| 1. |
- Álvaro, J. Javier, et al.
(författare)
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Submarine metalliferous carbonate mounds in the Cambrian of the Baltoscandian Basin induced by vent networks and water column stratification
- 2022
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Two massive precipitation events of polymetallic ore deposits, encrusted by a mixture of authigenic carbonates, are documented from the Cambrian of the semi-enclosed Baltoscandian Basin. δ34S (‒9.33 to ‒2.08‰) and δ33S (‒4.75 to ‒1.06‰) values from the basal sulphide breccias, sourced from contemporaneous Pb–Zn–Fe-bearing vein stockworks, reflect sulphide derived from both microbial and abiotic sulphate reduction. Submarine metalliferous deposits were triggered by non-buoyant hydrothermal plumes: plumes of buoyant fluid were trapped by water column stratification because their buoyancy with respect to the environment reversed, fluids became heavier than their surroundings and gravitational forces brought them to a halt, spreading out laterally from originating vents and resulting in the lateral dispersion of effluents and sulphide particle settling. Subsequently, polymetallic exhalites were sealed by carbonate crusts displaying three generations of ikaite-to-aragonite palisade crystals, now recrystallized to calcite and subsidiary vaterite. Th of fluid inclusions in early calcite crystals, ranging from 65 to 78 ºC, provide minimum entrapment temperatures for carbonate precipitation and early recrystallization. δ13Ccarb (‒1.1 to + 1.6‰) and δ18Ocarb (‒7.6 to ‒6.5‰) values are higher than those preserved in contemporaneous glendonite concretions (‒8.5 to ‒4.7‰ and ‒12.4 to ‒9.1‰, respectively) embedded in kerogenous shales, the latter related to thermal degradation of organic matter. Hydrothermal discharges graded from highly reduced, acidic, metalliferous, and hot (~ 150 ºC) to slightly alkaline, calcium-rich and warm (< 100 ºC), controlling the precipitation of authigenic carbonates.
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| 2. |
- Bazzi, Mohamad, et al.
(författare)
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Feeding ecology has shaped the evolution of modern sharks
- 2021
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Ingår i: Current Biology. - : Cell Press. - 0960-9822 .- 1879-0445. ; 31:23, s. 5138-5148.e4
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Tidskriftsartikel (refereegranskat)abstract
- Sharks are iconic predators in today’s oceans, yet their modern diversity has ancient origins. In particular, present hypotheses suggest that a combination of mass extinction, global climate change, and competition has regulated the community structure of dominant mackerel (Lamniformes) and ground (Carcharhiniformes) sharks over the last 66 million years. However, while these scenarios advocate an interplay of major abiotic and biotic events, the precise drivers remain obscure. Here, we focus on the role of feeding ecology using a geometric morphometric analysis of 3,837 fossil and extant shark teeth. Our results reveal that morphological segregation rather than competition has characterized lamniform and carcharhiniform evolution. Moreover, although lamniforms suffered a long-term disparity decline potentially linked to dietary “specialization,” their recent disparity rivals that of “generalist” carcharhiniforms. We further confirm that low eustatic sea levels impacted lamniform disparity across the end-Cretaceous mass extinction. Adaptations to changing prey availability and the proliferation of coral reef habitats during the Paleogene also likely facilitated carcharhiniform dispersals and cladogenesis, underpinning their current taxonomic dominance. Ultimately, we posit that trophic partitioning and resource utilization shaped past shark ecology and represent critical determinants for their future species survivorship.
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| 3. |
- Ahlberg, Per E., 1963-, et al.
(författare)
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The smallest known Devonian tetrapod shows unexpectedly derived features
- 2020
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Ingår i: Royal Society Open Science. - : ROYAL SOC. - 2054-5703. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- A new genus and species of Devonian tetrapod, Brittagnathus minutus gen. et sp. nov., is described from a single complete right lower jaw ramus recovered from the Acanthostega mass-death deposit in the upper part of the Britta Dal Formation (upper Famennian) of Stensio Bjerg, Gauss Peninsula, East Greenland. Visualization by propagation phase contrast synchrotron microtomography allows a complete digital dissection of the specimen. With a total jaw ramus length of 44.8 mm, Brittagnathus is by far the smallest Devonian tetrapod described to date. It differs from all previously known Devonian tetrapods in having only a fang pair without a tooth row on the anterior coronoid and a large posterior process on the posterior coronoid. The presence of an incipient surangular crest and a concave prearticular margin to the adductor fossa together cause the fossa to face somewhat mesially, reminiscent of the condition in Carboniferous tetrapods. A phylogenetic analysis places Brittagnathus crownward to other Devonian tetrapods, adjacent to the Tournaisian genus Pederpes. Together with other recent discoveries, it suggests that diversification of 'Carboniferous-grade' tetrapods had already begun before the end of the Devonian and that the group was not greatly affected by the end-Devonian mass extinction.
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| 4. |
- Bazzi, Mohamad, et al.
(författare)
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Tooth morphology elucidates shark evolution across the end-Cretaceous mass extinction
- 2021
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Ingår i: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 19:8
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Tidskriftsartikel (refereegranskat)abstract
- Sharks (Selachimorpha) are iconic marine predators that have survived multiple mass extinctions over geologic time. Their prolific fossil record is represented mainly by isolated shed teeth, which provide the basis for reconstructing deep time diversity changes affecting different selachimorph clades. By contrast, corresponding shifts in shark ecology, as measured through morphological disparity, have received comparatively limited analytical attention. Here, we use a geometric morphometric approach to comprehensively examine tooth morphologies in multiple shark lineages traversing the catastrophic end-Cretaceous mass extinction-this event terminated the Mesozoic Era 66 million years ago. Our results show that selachimorphs maintained virtually static levels of dental disparity in most of their constituent clades across the Cretaceous-Paleogene interval. Nevertheless, selective extinctions did impact apex predator species characterized by triangular blade-like teeth. This is particularly evident among lamniforms, which included the dominant Cretaceous anacoracids. Conversely, other groups, such as carcharhiniforms and orectolobiforms, experienced disparity modifications, while heterodontiforms, hexanchiforms, squaliforms, squatiniforms, and dagger synechodontiforms were not overtly affected. Finally, while some lamniform lineages disappeared, others underwent postextinction disparity increases, especially odontaspidids, which are typified by narrow-cusped teeth adapted for feeding on fishes. Notably, this increase coincides with the early Paleogene radiation of teleosts as a possible prey source, and the geographic relocation of disparity sampling "hotspots," perhaps indicating a regionally disjunct extinction recovery. Ultimately, our study reveals a complex morphological response to the end-Cretaceous mass extinction and highlights an event that influenced the evolution of modern sharks.
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| 5. |
- Bergström, Stig M., et al.
(författare)
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The δ13C chemostratigraphy of Ordovician global stage stratotypes : geochemical data from the Floian and Sandbian GSSPs in Sweden
- 2020
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 142:1, s. 23-32
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Tidskriftsartikel (refereegranskat)abstract
- The δ13C chemostratigraphy of five of the seven Ordovician global stages has been published previously but no such data have been available from the Floian GSSP and most of the Sandbian GSSP in Sweden. This lack of information has now been remedied by isotope data obtained from series of closely spaced shale samples collected from the Floian stratotype at Diabasbrottet in Västergötland and the Sandbian stratotype at Fågelsång in Scania. Although the bases of these stages cannot be precisely tied to levels of conspicuous δ13C excursions, that of the Floian Stage, which is marked by the appearance of the graptolite Tetragraptus approximatus, is between the closely spaced excursions named LTNICE and BFICE. The base of the Sandbian Stage, which is defined as the appearance level of the graptolite Nemagraptus gracilis, is just below a negative excursion previously known as the “Upper Kukruse Low”, which is nowadays known as the LSNICE. The relations between chemostratigraphy and graptolite and conodont biostratigraphy in the Swedish GSSPs and some coeval key sections in Baltoscandia, China, and America are briefly discussed. It is concluded that the data at hand indicate that there is good regional agreement in these relations.
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| 6. |
- Chen, Donglei, 1985-, et al.
(författare)
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The developmental relationship between teeth and dermal odontodes in the most primitive bony fish Lophosteus
- 2020
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Ingår i: eLIFE. - 2050-084X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The ontogenetic trajectory of a marginal jawbone of Lophosteus superbus (Late Silurian, 422 Million years old), the phylogenetically most basal stem osteichthyan, visualized by synchrotron microtomography, reveals a developmental relationship between teeth and dermal odontodes that is not evident from the adult morphology. The earliest odontodes are two longitudinal founder ridges formed at the ossification center. Subsequent odontodes that are added lingually to the ridges turn into conical teeth and undergo cyclic replacement, while those added labially achieve a stellate appearance. Stellate odontodes deposited directly on the bony plate are aligned with the alternate files of teeth, whereas new tooth positions are inserted into the files of sequential addition when a gap appears. Successive teeth and overgrowing odontodes show hybrid morphologies around the oral-dermal boundary, suggesting signal cross-communication. We propose that teeth and dermal odontodes are modifications of a single system, regulated and differentiated by the oral and dermal epithelia.
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| 7. |
- Gai, Zhikun, et al.
(författare)
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The Evolution of the Spiracular Region From Jawless Fishes to Tetrapods
- 2022
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media S.A.. - 2296-701X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- The spiracular region, comprising the hyomandibular pouch together with the mandibular and hyoid arches, has a complex evolutionary history. In living vertebrates, the embryonic hyomandibular pouch may disappear in the adult, develop into a small opening between the palatoquadrate and hyomandibula containing a single gill-like pseudobranch, or create a middle ear cavity, but it never develops into a fully formed gill with two hemibranchs. The belief that a complete spiracular gill must be the ancestral condition led some 20th century researchers to search for such a gill between the mandibular and hyoid arches in early jawed vertebrates. This hypothesized ancestral state was named the aphetohyoidean condition, but so far it has not been verified in any fossil; supposed examples, such as in the acanthodian Acanthodes and symmoriid chondrichthyans, have been reinterpreted and discounted. Here we present the first confirmed example of a complete spiracular gill in any vertebrate, in the galeaspid (jawless stem gnathostome) Shuyu. Comparisons with two other groups of jawless stem gnathostomes, osteostracans and heterostracans, indicate that they also probably possessed full-sized spiracular gills and that this condition may thus be primitive for the gnathostome stem group. This contrasts with the living jawless cyclostomes, in which the mandibular and hyoid arches are strongly modified and the hyomandibular pouch is lost in the adult. While no truly aphetohyoidean spiracular gill has been found in any jawed vertebrate, the recently reported presence in acanthodians of two pseudobranchs suggests a two-step evolutionary process whereby initial miniaturization of the spiracular gill was followed, independently in chondrichthyans and osteichthyans, by the loss of the anterior pseudobranch. On the basis of these findings we present an overview of spiracular evolution among vertebrates.
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| 8. |
- Peng, Shanchi, et al.
(författare)
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The Cambrian Period
- 2020
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Ingår i: Geologic Time Scale. - 9780128243619 - 9780128243633 ; 2, s. 565-565
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Bokkapitel (refereegranskat)abstract
- Appearance of metazoans with mineralized skeletons, “explosion” in biotic diversity and disparity, infaunalization of the substrate, occurrence of metazoan Konservat Fossil-lagerstätten, establishment of most invertebrate phyla, strong faunal provincialism, dominance of trilobites, generally warm climate but with possibleglacial-interglacial cycles in the later part, opening of the Iapetus Ocean, progressive equatorial drift and separation of Laurentia, Baltica, Siberia, and Avalonia from Gondwana characterize the Cambrian Period.
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| 9. |
- Peng, Shanchi, et al.
(författare)
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Trilobites
- 2020
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Ingår i: Geologic Timescale 2020. - 9780128243626 - 9780128243619 ; 1, s. 36-36
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Bokkapitel (refereegranskat)abstract
- Trilobites are marine arthropods that appeared in Cambrian Epoch 2 and became extinct at the end of the Permian. In some Paleozoic deposits, they number among the most abundant macrofossils. Trilobites are important for early Paleozoic biostratigraphy, especially Cambrian.
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| 10. |
- Pettersson, Johan, et al.
(författare)
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The fossil alga Chaetocladus gracilis revisited : new material from the Silurian of Sweden
- 2020
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 142:4, s. 304-308
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Tidskriftsartikel (refereegranskat)abstract
- In 2006, a new species of non-calcified dasycladalean alga, Chaetocladus gracilis, from the upper Silurian of Skåne (Scania), southernmost Sweden, was erected. The original description was based on a single incomplete fossil recovered from the abandoned limestone quarry at Bjärsjölagård, a classic geologic locality in Scania. Here we present four additional and, importantly, more complete specimens from this same site and type stratum. This new material largely corroborates the general anatomical features of C. gracilis, but also adds some intricate details, most notably with regards to the external sheet-like phytoleim and organisation of the laterals. Elemental mapping confirmed an expected carbonaceous composition of the fossils, which are embedded in a calcareous mudstone. These additional fossils show that the originally described specimen was not a singular occurrence at this locality. Based on the state of preservation of our algal fossils, we note that the mudstone facies of the Ludlow Bjärsjölagård Limestone Member of the Klinta Formation (Öved-Ramsåsa Group), from which all C. gracilis have been recovered, share characteristics with deposits typically referred to as “algal-Lagerstätten”.
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