The hyolith assemblage from the early Cambrian of Bornholm, Denmark, shows a higher diversity than contemporary assemblages in Baltoscandia. The most common species in the Green Shales (Laesa Formation, Norretorp Member, Cambrian Stage 3), is Hyolithes [=Hyolithus] (Orthotheca) johnstrupi Holm, 1893. A specimen of this species shows a well-preserved and almost complete digestive tract, folded into an approximately 22mm long chevron-like structure comprised of at least 20 arcuate loops on the ventral side and a flattened, gently sinuous to straight anal tube on the dorsal side. The thin, phosphatic outer shell layer of the conch is crushed under the digestive tract due to compaction while the digestive tract is preserved in three dimensions and appears undisturbed. The shape of the digestive tract is similar to that of the middle Cambrian Guduguwan hardmani (Etheridge) from Australia and the lower Cambrian specimens from Russia described by Mekova & Sysoev. The Danish specimen is probably an adult, lending support to the idea that the orthothecid digestive tract becomes more complex during ontogeny. Hyolithus (Orthotheca) johnstrupi is revised and here referred to Circotheca Sysoev, 1958.

The Lower Ordovician Bjørkasholmen Formation at Flagabro, Scania, southern Sweden, consists of a 0.8m thick succession of carbonates with three siliciclastic mudstones, 5, 1 and 100mm thick, intercalated in the central part of the unit. Carbonate and siliciclastic mudstone beds show both normal and inverse grading. The carbonates are mud-rich and subdivided into a mudstone, a wackestone and a packstone facies. Grain types in the carbonates are mostly shells and shell fragments of brachiopods and trilobites. The carbonate rocks are strongly bioturbated seen as in roundish burrows filled with mud and a clear cement; additionally, bioturbation is reflected in the random orientation of shells. The siliciclastic mudstones are subdivided into two facies; one contains large amounts of shells and is in part grain-supported, the other is matrix-dominated and laminated to massive. The succession reflects sedimentation on a low-inclined shelf equivalent to a mid-ramp to basinal setting. Most mud- and wackestones (facies 3 and 4) represent fair-weather sedimentation, and the intercalated wacke- and packstones (facies 4 and 5) represent concentration of shell debris during high-energy storm. The siliciclastic mudstones in the central part of the succession reflect deposition in a basinal setting. The entire BjOrkasholmen Formation at Flagabro is equivalent to a lowstand of third (?) order without a well-developed internal cyclicity and is in that respect similar to the Bjørkasholmen Formation of oland, but different from the age-equivalent Norwegian sections.

A previously undocumented diversity of Cambrian palaeoscolecids is described from localities in Sweden, Norway and Denmark. The material described here includes isolated sclerites as well as the first macroscopic specimens reported from the palaeocontinent Baltica. The sclerites are all of early middle Cambrian age (Ptychagnostus gibbus Biozone) and are assigned to at least four new species of Hadimopanella, two of which are formally introduced: H. incubo sp. nov. and H. oelandiana sp. nov. The two macroscopic specimens are of late early Cambrian (Ellipsocephalus lunatus Biozone) and early middle Cambrian age (Acadoparadoxides oelandicus Biozone), respectively. The early Cambrian specimen is described as Maotianshania? sp. and comprises an incomplete annulated trunk fragment which is uniformly covered with circular sclerites, indicative of the palaeoscolecid family Maotianshaniidae. This is the first record of this family outside China. The middle Cambrian specimen is almost complete and introduced as Wronascolex? johanssoni sp. nov. It is characterized by a previously undocumented distribution of its Hadimopanella-like sclerites which increase in size and change ornamentation from the anterior to the posterior end of the distinctly annulated trunk. The observed distribution pattern can explain the high variability of species of the sclerite-based genus Hadimopanella as well as the occurrence of rare morphotypes of Hadimopanella in otherwise rich samples. Available data on the ontogeny of palaeoscolecids regarding the relationship between body and sclerite size of a taxon are evaluated. It is concluded that sclerite size might be species specific and should be considered when comparing taxa with morphological similar sclerites.

Pengia Geyer & Corbacho is a Cambrian burlingiid trilobite with fused trunk segments devoid of any articulation in the anamorphic and epimorphic phases of development. The type species is Pengia fusilis (Peng etal.) from the Wanshania wanshanensis Zone of China. Here we describe a second species, Pengia palsgaardia sp. nov., from the Lejopyge laevigata Zone of the Paradoxides forchhammeri Superzone. It comes from a glacial erratic in Denmark which probably originated in the Alum Shale Formation of Vastergotland, Sweden. Pengia palsgaardia is a large burlingiid (similar to 10mm in length), with 14 fused segments in the trunk whose boundaries are marked by ridges. The axis is narrow, with the axial furrows faintly indicated or effaced across the median. Laterally along the axis and the tapering glabella, symmetrical globular lobes are developed that are pinched at their base. During ontogeny the glabellar furrows are pit-like adaxially but shallow towards the axial furrow as the globular lobes develop. Their pit-like appearance in Pengia palsgaardia and some other burlingiid species is not considered similar to the condition seen in oryctocephalid trilobites. A median preglabellar ridge resembling that of Schmalenseeia Moberg develops late in ontogeny but in early ontogeny the preglabellar field resembles that of Burlingia Walcott, Alumenella Geyer & Corbacho and Niordilobites Geyer & Corbacho. This gives Pengia a more basal position in the schmalenseeid lineage, outside the derived Schmalenseeia. In mature specimens the facial sutures in P.palsgaardia are fused, but an ocular suture may have been present. During ontogeny Pengia would have gone through the anamorphic and protomeric protaspid segmental conditions, but articulation between either the cephalon and pygidium, or pygidium and thoracic segments of the trunk never developed so it did not progress beyond the protaspid phase. This extreme protomeric development is considered to be a derived feature in Pengia.

Pterotheca hispanica nov. sp. is described from the basal beds (Stimulograptus sedgwickii graptolite Zone) of the Formigoso Fm., in the Cantabrian Zone of the Iberian Massif, north-western Spain. This specialized bellerophontoid gastropod is for the first time recorded in the Silurian of peri-Gondwana; it is the only Aeronian species known so far. Its most closely allied relatives are from higher beds placed in the Telychian of Scotland. Pterotheca is considered a highly derived genus within the Pterothecinae of the Carinaropsidae, with the strongly reduced to absent coiling and the growth of the septum being synapomorphies. In the present work it is shown that not only the apical angle of the septum can be used to distinguish species, but also the relative length and width of the septum. In some cases, the slit may extend as far back as the anterior part of the internal septum. Silurian species were hitherto only found in marginal Laurentian and Eastern Avalonian settings. Pterotheca is absent from central Laurentia and Baltica, where it could be expected to be present based on its wide Ordovician distribution. In the light of this, the occurrence of the genus in the Aeronian of Spain seems difficult to explain, albeit the genus was present in peri-Gondwana prior to the end-Ordovician extinction. The extreme scarcity of described taxa recorded from Avalonia, Baltica and Iberia during the Early Silurian may explain this patchy distribution.

This paper describes 3 species of ribeirioid and 2 species of conocardiid rostroconchs from fluvially transported erratics in the Dutch-German border area. The material probably stems from Ordovician deposits of the North Estonian Confacies Belt. The ribeirioid specimens from the flaljala group of erratics (Sandhian 2) are represented by Tolmachovia subliratu sp. nov., Beukeria plicata gen. nov. sp. nov. and Ischyrinia viator sp. nov. The single specimen of Tohnachovia is hitherto the youngest occurrence of this genus and the first in Baltica. The presence of subordinate radial ornamentation is added to the emended diagnosis of the genus. The new genus Beukeria is an ischyriniid rostroconch with an elongated conch, two thick pegmas and a plicate shell posterior to vertical axis. Ischyrinia viator is similar to the coeval. I. notTegica Soot-Ryon, 1960 but this has a ventrolateral sinus that is subparallel to the dorsal axis. Conocardild specimens from the Pirgu Ojlemyr chert (Katian 4) are represented by Bitrigonocardia lindstroemi (Isberg) and Pojetaconcha costulata sp. nov. The identification of Bitrigonocardia lindstroemi is circumstantial as the type specimens are missing, but as understood here new details of morphology and ornamentation are given. Pojetaconcha is for the first time recognized outside Laurentia and Australia. Pojetaconcha costulata sp. nov. is distinguished by 14 or 15 broad and flat-topped radial ribs on the body and snout and compares closely with the Chazyan P. alabamensis (Pojeta & Runnegar, 1976), USA. Ischyriniids occur mainly in Baltica with Ischyrinia migrating into Laurentia. A general exchange of Bitrigonocardia and Pojetaconcha is seen between Laurentia and Baltica.

The Late Ordovician Period witnessed the second largest mass extinction in the Phanerozoic Eon and the Hirnantian glaciation. To infer ocean redox conditions across the Ordovician-Silurian transition, we measured the U (as δ²³⁸U relative to standard CRM145 = 0‰) and Mo (as δ⁹⁸Mo relative to standard NIST SRM 3134 = +0.25‰) isotope compositions of 26 organic-rich mudrock samples from the Late Ordovician (Katian) Fjacka Shale and the Early Silurian (Aeronian-Telychian) Kallholn Formation (Siljan ring district, Sweden). The magnitude of Re, Mo, and U enrichments, Re_EF/Mo_EF and U_EF/Mo_EF ratios, and sedimentary Fe speciation point to locally euxinic bottom water conditions during deposition of the Fjacka Shale. The same proxies suggest that black shales of the Kallholn Formation were deposited under transiently euxinic conditions with the chemocline situated near the sediment-water interface, whereas gray shales stratigraphically equivalent to the upper Kallholn Formation were deposited from oxygenated bottom waters. These observations are consistent with higher δ⁹⁸Mo and δ²³⁸U in the Fjacka Shale compared with the Kallholn Formation.

Because the Fjacka Shale was deposited from persistently euxinic bottom waters, the Mo and U isotope compositions from these rocks can be used to estimate the extent of global ocean euxinia and ocean anoxia (euxinic plus ferruginous conditions), respectively. Elevated Mo_EF and Mo/TOC ratios in the euxinic Fjacka Shale suggest no more than moderate basin restriction from the open ocean as well as non-quantitative removal of Mo from the euxinic bottom waters, thus pointing to Mo isotope fractionation between seawater and the euxinic sediments. Hence, we infer that even the highest δ⁹⁸Mo (+1.28‰) preserved in the Fjacka Shale is only a minimum estimate for the Mo isotope composition of coeval global seawater. Correcting for seawater-sediment Mo isotope fractionation, the δ⁹⁸Mo of late Katian seawater may have been +1.4-2.1%0, which corresponds to similar to 10-70% Mo removal into the euxinic sink. The average authigenic δ²³⁸U of the Fjacka Shale is 0.05‰ to +0.02‰ after correcting for a range of possible detrital δ²³⁸U values, thus yielding an overall average of-0‰. Taking into account isotope fractionation during U removal to euxinic sediments, we infer that late Katian seawater δ²³⁸U was about 0.85‰ to 0.60‰. A steady-state U isotope mass balance model reveals that 46-63% of riverine U input was removed in anoxic settings. Based on the Mo and U isotope data, we infer that euxinic and anoxic waters may have covered <1% and at least 5% (potentially tens of percent) of the total seafloor area during the late Katian, respectively, based on previously published models that relate the magnitude of Mo and U burial fluxes to the areal extent of euxinic and anoxic seafloor. By comparison, only 021-035% and <1% of the total seafloor area was covered by anoxic waters today and during the Cenozoic, respectively. The difference between the estimated extent of ocean anoxia (euxinic plus ferruginous) and ocean euxinia points to an appreciable extent of ferruginous water masses during the late Katian. Integration of our data with previous studies thus supports the hypothesis that ocean oxygenation intensified during the subsequent Hirnantian glaciation (when seawater δ⁹⁸Mo temporarily reached values similar to today). Hence, environmental stresses related to glaciation, not an expansion of ocean anoxia, may have triggered the first phase of the Hirnantian mass extinction.

The small problematic mollusc Jinonicella kolebabai Pokorný, 1978 is described from the lower Silurian Laketown Dolostone at Barn Hills in Utah, USA. The associated conodonts suggest a late Telychian age for the assemblage, which makes this the oldest occurrence of this species. Previous Silurian records of Jinonicellawere known from the Sheinwoodian to Ludfordian of Bohemia, the Czech Republic, Gotland, Sweden and the Carnic Alps of Austria.

Late Ordovician mud-mounds in the Boda Limestone, Siljan area, central Sweden, consist mainly of massive spiculitic stromatactis limestone similar to other well-known Paleozoic mud-mounds. The mound cores are predominantly formed by spiculite and ostracod-rich mudstone and/or wackestone, and networks of spar-filled syndepositional cavities. The mounds of the Boda Limestone are specific in two ways: (1) large parts of the lower mound cores are formed by a Palaeoporella framestone and/or bafflestone with signs of early recrystallization and cementation; and (2) the stromatactis facies is accompanied by masses of limestone with non-stromatactis cryptocrystalline patches. Cryptocrystalline patches are filled with massive, fibrous low-Mg calcite, have cloudy, transitional margins, contain randomly spaced skeletal grains and dolomitic micro-inclusions, and are interpreted as recrystallized patches of the original host lime mud. Models of formation of Paleozoic mud-mounds generally hypothesize accretionary processes that are based on sponge biomass degradation and associated diagenetic processes. In the Boda Limestone Palaeoporella skeleton disintegration, early recrystallization, and additionally, cementation were essential for the mound formation. The Boda mounds exemplify that formation of Paleozoic mud-mounds reflects a spectrum of different essentially diagenetic accretionary mechanisms. This diversity should be taken into account in future discussions about Paleozoic mud-mound formation. The new name Osmundsberget Formation is given for a Hirnantian succession of brachiopod-rich limestone above the Boda Limestone. The Osmundsberget Formation occurs only in direct geographical vicinity to the mud-mounds.

In 1908, Carl Wiman of Uppsala University, Sweden, discovered rich horizons with Triassic vertebrate remains in Spitsbergen on Svalbard, Norway. This marked the beginning of vertebrate palaeontology as a science in Sweden, subsequently developed mainly through the collection and study of non-Swedish fossil remains. Wiman's accomplishments, resolute personality and a tight network of influential friends and supporters enabled him to become the first person in Sweden to hold a university chair in Palaeontology and Historical Geology. He also managed to amass large numbers of unique fossil vertebrate specimens culminating in an extensive Chinese collection of both world famous dinosaurs and Neogene mammals deposited at Uppsala University. Joint scientific Sino-Swedish collaboration and a deliberate Swedish scientific agenda ensured this unprecedented situation in an opportune moment. Governmental support and initiative allowed Uppsala University and Carl Wiman's Palaeontological Institute to erect a museum building dedicated foremost to the Chinese material, now known as the Lagrelius Collection in recognition of the patron behind Wiman's ambitious endeavours. In addition, the museum served as a permanent repository for seminal collections of Mesozoic fossils from Svalbard and North America. Collectively, these represent a landmark research and teaching resource that remains of intense scientific interest even today.