| 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. |
- 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.
|
|
| 3. |
- Lindgren, Johan, et al.
(författare)
-
Fossil insect eyes shed light on trilobite optics and the arthropod pigment screen
- 2019
-
Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 573:7772, s. 122-125
-
Tidskriftsartikel (refereegranskat)abstract
- Fossilized eyes permit inferences of the visual capacity of extinct arthropods1–3. However, structural and/or chemical modifications as a result of taphonomic and diagenetic processes can alter the original features, thereby necessitating comparisons with modern species. Here we report the detailed molecular composition and microanatomy of the eyes of 54-million-year-old crane-flies, which together provide a proxy for the interpretation of optical systems in some other ancient arthropods. These well-preserved visual organs comprise calcified corneal lenses that are separated by intervening spaces containing eumelanin pigment. We also show that eumelanin is present in the facet walls of living crane-flies, in which it forms the outermost ommatidial pigment shield in compound eyes incorporating a chitinous cornea. To our knowledge, this is the first record of melanic screening pigments in arthropods, and reveals a fossilization mode in insect eyes that involves a decay-resistant biochrome coupled with early diagenetic mineralization of the ommatidial lenses. The demonstrable secondary calcification of lens cuticle that was initially chitinous has implications for the proposed calcitic corneas of trilobites, which we posit are artefacts of preservation rather than a product of in vivo biomineralization4–7. Although trilobite eyes might have been partly mineralized for mechanical strength, a (more likely) organic composition would have enhanced function via gradient-index optics and increased control of lens shape.
|
|
| 4. |
- 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.
|
|
| 5. |
- Ahlberg, Per, 1963-
(författare)
-
Follow the footprints and mind the gaps : a new look at the origin of tetrapods
- 2019
-
Ingår i: Earth and environmental science transactions of the Royal Society of Edinburgh. - : CAMBRIDGE UNIV PRESS. - 1755-6910 .- 1755-6929. ; 109:1-2, s. 115-137
-
Tidskriftsartikel (refereegranskat)abstract
- The hypothesis that tetrapods evolved from elpistostegids during the Frasnian, in a predominantly aquatic context, has been challenged by the discovery of Middle Devonian tetrapod trackways predating the earliest body fossils of both elpistostegids and tetrapods. Here I present a new hypothesis based on an overview of the trace fossil and body fossil evidence. The trace fossils demonstrate that tetrapods were capable of performing subaerial lateral sequence walks before the end of the Middle Devonian. The derived morphological characters of elpistostegids and Devonian tetrapods are related to substrate locomotion, weight support and aerial vision, and thus to terrestrial competence, but the retention of lateral-line canals, gills and fin rays shows that they remained closely tied to the water. Elpistostegids and tetrapods both evolved no later than the beginning of the Middle Devonian. The earliest tetrapod records come from inland river basins, sabkha plains and ephemeral coastal lakes that preserve few, if any, body fossils; contemporary elpistostegids occur in deltas and the lower reaches of permanent rivers where body fossils are preserved. During the Frasnian, elpistostegids disappear and these riverine-deltaic environments are colonised by tetrapods. This replacement has, in the past, been misinterpreted as the origin of tetrapods.
|
|
| 6. |
|
|
| 7. |
- AHLBERG, PER, et al.
(författare)
-
Integrated Cambrian biostratigraphy and carbon isotope chemostratigraphy of the Grönhögen-2015 drill core, Öland, Sweden
- 2019
-
Ingår i: Geological Magazine. - 0016-7568. ; 156:06, s. 935-949
-
Tidskriftsartikel (refereegranskat)abstract
- The Grönhögen-2015 core drilling on southern Öland, Sweden, penetrated 50.15 m of Cambrian Series 3, Furongian and Lower–Middle Ordovician strata. The Cambrian succession includes the Äleklinta Member (upper Stage 5) of the Borgholm Formation and the Alum Shale Formation (Guzhangian–Tremadocian). Agnostoids and trilobites allowed subdivision of the succession into eight biozones, in ascending order: the uppermost Cambrian Series 3 (Guzhangian) Agnostus pisiformis Zone and the Furongian Olenus gibbosus, O. truncatus, Parabolina spinulosa, Sphaerophthalmus? flagellifer, Ctenopyge tumida, C. linnarssoni and Parabolina lobata zones. Conspicuous lithologic unconformities and the biostratigraphy show that the succession is incomplete and that there are several substantial gaps of variable magnitudes. Carbon isotope analyses (δ13Corg) through the Alum Shale Formation revealed two globally significant excursions: the Steptoean Positive Carbon Isotope Excursion (SPICE) in the lower–middle Paibian Stage, and the negative Top of Cambrian Excursion (TOCE), previously referred to as the HERB Event, in Stage 10. The δ13Corg chemostratigraphy is tied directly to the biostratigraphy and used for an improved integration of these excursions with the standard agnostoid and trilobite zonation of Scandinavia. Their relations to that of coeval successions in Baltoscandia and elsewhere are discussed. The maximum amplitudes of the SPICE and TOCE in the Grönhögen succession are comparable to those recorded in drill cores retrieved from Scania, southern Sweden. The results of this study will be useful for assessing biostratigraphic relations between shale successions and carbonate facies on a global scale.
|
|
| 8. |
- Álvaro, J. Javier, et al.
(författare)
-
Ediacaran–Cambrian phosphorites from the western margins of Gondwana and Baltica
- 2016
-
Ingår i: Sedimentology. - : Wiley. - 0037-0746. ; 63:2, s. 350-377
-
Tidskriftsartikel (refereegranskat)abstract
- The late Ediacaran–mid Cambrian occurrence s of phosphorites in the wes-tern Mediterranean region (West Gondwana) and southern Sweden (north -west Baltica) are related to the poleward drift of West Gondwana and thenorthern drift of Baltica. As a result, these regions crossed subtropical andtemperate palaeolatitudes of the Southern Hemisphere, in which oceanicupwelling and high organic productivity were the probable sources of phos-phorus along their western margins. A parallel south-west/north-east migra-tion trend of evaporites and delayed, time transgressive phosphorites pointto distal upwelling environments associated with shallower arid conditions.Concentration of hardground-derived phosphate accumulations took placeby repeated alternations of low sedimentation rates and condensation,in situ early diagenetic and microbially mediated precipitation of amorphousand cryptocrystalline, carbonate-bearing francolite, winnowing and poly-phase reworking of previously phosphatized skeletons and hardground-derived clasts. Thicker phosphorites of economic importance display aspiculate sponge-thromboid consortium that points to a distinct benthiccommunity developed on suboxic, slope to basinal substrates. For mostphosphorite samples an up to ten-fold enrichment in rare earth elementconcentration relative to post-Archaean average Australian shale reflects sig-nificant incorporation of rare earth elements and yttrium after deposition.Considerable scavenging took place from anoxic pore waters, followingreductive dissolution of iron oxides as evidenced from the medium rareearth element enrichment in most samples. This contrasts with the rare pre-servation of primary sea water features, such as cerium depletion andyttrium enrichment, in phosphatized thrombolites from the shallower realms(for example, Montagne Noire). The data are consistent with phosphogenesisafter upwelling and transgression of nutrient-rich, suboxic–anoxic, ferrugi-nous waters over more oxygenated, rifting settings and inland portions of anevolving passive margin.
|
|
| 9. |
- 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.
|
|
| 10. |
- Bergström, Stig M., et al.
(författare)
-
Darriwilian (Middle Ordovician) chemostratigraphy linked to graptolite, conodont and trilobite biostratigraphy in the Fågelsång-3 drill core, Scania, Sweden
- 2018
-
Ingår i: GFF. - : Informa UK Limited. - 2000-0863 .- 1103-5897. ; 140:3, s. 229-240
-
Tidskriftsartikel (refereegranskat)abstract
- A recent core drilling in the geologically classical Fågelsång area resulted in a 58.70-m-long drill core through the lowermost Sandbian Sularp Shale, the Darriwilian Almelund Shale and Komstad Limestone, and part of the late Tremadocian to earliest Darriwilian Tøyen Shale. The shales contain zone index graptolites that are used for an update of the standard Darriwilian graptolite zone succession in Baltoscandia in which six zones are now recognized. The Komstad Limestone interval and lowermost part of the Almelund Shale have beensubdivided into four conodont zones. The δ13Corg chemostratigraphy, which has been established through the entire drill core based on 120 closely spaced samples, shows a somewhat subdued development of the middle Darriwilian Isotope Carbon Excursion (MDICE), which is dated in terms of graptolite biostratigraphy. The Fågelsång isotope curve is correlated with a closely similar δ13Ccarb curve from a coeval, apparently stratigraphically essentially continuous, succession at Kårgärde in south-central Sweden, which previously has been subdivided into 13 conodont zones and subzones. For the first time, these conodont zonal units can be calibrated with Fågelsång graptolite zones using δ13Corg chemostratigraphy. The several new results of this study are expected to be useful for assessing biostratigraphic relations between units in shale and carbonate facies in Baltoscandia and elsewhere in the world.
|
|
