Björn Kröger

Björn Kröger
University of Helsinki | HY · Finnish Museum of Natural History

PhD

About

126
Publications
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Introduction
Björn Kröger works at the Finnish Museum of Natural History in Helsinki as Curator of the Paleontological Collections and is docent at University of Helsinki. Björn does research in marine paleoecology and paleobiology and has an interest in the history and philosophy of the earth sciences.

Publications

Publications (126)
Article
Full-text available
The clade dynamics of marine animals have changed markedly over the Phanerozoic. Long-term diversification is associated with decreasing origination and extinction rates, and with increasing taxon longevity. Here we use the diversification trajectories of skeletal non-colonial marine families to infer the mechanisms that generated these trends. Sug...
Article
Cephalopods are extraordinary molluscs equipped with vertebrate-like intelligence and a unique buoyancy system for locomotion. A growing body of evidence from the fossil record, embryology and Bayesian molecular divergence estimations provides a comprehensive picture of their origins and evolution. Cephalopods evolved during the Cambrian (∼530 Ma)...
Article
Full-text available
The Late Ordovician succession of the Baltic Basin contains a characteristic fine-grained limestone, which is rich in calcareous green algae. This limestone occurs in surface outcrops and drill-cores in an extensive belt reaching from Sweden across the Baltic Sea to the Baltic countries. This limestone, which is known in the literature under severa...
Article
Full-text available
The early Palaeozoic Era records the initial biodiversification of the Phanerozoic. The increase in biodiversity involved drastic changes in taxon longevity, and in rates of origination and extinction. Here, we calculate these variables in unprecedented temporal resolution. We find that highly volatile origination and extinction rates are associate...
Article
Full-text available
The greatest relative changes in marine biodiversity accumulation occurred during the Early Paleozoic. The precision of temporal constraints on these changes is crude, hampering our understand- ing of their timing, duration, and links to causal mechanisms. We match fossil occurrence data to their lithostratigraphical ranges in the Paleobiology Data...
Conference Paper
Full-text available
Fossils of cephalopods are ubiquitous in collections and museum exhibitions, with belemnites and ammonoids being particularly well represented. This has led to a strong research interest in these taxa and our knowledge on them has accordingly grown considerably in recent decades. In contrast, the earliest fossil cephalopods - informally called "nau...
Article
More than 30 species of tergomyan, gastropod, bivalve and cephalopod molluscs are described from the Late Ordovician of central and eastern Anti-Atlas, Morocco. For the cephalopods this represents the first systematically known taxa of the region. Tergomyans and gastropods are most common in the more shaly part of the Lower Ktaoua Formation, while...
Data
Text S1. Character definitions, including hierarchical relationships and detailed discussions and justifications of each character. Text S2. Character sets, list of all characters that were excluded for each analysis. Text S3. Taxon sets, list of all taxa that were excluded for each analysis. Text S4. Supplementary references cited in Text S1. Fig....
Article
Full-text available
Background: Despite the excellent fossil record of cephalopods, their early evolution is poorly understood. Different, partly incompatible phylogenetic hypotheses have been proposed in the past, which reflected individual author’s opinions on the importance of certain characters but were not based on thorough cladistic analyses. At the same time, m...
Article
Full-text available
The collection of cephalopods from eight sampling horizons within the Olenidsletta Member, Valhallfonna Formation, Floian–Dapingian, from Profilstranda and nearby Profilbekken, Ny Friesland, Spitsbergen, resulted in the detection of 31 species, 20 genera, and 12 families from the Ellesmerocerida, Endocerida, Riocerida, Dissidocerida, Orthocerida, T...
Article
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Palaenigma wrangeli (Schmidt) is a finger-sized fossil with a tetraradiate conical skeleton; it occurs as a rare component in fossiliferous Upper Ordovician strata of the eastern Baltic Basin and is known exclusively from north Estonia. The systematic affinities and palaeoecology of P. wrangeli remained questionable. Here, the available specimens o...
Article
Full-text available
The Geology Collection is part of the national collections of the Finnish Museum of Natural History Luomus. General principles and guidelines for the collections are defined in the General Collection Policy of Luomus. The Geology Collection Policy is subordinate to the General Collection Policy of Luomus, clarifying its content with reference to th...
Article
Phylogenetic studies are rare in early Palaeozoic cephalopods. Here, we present the first cladistic analysis of the order Lituitida based on published, as well as some new, material. Three clades are recovered within the ingroup of lituitids, Sinoceras, Ancistroceras and Lituites; the former two groups correspond to the family Sinoceratidae, and th...
Article
Full-text available
The Ordovician–Silurian (~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-specif...
Article
Full-text available
The Paleontological Collection (PalCo) is one of partial collections of the Finnish Museum of Natural History Luomus. General principles and guidelines for the collections are defined in the General Collection Policy of Luomus. The PalCo Policy is subordinate to the General Collection Policy of Luomus, clarifying its content with reference to the s...
Article
Full-text available
The Genomic Resources Collection is a separate, independently managed part of the natural history collections of the Finnish Museum of Natural History Luomus specifically intended for consumptive research. The GRC policy deals with the materials that are archived for the very purpose of enabling the study of biological diversity at the genome level...
Article
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...
Article
Full-text available
As part of its quality management and goal-driven strategic development, the Finnish Museum of Natural History Luomus drafts policy documents to guide its operational sectors. The purpose of such policies is to define the content and procedures of the Museum’s activities. They answer the questions “what”, “why”, “who” and “for whom” about the activ...
Article
Full-text available
The herbarium collections are sub-collections of the Finnish Museum of Natural History Luomus that manages national natural history collections, as referred to in the Universities Act. The general collections policy defines the overall principles and guidelines concerning the collections practices. The sub-collections policies specify its guideline...
Article
Full-text available
The collections policy of the Finnish Museum of Natural History Luomus is hierarchically structured. The general collections policy defines the overall principles and guidelines. The sub-collections policies, such as the Living collections policy, comply with and apply the general collections policy and specify its guidelines and instructions, taki...
Article
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...
Article
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, thromboli...
Article
Full-text available
The unprecedented diversifications in the fossil record of the early Palaeozoic (541–419 million years ago) increased both within-sample (α) and global (γ) diversity, generating considerable ecological complexity. Faunal difference (β diversity), including spatial heterogeneity, is thought to have played a major role in early Palaeozoic marine dive...
Article
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 hi...
Article
Full-text available
Tragoceras falcatum (Schlotheim, 1820) is a common, loosely coiled estonioceratid (Tarphycerida, Cephalopoda) occurring in the Kunda Regional Stage (early Darriwilian, Middle Ordovician) of Estonia. Although the species is quite well-known, we document some features for the first time. For example, one specimen from the Harku quarry (Estonia) with...
Conference Paper
It is indisputable that total global biodiversity has increased since the beginning of the Phanerozoic eon around 540 million years ago. The question is why this is the case. Previous work often focused on novelty as a driver of the Phanerozoic biodiversity increase and global diversity as a balance between origination and extinction. According to...
Article
Full-text available
An essential aspect of earth science data is the age they represent. The age, in most cases, is not a simple time stamp measured in years, but often specified as a stratigraphic interval or unit. Numerous schemes exist for age attribution in geological data, referring to various methods of e.g. biostratigraphy, chronostratigraphy, sequence-stratigr...
Article
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...
Article
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...
Article
Diploporitans had subspherical thecae, which usually were attached to hard substrates either directly with an attachment disc at the base of their theca or with a stem and holdfast. After the death of the animal, isolated thecae were easily transported by currents over more or less consolidated sediment. We describe a case where 13 diploporitan the...
Article
Full-text available
Since the early 20th Century, when the first cephalopods from late Cambrian strata were discovered in North China, more than 160 species belonging to 39 genera in nine families and five orders, have been described from both North and South China, together with North America, Siberia and Kazakhstan. We compiled and analysed all published Cambrian ce...
Article
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 nea...
Article
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-tro...
Article
The Ordovician sections along the western shore of the Hinlopen Strait, Ny Friesland, Spitsbergen were discovered in the late 1960s and since then prompted numerous paleontological publications; several of these publications are now considered classical in the literature of paleontology of Ordovician trilobites and of Ordovician paleogeography and...
Article
Bryozoans, stromatoporoid sponges, and tabulate corals, all colonial metazoans with lamellar, encrusting growth forms, developed and simultaneously diversified during the Great Ordovician Biodiversification Event (GOBE). After revisiting some classic Lower, Middle, and Upper Ordovician reef localities in Laurentia (Franklin Mountains, west Texas, M...
Conference Paper
Full-text available
After shifting into Icehouse conditions in Middle Ordovician times, the Late Ordovician is characterized by intensive glaciations of south-polar Gondwana accompanied by major regressions subaerally exposing wide areas of low-latitude palaeocontinents covered by epicontinental seas. The exposure of carbonate platforms led to their widespread karstif...
Article
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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 av...
Conference Paper
The timing and extent of changes in biodiversity have to be accurately estimated if we want to understand processes leading to the dramatic increase in biodiversity during the Great Ordovician Biodiversification Event (GOBE). The palaeontological data we have available for estimating biodiversity are biased and incomplete. Hence, when using these d...
Article
The widespread growth of reefs formed by a framework of biogenic constructors and frame-lacking carbonate mounds began on Baltica during Ordovician time. Previously, Ordovician reef and mound development on Baltica was considered to be sporadic and local. A review of all known bioherm localities across the Baltic Basin reveals a more consistent pat...
Article
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 mou...
Article
Integration of new isotopic data and earlier biostratigraphic information from eight sections through the terminal Ordovician (Pirgu and Porkuni stages) of the Siljan district, Sweden, allows a more precise correlation of sections in terms of biostratigraphy and carbon isotope dating. Four levels with positive δ13C excursions are identified (from b...
Chapter
Full-text available
In order to put the origin of the Ammonoidea into the broader evolutionary context, we review the hypothesis on the origin of cephalopods in general, the origin of bactritids as well as the origin of bactritids with their respective Bauplan characters. We also list major morphological changes that occurred between the origin of cephalopods until th...
Article
Full-text available
During and after the Cambrian explosion, very large marine invertebrate species have evolved in several groups. Gigantism in Carboniferous land invertebrates has been explained by a peak in atmospheric oxygen concentrations, but Palaeozoic marine invertebrate gigantism has not been studied empirically and explained comprehen-sively. By quantifying...
Article
The limestones of the upper Katian Boda mud mounds (Ordovician) of the Siljan district in central Sweden are deeply fractured. The fissures were partly synsedimentary and are often lined with stromatolite-like crusts. These crusts thus far are the only known subaerial Ordovician speleothems. They reach depths of up to 30 m below the former mound to...
Article
The limestones of the upper Katian Boda mud mounds (Ordovician) of the Siljan district in central Sweden are deeply fractured. The fissures were partly synsedimentary and are often lined with stromatolite-like crusts. These crusts thus far are the only known subaerial Ordovician speleothems. They reach depths of up to 30 m below the former mound to...
Article
Reefs developed simultaneously during the latest Sandbian/earliest Katian global Guttenberg Isotopic Carbon Excursion (GICE) in several places across Baltoscandia. Latest Sandbian/earliest Katian patch reefs are also described from the Vasalemma Formation of northern Estonia. The Saku Member of the Vasalemma Formation was previously considered as a...
Article
The Vasalemma Formation (early Katian, Late Ordovician) of northern Estonia consists of a succession of biodetrital grainstones up to 15 m thick with numerous intercalated reef bodies, which reach diameters of more than 50 m. Four dominant facies types are distinguished within the reef core limestones: (1) a bryozoan framestone—bindstone, (2) an ec...
Article
Full-text available
Four cephalopod taxa are described from the Abastu Formation at a locality near the village of Abarsaj, northern Iran. The described fauna includes Orthocerida indet, Eosomichelinoceras sp., Proterovaginoceras incognitum? and Sactorthoceras sp. suggesting a late Dapingian to Darriwilian (Middle Ordovician) age of the strata. The reported assemblage...
Article
During the Middle Ordovician cephalopods became an important part of the macrofauna of the Baltoscandian carbonate platform. The earliest cephalopod abundance peak was reached during the early Darriwilian, within the Kunda Stage Yangtzeplacognathus crassus and Lenodus pseudoplanus conodont zones. In sediments of this time interval large orthoconic...
Article
Full-text available
Quantitative analyses of the taxonomic composition and palaeoecology of five Early Devonian faunules (earliest Lochkovian to early Emsian) collected from the locality Jebel Ouaoufilal in the Tafilalt (Morocco) were conducted. We examined 3376 specimens belonging to 158 species and their stratigraphic distribution. The quantitative data sets were an...
Article
The carbonates associated with the Late Ordovician (Katian–Hirnantian) Boda mounds of the Siljan district, Sweden, contain a rich cephalopod fauna. Cephalopods are rare in the micritic stromatactis facies of the Katian Boda Core Member, but are concentrated together with other molluscs and trilobites in synsedimentary fillings of caves and crevices...
Article
Full-text available
The late Katian, Late Ordovician Boda Limestone of Dalarna, Sweden contains a rich cephalopod assemblage. The assemblage consists of 61 species, of 31 genera, comprising almost all major Ordovician cephalopod orders. Most common and diverse are the Orthocerida. The Ascocerida are also remarkably comman and diverse. The new ascocerid species, Redpat...
Poster
Full-text available
We discuss changes in palaeoecology through the Early Devonian of the southern Tafilalt (Morocco).
Article
Pyritized, elongate, conical conchs of “Allatheca” degeeri s.l. are common in dysoxic, dark gray mudstone intervals in the Early Cambrian (upper Terreneuvian–Series 2 boundary interval) Cuslett Formation at Keels, eastern Newfoundland. Wave-oriented, horizontal specimens are most abundant in this cool-water, high latitude, off-shore shelf facies of...
Article
In the central Anti-Atlas (Morocco), the Early Ordovician succession consists of about 1000 m of fossiliferous argillites and siltstones. The Upper Fezouata Formation (Floian) contains a comparatively rich and abundant cephalopod association. A small collection of these cephalopods is described herein for the first time. The cephalopods are interpr...
Article
Full-text available
In the central Anti-Atlas (Morocco), the Early Ordovician succession consists of about 1000 m of fossiliferous argillites and siltstones. The Upper Fezouata Formation (Floian) contains a comparatively rich and abundant cephalopod association. A small collection of these cephalopods is described herein for the first time. The cephalopods are interpr...
Article
The lower part of the Baltoscandic Orthoceratite Limestone (Kunda Stage, Darriwilian) is characterized by abundant and often large orthoconic endocerid cephalopods. The endocerids of this limestone, known historically as the “Vaginaten”, are among the historically earliest figured Swedish fossils. The taxonomic history of the two most common and mo...
Article
Full-text available
Slow subsidence and tectonic quiescence along the New York Promontory margin of Laurentia mean that the carbonate-dominated Tribes Hill and overlying Rochdale formations serve as proxies for the magnitude and timing of Tremadocian eustatic changes. Both formations are unconformity-bound, deepening–shoaling, depositional sequences that double in thi...
Article
A manuscript of a lecture by the Prussian geologist Leopold von Buch given at the Berlin Society of the Friends of the Humanity was discovered at the Museum für Naturkunde, Berlin. The text is a raw version of a passionate plea for the formation of natural history collections as science places, with a partly biting humor. Based on until now unknown...
Article
On Natural History Museums and Their Purpose. A Lecture Given by Leopold von Buch (1774–1853) in April 1838. A manuscript of a lecture by the Prussian geologist Leopold von Buch given at the Berlin Society of the Friends of the Humanity was discovered at the Museum für Naturkunde, Berlin. The text is a raw version of a passionate plea for the forma...
Article
Full-text available
The ammonoids from the middle Famennian black limestone nodules at Kattensiepen (Rhenish Mountains) are known for their excellent preservation and show frequent sublethal shell damage of varying dimensions and of the finest detail. 76% of all specimens show traces of predation. This is the highest frequency of shell repairs known from the Palaezoic...
Article
Nearly one third of all conchs of Anthoceras buchi (Lesnikowa, 1949) from Baltoscandia display healed apertural breakages. Often multiple of these repair scars can be found in single conchs. Most of the scars are less than 2 mm deep, but deeper slit-like repaired breakages occasionally occur. Small injuries are usually around the entire apertural c...
Article
Nearly one third of all conchs of Anthoceras buchi (Lesnikowa, 1949) from Baltoscandia display healed apertural breakages. Often multiple of these repair scars can be found in single conchs. Most of the scars are less than 2 mm deep, but deeper slit-like repaired breakages occasionally occur. Small injuries are usually around the entire apertural c...
Conference Paper
Cephalopods are common in the Silurian carbonate platform succession of the Severnaya Zemlya Archipelago, Arctic Russia. Hitherto, these fossils were not sufficiently collected and studied. We present the first study of the nautiloid fauna from this area. The preliminary identification list includes the following taxa: Elrodoceras sp., Ephippiortho...
Article
Full-text available
Two completely dissimilar faunal changes occur between the Sunwaptan and Skullrockian Stages (Ptychaspid and Symphysurid ‘Biomeres’) in the uppermost Cambrian on the east Laurentian craton. An undolomitized section in the Little Falls Formation in Washington County, New York, shows a typical ‘biomere’ extinction, with highest Sunwaptan trilobites f...
Article
The Early Ordovician successions of the southern Montagne Noire consist of a thick sequence of predominantly siliciclastic sediments of which the late Tremadocian St. Chinian Formation and the earliest Floian La Maurerie Formation contain a comparatively rich and abundant cephalopod association. The cephalopods of the St. Chinian and La Maurerie Fo...
Article
The Hirnantian Glisstjärn Formation (Normalograptus persculptus graptolite Biozone) is a succession of limestones and shales onlapping the Katian Boda Limestone in the Siljan District, Sweden. It contains a conspicuous, up to several decimeter thick bed densely packed with bipolarly oriented, orthoconic cephalopod conchs that can reach lengths of m...