The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden

The late Katian, Late Ordovician Boda Limestone of Dalarna, Sweden contains a rich cephalopod assemblage. The assemblage consists of 61 species, in 31 genera, comprising almost all major Ordovician cephalopod orders. Most common and diverse are the Orthocerida. The Ascocerida are also remarkably common and diverse. The new ascocerid species, Redpathoceras bullatum sp. nov., R. depressum sp. nov., R. magnum sp. nov., and Probillingsites scandinavicum sp. nov., give reason to revise current hypotheses on the origin and evolution of this group. An ascocerid origin from barrandeoceratids or aspidoceratids is hypothesised. The absence of actinocerids in the Boda Limestone is notable, and is interpreted as an indication of relatively cool and/or deep depositional environments. The dominance of orthocerids is provisionally interpreted as evidence for nutrient-rich waters during the time of the deposition of the Boda Limestone. Additionally, the assemblage contains the new barrandeocerids Schuchertoceras fryi sp. nov., Siljanoceras varians gen. et sp. nov., Warburgoceras gen. nov. (for Cyrtoceras longitudinale Angelin in Angelin & Lindström, 1880), the new endocerid Cameroceras turrisoides sp. nov., the new oncocerid Cyrtorizoceras thorslundi sp. nov., and the new orthocerids Dawsonoceras stumburi sp. nov., Isorthoceras angelini sp. nov., I. curvilineatum sp. nov., Nathorstoceras adnatum gen. et sp. nov., N. kallholnense gen. et sp. nov., Palaeodawsonocerina? nicolletoides sp. nov., Pleurorthoceras osmundsbergense sp. nov., and Striatocycloceras isbergi sp. nov

RNames, a stratigraphical database designed for the statistical analysis of fossil occurrences : the Ordovician diversification as a case study

RNames (rnames.luomus.fi/) is an open access relational database linking stratigraphic units with each other that are considered to be time-equivalent or time overlapping. RNames is also a tool to correlate among stratigraphic units. The structure of the database allows for a wide range of queries and applications. Currently three algorithms are available, which calculate a set of correlation tables with Ordovician stratigraphic units time binned into high-resolution chronostratigraphic slices (Global Ordovician Stages, Stage Slices, Time Slices). The ease of availability of differently binned stratigraphic units and the potential to create new schemes are the main advantages and goals of RNames. Different timebinned stratigraphic units can be matched with other databases and allow for simultaneous up-to-date analyses of stratigraphically constrained estimates in various schemes. We exemplify these new possibilities with our compiled Ordovician data and analyse fossil collections of the Paleobiology Database based on the three different binning schemes. The presented diversity curves are the first sub-stage level, global, marine diversity curves for the Ordovician. A comparison among the curves reveals that differences in time slicing have a major effect on the shape of the curve. Despite uncertainties in Early and Late Ordovician diversities, our calculations confirm earlier estimates that Ordovician diversification climaxed globally during the Darriwilian stage.Peer reviewe

Onset of the Ordovician cephalopod radiation – evidence from the Rochdale Formation (middle Early Ordovician, Stairsian) in eastern New York

The Rochdale Formation of eastern New York (= Fort Ann and lower Bascom formations, designations abandoned) is now recognized to record the earliest stages of the Great Ordovician Radiation of cephalopods. The earliest Bassleroceratidae, Tarphyceratidae and endoceridans on the east Laurentian shallow carbonate platform occur in the upper, thrombolite-bearing member of the Rochdale. This fauna demonstrates that the earliest radiation of Ordovician nautiloids took place in the late Tremadocian and is best recorded in tropical platform facies. Revision of this cephalopod fauna based on approximately 190 specimens collected along a 200 km, N–S belt in easternmost New York has provided new information on inter- and intraspecific variation of earlier described species. The ellesmerocerid Vassaroceras and the endocerids Mcqueenoceras and Paraendoceras are emended. New taxa include Bassleroceras champlainense sp. nov. and B. triangulum sp. nov., Mccluskiceras comstockense gen. et sp. nov., Exoclitendoceras rochdalense gen. et sp. nov. and Paraendoceras depressum sp. nov. A rank abundance plot of 146 specimens from a locality in the Lake Champlain lowlands provides information on the community structure of a nautiloid fauna in which the longiconic cyrtoconic Bassleroceras is shown to dominate strongly. The nautiloid community structure of the Rochdale Formation is similar to that of the underlying Tribes Hill Formation (late early Tremadocian) with respect to the depositional setting, diversity and evenness but displays a remarkably increased taxonomic distinctness.Peer Reviewe

The cephalopods of the Kullsberg Limestone Formation, Upper Ordovician, central Sweden and the effects of reef diversification on cephalopod diversity

The cephalopods collected from the mud mounds of the Kullsberg Limestone Formation, late Sandbian-earliest Katian(?), south central Sweden, are highly diverse and comprise 26 identifiable species of 12 families and six orders in a sample of c. 180 specimens. The assemblage is strongly dominated by orthocerids in abundance and diversity. In contrast, the time-equivalent assemblage of the reef limestone of the Vasalemma Formation of Estonia is dominated by actinocerids and less diverse. Only one-third of the species co-occur in these two palaeogeographically relatively close assemblages. The taxonomic composition of the Kullsberg assemblage is, on the order level, more similar to that of the late Katian-early Hirnantian Boda Limestone Formation of south central Sweden, which represents a similar relatively deep depositional environment. The high local differentiation of cephalopod reef faunas exemplifies the importance of the emergent Baltic reef habitats in diversification processes during the early Late Ordovician. Of the described taxa, the following are new: Beloitoceras thorslundi sp. nov., Cameroceras motsognir sp. nov., Clothoceras thornquisti gen. et sp. nov., Danoceras skalbergensis sp. nov., Discoceras amtjaernense sp. nov., D. nilssoni sp. nov., Endoceras naekki sp. nov., Furudaloceras tomtei gen. et sp. nov., Isbergoceras consobrinum gen. et sp. nov., I. niger gen. et sp. nov., Isorthoceras nikwis sp. nov., I. sylphide sp. nov., I. urdr sp. nov., I. verdandi sp. nov., Kullsbergoceras nissei gen. et sp. nov., Ordogeisonoceras uppsalaensis sp. nov. and Valkyrioceras dalecarlia gen et sp. nov.Peer reviewe

Early-Middle Ordovician Seascapescale aggregation pattern of sponge-rich reefs across the Laurentia paleocontinent

During the late Cambrian–Early Ordovician interval the predominant non-microbial reef builders were sponges or sponge-like metazoans. The lithological and faunal composition of Cambro-Ordovician sponge-dominated reefs have previously been analyzed and reviewed. Here we take the relationship between reef aggregation pattern at reef to seascape scale into account, and look for changes during the Early–Middle Ordovician interval, in which metazoans became dominant reef builders. In a comparison of sponge-rich reefs from eight sites of the Laurentia paleocontinent three different seascape level reef growth patterns can be distinguished: (1) mosaic mode of reef growth, where reefs form a complex spatial mosaic dependent on hard substrate; (2) episodic mode, where patch reefs grew exclusively in distinct unconformity bounded horizons within non-reefal lithological units that have a much larger thickness; and (3) belt-and-bank mode, where reefs and reef complexes grew vertically and laterally as dispersed patches largely independent from truncation surfaces. The distinct modes of growth likely represent specific reef forming paleocommunities, because they differ in content and abundance of skeletal metazoan framebuilders, bioturbation intensity of non-skeletal reef sediment matrix, and in association of reef growth with underlying hard substrate. We suggest, based on a review of Laurentian reef occurrences, that the mosaic mode dominated in Early Ordovician strata and that the dominance shifted toward the belt and bank mode from Middle Ordovician strata onward.Peer reviewe

Cephalopods from reef limestone of the Vasalemma Formation, northern Estonia (latest Sandbian, Upper Ordovician) and the establishment of a local warm-water fauna

The cephalopods of the reef limestones of the Vasalemma Formation, northern Estonia, are highly diverse and comprise 22 species belonging to 10 families and seven orders in a sample of >300 specimens. Most of the specimens were collected from shell concentrations in synsedimentary cavities and are interpreted as parautochthonous, washed in from nearby habitats. Nearly all of the shells are fragmented and nearly 15% are partially encrusted by epibionts. The assemblage is dominated by small (mostly less than 30mm wide), straight-shelled actinocerids and orthocerids; in addition, coiled tarphycerids are common. The high-level taxonomic composition of the Vasalemma cephalopod assemblage, with a dominance of actinocerids and an absence of endocerids, is in agreement with deposition in a warm-water (tropical or subtropical), shallow, subtidal regime. At the species level the assemblage is highly endemic, but the generic composition allows for a statistical comparison with other faunas. A cluster analysis of contemporary assemblages reveals a high degree of similarity with late Sandbian cephalopod faunas of epicontinental Laurentia. The palaeogeographical distribution pattern is similar to that of brachiopods, which supports earlier interpretations of these clusters as mainly controlled by water temperature and depositional depth. Several of the Vasalemma genera became conspicuous elements of epicontinental Laurentia during the Katian, which emphasizes that immigration towards Laurentia was an important factor in Late Ordovician diversity dynamics. Of the described taxa, the following are new: Beloitoceras cautis sp. nov., Curtoceras abditus sp. nov., Hemibeloitoceras arduum sp. nov., H. molis sp. nov., Hoeloceras muroni sp. nov., Isorthoceras cavi sp. nov., I. maris sp. nov., I. padisense sp. nov., I. vexilli sp. nov., Ordogeisonoceras tartuensis sp. nov., Orthonybyoceras isakari sp. nov., O. moisense sp. nov., Pleurorthoceras organi sp. nov., Rummoceras rummuensis gen. et sp. nov. and Trocholites gennadii sp. nov.http://zoobank.org/urn:lsid:zoobank.org:pub:E5211305-A5D0-4366-AAB1-08F96F817122Peer reviewe

Changes in the latitudinal diversity gradient during the Great Ordovician Biodiversification Event

Near-equatorial peak diversities are a prominent first-order feature of today's latitudinal diversity gradient (LDG), but were not a persistent pattern throughout geological time. In an analysis of Ordovician (485-444 Ma) fossil occurrences, an equatorward shift of the latitudinal diversity peak can be detected. A modern-type LDG and out-of-the-tropics range shift pattern were synchronously established during emerging icehouse conditions at the climax of the Great Ordovician Biodiversity Event. The changes in the LDG pattern and range shift trends can be best explained as a consequence of global cooling during the Middle Ordovician and of diversification in the tropical realm following a greenhouse period with temperatures too hot to support diverse tropical marine life. These results substantiate a fundamental role of temperature changes in establishing global first-order diversity patterns.Peer reviewe

Metazoan reef construction in a Middle Ordovician seascape : A case study from the Mingan Archipelago, Quebec

The Ordovician (485–444 Ma) saw a global shift from microbial- to skeletal-dominated reefs, and the rise of corals and bryozoans as important reef-builders. Hypothetically, increasingly morphologically diverse and abundant reef-building metazoans increased spatial habitat heterogeneity in reef environments, an important component of reefs' capacity to support diverse communities. Quantifying the spatial scale and extent of this heterogeneity requires three-dimensional exposures of well-preserved reefs whose composition and spatial arrangement can be measured. The Darriwilian (c. 467–458 Ma) carbonate sequence of the Mingan Archipelago, Quebec, presents such exposures, and also provides an opportunity to establish how the distribution of skeletal-dominated metazoan reefs contributed to, and was influenced by, seafloor relief. This study includes two transects through a 200–300 m wide paleo-reef belt, which developed along a rocky paleo-coast line. The reefs are typically micrite-rich, meter-scale mounds, locally forming larger complexes. Here, we present quantitative evaluations of the composition of these reefs, and detailed mapping of reef distributions. There is high compositional heterogeneity between reefs at spatial scales ranging from meters to kilometers, contributed by differences in the volumetric contribution of skeletal material to the reef core, and in the identity of the dominant reef-builders. We suggest that the abundance and morphological diversity of Middle Ordovician reef building metazoans made them important contributors to environmental and substrate heterogeneity, likely enhancing the diversity of reef-dwelling communities.Peer reviewe

First record of a nonpaleotropical intejocerid cephalopod from Darriwilian (Middle Ordovician) strata of central Spain

The order Intejocerida is an enigmatic, short-lived cephalopod taxon known previously only from Early-Middle Ordovician beds of Siberia and the United States. Here we report a new genus, Cabaneroceras, and a new species, C. aznari, from Middle Ordovician strata of central Spain. This finding widens the paleogeographic range of the order toward high-paleolatitudinal areas of peri-Gondwana. A curved conch, characteristic for the new genus, was previously unknown from members of the Intejocerida.Peer reviewe

Carbonate shelf development and early Paleozoic benthic diversity in Baltica : a hierarchical diversity partitioning approach using brachiopod data

The Ordovician-Silurian (similar to 485-419 Ma) was a time of considerable evolutionary upheaval, encompassing both great evolutionary diversification and one of the first major mass extinctions. The Ordovician diversification coincided with global climatic cooling and paleocontinental collision, the ecological impacts of which were mediated by region-specific processes including substrate changes, biotic invasions, and tectonic movements. From the Sandbian-Katian (similar to 453 Ma) onward, an extensive carbonate shelf developed in the eastern Baltic paleobasin in response to a tectonic shift to tropical latitudes and an increase in the abundance of calcareous macroorganisms. We quantify the contributions of environmental differentiation and temporal turnover to regional diversity through the Ordovician and Silurian, using brachiopod occurrences from the more shallow-water facies belts of the eastern Baltic paleobasin, an epicontinental sea on the Baltica paleocontinent. The results are consistent with carbonate shelf development as a driver of Ordovician regional diversification, both by enhancing broadscale differentiation between shallow- and deep-marine environments and by generating heterogeneous carbonate environments that allowed increasing numbers of brachiopod genera to coexist. However, temporal turnover also contributed significantly to apparent regional diversity, particularly in the Middle-Late Ordovician.Peer reviewe