Olenid Trilobites Research Articles

First occurrence of well-preserved Ordovician trilobites of the family Olenidae from Africa

Abstract Here we describe the first articulated olenid trilobite specimens recovered from the lowermost Fezouata Shale Formation (lower Tremadocian, Ordovician) of Morocco. Prior to the discovery of this sample, only two partial olenid trilobite specimens had been found from this part of the rock record. The specimens are well preserved enough to confidently identify as Leptoplastides salteri (Callaway, 1877), extending the species geographic range from Avalonia into Gondwana. We argue that the Moroccan occurrences formerly referred to as “Beltella sp.” in the literature are likely to be those of L. salteri. This species is the only olenid trilobite known from African Gondwana.

The Central Andean Basin as a dispersal centre: Biogeographic patterns of olenid trilobites during the late Cambrian – Early Ordovician

The biogeographic histories of two cosmopolitan groups of Olenida: Hypermecaspididae and Parabolinella (Olenidae) are studied herein. Different biogeographical models were compared, and the results were discussed in a palaeogeographic and palaeoceanographic context. Dispersal pathways were proposed for both groups, identifying potential environmental factors that affected their distribution. Calibrated phylogenetic hypotheses for each taxon were used to compare different models of geographical evolution with R package BioGeoBEARS. Time-stratified analyses were carried out, using different distance matrices, for three intervals (Furongian, Early Ordovician and Middle Ordovician). Numbers and types of biogeographical events were estimated under the best-fitting models by using Biogeographic Stochastic Mapping (BSM). For both groups, the best-fit model incorporated jump dispersal, indicating that this was an important speciation strategy. Vicariance was unimportant for these trilobites, which would have been favoured by the stable conditions of their habitat. Ocean currents were key in the dispersal patterns of Parabolinella, but not in those of Hypermecaspididae. The main strategy used for both groups would have been “island hopping”, taking advantage of the microterranes and volcanic island arc chains surrounding Laurentia, Baltica, Avalonia, and Gondwana. Creeping also operated as a dispersal mechanism in Parabolinella. This genus originated in the late Miaolingian, when the more uniform sea conditions would have favoured its dispersal capabilities. On the other hand, Hypermecaspididae diversified mainly in the Early Ordovician, when cooling seas and changes in ocean circulation patterns generated more segmented habitats, affecting chances of dispersal, and favouring jump-founder events. Despite these differences, in both clades founder and dispersal events were more abundant from the western margin of Gondwana, which constituted an important dispersal centre during the Furongian and Early Ordovician.

The Cambrian (Furongian) olenid trilobitePelturafrom Avalonian Nova Scotia, Canada, with a review of some species from Baltica

The Cambrian olenid trilobite Peltura Milne-Edwards, 1840 is widespread in the Furongian strata of the Cambrian continents of Baltica and Avalonia, and has played a significant role in biostratigraphic zonations for both regions. Despite this importance, the genus is poorly known in Avalonian Canada. New collections from the Chelsey Drive Group on Cape Breton Island, Nova Scotia, yielded numerous sclerites of a new species, Peltura hutchinsoni sp. nov., that may also occur in the Parabolina lobata Zone of Baltica. Archival specimens from Sweden and Norway allow the revision of Peltura scarabaeoides ( Wahlenberg, 1821 ) and Peltura acutidens Brögger, 1882 , respectively.

The Central Andean Basin as a Dispersal Centre: Biogeographic Patterns of Olenid Trilobites During the Late Cambrian – Early Ordovician

The Central Andean Basin as a Dispersal Centre: Biogeographic Patterns of Olenid Trilobites During the Late Cambrian – Early Ordovician

The Furongian (upper Cambrian) Alum Shale of Scandinavia: revision of zonation

The zonation of the Furongian Alum Shale in Scandinavia, based on olenid trilobites, is reviewed and revised. The current scheme is rooted in a detailed zonation introduced in the late 1950s with subzones that subsequently have been elevated to zonal rank. Ten of these zones are difficult to recognize in all Alum Shale districts, and a revised zonation is proposed, focused on unambiguous identification throughout Scandinavia. The difficulties in recognizing zones in some districts mostly relate to biofacies differentiation. Representatives of Ctenopyge are, for instance, common in palaeo-offshore areas, whereas pelturines are rare in these settings and vice versa in palaeo-inboard settings. The following modifications of the olenid zonation are proposed: the Olenus scanicus Zone is renamed the O. scanicus–O. rotundatus Zone; the Ctenopyge similis and Ctenopyge spectabilis zones are replaced by the Sphaerophthalmus modestus–Sphaerophthalmus angustus Zone; the Ctenopyge tumida Zone is renamed the Peltura acutidens–Ctenopyge tumida Zone; the Peltura scarabaeoides Subzone is restored (as a zone) and replaces the Ctenopyge bisulcata and Ctenopyge linnarssoni zones. The Parabolina heres megalops (Sub)Zone is reinstated and replaces the Peltura paradoxa Zone; the Acerocarina granulata and P. costata zones are combined as the Acerocarina granulata–Peltura costata Zone. In addition, the name Proceratopyge nathorsti–Simulolenus alpha Zone is suggested for the polymerid zone corresponding to the upper Miaolingian Agnostus pisiformis Zone. The proposed changes reduce the number of Furongian Zones to 23, allocated to six superzones. No subzones are recognized, but some zones can potentially be subdivided for improved local correlation. The stratigraphical ranges of all Furongian olenid trilobites and agnostoids described from Scandinavia are summarized. (Less)

Lipid biomarker and stable isotopic profiles through Early-Middle Ordovician carbonates from Spitsbergen, Norway

One of the most dramatic episodes of sustained diversification of marine ecosystems in Earth history took place during the Early to Middle Ordovician Period. Changes in climate, oceanographic conditions, and trophic structure are hypothesised to have been major drivers of these biotic events, but relatively little is known about the composition and stability of marine microbial communities controlling biogeochemical cycles at the base of the food chain. This study examines well-preserved, carbonate-rich strata spanning the Tremadocian through Upper Dapingian stages from the Oslobreen Group in Spitsbergen, Norway. Abundant bacterial lipid markers (elevated hopane/sterane ratios, average = 4.8; maximum of 13.1), detection of Chlorobi markers in organic-rich strata, and bulk nitrogen isotopes (δ15Ntotal) averaging 0 to −1‰ for the open marine facies, suggest episodes of water column redox-stratification and that primary production was likely limited by fixed nitrogen availability in the photic zone. Near absence of the C30 sterane marine algal biomarker, 24-n-propylcholestane (24-npc), in most samples supports and extends the previously observed hiatus of 24-npc in Early Paleozoic (Late Cambrian to Early Silurian) marine environments. Very high abundances of 3β-methylhopanes (average = 9.9%; maximum of 16.8%), extends this biomarker characteristic to Early Ordovician strata for the first time and may reflect enhanced and sustained marine methane cycling during this interval of fluctuating climatic and low sulfate marine conditions. Olenid trilobite fossils are prominent in strata deposited during an interval of marine transgression with biomarker evidence for episodic euxinia/anoxia extending into the photic zone of the water column.

A revised ontogeny of the early Ordovician trilobite Leptoplastides salteri (Callaway, 1877)

ABSTRACTThe ontogeny of the pelturine olenid trilobite Leptoplastides salteri (Callaway, 1877) from the Shineton Shales, Shropshire, England, was first described in 1925 by Frank Raw. Since that time, scanning electron microscopy and other new technologies have revealed many more details of structure, of early developmental stages in particular, than were available to Raw. Whereas protaspides are not preserved and the state of preservation is less than perfect for the smallest meraspides, we have established that the latter had an array of delicate, long thoracic and pygidial spines, as well as paired procranidial spines, which disappear by meraspid degree 8. Raw's reconstructions of early meraspides, and his measurements of the early stages in development, are here amended in the light of new information. Dorsal spines in the adult are much more highly developed than have been documented in any other olenid. The hypostome is preserved in place in several specimens. Initially conterminant (attached to the doublure), it becomes natant (free) in late meraspid to early holaspid stages of development, with its anterior contour fitting exactly to that of the glabella. The ecology of the widespread Leptoplastides is best known from very extensive sections in South America, which provide a useful basis for comparison. It was well adapted to a range of environments, both oxygenated and dysoxic, and is usually the dominant taxon in the biofacies in which it is found.

Broeggeria Walcott and other upper Cambrian and Tremadocian linguloid brachiopods from NW Argentina

The Broeggeria assemblage is a peculiar brachiopod association that has been recorded mainly from Tremadocian black shales of Baltoscandia, the Anglo‐Welsh Basin, Nova Scotia, South Urals and Kazakhstan. Here, we report a low diversity brachiopod association dominated by Broggeria omaguaca n. sp. from upper Tremadocian open‐shelf mudstones of northwestern Argentina. The dark‐grey transgressive muddy interval bearing the Broeggeria assemblage starts with an erosive flooding surface marked by a glauconite‐rich bed containing reworked bioclasts, which overlies storm‐dominated shoreface sandstones. Lithologic and taphonomic evidence indicates that the fauna from the mudstones represents a palaeocommunity inhabiting oxygen‐depleted bottoms. Besides Broeggeria omaguaca, which by far is the more abundant linguloid, the assemblage includes the obolids Palaeoglossa elongata (Harrington) and Libecoviella aff. tilcarensis Benedetto and Muñoz, and the punctate orthide Lipanorthis andinus Benedetto. Associated trilobites are abundant and low diversity, the more common being the large asaphid Asaphellus jujuanus Harrington. Coeval strata exposed in the Santa Victoria area contain rare specimens of Broeggeria omaguaca associated with Leptembolon argentinum Benedetto and Muñoz and Palaeoglossa elongata. Comparable dysoxic black shales of Furongian age bearing the olenid trilobite Parabolina (Neoparabolina) frequens have yielded a monospecific association of Lingulella n. sp. The records of Broeggeria at global scale support its late Cambrian origin in the Anglo‐Welsh Basin (Avalonia) and its rapid migration into the Karatau–Naryn terrane (a part of the Kazakhstanian collage). By the early Tremadocian, Broeggeria spread to Belgium and to the neighbouring Megumia terrane, migrating later (mid‐late Tremadocian) to Baltica, Southern Urals, Kazakhstanian terranes, Perunica and the Central Andean Basin. By the late Floian/early Dapingian, Broeggeria colonized palaeoequatorial deep shelves (Spitsbergen). Copyright © 2017 John Wiley & Sons, Ltd.

Aligned trace fossils from the Utica Shale: implications for mode of life and feeding in the trilobiteTriarthrus beckii

The olenid trilobite Triarthrus commonly occurs in nearly monospecific assemblages within otherwise relatively barren black shales. As such, it has been proposed that these trilobites preferred dysoxic or even anoxic habitats and suggested feeding habits range from predation and particle feeding to chemoautotrophism. A unique bedding-plane assemblage of aligned traces that grade from Rusophycus to Cruziana, with associated Triarthrus beckii carcasses, are described from three localities in the Indian Castle Formation (upper Utica Shale) just below a K-bentonite bed. Although few body fossils are preserved, it is clear that the 15-cm-thick, laterally extensive Thruway K-bentonite created a unique taphonomic window that preserved the activities of numerous olenid trilobites. Rusophycus and Cruziana, consistently observed in densities above 100 trackways/m2, were excavated by the trilobites into the upper surface of a micro-graded bed, likely a distal turbidite deposit. Sedimentological and trace metal data (Mo, Mn, V and U) support dysoxic but not persistently anoxic conditions through this interval. Measurements from over 500 individual trackways have mean orientations of 259.1° (WSW) at the Myers Rd. locality and 224.59° (SW) at the Dolgeville Dam locality. These orientations are closely similar to independent sedimentological indicators of current transport direction at these sites, which indicates that the trilobites preferentially faced into the prevailing current. The trackways provide compelling evidence that Triarthrus beckii individuals were engaged in feeding, probably assisted by current transport of particles. These results do not support previous suggestions that Triarthrus may have relied upon a chemoautotrophic life habit, but are consistent with suggestions of predation or scavenging from the sediment.

Proposed Auxiliary Boundary Stratigraphic Section and Point (ASSP) for the base of the Ordovician System at Lawson Cove, Utah, USA

The Global boundary Stratotype Section and Point (GSSP) for the base of the Ordovician System is at the First Appearance Datum (FAD) of the conodont Iapetognathus fluctivagus at Green Point in Newfoundland, Canada. Strata there are typical graptolitic facies that were deposited near the base of the continental slope. We propose establishing an Auxiliary boundary Stratotype Section and Point (ASSP) at the FAD of I. fluctivagus at the Lawson Cove section in the Ibex area of Millard County, Utah, USA. There, strata consist of typical shelly facies limestones that were deposited on a tropical carbonate platform and contain abundant conodonts, trilobites, brachiopods, and other fossil groups. Cambrian and Ordovician strata in this area are ~5300m thick, with the Lawson Cove section spanning 243m in three overlapping segments. Six other measured and studied sections in the area show stratigraphic relationships similar to those at Lawson Cove. Faunas have been used to divide these strata into 14 conodont and 7 trilobite zonal units. The widespread olenid trilobite Jujuyaspis occurs ~90cm above the proposed boundary at Lawson Cove; this genus is generally regarded as earliest Ordovician. Rhynchonelliform and linguliform brachiopods are common to abundant and are useful for correlation. The FAD of Iapetognathus fluctivagus and occurrences of Jujuyaspis and the Lower Ordovician planktonic graptolite Anisograptus matanensis all occur within a 2.4m interval of strata at a nearby section. Non-biological correlation tools include a detailed sequence stratigraphic classification and a detailed carbon-isotope profile. Especially useful for correlation is a positive δ13C excursion peak ~15cm below the proposed boundary horizon. All of these correlation tools form an integrated framework that makes the Lawson Cove section especially useful as an ASSP for global correlation of strata with faunas typical of shallow, warm-water, shelly facies.

Testing symbiotic morphology in trilobites under dysoxic and oxic conditions from Cambrian to Early Ordovician Lagerstätten

Dysoxic conditions were prevalent in Cambrian and Early Ordovician oceans. Adaptations of trilobites to these conditions yield insight into the selective forces driving their evolution and the potential for modern arthropods to adapt to anthropogenically-driven dysoxia. In the early Paleozoic, olenid trilobites may have adapted to dysoxia through olenimorphy, special morphologic adaptations facilitating symbiosis with sulfur-oxidizing bacteria. Olenimorphy's link to symbiosis has never been tested and might instead be related to phylogeny. Here, we tested whether olenimorphy occurs predominately in dysoxic environments, as expected, or whether it occurs within certain trilobite groups regardless of environment. Trilobites were selected from nine fossil Lagerstätten representing the early-to-middle Cambrian prior to olenid evolution and the middle Cambrian–Early Ordovician Alum Shale with olenids, putative exemplars of symbiosis. Trilobite morphology was scored as ranked characters and reduced via non-metric multidimensional scaling (NMDS) to a single metric describing suitability for symbiosis. Results indicated that olenimorphy was significantly related to phylogeny and not environment. In the early-to-middle Cambrian, dysoxic corynexochids and oxic redlichiids were equally unsuitable for symbiosis, while ptychopariids from both oxic and dysoxic conditions were equally well suited for symbiosis. In the Alum Shale, asaphids and ptychopariids from both oxic and dysoxic conditions were equally well suited for symbiosis, and redlichiids from oxic conditions were poorly suited. Olenids were not the best-suited trilobites within their data set, nor even within their order. Secular trends in thoracic segmentation did not bias our results. Trilobite hard parts do not appear to provide evidence for symbiosis, which is consistent with modern arthropods that have few morphological adaptations for dysoxic conditions. In fact, arthropods are rare in persistently dysoxic conditions, raising concerns about the spread of anthropogenically-triggered benthic dysoxia in the future, particularly given the extinction of trilobites under similar conditions at the end of the Permian.

The late Cambrian (Furongian) Acerocarina Superzone (new name) on Kinnekulle, Västergötland, Sweden

The traditional Furongian biozones of Scandinavia, based on olenid trilobites, are proposed elevated to superzonal rank. For the time being they are treated informally, except that the designation Acerocarina Superzone is proposed as replacement name for the uppermost superzone, formerly referred to as the Acerocare Zone. It comprises four zones. The lowest of these zones, hitherto referred to as the Peltura transiens Zone, is renamed as the Acerocarina granulata Zone. The distribution of the Acerocarina Superzone in Baltoscandia is mapped. A newly discovered 1.4 m thick succession on Kinnekulle, Västergötland, yielded Parabolina heres heres, P. transiens, Peltura costata, Peltura scarabaeoides westergaardi and Sphaerophthalmus alatus. In addition, A. granulata, Pelturina punctifera and Leptoplastides? sp. were collected from loose boulders deriving from the same interval. This is the first unambiguous record of P. costata and P. punctifera in Sweden. The fossil assemblage, assigned to the P. costata Zone, contains species hitherto considered characteristic of five different biozones, viz. the Ctenopyge tumida Zone, the Parabolina lobata Zone, the P. transiens Zone, the P. costata Zone and the Westergaardia scanica Zone. P. transiens, P. scarabaeoides westergaardi and S. alatus are assumed to have been reworked, whereas P. punctifera appears one zone earlier than in Norway. Parabolina (Parabolina) heres lata, not found during this study, may turn up in the P. costata Zone or even earlier. The Acerocarina Superzone is resting on the P. lobata Zone, and the intervening zone, characterized by Peltura paradoxa (uppermost “Peltura scarabaeoides” superzone), is missing in the succession on Kinnekulle.

Ontogeny of the Upper Cambrian (Furongian) Olenid trilobite Protopeltura aciculate (Angelin, 1854) from Skåne and Västergötland, Sweden

Abstract: The ontogeny of the trilobite Protopeltura aciculata (Angelin, 1854) is described on the basis of material from the upper Cambrian (Furongian) of Andrarum (Skåne) and Hjelmsäter (Västergötland), Sweden. P. aciculata is present in the Parabolina brevispina and Parabolina spinulosa zones. Protopeltura aciculata is represented by all stages of growth, from early protaspides to holaspides, although most of the specimens are disarticulated and precise degrees are unknown. The cranidia have therefore been allocated to five morphological groups. Cuticular sculpture of the cranidia changes throughout ontogeny. Large tubercles are present in earlier stages, disappear gradually in middle meraspid stages and are replaced with a very faint granulation. The transitory pygidium, relatively large and shield‐shaped with upwardly and backwardly directed marginal spines in early meraspides, later becomes very small, triangular‐shaped and lacking spines as a late meraspid and holaspid. The development of hypostomes and librigenae is also described. Protopeltura aciculata shows major intraspecific variations throughout development, especially regarding the pygidium where variation is much less constrained than in many other olenids. This high developmental plasticity may be a survival strategy for a trilobite living in a stressed environment. Protopeltura inhabited a dysoxic environment, possibly unusually prone to localised spreading of anoxic or toxic water. Some morphs may have been less vulnerable than others to such stresses, surviving by chance and thus enabling the species to continue.

PALEOECOLOGY OF THE OLENID TRILOBITE TRIARTHRUS: NEW EVIDENCE FROM BEECHER'S TRILOBITE BED AND OTHER SITES OF PYRITIZATION

Olenid trilobites are characteristic of low-oxygen environments in the early Paleozoic, and researchers have proposed that olenids may have harbored chemoautotrophic symbionts, allowing them to live in borderline sulfidic environments. Beds with soft-tissue preservation at the Beecher's Trilobite Bed site in the Frankfort Shale and the Martin Quarry in the Whetstone Gulf Formation (both Ordovician, New York State) are dominated by the olenid Triarthrus. A bed-by-bed analysis of the sedimentology, taphonomy, paleoecology, and ichnology demonstrates that the exceptionally preserved organisms did not undergo extensive transport, and that the intervals bearing Triarthrus accumulated predominantly in the lower part of the dysaerobic zone. These intervals contain a low-diversity benthic fauna occurring in relatively low abundance, and consisting primarily of small brachiopods and trilobites. The taphonomy, in particular localized pyritization, the associated fauna, and the distribution of Triarthrus elsewhere in the Taconic foreland basin demonstrate that the environments in which Triarthrus lived were not sulfidic, and that these trilobites were unlikely to have adopted a chemoautotrophic mode of life.

The Furongian trilobite Irvingella from Jämtland and Ångermanland, Sweden

New material of Irvingella from central Sweden includes a cranidium of Irvingella major which is associated with fragmentary olenid trilobites that represent the Parabolina brevispina Subzone of the P. spinulosa Zone. This affords a direct correlation between the olenid trilobite zonation of Baltica and the Irvingella major Zone at the base of the Sunwaptan Stage in Laurentia. Several topotypic cranidia of Irvingella suecica Westergård confirm the features of that species but do not provide a direct indication of its position within the olenid zonal succession.

Faunal turnovers and trilobite morphologies in the upper CambrianLeptoplastusZone at Andrarum, southern Sweden

The Furongian (upper Cambrian) Leptoplastus Zone marks a time of critical changes in the evolution of olenid trilobites. This zone, unexposed at Andrarum in Skåne, southern Sweden, has been re-excavated and the sequence of faunas and sediments logged in detail. The faunal succession accords with that previously described from borehole cores by Westergård, and the subzones of L. paucisegmentatus, L. raphidophorus, L. crassicornis, L. ovatus, L. angustatus, and L. stenotus have been recognized. In the first two subzones the olenid assemblages are monospecific. At the base of the L. crassicornis Subzone more than one species is present and morphotypes with long genal spines appear for the first time. Faunal turnover is rapid, but the incoming of new species is invariably linked to an abrupt change in sedimentation, or follows an unfossiliferous interval; species either arose or migrated in after a time of environmental perturbation. Particular faunal associations are often confined to discrete sedimentary packages though some species may range through a succession of sedimentary changes. Leptoplastus crassicornis has very long genal spines, adapted for resting on the sea floor; it may have competed with the coeval, and very similar, L. angustatus. Subsequently, L. angustatus is accompanied by the stout-bodied, short-spined L. ovatus, which presumably occupied a different niche within the same environment. Leptoplastus stenotus is convergent on the much earlier L. paucisegmentatus, and likewise is found as a monospecific assemblage, presumably being adapted to a similar niche.

Late Cambrian acritarchs from the “Túnel Ordovícico del Fabar”, Cantabrian Zone, N Spain

A single sample from the La Matosa Member of the Barrios Formation, exposed during the excavation of the El Fabar Tunnel in Asturias, N Spain, yielded a rich and well-preserved Late Cambrian acritarch assemblage. The Middle? to Upper Cambrian La Matosa Member consists mainly of quartz sandstone and includes locally a thick fossiliferous intercalation of dark shale (“El Fabar beds”) from which the acritarch sample was collected. The latter shale levels yielded also some linguliform brachiopods, olenid trilobites and phyllocarid crustaceans. Characteristic genera of the study sample are Acanthodiacrodium, Lusatia and Cristallinium. Other significant components are Cymatiogalea, Timofeevia and Vulcanisphaera. Lusatia dendroidea Burmann 1970, recorded for the first time in Spain, is a characteristic element of this assemblage. In the study sample, the latter species is abundant, well-preserved and exhibits appreciable morphological variability. This acritarch assemblage is correlated with the lower part of microflora RA5 of Parsons and Anderson [Parsons, M.G., Anderson, M.M., 2000. Acritarch microfloral succession from the Late Cambrian and Ordovician (early Tremadoc) of Random Island, eastern Newfoundland, and its comparison to coeval microfloras, particularly those of the East European Platform. AASP Contr. Ser. 38, 129 pp.] corresponding to the Protopeltura praecursor trilobite Zone.

Heterochrony of the Late Cambrian olenid trilobites from the Machari Formation, Yeongwol, Korea: implications for biostratigraphy and intercontinental correlation

This study deals with the heterochrony of two Late Cambrian olenid trilobites,Olenus asiaticus Kobayashi, 1944 from theGlyptagnostus reticulatus Zone andHancrania brevilimbata Kobayashi, 1962 from theHancrania brevilimbata Zone, recovered from the Machari Formation in Yeongwol, Korea. Comparison of ontogenetic developments ofOlenus asiaticus andHancrania brevilimbata led to consider that the two species are phylogenetically related: viz.,Hanerania brevilimbata is a probable descendant ofOlenus asiaticus. The ontogenetic trajectories of the two species are closely comparable in the protaspid and early meraspid stages, but deviate in the late meraspid and holaspid stages. The morphological changes with growth in theOlenus asiaticus-Hancrania brevilimbata lineage may have resulted from combined heterochronic processes: i.e., the reduction of preglabellar field in the descendant is attained by paedomorphic progenesis, whereas the expansion of glabella is a consequence of peramorphic acceleration. Of these, the progressive reduction of preglabellar field has been known to occur in other parts of the world and thus is assumed to be useful in improving the biostratigraphic correlation among widely separated paleogeographic provinces, such as Baltica and Avalonia. TheGlyptagnostus reticulatus Zone of the Paleozoic Gondwana can be correlated with theOlenus gibbosus Subzone of Avalonia and Baltica, while theHancrania brevilimbata Zone of Korea with theO. attenuatus andO. dentatus subzones of Baltica and the lower part of theO. cataractes Subzone of Avalonia.

Trilobites and intercontinental tie points in the Upper Cambrian of Scandinavia

The Upper Cambrian faunas of Scandinavia are generally dominated by olenid trilobites, which provide a firm basis for the biostratigraphic classification. The olenids tend, however, to be provincial and facies controlled. By contrast, many agnostoid genera and species have a nearly worldwide distribution and are excellent biostratigraphic indices in Middle and Upper Cambrian strata. Three distinctive and geographically widely distributed agnostoid species are known from the lower part of the Upper Cambrian in Scandinavia: Linguagnostus reconditus POLETAEVA and ROMANENKO, 1970, Aspidagnostus lunulosus (KRYSKOV in Borovikov and Kryskov, 1963), and Glyptagnostus reticulatus (ANGELIN, 1851). They are the most valuable species available for correlations with Upper Cambrian deposits outside Baltica. L. reconditus is seemingly confined to the Agnostus pisiformis Zone and provides strong evidence for correlation of that zone with the recently defined L. reconditus Zone of Peng and Robison. G. reticulatus appears in the Olenus gibbosus Subzone and ranges up into the O. wahlenbergi Subzone, suggesting that the lower part of the Olenus/Agnostus (Homagnostus) obesus Zone correlates with the G. reticulatus Zone in, e.g., Australia, China, and Kazakhstan. The presence of A. lunulosus in the O. gibbosus Subzone provides additional evidence for this correlation. Higher in the sequence agnostoids become rare, and the species recorded from the medial and upper Upper Cambrian of Baltica permit only broad correlations with other continents.

Ontogeny and Structure of a New, Miniaturised and Spiny Olenid Trilobite from Southern Sweden

Several hundred specimens of a tiny olenid trilobite, Ctenopyge ceciliae sp. nov., have been found in stinkstone nodules in the upper Cambrian Peltura scarabaeoides Zone in southern Sweden. This exceptionally spinose form is known only from disarticulated specimens, but is quite well preserved, and all growth stages are represented. The early ontogenetic stages are exceptionally small, the protaspis being only half the size of that of the associated Peltura species. There may have been no more than three thoracic segments. Thus the whole ontogeny was compressed, and this together with the very small size of the adult indicates a true miniaturisation. Whereas the likely control of the origin of the tiny C. ceciliae was basically progenesis, the extreme spinosity had a different origin; allometric growth or possibly peramorphosis. C. ceciliae is small enough for the spines to have appreciably retarded sinking through frictional effects, and this small trilobite is interpreted as a free‐swimming or floating form.