| 1. |
- Davydenko, Svitozar, et al.
(author)
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A small whale reveals diversity of the Eocene cetacean fauna of Antarctica
- 2021
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In: Antarctic Science. - Cambridge : Cambridge University Press. - 0954-1020 .- 1365-2079. ; 33:1, s. 81-88
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Journal article (peer-reviewed)abstract
- Cetacean fossils have been recorded from middle and late Eocene deposits on Seymour Island since the beginning of the twentieth century and include fully aquatic Basilosauridae and stem Neoceti. Here, we report a small cetacean vertebra tentatively referred to as Neoceti from the late Eocene of Seymour Island. It shows a mosaic of traits, some of which are characteristic of early Neoceti (anteroposteriorly long transverse processes; a ventral keel on the ventral side of the centrum; thin pedicles of the neural arch), whereas others are shared with Basilosauridae (low-placed bases of the transverse processes). However, some traits are unique and may be autapomorphic: presence of separate prezygapophyses on the vertebra at the thoracic/lumbar boundary and a proportionally short centrum. Both traits imply a fast swimming style, which is characteristic of modern dolphins rather than Eocene cetaceans. Thus, this specimen can be identified as Neoceti indet., with some hypothetical odontocete affinities. Along with a few other Eocene whale taxa, it seems to be among the earliest known members of Neoceti on Earth. The finding of small and fast-swimming Neoceti in Antarctica also demonstrates early diversification of cetaceans and ecological niche partitioning by them dating back as early as the late Eocene.
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| 2. |
- Friis, Else Marie, et al.
(author)
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Early flowers of primuloid Ericales from the Late Cretaceous of Portugal and their ecological and phytogeographic implications
- 2021
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In: Fossil Imprint. - Prague : Národní muzeum. - 2533-4050 .- 2533-4069. ; 77:2, s. 214-230
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Journal article (peer-reviewed)abstract
- A distinctive feature of the major eudicot diversification that occurred through the Late Cretaceous is the unequivocal presence of Cornales and diverse Ericales. Here we describe well-preserved fossil flowers from the Mira locality in western Portugal, of Campanian-Maastrichtian age, that we assign to a new extinct genus of Ericales with two new species; Miranthus elegans gen. et sp. nov. and Miranthus kvacekii sp. nov. The fossil flowers are pedicellate, structurally bisexual, actinomorphic, pentamerous and isomerous, with five narrowly triangular persistent calyx lobes, a five-lobed corolla, five antepetalous stamens, five staminodes alternating with the petals and a semi-inferior, unilocular ovary. The ovary consists of five carpels and has a raised nectariferous ring with stomata-like openings above the insertion of the perianth, and a long five-angled style. A key feature, which confirms a relationship with Primulaceae s. l., is the free, central dome-shaped placenta that bears numerous, densely spaced ovules. The ovary matures into a capsule containing many, minute, reticulate seeds. Flowers of Miranthus are especially similar to those of extant Samolus, a genus of about twelve species that is sister group to other genera of subfamily Theophrastoideae and that has a disjunct distribution mainly in the Southern Hemisphere. Miranthus also appears to have grown in environments influenced by marine conditions, an ecological preference also seen in Samolus. Miranthus expands the diversity of Ericales known from the Late Cretaceous, and together with previously described fossils provides further evidence that the diversification of Ericales was already underway by the Campanian-Maastrichtian stages of the Late Cretaceous.
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| 3. |
- Katrantsiotis, Christos, et al.
(author)
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Seasonal variability in temperature trends and atmospheric circulation systems during the Eemian (Last Interglacial) based on n-alkanes hydrogen isotopes from Northern Finland
- 2021
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In: Quaternary Science Reviews. - Amsterdam : Elsevier. - 0277-3791 .- 1873-457X. ; 273, s. 107250-107250
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Journal article (peer-reviewed)abstract
- The Last Interglacial warm period, the Eemian (ca. 130-116 thousand years ago), serves as a reference for projected future climate in a warmer world. However, there is a limited understanding of the seasonal characteristics of interglacial climate dynamics, especially in high latitude regions. In this study, we aimto provide new insights into seasonal trends in temperature and moisture source location, linked to shifts in atmospheric circulation patterns, for northern Fennoscandia during the Eemian. Our study is based on the distribution and stable hydrogen isotope composition (dD) of n-alkanes in a lake sediment sequence from the Sokli paleolake in NE Finland, placed in a multi-proxy framework. The dD values of predominantly macrophyte-derived mid-chain n-alkanes are interpreted to reflect lake water dD variability influenced by winter precipitation dD (dDprec), ice cover duration and deuterium (D)-depleted meltwater. The dD values of terrestrial plant-derived long-chain n-alkanes primarily reflect soil water dD variability modulated by summer dDprec and by the evaporative enrichment of soil and leaf water. The dDprec variability in our study area is mostly attributed to the temperature effect and the moisture source location linked to the relative dominance between D-depleted continental and polar air masses and Denriched North Atlantic air masses. The biomarker signal further corroborates earlier diatom-based studies and pollen-inferred January and July temperature reconstructions from the same sediment sequence. Three phases of climatic changes can be identified that generally follow the secular variationsin seasonal insolation: (i) an early warming trend succeeded by a period of strong seasonality (ii) a midoptimum phase with gradually decreased seasonality and cooler summers, and (iii) a late climatic instability with a cooling trend. Superimposed on this trend, two abrupt cooling events occur in the early and late Eemian. The Sokli dD variability is generally in good agreement with other North Atlantic and Siberian records, reflecting major changes in the atmospheric circulation patterns during the Eemian as a response to orbital and oceanic forcings.
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| 4. |
- Kiel, S., et al.
(author)
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Brachiopods in early Mesozoic cryptic habitats: Continuous colonization, rapid adaptation, and wide geographic distribution
- 2021
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In: Palaeogeography, Palaeoclimatology, Palaeoecology. - Amsterdam : Elsevier. - 0031-0182 .- 1872-616X. ; 583, s. 110668-110668
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Journal article (peer-reviewed)abstract
- Late Triassic and early Jurassic dikes and fissures in the Dachstein Limestone in the Northern Calcareous Alps harbor mass occurrences of the rhynchonellide brachiopods Sulcirostra juvavica and Halorella amphitoma. To test recent hypotheses about their paleoecology, we characterized these habitats using petrography, carbon stable isotopes, and trace element patterns, and found no evidence for hydrocarbon seepage or hydrothermal venting. Thus the brachiopods lived under normal-marine conditions, in darkness and absence of local photosynthetic primary production, hence relying on the supply of limited and presumably small-sized food washed into the dikes and fissures. Because Halorella and Sulcirostra occur in dikes and fissures since the beginning of their stratigraphic ranges, these rhynchonellides are not relics of formerly widely distributed taxa, but instead are two genera that rapidly adapted to these habitats. Both Halorella and Sulcirostra occur also in late Triassic and early Jurassic deep-water settings such as deep-marine sills and hydrocarbon seeps, indicating that close phylogenetic relationships between submarine cave faunas and deep-sea faunas, as seen today, existed also in the early Mesozoic, albeit among very different taxa. Another analogy to the modern cave fauna is the wide but disjunct geographic distribution of Sulcirostra and Halorella, both found throughout the Tethys and Panthalassa oceans. Our findings support the view that submarine cave habitats were continuously colonized by new taxa throughout Earth’s history.
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| 5. |
- Rijal, Dilli P., et al.
(author)
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Sedimentary ancient DNA shows terrestrial plant richness continuously increased over the Holocene in northern Fennoscandia
- 2021
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In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:31
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Journal article (peer-reviewed)abstract
- The effects of climate change on species richness are debated but can be informed by the past. Here, we generated a sedimentary ancient DNA dataset covering 10 lakes and applied novel methods for data harmonization. We assessed the impact of Holocene climate changes and nutrients on terrestrial plant richness in northern Fennoscandia. We find that richness increased steeply during the rapidly warming Early Holocene. In contrast to findings from most pollen studies, we show that richness continued to increase thereafter, although the climate was stable, with richness and the regional species pool only stabilizing during the past three millennia. Furthermore, overall increases in richness were greater in catchments with higher soil nutrient availability. We suggest that richness will increase with ongoing warming, especially at localities with high nutrient availability and assuming that human activity remains low in the region, although lags of millennia may be expected.
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| 6. |
- Yun, Hao, et al.
(author)
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Biomineralization of the Cambrian chancelloriids
- 2021
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In: Geology. - : Geological Society of America. - 0091-7613 .- 1943-2682. ; 49, s. 623-
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Journal article (peer-reviewed)abstract
- As extinct animals that flourished during the Cambrian explosion, chancelloriids have a unique body plan lacking guts but with a flexible integument and a suite of star-shaped, hollow sclerites. Due to this body plan, along with the paucity of knowledge on sclerite biomineralization, the phylogenetic position of chancelloriids within the Metazoa is still controversial. Integration of analyses of diverse fossils from Cambrian stage 2 to the Wuliuan Stage of China and Australia indicates that chancelloriid sclerites possess an encasement-like organic layer and a fibrous aragonitic layer. The organic layer is inferred to be a specialized trait derived from the epidermal integument of the animal body. The sclerites were likely biomineralized by using the outer organic layer as a template to absorb cations and precipitate crystal nuclei, reflecting a strategy adopted by a range of eumetazoans with a developed epidermis. Therefore, the hypothesis that chancelloriids represent an epitheliozoan-grade animal and an early explorer of template-based biomineralization is supported.
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| 7. |
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| 8. |
- Bunrit, Anon, et al.
(author)
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A General Route to beta-Substituted Pyrroles by Transition-Metal Catalysis
- 2016
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In: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 81:4, s. 1450-1460
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Journal article (peer-reviewed)abstract
- An atom-efficient route to pyrroles substituted in the beta-position has been achieved in four high yielding steps by a combination of Pd, Ru, and Fe catalysis with only water and ethene as side-products. The reaction is general and gives pyrroles substituted in the beta-position with linear and branched alkyl, benzyl, or aryl groups in overall good yields. The synthetic route includes a Pd-catalyzed monoallylation step of amines with substituted allylic alcohols that proceeds to yield the monoallylated products in moderate to excellent yields. In a second step, unsymmetrical diallylated aromatic amines are generated from the reaction of a second allylic alcohol with high selectivity in moderate to good yields by control of the reaction temperature. Ru-catalyzed ring-closing metathesis performed on the diallylated aromatic amines yields the pyrrolines substituted in the beta-position in excellent yields. By addition of ferric chloride to the reaction mixture, a selective aromatization to yield the corresponding pyrroles substituted in the beta-position was achieved. A reaction mechanism involving a palladium hydride, generated from insertion of palladium to O-H of an allyl alcohol, that is responsible for the C-O bond cleavage to generate the pi-allyl intermediate is proposed.
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| 9. |
- Bunrit, Anon, et al.
(author)
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Brønsted Acid-Catalyzed Intramolecular Nucleophilic Substitution of the Hydroxyl Group in Stereogenic Alcohols with Chirality Transfer
- 2015
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 137:14, s. 4646-4649
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Journal article (peer-reviewed)abstract
- The hydroxyl group of enantioenriched benzyl, propargyl, allyl, and alkyl alcohols has been intramolecularly displaced by uncharged O-, N-, and S-centered nucleophiles to yield enantioenriched tetrahydrofuran, pyrrolidine, and tetrahydrothiophene derivatives with phosphinic acid catalysis. The five-membered heterocyclic products are generated in good to excellent yields, with high degree of chirality transfer, and water as the only side-product. Racemization experiments show that phosphinic acid does not promote S(N)1 reactivity. Density functional theory calculations corroborate a reaction pathway where the phosphinic acid operates as a bifunctional catalyst in the intramolecular substitution reaction. In this mechanism, the acidic proton of the phosphinic acid protonates the hydroxyl group, enhancing the leaving group ability. Simultaneously, the oxo group of phosphinic acid operates as a base abstracting the nucleophilic proton and thus enhancing the nucleophilicity. This reaction will open up new atom efficient techniques that enable alcohols to be used as nucleofuges in substitution reactions in the future.
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| 10. |
- Bunrit, Anon, 1986-
(author)
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Direct Catalytic Nucleophilic Substitution of Non-Derivatized Alcohols
- 2017
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Doctoral thesis (other academic/artistic)abstract
- This thesis focuses on the development of methods for the activation of the hydroxyl group in non-derivatized alcohols in substitution reactions. The thesis is divided into two parts, describing three different catalytic systems.The first part of the thesis (Chapter 2) describes nucleophilic allylation of amines with allylic alcohols, using a palladium catalyst to generate unsymmetrical diallylated amines. The corresponding amines were further transformed by a one-pot ring-closing metathesis and aromatization reaction to afford β-substituted pyrroles with linear and branched alkyl, benzyl, and aryl groups in overall moderate to good yields.The second part (Chapters 3 and 4) describes the direct intramolecular stereospecific nucleophilic substitution of the hydroxyl group in enantioenriched alcohols by Lewis acid and Brønsted acid/base catalysis.In Chapter 3, the direct intramolecular substitution of non-derivatized alcohols has been developed using Fe(OTf)3 as catalyst. The hydroxyl groups of aryl, allyl, and alkyl alcohols were substituted by the attack of O- and N-centered nucleophiles, to provide five- and six-membered heterocycles in up to excellent yields with high enantiospecificities. Experimental studies showed that the reaction follows first-order dependence with respect to the catalyst, the internal nucleophile, and the internal electrophile of the substrate. Competition and catalyst-substrate interaction experiments demonstrated that this transformation proceeds via an SN2-type reaction pathway.In Chapter 4, a Brønsted acid/base catalyzed intramolecular substitution of non-derivatized alcohols was developed. The direct intramolecular and stereospecific substitution of different alcohols was successfully catalyzed by phosphinic acid (H3PO2). The hydroxyl groups of aryl, allyl, propargyl, and alkyl alcohols were substituted by O-, N-, and S-centered nucleophiles to generate five- and six-membered heterocycles in good to excellent yields with high enantiospecificities. Mechanistic studies (both experiments and density functional theory calculations) have been performed on the reaction forming five-membered heterocyclic compounds. Experimental studies showed that phosphinic acid does not promote SN1 reactivity. Rate-order determination indicated that the reaction follows first-order dependence with respect to the catalyst, the internal nucleophile, and the internal electrophile. DFT calculations corroborated with a reaction pathway in which the phosphinic acid has a dual activation mode and operates as a bifunctional Brønsted acid/Brønsted base to simultaneously activate both the nucleophile and nucleofuge, resulting in a unique bridging transition state in an SN2-type reaction mechanism.
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