A classification of the 26 taxa of fossil and recent fishes is presented together with thoughts regarding their phylogenetic relationships. In addition to myllokunmingiids, dated as middle Cambrian, cyclostomes (including present-day myxinids and lampreys) are also recognized here as having Cambrian origins, based on their divergence time estimated from a molecular analysis. Ostracoderms (agnathans characterized by exoskeletons), a paraphyletic grouping including pteraspidomorphs, anaspids, thelodonts, and cephalaspidomorphs, were dominant in the Palaeozoic Era; pteraspidomorphs, comprising arandaspids, astraspids, and Eriptychius in the Ordovician and heterostracans in the Siluro-Devonian Periods; anaspids comprising birkenids, Jamoytius, and euphaneropids in Siluro-Devonian Periods, therodonts in Ordovician and Siluro-Devonian Periods, and cepharaspidomorphs, including osteostracans, galeaspids, and pituriaspids, also being Siluro-Devonian ostracoderms. Osteostracans and gnathostomes share the perichondral bone derived from other ostracoderms. Gnathostomes (jawed fishes) consist of placoderms, maxillate placoderms, Janusiscus-Ramirosuarezia, osteichthyans, and chondrichthyans. Placoderms diversified remarkably during the Devonian, and are located here at the base of gnathostomes, due to some ostracoderm similarities; maxillate placoderms with dermal premaxillary, maxillary, and dentary-like osteichthyans in the Silurian. Janusiscus-Ramirosuarezia have no otico-occipital fissure. Osteichthyans and chondrichthyans share dental lamina and otico-occipital fissure that differ from placodermi. Osteichthyans include ancestral stem osteichthyans in the Upper Silurian and Middle Devonian which were divided into actinopterygians and sarcopterygians in the Middle Devonian. Chondrichthyans include Ordovician chondrichthyan-like scales, ancestral stem chondrichthyans, acanthodians, and chondrichthyan crown group. Stem chondrichthyans and acanthodians (previously all combined under acanthodians) are now separated on the basis of scale microstructure from each other, and are differentiated from the chondrichthyan crown group, including pucapampellids, holocephalans, and elasmobranchs. Only cyclostomes, actinopterygians, sarcopterygians, holocephalans, and elasmobranchs are now represented among recent fishes.
First, a comprehensive review is conducted of recent studies examining the interplay between the diversity of physical geographic environments, primarily shaped by landforms, and biodiversity within mountainous regions. Global warming increases the threat of the extinction of flora and fauna in alpine zones. Meanwhile, the role of landforms and geomorphic processes as refugia for cold-adapted species has garnered attention for potentially mitigating global warming effects. The concept, termed "conserving nature's stage," emphasizes the importance of geodiversity & horbar;the variety of abiotic factors constituting nature's stage & horbar;in maintaining biodiversity. Although broad-scale studies suggest a positive correlation between geodiversity and biodiversity, fine-scale research studies are scant. Understanding the impacts of geodiversity on biodiversity at a fine scale, particularly in individual geosites or small natural features (SNFs), is crucial. Biological distributions are influenced by both historical and ecological biogeographic processes, involving organism dispersal with local abiotic and biotic factors. Fine-scale analyses are essential to elucidate these processes, thereby enhancing an understanding of broad-scale distribution patterns and their underlying mechanisms. Second, research conducted on ponds in the mountainous areas of Japan is reviewed. This allowsa emore specific examination of the relationship between geodiversity and biodiversity identified in existing literature reviews. The relationship between geodiversity and biodiversity has been investigated in one of the SNF & horbar;mountain ponds in the Northern Japanese Alps. The findings reveal that species-level diversity of aquatic insects and diatoms is shaped by micro-and small-scale landform-induced environmental variations in ponds. In addition, genetic diversity of aquatic insects is influenced by geographic separation and elevation differences between ponds that are governed by medium-scale landforms acting as dispersal barriers. Furthermore, these dispersal barriers also influence diatom species diversity in ponds. Distinct dispersal capabilities of aquatic insects and diatoms within the same watershed & horbar;active versus passive & horbar;may explain these differences. By integrating findings from these studies on the present-day organisms of mountain ponds with those from investigations on pond sediments, methodological challenges are described in integrating geological, paleoecological, and mountain ecological biogeographic knowledge to reconcile broad-scale and fine-scale patterns of biological distributions.
A carbonate rock boulder with a cone-in-cone structure was discovered in the Youbake riverbed of Akabira-kawa at Oganomachi. This sample is the second example of a cone-in-cone structure found in Japan, following a sample from the Itsukaichi-machi Group. The cone-in-cone comprises fibrous calcite and fine quartz grains. A thin clay band covering the cone has a stepped profile on one side and is rich in chlorite and illite crystals. The carbonate has low delta C-13 values of-12.1 parts per thousand to-13.4 parts per thousand and low delta O-18 values of-6.8 parts per thousand to-7.4 parts per thousand. These isotope data agree well with those of previous studies.
Mass movements of gravel are investigated on periglacial smooth slopes at Mikunizakai, Mt. Hakuba, and Mt. Shakushi in the Hakuba Mountains, northern Japanese Alps, using unmanned aerial vehicle (UAV)-derived orthoimages. UAV orthoimages are generated from aerial photographs acquired with UAV between 2020 and 2022 using structure-from-motion multi-view stereo (SfM-MVS) photogrammetry. Based on field surveys and UAV-derived orthoimages, surface gravel areas are classified into three categories: matrix-filled fine-gravel (< 8 cm), matrix-free fine-gravel (< 8 cm), and matrix-free large-gravel (>= 8 cm). Subsurface materials are examined to a depth of 50 cm, together with snow-cover conditions. From autumn 2021 to autumn 2022, annual mean distances of gravel mass movements are 11.7 cm at Mikunizakai, 7.9 cm at Mt. Hakuba, and 13.4 cm at Mt. Shakushi. Large mobility is observed in matrix-filled and matrix-free fine-gravel areas. In these areas, gravel mass movements are attributed mainly to daily freeze thaw cycles in spring and autumn, with an additional contribution from wash processes induced by summer rainfall events.
In recent years, an increasing frequency of heavy rainfall events has led to more frequent slope failures on fossil periglacial slopes in Hokkaido. These slope failures, observed in areas such as the Hidaka Mountains, can be classified into three types-deep-type, shallow-type, and gully-type-based on their scale, morphology, and depth of occurrence. Deep-type failures extend across the postglacial dissection front, from the upper sideslope to the lower sideslope. Shallow-type failures commonly occur in head hollows, whereas gully-type failures typically develop on upper sideslopes with smooth ground surfaces. At the lowermost part of the periglacial slope deposits, layers of gravel facies and the underlying heavily weathered bedrock beneath exhibit high permeability, which causes groundwater to accumulate in these zones. Deep-type slope failures are triggered when pore-water pressure increases near horizons with contrasting permeability. In contrast, the uppermost part of the periglacial slope deposits is generally composed of low-permeability massive silt facies, overlain by more permeable black soil. This stratigraphic configuration promotes the concentration of rainwater above the periglacial deposits, resulting in shallow-type slope failures mainly within the black soil layer. When piping erosion develops in the lower part of the highly permeable layer, it can cause a collapse of the overlying topsoil, resulting in gully-type slope failures. Given the increasing frequency of heavy rainfall events, understanding these failure mechanisms is crucial for disaster prevention. Accurate prediction of failure type based on the position within the periglacial slope can aid in risk assessment and mitigation efforts.
The rheology of magma is one of the most crucial physical properties in volcanic eruptions. Eruptions are phenomena where magma reaches the Earth's surface, so how magma can move easily before solidification directly influences the occurrence of eruptions and their eruption styles. If magma close to the surface fragments into small pieces, explosive eruptions occur, affecting a wide area. Brittle fragmentation may be required to generate small fragments of magma, and this process also depends on the rheology of magma. Magma is a suspension in which crystalline particles and gas bubbles float in a silicate melt composed of molten rock. The silicate melt is generally regarded as a Maxwell fluid; however, the presence of crystals complicates the rheology of magma. In densely packed suspensions, solid particles interact with each other, and repeated transitions between solid-like and liquid-like states appear, depending on strain and strain rate. Recently, similar measurements have been reported for actual molten magma. Such measurements are based on oscillatory rheology measurements. In oscillatory rheology measurements, a sinusoidal strain is applied to a sample, and the ratio of the elastic component to the viscous component of the sample can be calculated from the phase difference between strain and stress. Oscillatory rheology measurements of crystal-bearing magma are introduced in this paper.
More than ten years of geodetic and seismic observations after the 2011 Tohoku-oki earthquake (Mw 9.0) are reviewed to investigate the rheological properties of the crust and mantle beneath NE Japan. Postseismic deformation, driven by viscoelastic mantle relaxation and afterslip on the plate interface, has been extensively recorded using dense GNSS and seafloor networks. Numerical models incorporating depth-dependent viscosity, non-linear rheology, and localized low-viscosity zones successfully reproduce observed horizontal and vertical displacements. These analyses reveal strong rheological heterogeneity in the mantle wedge, oceanic mantle, and volcanic regions. The results demonstrate that postseismic deformation controls crustal uplift and subsidence and subsequent seismic activity, highlighting its critical role in earthquake cycle dynamics and hazard assessments in subduction zones.
Rocks are composed of multiple mineral phases organized as polyphase crystal aggregates. However, previous studies assumed that the viscosity of a rock is represented by the viscosity of the primary phase in the rock, which oversimplifies the systems. The rheological properties of two-phase crystal aggregates are reviewed, focusing on two minerals representative of the upper mantle (olivine and pyroxene). Our research group performed several deformation and grain growth experiments on olivine and pyroxene aggregates with different volume fractions of pyroxene. Based on the experimental results, a constitutive law is proposed that relates grain size, viscosity, and mineral fraction in two-phase systems when a sample deforms under grain size sensitive creep. High strain torsion experiments were performed on olivine and pyroxene aggregates to understand the weakening process due to phase mixing. The microstructures observed in deformed samples are consistent with those found in naturally deformed rocks. The microstructural evolution of well-mixed fine-grained olivine and pyroxene aggregates can be explained from differences in diffusivity among Me (Fe or Mg), O, and Si, with the transport of MeO being significantly faster than that of SiO2. It is proposed that pyroxene plays a key role in plastic deformation, leading to long-term weakening associated with phase mixing.
Rheological studies on the Earth's materials started in the 1970s following the establishment of the dislocation theory of metals, which occurred around the same time as the concept of global plate tectonics was proposed. Since then, many studies on the dislocation theory of oxides and halides and experimental and TEM investigations on dislocation structures have been carried out. The authors (S. Karato and M. Toriumi) began studies on the high-temperature dislocation annihilation of olivine, and later performed high-temperature and low-stress creep experiments on olivine single crystals from incubation to the third creep stage in a very large strain through steady state creep. A brief history is introduced of promising rheology research conducted by the authors' group during the period when the Earth's mantle rheology was established.
Quartz is the most dominant constitutive mineral in the continental crest; thus, recognizing the deformation mechanism of quartz is essential for understanding the Theology of the continental crust. Under crustal conditions, dislocation creep is the dominant deformation mechanism of quartz aggregates; based on previously proposed flow laws, their flow strength with a dominant basal slip system differs from that with a dominant prism slip system by tens of megapascals under mid-crustal conditions, where the crustal strength is at its maximum. Thus, identifying the dominant slip systems in naturally deformed quartz is crucial for understanding continental crust rheology. Although the basal slip system is considered to be dominant in quartz under upper to middle crustal conditions, its activity has beert challenged because some microstructural observations support an oriented nucleation and growth model for c-axis distribution near the minimum strain axis that has been believed to be indicative of the activity of the basal slip system. Based on misorientation analyses via EBSD Hata, a recent micro-structural study on quartz phenocrysts in a granitic porphyry naturally deformed at similar to 400-500 degrees C in the Ryoke belt, SW Japan, reveals that the dominant slip systems are both prism and basal ra>, and shows that c-axis orientations of basal phenocrysts distribute at pole figures peripheries, indicating basal activation over the proposed oriented nucleation and growth model! When prism and basal slip systems are dominant at mid-custal depths, crustal strength is controlled fundamentally by the activity of basal because the strength of basal may be much lower than that of prism at those depths.
To understand the processes of time-dependent phenomena such as transient creep and brittle failure, a WidePIX CdTe photon-counting detector was installed at the BL04B1, SPring-8. The detector enables the exposure time to be shortened for acquiring high-energy two-dimensional X-ray diffraction patterns of minerals. In situ triaxial deformation experiments on olivine aggregates were conducted at pressures 13 GPa and temperatures 7601150 K using a deformationDIA apparatus, installed at BL04B1, SPring-8. Two-dimensional X-ray diffraction patterns (40 s of exposure time for each image) and radiographic images (2 s for each) were alternately acquired by adjusting the sizes of the incident slit and operating a CdTe detector equipped with a CMOS camera using a high-energy monochromatic X-ray beam (energy -60 keV). Pressure and differential stress were determined from the d-spacing of olivine. Strain at a deforming sample was evaluated from the distance between platinum strain markers, which were placed at both ends of the sample. Yield of the deforming sample was clearly recognized at strains of less than 0.05 and apparent steady-state strength was achieved at strains of -0.1 or higher. The CdTe detector combined with a CMOS camera is a powerful tool for understanding the process controlling the timedependent rheological phenomena such as transient creep and brittle failure at high pressures.
The rheology of rocks is reviewed in the brittleplastic transition (BPT), a key depth range in the continental crust and subduction plate boundaries where earthquakes, slow earthquakes, and stable sliding can all occur. Understanding the physical processes governing deformation in this zone is essential for linking laboratory observations to fault-slip behavior at the scale of plate boundaries. Quartz aggregates are a key material because quartz is abundant in the upper crust, as well as in pelitic and psammitic rocks in the subduction zone, and they serve as an analog for other rocks due to their well-studied deformation mechanisms. This focus is on fault zones within the BPT that contain abundant pore water, drawing primarily upon experimental studies on polycrystalline quartz. High-temperature, high-pressure deformation tests with controlled fluid content show that fluid-filled porosity markedly weakens quartz shear zones across the BPT. The rheology of these zones is controlled by pore fluid pressure, porosity, and fluid topology. Within the BPT, strain is partitioned between brittle and plastic deformation, but the degree of partitioning is complex and non-linear. The variability and complexity of deformation and fluid-filled porosity in the BPT may help explain the diverse spectrum of slip behaviors observed along plate boundaries.
Muography is a technique that employs muons in cosmic rays to facilitate visualization of the Earth's crust and underlying large-scale architectural structures. As a novel application of muography, we are investigating the interior of Kofun, ancient burial mounds in Japan. This report presents the preliminary results of muographic imaging of an unexcavated Kofun, which is believed to contain artifacts. A high-sensitivity Multi-Wire-Proportional-Chamber (MWPC) detector was employed as the measurement device, and 128 x 64 pixel muon transmission images were acquired. The images were compared with muon transmission simulations assuming the presence of a stone chamber inside. As a result, it was indicated that there was a possibility of an uneven area around the projected image of the virtual stone chamber. Although the lack of resolution did not allow the identification of artefacts with a high degree of confidence, it demonstrated the potential for using muography to explore the interior of the Kofun.
Muography is a novel green nuclear imaging technology that has rapidly advanced in recent years. This technique utilizes natural muon rays to achieve non-destructive, high-precision threedimensional imaging of objects. Several universities and research institutes in China have engaged in research related to muography, including system development, application scenarios, and some imaging algorithm studies. This paper provides an overview of research progress in China on two different principles of muography and, through the introduction of several typical cases, demonstrates the significant economic, cultural, and social value and potential of this technology. Given China's vast territory and comprehensive industrial system, muography has a wide range of applications in various fields. With the advancement of related research, this technology is expected to continue developing and find broad applications in cultural relics protection and excavation, mineral exploration, infrastructure monitoring, and natural disaster early warning.
