can be disproved, an ad hoc ‘loss’ of the euarthropod head in this taxon would have to be invoked. A major dilemma that besets any attempt at placing Trilobita and these 'trilobitomorph' taxa in the phylogenetic system of arthropods, is that no clearly defined synapomorphy with any of the major extant groups is currently recognized. Placement in the mandibulatan stem lineage has been jus- tified by the sensory antennulae or the presence of a head incorporating no less than four appendage-bearing segments (Scholtz & Edgecombe 2005, 2006). Both arguments are problematic; the presence of flagelliform antennulae alone may not suffice, as outlined above, and the head with four limb- bearing segments is likely a ground pattern feature of Euarthropoda. Other characters, such as the lamellar exopods, may represent autapomorphies of the group, while an endopod with seven podomeres intermediates between nine or ten in the euarthropod ground pattern and five to six in Crustacea and is difficult to evaluate. It becomes clear that the problem needs thorough reinvestigation, also in the light of problematic taxa such as Sidneya inexpectans or another problematic taxon that may be allied based on antennular morphology, the Marellomorpha.

20 Paper III Stein, M., Waloszek, D., Maas, A., Haug, J. T. & Müller, K. J. 2008. The stem crustacean Oelandocaris oelandica re-visited. Acta Palaeontologica Polonica 53:461–484.

Figure 4: Oelandocaris oelandica; A, Holotype from Öland, Sweden; B, reconstruction of the large stage present in the material; C, larval specimen from Västergöt- land, Sweden; D, reconstruction of different stages.

The third paper provides a detailed study of the stem lineage crustacean Oe- landocaris oelandica Müller, 1983 from the ‘Orsten’ lagerstätte of Sweden. The ‘Orsten’ is not a fossil lagerstätte in the sense of a geographically and stratigraphically confined unit, as the fossils occur in bituminous concretions that occur in the Alum Shale successions that crops out in several regions of

21 Sweden and span the Cambrian series 3 and Furongian boundary interval. Fossils of this ‘Orsten’ type preservation have also been reported from other deposits in several areas of the world and different geological times (see Maas et al. 2006 for a review). The fossils are usually in the submillimetric range and, in contrast to many other lagerstätten, preserved in full three-dimensional detail. ‘Orsten’ type preservation is also notable for being one of the few lagerstätten that has yielded largely complete ontogenetic series of arthropod fossils. Oelandocaris oelandica was originally described on the basis of a single fragmentary specimen from the Cambrian Stage 7 (Series 3) of the island of Öland, Sweden (Müller 1983). Subsequently identified material from the Paibian Stage (Furongian) of Västergötland in mainland Sweden permitted a more complete description of the species and a discussion of its phylogenetic significance, which was presented in an initial report by Stein et al. (2005). In the present paper, additional information, including the recognition of different ontogenetic stages in the material is provided, the life habits are discussed, and the phylogenetic position suggested by Stein et al. (2005) is further confirmed. The species, together with other representatives of the crustacean stem lineage from the ‘Orsten’, provides important evidence for the structure of the cephalic feeding apparatus in the ground pattern of Crus- tacea. By comparison to other fossil euarthropods, the morphology of the postantennular limbs in this early representative of the crustacean stem lineage also provides important insight into some aspects of limb morphology in the euarthropod ground pattern, in particular of the exopods

Paper IV Stein, M. A new arthropod from the Early Cambrian of North Greenland with a ‘great appendage’ like antennula. Submitted to Zoological Journal of the Linnean Society.

The fourth paper is the first in a series of three on fossils from the Sirius Pas- set Lagerstätte of the Cambrian Stage 3 (Series 2) of North Greenland. This lagerstätte, roughly coeval with the Chengjiang Lagerstätte (Maotianshan Shale) of China, is one of the oldest Cambrian lagerstätten yielding exceptionally preserved arthropod macrofossils. The paper describes a new fossil arthropod species, Kiisortoqia avannaarsuensis, that has a large and robust antennula remarkably similar to the antero-ventral raptorial appendage of the problematic anomalocaridids. While the phylogenetic scope, position, and significance of the latter is contentious- ly debated (e.g. Budd 2002, Chen et al. 2004, Hou & Bergström 2006) with some authors questioning euarthropod or even arthropod affinities, K. avan-

22 naarsuensis shares features with euarthropods that justify placement in this taxon or in the stem lineage in direct proximity to the euarthropod node. While this does not resolve the question of anomalocaridid affinities, it does provide strong support for homology between the antero-ventral appendage of anomalocaridids with the deutocerebral antennula of euarthropods and further for the antennula as a primary feeding limb in the euarthropod stem species.

Figure 5: Kiisortoqia avannaarsuensis from the Sirius Passet Lagerstätte, North Greenland; A, holotype; B, detail of the most complete antennulae in the material; C, D, reconstructions in ventral and lateral view.

23 Paper V Stein, M., Peel, J. S., Siveter, D. J. & Williams, M. Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland. Manuscript.

In this paper an account is given of the soft anatomy of Isoxys volucris Williams, Siveter & Peel, 1996, from the Sirius Passet Lagerstätte. This species has a large, more or less bivalved shield encasing most of the body. There are numerous fossil and extant arthropods with such a shield, and it is widely accepted that this feature arose independently in several groups. In the fossil record, they are known often by the shield alone, which is why phylogenetic or taxonomic assignments of a species to a certain group often rests on the morphology of the shield alone. In some cases it has been shown that the assignment by shield morphology was misleading, with the Phos- phatocopina originally considered to be ostracods, now recognized as the sister taxon to Eucrustacea (Siveter et al. 2003) as a prime example.

Figure 6: Isoxys volucris from the Sirius Passet Lagerstätte, North Greenland; A, specimen preserving limbs; B, specimen showing shield in dorsal view; C, specimen preserving possible eye.

There are numerous species assigned to Isoxys Walcott, 1890, mostly known by the shield morphology alone. Ventral morphology is known only in a few instances and there are indications that it may differ between species (e.g. Vannier & Chen 2000). The present paper gives a review of what is known and makes comparisons with the new data from the Sirius Passet lagerstätte.

24 There are sufficient similarities between I. volucris and one species from the Chengjiang fauna of China to justify close relationships, but relationships with other species remain problematic. This cautions against composite reconstructions and palaeoecological considerations based on multiple species.

Paper VI Lagebro, L., Stein, M. & Peel, J. S. A new arthropod from the early Cambri- an Sirius Passet Fauna of North Greenland. Manuscript.

Figure 7: Siriocaris trolla from the Sirius Passet Lagerstätte, North Greenland; A, holotype; B, specimen showing the morphology of the tergites.

The sixth and final paper describes Siriocaris trolla, a new species of fossil arthropod from the Sirius Passet Lagerstätte. It shares some features of certain ‘trilobitomorph’ arthropods, including flagelliform antennulae and articulation devices of the thoracic tergites, such as flanges on the tergopleurae and an edge-to-edge articulation with larger overlap in the axis and a hori- zontal inner portion of the tergopleurae. It is intriguing to consider ‘trilobitomorph’ affinities based on these features, as at least the tergal morphology may imply particularly close affinities with trilobites and helmetiids (Ram- sköld et al. 1997, Edgecombe & Ramsköld 1999). The prominent tergopleu- ral spines and the small tail shield are even reminiscent of olenelline trilo-

25 bites, commonly considered to be ‘basal’ trilobites (e.g. Lieberman 2001 and references therein). An indication of trilobation in the head shield and an axial furrow at least in the posterior part of the thorax are other features that in- vite comparison with trilobites. Unfortunately, with the limited material at hand, alignment with trilobites and helmetiids can at present not be substan- tiated, as some characters in S. trolla remain unclear. While there are indications that the exopods may be bipartite as in helmetiids and trilobites, com- pelling evidence for lamellar setae on a putative proximal element is not available, and there is no direct evidence of fringing setae on the putative outer lobe. It is not clear whether or not the tail of S. trolla is a pygidium. This character, however, is difficult to evaluate, as certain olenelline trilobites have a similarly small pygidium that in some species even contains only a single axial ring (Paterson & Edgecombe 2006).

26 Svensk sammanfattning

Leddjur (Arthropoda) är den artrikaste gruppen av flercelliga djur och utgör uppskattningsvis tre fjärdedelar av alla nu levande arter. De bebor många habi- tat, både i havet och på land. De nu levande leddjuren är fördelade på fyra stora grupper: spindeldjur (Chelicerata), kräftdjur (Crustacea), mångfotingar (Myriapoda) och insekter (Insecta), som utgör den största gruppen. Alla dessa djur har ett unikt yttre skelett uppbyggt av härdade (sklerotiserade) plattor som är ledade mot varandra. Tillsammans utgör de gruppen Euarthropoda. Hur de fyra grupperna är besläktade med varandra är mycket omdiskuterat. Dessutom finns det några mindre grupper som t. ex. havsspindlar (Pycnogonida), som av vissa forskare betraktas som spindeldjur, men som av andra anses vara syster- grupp till Euarthropoda, dvs. euarthropodernas närmaste släktingar. Det är inte heller helt klarlagt, vilka de övriga arthropoderna är, alltså de som inte hör hemma i Euarthropoda. Medan det är en allmänt utbredd uppfattning att klo- maskar (Onychophora) är arthropoder, finns det fortfarande oenighet om huruvida trögkrypare (Tardigrada) tillhör gruppen eller i stället är närmare besläk- tade med rundmaskar. Ytterligare en omdiskuterad grupp är tungmaskar (Pen- tastomida), som är parasiter på bl. a. ren. De betraktas allmänt som athropoder, men det råder delade meningar om huruvida de är euarthropodernas syster- grupp eller starkt specialiserade kräftdjur. Med den stora diversiteten och spridningen som arthropoder har idag är det föga förvånande att gruppen har haft en lång utvecklingshistoria, rikligt belagd med fossil. De tidigaste leddjursfossilen uppträder redan i nedre kambrium, bland de äldsta fossilen av flercelliga djur. Oftast är det arter med kutikula förstärkt av mineralinlagringar som bevarats, som t. ex. musselkräftor och trilobiter. Dessa är vanliga i havsavlagringar och viktiga verktyg för relativa ålders- dateringar (stratigrafi). Trilobiter är särskilt viktiga i detta sammanhang, då de uppträder tidigt i kambrium, det äldsta avsnittet av det så kallade fanerozoikum (den del av jordens historia som började för 542 miljoner år sedan och som är tydligt präglad av spår av flercelliga djur) och hade stor spridning genom hela paleozoikum tills de dog ut i slutet av permtiden för ca. 250 miljoner år sedan. Under särskilda förhållanden kan dock även andra djur utan mineraliserade kroppsdelar bevaras. Även i sådana avlagringar är leddjur bland de vanligaste fossilen. I kambrium har man hittat många avlagringar som bevarar mer än bara mineraliserade delar av organismer. Dessa avlagringar, särskild de berömda fossila faunorna från Burgess Shale i Kanada och Chengjiang i Kina har väckt stort

27 intresse, inte minst bland forskarna. Detta intresse kan nog förklaras med fasci- nationen av det till synes plötsliga uppträdandet av många grupper av flercelliga djur i början av fanerozoikum (även om det finns spår av flercelligt liv i tidigare avsnitt av jordens historia). Många forskare tror att det var en kritisk fas i de flercelliga djurens tidiga evolution. Även om det finns argument för att flercelliga djur, inklusive arthropoder, uppstod tidigare, så ger oss de kambriska avlagringarna de äldsta direkta bevisen för hur de tidiga djuren såg ut, vilket i sin tur har stor betydelse för teorier om djurgruppers släktskap. Mina studier behandlar såväl frågor om leddjurens tidiga evolution som relativa dateringar av avlagringar med hjälp av trilobiter.

Trilobit-stratigrafi på Grönland Kambrium sträcker sig från 542 till 488 miljoner år sedan. Framförallt i detta äldsta avsnitt av paleozoikum är trilobiter ett viktigt verktyg för stratigrafi. Det finns dock många problem med relativ datering av avlagringar med hjälp av dessa fossil. Dels uppträder många arter bara i vissa regioner av jorden, dels var de som alla organismer beroende av miljöförhållanden vilket gör att vissa arter bara uppträder i vissa sorters avlagringer. Dessutom finns det många om- råden på jorden, där fossilen inte har studerats tillräckligt för att möjliggöra jämförelser med andra regioner. Under de senaste årtionden har man upptäckt att vissa relativa dateringar av avlagringar jorden över inte håller, och en rev- idering av den kambriska tidsskalan är just nu på gång. Ett särskilt problem rör gränsen mellan de två mellersta avsnitten av kambrium. Här tycks trilobitfau- nan från norra Grönland ha en stor potential för att förbättra korrelationen mellan olika delar av världen. Det finns dock även avlagringar på nord östra Grön- land som inte är ordentligt studerade. De första två publikationerna handlar om enstaka trilobit-arter som kan bidra till att förbättra korrelationen av de två re- gionerna och därmed också bidra till att förbättra den relativa dateringen av de viktiga avlagringarna i Norra Grönland. Den första publikationen handlar om Fritzolenellus lapworthi, en art som uppträder i tidiga kambriska lager både i nord östra Grönland och i nord väs- tra Skottland och som kan bidra till att korrelera dessa delar av Skottland med resten av den kambriska kontinenten Laurentia. Lite högre i lagerfölj- den på nord östra Grönland uppträder Olenellus hanseni, en som också kan finnas i norra Grönland, och därmed hjälpa till att korrelera nord östra med norra Grönland. Den andra publikationen diskuterar förekomster av flera arter av den dis- tinkta trilobiten Perissopyge på olika ställen i Nordamerika och Grönland, och deras möjliga betydelse för stratigrafin. Nya förekomster rapporteras från norra och nord östra Grönland som möjligtvis kan förbätta korrelationen av dessa regioner.

28 De tidiga leddjurens evolution Som tidigare nämnts råder stor oenighet om hur de olika euarthropod-grupperna är besläktade med varandra. Förhoppningar att gamla kontroverser skulle kunna lösas med hjälp av molekylära data har än så länge inte upp- fyllts. Den rådande osäkerheten om släktskap innebär att det är svårt att kartlägga vilka av de olika morfologiska särdrag som finns i nu levande grupper redan fanns i leddjurens gemensamma anfader. Detta är ett dilemma, då kunskap om anfadern tvärtom skulle kunna bidra till att utvärdera hy- poteser om släktskap. Chansen att hitta själva anfadern som fossil är realis- tiskt sett obefintlig. Däremot hittar vi fossil som kan vara nära besläktade med anfadern; arter som hör hemma i den evolutionära linje som ledde till anfadern. De är i princip de enda direkta belägg för vilka särdrag anfadern kan ha haft. Det är dock klart att vi till viss mån även här konfronteras med ett cirkulär problem, då vi behöver en viss uppfattning av släktskapen av de levande djuren för att kunna hänvisa ett fossil till ett stamlinje. Fossil, precis som morfologiska eller molekylära data från nu levande djur, är alltså bara pusselbitar och måste diskuteras i sammanhang med helheten. De resterande publikationerna i avhandlingen beskriver nya data från fossila arthropoder, dels från senkambriska avlagringar i Sverige, dels från tidiga kambriska avlagringar i Grönland. Där det är möjligt diskuteras dessa fossils innebörd för evolutionen av morfologiska särdrag i vissa arthropod-grupper. Den tredje publikationen är ett detaljstudie av en tidig släkting till kräftd- juren, Oelandocaris oelandica från orstensavlagringar på Öland och i Västergötland. Tillsammans med andra arter från orsten och liknande avlagringar i hela världen ger Oelandocaris oelandica och dess morfologi och möjliga levnadssätt viktig kunskap om kräftdjurens anfader. De resterande publikationerna handlar om fossil från tidiga kambriska avlagringar på norra Grönland. I den fjärde publikationen beskrivs Kiisorto- qia avannaarsuensis, en ny art som med stor sannolikhet antingen var en tidig euarthropod eller en nära släkting till euarthropodernas anfader. Arten har vissa likheter med några mycket svårtolkade fossil kända från kambriska avlagringar världen över och kan bidra till en bättre förståelse av dessa djur. Den femte publikationen beskriver kroppsbyggnaden av Isoxys volucris, tidigare bara känd genom den stora sköld som täckte större delen av krop- pen. Det finns många arter som tycks tillhöra Isoxys, men bara av några få finns lämningar av andra delar än just skölden. Publikationen diskuterar likheter och olikheter mellan de bättre kända arterna och granskar tidigare publicerade idéer om möjliga levnadssätt. I den sjätte och sista publikationen beskrivs Siriocaris trolla, en ny art som har vissa likheter med trilobiter och deras nära släktingar.

29 Acknowledgments

First and foremost I want to thank my supervisors without whom I would not have been able to complete these studies: John S. Peel provided most of the material studied and spent immeasurable time and effort on advice and discussions as well as reviewing countless iterations of manuscripts. Financial support from Vetenskapsrådet (Swedish Research Council) through Grants to J. S. Peel is gratefully acknowledged. Dieter Waloszek was an invaluable source of inspiration, advice, and criticism. He, too, took the time to review manuscripts at various stages and is also thanked for his hospitality during various visits to his department in Ulm. In his efforts, he was often assisted by Andreas Maas, whom I also wish to thank. David J. Siveter helped with advice and reviews of manuscripts and invited me to visit Leicester Univer- sity. Even he had his backup, Mark Williams. Reinhardt M. Kristensen helped with numerous discussions and kindly hosted a brief visit to Copen- hagen. I also wish to thank Jan Bergström who supervised the first half of my studies, but even continued to lend advice during the remaining years. Working with fossils requires technical skills which have to be learned, not least when it comes to preparation and photography. In this context I wish to thank Jan Ove Ebbestad and Pär Eriksson who have been of great help. Learning the modeling software used for the reconstructions could be a long-winded process at times. I was fortunate to be accompanied by Joachim T. Haug on the way. On the theoretical side, Uwe Balthasar has to be thanked for trying to raise my awareness of the convoluted problems of the peculiar preservation of the fossils of the Sirius Passet Lagerstätte. One of the greater challenges in final completion of the thesis was to write a Swedish summary. Anders Nordin is thanked for his help with that. Getting a thesis into printed form involves a surprising amount of paperwork and er- rands. I managed to unload the bulk of this onto my supervisor, John S. Peel. Sebastian Willman is thanked for helping me handle the remainder. Finally, I wish to thank my colleagues at the Museum of Evolution for bearing with me and keeping my spirits up during this venture.

30 References

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35 Acta Universitatis Upsaliensis Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 558

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