| 1. |
- Byrne, Hannah
(författare)
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Novel approaches to the environments and ecosystems of the fish-tetrapod transition
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fish-tetrapod transition is one of the most important evolutionary events in Earth’s history, giving rise to terrestrial vertebrates around 390 million years ago. It set the stage for a series of evolutionary events that ultimately resulted in modern-day terrestrial vertebrates including ourselves. The fish-tetrapod transition occurred during the Middle Palaeozoic and although it has been the subject of intense study over the last century, many questions remain unanswered. In this thesis, novel techniques were used to help elucidate certain aspects of the fish-tetrapod transition. The first project sought to use numerical tidal simulations to test the premise of a hypothesis that large tides occurred during the Middle Palaeozoic and acted as a driver for the evolution of lungs and limbs. The simulations produced for the Late Silurian-Late Devonian revealed unusually large tides during the Late Silurian, thus the origin of lungs, supporting the hypothesis that deoxygenated tidal pools could have been the setting for this evolutionary step. The following three projects used propagation phase-contrast synchrotron microtomography (PPC-SRμCT) to analyse new tetrapod material from the terminal Famennian (latest Devonian) and coprolite material from the earliest Tournaisian of Greenland (earliest Carboniferous), spanning a mass extinction event (the Hangenberg crisis) believed to have impacted early tetrapod diversity. Spectacular data sets were generated using this technique, with analysis of the tetrapod material revealing the presence of new taxa, making East Greenland home to the greatest known diversity of tetrapods in the world during the Devonian. Synchrotron scanning allowed for the accurate determination of coprolite morphotypes from a post-Hangenberg crisis lake deposit, revealing greater diversity among the coprolites compared with vertebrate body fossil taxa and thus demonstrating that the fauna contained additional taxa not captured by the body fossil record. Most of the large coprolites are non-spiral and were probably produced by a large aquatic tetrapod. One large coprolite is spiral and is postulated to have been produced by a chondrichthyan. Virtual reconstructions of several coprolites were generated using the scan data. The largest coprolites were full of actinopterygian and acanthodian remains, showing that the probable tetrapod was a proficient aquatic predator. Another large coprolite contained remains of two new body fossil taxa; an actinopterygian and small tetrapod. The coprolite data challenge our initial interpretation of a low-diversity lake fauna, revealing instead a complex ecosystem immediately after a major mass extinction event. Tetrapods and chondrichthyans appear to have been the apex predators in this ecosystem. This thesis demonstrates the capabilities of two novel analytical techniques, tidal simulation and synchrotron microtomography, to uncover previously inaccessible information about the fish-tetrapod transition and its environmental-ecological context.
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| 2. |
- Brazeau, Martin D., 1981-
(författare)
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Endocranial Morphology and Phylogeny of Palaeozoic Gnathostomes (Jawed Vertebrates)
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gnathostomes, or jawed vertebrates, make up the overwhelming majority of modern vertebrate diversity. Among living vertebrates, they comprise the chondrichthyans (“cartilaginous fishes” such as sharks, skates, rays, chimaeras) and the osteichthyans (“bony fishes” or bony vertebrates, inclusive of tetrapods). Gnathostomes appear to have originated in the early Palaeozoic Era, but their early fossil record is fairly scant. The best fossils appear first in the Late Silurian and Devonian periods. Much of gnathostome diversity owes to unique adaptations in the internal skeleton of their head (the endocranium). The endocranium is composed of the braincase, jaws, hyoid arch, and branchial arches, which sometimes fossilise when they are composed of bone or calcified cartilage. The purpose of this thesis is to describe and compare the fossilised cranial endoskeletons of a variety of different Palaeozoic gnathostomes. The objective is to test current conceptions of gnathostome interrelationships (i.e. phylogeny) and infer aspects of key morphological transformations that took place during the evolution of Palaeozoic members of this group. Two key areas are examined: the morphology and interrelationships of Palaeozoic gnathostomes and the morphology of the visceral arches in sarcopterygian fishes. New data on the visceral arches are described from the stem tetrapods Panderichthys and rhizodontids. These provide insight into the sequence of character acquisition leading to the tetrapod middle ear. Panderichthys shows key features of the tetrapod middle ear chamber were established prior to the origin fo digited limbs. New morphological data are described from the “acanthodian” fish Ptomacanthus. Ptomacanthus provides only the second example of a well-preserved braincase from any member of this group. It shows dramatic differences from that of its counterpart, Acanthodes, providing new evidence for acanthodian paraphyly. New interpretations of basal gnathostome and osteichthyan phylogeny are presented, challenging or enriching existing views of these problems.
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| 3. |
- Blom, Henning, Dr, 1969-, et al.
(författare)
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Thelodont scales from the Lower Devonian of Novaya Zemlya Archipelago, Arctic Russia.
- 2022
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Ingår i: Spanish Journal of Palaeontology. - : Universitat de Valencia. - 2255-0550 .- 2660-9568.
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Tidskriftsartikel (refereegranskat)abstract
- Scales of a new thelodont species, Amaltheolepis terranovi sp. nov., are described from the upper Emsian, Lower Devonian Shevchenkinskaya Formation of Novaya Zemlya, Arctic Russia. The new species shows strong resemblance with the Emsian “Verdalen assemblage” from Spitsbergen, supporting an Emsian age for the upper part of the Shevchenkinskaya Formation. This conclusion in the context of the various Amaltheolepisassemblages from Spitsbergen allows for a more accurate comparison and correlation between assemblages from different regions in the Northern Hemisphere, suggesting that the type species, Amaltheolepis winsnesifrom Spitsbergen, is Eifelian in age
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| 4. |
- Perman, Karin
(författare)
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Från el till värme : en diskursanalytisk policystudie av energiomställning på statlig, kommunal och hushållsnivå
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to analyse how space heating for single-family houses, and energy system conversion has been constructed and discussed at national, municipal and household levels. Political documents have been studied, and interviews have been carried out with politicians, civil servants and householders in the municipality of Falun. In order to study and analyse similarities and differences between these three political levels, the following main questions were asked: In which sense is the use of electrical heating formulated as problematic? How are the causes of these problems presented, and which solutions are suggested? What are the effects of how problems, causes and solutions are constructed?At the national level, the use of electricity produced by nuclear power was considered a problem. Initially the municipality’s policy documents present the same problem, but there is a change of focus to the problem of imported electricity produced by fossil fuel, and the resulting emissions. At household level, the problem was often an old and badly functioning space-heating system. But some households did not formulate a problem before they converted. Instead they were influenced by their neighbours and thereby convinced.At all three political levels, there is consensus on the households’ responsibility concerning energy transition. While industry tends to be considered incapable of cutting down its energy consumption, households are expected to take the responsibility seriously. Furthermore, within the household, the heating system tends to be constructed as a predominantly male concern.At all three levels, households are perceived as dependant on economical subsidies when taking the decision to convert from electrical heating. Although it is interesting that the interviewed householders only apply this view to others than themselves. They are convinced that other households need subsidies to act in an environmentally correct way.The discourse concerning the Swedish energy transition illustrates a shift away from a definition of ecological modernisation where environmental considerations influence economic development. The thesis clearly shows how economic arguments repeatedly influence environmental concerns. However, the tension between the two is played down and concealed through the lack of problematisation of the responsibility of industry, and through the focus on the need for education and future opportunities. Political dialogues concerning the use of electrical heating and the conversion of energy systems towards more renewable energies are dominated by economic arguments at the three levels. One effect of this is an assumption that energy policy instruments such as information and economic subsidies are essential for the energy transition. However, if householders rather are influenced by their neighbours should the government use economic subsidy as the main energy policy instrument?
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| 5. |
- Snitting, Daniel, 1977-
(författare)
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Morphology, Taxonomy and Interrelationships of Tristichopterid Fishes (Sarcopterygii, Tetrapodomorpha)
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tristichopterids (Sarcopterygii, Tetrapodomorpha) form a monophyletic group of exclusively Devonian fishes. This thesis consists of descriptions of new material of tristichopterids and closely related taxa, as well as new interpretations and descriptions of previously figured material. Redescribed specimens were originally figured as far back as 1861, and publications as old as this are almost always of limited use as anatomical and systematical references, in addition to being difficult to acquire. The possibility of using new techniques and new theoretical frameworks also provides good justification for taking a second look at such specimens. In the case of this thesis, this includes the use of computed tomography scanning methods, and the cladistic approach to describing the interrelationships of taxa. The thesis includes a complete taxonomy of valid tristichopterid taxa, in addition to two new phylogenetic analyses incorporating the taxa that were described or redescribed. One of the analyses deals with the interrelationships of taxa along the entire tetrapod stem, and establishes the monophyly of the Tristichopteridae. The other analysis focuses on tristichopterid interrelationships. An account is given of evolutionary trends within Tristichopteridae, and instances of parallel evolution between tristichopterids and other tetrapodomorph groups are discussed. The biogeographical implications of tristichopterid occurences world-wide seem to corroborate the picture provided by other vertebrate groups, and give further support to one of two main hypotheses concerning the relative positions of Gondwana and Laurussia, the two major palaeocontinents during the Late Devonian. The supported hypothesis proposes a close proximity between southern Laurussia and northwestern Gondwana, as evidenced by the wide dispersal of derived tristichopterids by the Late Devonian. A Laurussian origin of tristichopterids is proposed.
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