Fakultät für Geowissenschaften - Digitale Hochschulschriften der LMU

The Archosauria represent the most successful clade within tetrapods, having a large diversity in terms of species, diet spectra, body plans and locomotion styles. This is also true for the skull morphology, which shows a wide variety in shape and size, as well as in the common formation of beaks, crests, domes or horns. Archosaur skulls have been studied intensively in terms of their morphology, ontogeny, function, ecology and behavior in the past, but most of these studies have largely been restricted to case studies of single species or only a small number of taxa. The aim of the current thesis is to obtain better and comprehensive insight into skull shape diversity of archosaurs by using a two-dimensional geometric morphometric approach, with a special focus on ontogenetic and macroevolutionary patterns and their relation to function and ecology. Skull shape variation was quantified for Crocodylomorpha (including an ontogenetic series of the recent caimanine alligatorid Melanosuchus niger), Pterosauria, Sauropodomorpha and Theropoda. The material used for the analyses consists of skull reconstructions published in the scientific literature and photographs of skull material. The most important results of the thesis are summarized as follows:

•The use of different skull reconstructions of the same specimen from the scientific literature has no significant influence on the results of morphometric analyses. However, the results could be potentially falsified by the use of reconstructions based on highly incomplete, strongly deformed or pathologic specimens.

•In some cases the degree of intraspecific variation of one species can be as great as the interspecific variation of closely related species with similar ecological niches. Thus, species with great intraspecific diversity could have an impact on the results of morphometric analyses.

•The skull shape of Archosauria is strongly correlated with function. A closer examination within theropod skulls reveals that the shape of the postrostrum is probably more affected by functional constraints than the snout, but the greatest correlation to the function was found in the orbital shape. The latter result supports previous studies on the biomechanics of theropod skulls. A comparison of the ontogenetic bite force performance with the cranial growth in the alligatorid Melanosuchus and biomechanical studies on crocodile skulls reveals that ontogenetic shape changes, especially in the orbital and postorbital region, are functional constrained.

•Both ontogenetic and interspecific skull shape variation in archosaurs is correlated to diet preferences and feeding behaviour. A comparison between carnivorous and non-carnivorous (i.e. omnivorous and herbivorous) theropods reveals that both ecological groups occupy large areas within the morphospace without showing a significant overlap. Furthermore, small-bodied theropods tend to have a larger diet spectrum, suggesting that diet preferences within theropods are probably size related.

•The distribution of taxa within the morphospace of Crocodylomorpha, Pterosauria, Sauropodomorpha and Theropoda is strongly correlated with the phylogenetic interrelationship of these clades: Closely related taxa appear closer to one another within the morphospace than more distantly related taxa. This result indicates that skull shape in archosaurs is further constrained by phylogeny.

•When inferred from geometric morphometric data, disparity results proved to be similar to those based on limb measurements and discrete characters from phylogenetic analyses. This results justifies the use of geometric morphometric data as a further and equally useful proxy for addressing disparity.

•Early archosaur hatchlings share features of the skull shape, including short, pointed snouts, enlarged orbits and large postorbital regions. However, ontogenetic shape changes are only congruous in terms of a relative increase of the snout length and a relat

Volcanic landscapes often present advantages for people who inhabit the surrounding areas, but the increasing numbers of people threatened by potential activity increases as these settlements grow. It is thus of vital importance to glean as much information as possible by monitoring active volcanoes (including seismicity, ground deformation, gas flux and temperature changes). Although volcanic behaviour can be difficult to predict, precursory information can often be identified retrospectively (once an eruption begins) to help link antecedent behaviour to eruption attributes. Likewise, eruption relics can be used to identify processes in pre-eruptive magma. Additionally, a huge amount of information may be gathered through experimentation on rock and magma samples. This study combines field and analytical studies of natural samples from Volcán de Colima (Mexico), Mount St. Helens (USA) and Soufrière Hills (Montserrat) with high-temperature magma deformation experiments to investigate the processes involved with magma ascent during dome-building eruptions (Figure S-1).

The study of conduit-dwelling magma is of the utmost importance for understanding transitions from effusive to explosive eruptions. Of primary interest is the rheology of highly crystalline magmas that make up the magma column. Rheology is integrally linked to the composition and textural state (porosity, crystallinity) of magma as well as the stress, temperature and strain rate operative during flow. Many studies have investigated the rheology of multi-phase magmas, but in Chapter 2 this is notably linked to the evolution of the physical properties of the magmas; tracing the changes in porosity, permeability, Poisson’s ratio, Young’s modulus during strain dependent magmatic flow. Especially at high strain rates mechanical degradation of the magma samples may supersede magmatic flow and crystal rearrangement as the dominant form of deformation, resulting in lower apparent viscosities than those anticipated from magmatic state. This leads to an evolution of the fracture network to form inhomogeneous distribution of the permeable porous network; with damage zones cutting through areas of densification. In a conduit setting this is analogous to the formation of a dense, impermeable magma plug which would prohibit degassing through the bulk of the magma. Degassing may or may not proceed along conduit margins, and the plug formation could lead to critical overpressures forming in the conduit and result in highly explosive eruption.

During the multi-scale process of strain localisation it is also probable that another previously unforeseen character acts upon magma rheology. Chapter 3 details the first documentation of crystal plasticity in experimentally deformed multi-phase magmas. The extent of the crystal plasticity (evidenced by electron backscatter diffraction (EBSD)) increases with increasing stress or strain, and thus remnant crystals may be used as strain markers. Thus it seems that crystal-plastic deformation plays a significant role in strain accommodation under magmatic conditions. Indeed plastic deformation of phenocrysts in conduit magmas may be an important transitional regime between ductile flow and brittle fracture, and a time-space window for such deformation is envisaged during the ascent of all highly-crystalline magmas. This phenomenon would favour strain localisation and shear zone formation at conduit margins (as the crystal-plastic deformation leads the magma toward brittle failure) and ultimately preferentially result in plug flow.

During volcanic eruptions, the extrusion of high-temperature, high-viscosity magmatic plugs imposes frictional contact against conduit margins in a manner that may be considered analogous to seismogenic faults. During ascent, the driving forces of the buoyant magma may be superseded by controls along conduit margins; where brittle fracture and sliding can lead to formation of lubricating cataclasite, gouge

Die Gattung Ptychogaster POMEL, 1847 (REPTILIA, TESTUDINES) gehört zur Familie der Geoemydidae und wurde vom Mittel-Eozän bis zum Ober-Miozän in Mitteleuropa nachgewiesen. Es handelt sich um Sumpfschildkröten mit einer, je nach Spezies, mehr oder weniger terrestrisch/amphibischen Lebensweise. Wesentliche Charakteristika der Gattung sind der mobile Plastronhinterlappen, die frühe Ankylose der Knochenplatten des Panzers, die testudinide Neuralreihe, das emydine Pygale und die charakteristische Form der Epiplastrallippe. Im Laufe der langen Forschungsgeschichte kam es aufgrund der hohen individuellen Variabilität zur Aufstellung zahlreicher Synonyme und Nomina dubia. In dieser Arbeit wird von der Validität von 21 Arten ausgegangen, wobei 2 neue Arten vorgestellt werden. Synonyme (14) und Nomina dubia (7) werden erläutert. Es werden alle bekannten europäischen Ptychogaster-Fundorte aufgelistet und eine Merkmalstabelle präsentiert. Anatomie und Osteologie der Gattung werden eingehend dargestellt. Stratigraphische und geographische Verbreitung wie auch die Paläoökologie von Ptychogaster werden beschrieben. Die beiden neuen Ptychogaster-Arten werden mit Ptychogaster bavaricus n.sp. und Ptychogaster suntgowensis n.sp. benannt.

In recent years, high-resolution topographic images from Mars’ surface as well as mineralogical and chemical data, have rapidly become more accessible. Martian volcanic landforms are characterized by giant low slope shield volcanoes, abundant lava flood plains and long lava flows. In-situ rock analysis and remote sensing spectroscopy reveal mainly basaltic compositions with particularly high iron concentrations, distinct from terrestrial basalts. As yet, very little is known about the rheological properties of such iron-rich Martian magmas that are essential to understand magmatic processes. Understanding the chemical and physical contributions to lava rheology is fundamental to provide constraints on magma ascent and lava flow emplacement that shaped the volcanic landforms on Mars. This study provides an experimental investigation of the rheological properties of Martian lavas and discusses the diversity of compositions in terms of lava viscosity / flow morphology relationship. The effect of iron, and its redox state on silicate melt viscosity is experimentally investigated and the viscosities of five synthetic silicate liquids having compositions representative of the diversity of Martian volcanic rocks were measured under controlled ambient oxygen fugacity. The results highlight the low viscosity of the iron-rich Martian melts that is consistent with viscosity values derived from morphological observations. A solidified lava flow on Earth was studied by combining analyses of remote sensing images (as commonly done on Mars), as well as experimental investigations of the rheological properties of the sampled rocks, in order to describe the viscous behavior of lava as emplacement, cooling, and crystallization occur. We show that a cooling-limited basaltic flow seemingly stop flowing when it reaches a critical viscosity value that is function of crystals content and shapes. As a result, the lava apparent viscosity appears to be largely influenced by the details of the crystallization sequence and is not uniquely and simply related to the bulk chemical composition of the erupted material. Variation of the chemical evolution of Martian primary mantle melts through the volcanic history is not large to produce an significant shift of the viscosity range that could be observed them from their morphologies. Low apparent viscosities inferred from lava flow morphology on Mars may in turn be attributed to lavas with primary mantle melt composition crystallizing high proportion of olivine and possibly forming spinifex textures. Higher viscosity values derived from the morphology are compatible with mildly alkaline or trachybasalts and do not necessarily imply the occurrence of silica-rich lavas.

The two main subjects of this thesis are the realization of supramolecular self-assembled monolayers at surfaces and the formation of surface-supported two-dimensional covalent organic frameworks. Both topics, albeit different, yield long-range ordered open-pore networks with quite different stabilities, depending on the strength and type of bonds holding them together. The surface of choice is mainly graphite, which is considered an inert substrate. Graphite yields pristine clean, very large and flat surfaces when cleaved, facilitating the observation in real space of the molecular networks adsorbed on these surfaces by means of the Scanning Tunneling Microscope (STM). STM is the main experimental technique used here. It was used to image mostly at the liquid-solid interface under ambient conditions.

Using a large tricarboxylic acid adsorbate, long-range order supramolecular self-assembled monolayers were obtained. These monolayers are formed via a delicate interaction balance between adsorbates, substrate, and solvent molecules. Weak van der Waal forces mediate the adsorbate-substrate interaction; hydrogen bonds, the adsorbate-adsorbate interaction. Also, depending on the solvent used and the concentration of adsorbates dissolved in it, different polymorphs are found on the substrate. To understand the nucleation and growth mechanism that give rise to the different self-assembled monolayers, thermodynamical considerations are used. Enthalpic and entropic contributions are evaluated for several of the polymorphs found, explaining their occurance on the basis of the Gibbs free energy per unit area. However, even if this work sheds some light on supramolecular self-assembly, adding also that much research has been done in this field, it is still very difficult to know a priori how adsorbates will behave on a substrate. Thus predictions of which patterns will ultimately arise are hampered.

To realize structures that are more stable than those formed via supramolecular self-assembly, several strategies have been proposed. Covalent bond formation is one of them, yielding strong and lightweight structures by using organic molecules composed primarily of light elements. The strength of covalent bonds ranges from strong to very strong, when compared to van der Waals and hydrogen bonds. This characteristic makes correction of possible structural errors difficult to almost impossible. However, when molecules with suitable functional groups are allowed to react under reversible conditions, error correction of covalent bonds becomes feasible, yielding regular structures with the energetically most favorable configurations. In this thesis, this is exemplified with the small 1,4-benzenediboronic acid molecules, yielding monolayers composed of very regular, long-range ordered covalent organic frameworks on graphite. Thermal stability is probed by exposing the structures to relatively high temperatures for prolonged times under atmospheric conditions. Further experiments with larger para-diboronic acids, under similar reversible conditions, yield the expected isotopological regular frameworks with larger unit cell parameters. This demonstrates the proof of principle for the formation of two-dimensional covalent organic frameworks.

These two main topics, supramolecular self-assembly and covalent bond formation on surfaces, constitute the basis of this thesis. It is organized as follows: A first part deals with the theoretical background of the main analytical instruments used in this work. Then, the thermodynamics of supramolecular self-assembly is presented, along with the studies of the different polymorphs found using a large tricarboxylic acid as building block. The final part deals with the formation of two-dimensional, long-range ordered covalent organic frameworks, made from organic molecules composed only of light elements. This work show that these last mentioned networks exhibit higher thermal stabilities when compared to