| 1. |
- Lindgren, Johan, et al.
(författare)
-
Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur
- 2018
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 564:7736
-
Tidskriftsartikel (refereegranskat)abstract
- Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.
|
|
| 2. |
- Álvaro, J. Javier, et al.
(författare)
-
Global Cambrian trilobite palaeobiogeography assessed using parsimony analysis of endemicity
- 2013
-
Ingår i: Early Palaeozoic Biogeography and Palaeogeography. - 0435-4052. - 9781862393738 ; Memoir 38:38, s. 273-296
-
Bokkapitel (refereegranskat)abstract
- Palaeobiogeographical data on Cambrian trilobites obtained during the twentieth century are combined in this paper to evaluate palaeoceanographic links through c. 30 myr, once these arthropods biomineralized. Worldwide major tectonostratigraphic units are characterized at series intervals of Cambrian time and datasets of trilobite genera (629 for Cambrian Series 2, 965 for Cambrian Series 3, and 866 for the Furongian Series) are analysed using parsimony analysis of endemicity. Special attention is given to the biogeographical observations made in microcontinents and exotic terranes. The same is done for platform-basinal transects of well-known continental margins. The parsimony analysis of endemicity analysis resulted in distinct palaeogeographical area groupings among the tectonostratigraphic units. With these groupings, several palaeobiogeographical units are distinguished, which do not necessarily fit the previously proposed biogeographical realms and provinces. Their development and spatial distributions are broadly controlled by Cambrian palaeoclimates, palaeogeographical conditions (e.g. carbonate productivity and anoxic conditions) and ocean current circulation.
|
|
| 3. |
- Álvaro, J. Javier, et al.
(författare)
-
Submarine metalliferous carbonate mounds in the Cambrian of the Baltoscandian Basin induced by vent networks and water column stratification
- 2022
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 12:1
-
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.
|
|
| 4. |
|
|
| 5. |
- Ahlberg, Per, et al.
(författare)
-
Cambrian stratigraphy of the Tomten-1 drill core, Västergötland, Sweden
- 2016
-
Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 138:4, s. 490-501
-
Tidskriftsartikel (refereegranskat)abstract
- The Tomten-1 drilling at Torbjörntorp in Västergötland, southern Sweden, penetrated 29.85 m of Cambrian Series 2, Cambrian Series 3, Furongian, and Lower–Middle Ordovician strata. Lithostratigraphically, the succession includes the File Haidar, Borgholm and Alum Shale formations, and the Latorp and Lanna limestones. The drill core succession is described herein for the first time, with special focus on the biostratigraphy of the Cambrian Alum Shale Formation. In the Cambrian Series 3, through Furongian Alum Shale Formation, agnostoids and trilobites have been identified to species level and the succession is subdivided into nine biozones (in ascending order): the Ptychagnostus gibbus, Ptychagnostus atavus, Lejopyge laevigata, Agnostus pisiformis, Olenus gibbosus, Parabolina spinulosa, Ctenopyge tumida, Ctenopyge bisulcata and Ctenopyge linnarssoni zones. The succession is interrupted by numerous stratigraphic gaps of variable magnitudes, as is evident from the biostratigraphy and conspicuous unconformities.
|
|
| 6. |
- Babcock, Loren E., et al.
(författare)
-
Cambrian trilobite biostratigraphy and its role in developing an integrated history of the Earth system
- 2017
-
Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164. ; 50:3, s. 381-399
-
Tidskriftsartikel (refereegranskat)abstract
- One of the principal biostratigraphical tools used in the lower Palaeozoic, and especially the Cambrian System, is trilobites. Historically, both polymerids and agnostoids have commonly been included as 'trilobite' groups, although currently the question of whether they comprise a monophyletic group or are polyphyletic is unsettled. Beginning in the late 1800s, the base of the Cambrian System was marked by the lowest occurrence of olenelline trilobites. Discovery of a rich pre-trilobite metazoan record in the mid-1900s led to significant modification of that concept, but polymerids and especially agnostoids still rank among the leading biostratigraphical and chronostratigraphical guides through much of the Cambrian. Chronostratigraphical sub-division of the trilobite-bearing part of the Cambrian System derives largely from biostratigraphical, ecological and evolutionary concepts about agnostoids and polymerids introduced in the 1940s to 1970s by A.H. Westergård, A.R. Palmer and R.A. Robison. Westergård introduced a zonation for Scandinavia that was largely based on agnostoids. Palmer explained the distribution of Cambrian trilobite faunas in terms of restricted and unrestricted access to open oceans. Together, these ideas coalesced in Robison's recognition of separate zonation schemes for restricted-shelf polymerids, open-shelf polymerids and open-shelf (cosmopolitan) agnostoids. Palmer also introduced the concept of biomeres, which placed sharp limits on biostratigraphical intervals recognizable from trilobites. Global correlation in the upper half of the Cambrian today depends to a large extent on the ranges of agnostoids and some polymerids characteristic of open-shelf to slope areas, ones that facilitate identification of precise intercontinental tie points. Agnostoid and polymerid biostratigraphy is now being integrated with information about coastal onlap and eustatic sea-level history, geochemical cycling and other data to provide a more complete understanding of the early Palaeozoic biosphere and its complex physico-chemical context.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Babcock, Loren, et al.
(författare)
-
Global climate, sea level cycles, and biotic events in the Cambrian Period
- 2015
-
Ingår i: Palaeoworld. - : Elsevier BV. - 1875-5887 .- 1871-174X. ; 24:1-2, s. 5-15
-
Tidskriftsartikel (refereegranskat)abstract
- The developing high-resolution chronostratigraphy of the Cambrian provides an updated age model for various geologic and biotic events that occurred during this critical period of Earth history. Broad, time-specific patterns of lithofacies, such as organic-rich deposits, and biofacies appear to be consistent across all Cambrian paleocontinents. Records of important evolutionary events including first appearances of certain metazoan taxa, migrations, and extinctions, tend to coincide with changes in eustatic sea level, as do the positions of many Konservat-Lagerstatten, concretion horizons, agnostoid-rich beds, and other sedimentary features. Most of these events or horizons also show a relationship to perturbations in the global carbon cycle. The positions of organic-rich deposits bear strong relationship to both paleogeographic position and sea level history. Cambrian strata show evidence of cyclicity at multiple scales. Synchronous or near-synchronous global cyclicity is inferred to be associated with oceanographic and climatic cycles characteristic of glacial expansion and deglaciation. (C) 2015 Published by Elsevier B.V. on behalf of Nanjing Institute of Geology and Palaeontology, CAS.
|
|
| 10. |
- Bergström, Stig M., et al.
(författare)
-
The δ13C chemostratigraphy of Ordovician global stage stratotypes : geochemical data from the Floian and Sandbian GSSPs in Sweden
- 2020
-
Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 142:1, s. 23-32
-
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.
|
|
