Search

A new species of Grylloblattida, Ideliopsina aristovi sp. nov., is described from the Upper Triassic Ominé locality (Momonoki Formation, Mine Group, Japan). It belongs to a typical Triassic genus, Ideliopsina Storozhenko, 1996, which species have been previously reported from the Kyrgyz Republic and the Kazakhstan in Central Asia. The new species shows that the corresponding family, the Ideliidae ranging from the Cisuralian to the Late Triassic, remained widely distributed during the latter period, before its extinction.

The Late Triassic saw a flourish of plant–arthropod interactions. By the Late Triassic, insects had developed all distinct strategies of herbivory, notably including some of the earliest occurrences of leaf-mining. Herein we describe exceptionally well-preserved leaf-mine trace fossils on a Cladophlebis Brongniart fern pinnule from the Momonoki Formation, Mine Group, Japan (Middle Carnian), representing the oldest unequivocal leaf-mines from East Asia. The mines all display a distinctive frass trail—a continuous meandering line, which later becomes a broad band containing spheroidal particles—demonstrating larval development. Although the shapes of the frass trails are generally comparable to those of Lepidoptera or Coleoptera, they cannot be unequivocally assigned to a specific extant leaf-mining taxon. Furthermore, elemental analyses by X-ray fluorescence (XRF) reveals that the frass trail comprises phosphate coprolites. The quantitative variations in P, S, and Si between coprolites and leaf veins may reflect physiological processes (e.g., consumption, absorption, and excretion) mediated by plant chemicals. Our findings reinforce the idea that leaf-mining had become a pervasive feeding strategy of herbivorous insects by the Late Triassic.

It is generally accepted that oceanic plate subduction has occurred along the eastern margin of Asia since about 500 Ma ago. Therefore, the Japanese Islands have a >500 Ma history of oceanic plate subduction in their geological records. In this paper, the accretionary history of the Japanese Islands is divided into six main stages based on the mode and nature of tectonic events and the temporal gaps in the development of accretionary processes. In the first stage, oceanic plate subduction and accretion started along the margin of Gondwana. After detachment of the North and South China blocks in Devonian time, accretionary complexes developed along island arcs offshore of the South and North China blocks. After the formation of back arc basins such as the Japan Sea, accretionary processes occurred only along the limited convergent margin, e.g. Nankai Trough. Detrital zircons of sandstones revealed the accretionary history of Japan. An evaluation of a comprehensive dataset on detrital zircon populations shows that the observed temporal gaps in the development of the Japanese accretionary complexes were closely related to the intensity of igneous activity in their provenance regions. Age distributions of detrital zircons in the accretionary complexes of Japan change before and after the Middle Triassic period, when the collision of the South and North China blocks occurred.

A primitive sawfly, Madygella humioi sp. nov., belonging to the family Xyelidae (Hymenoptera: Symphyta), is newly described from the Upper Triassic Mine Group, Yamaguchi Prefecture, southwest Japan. The new species differs from the five previously known Madygella species in having a cell length of 1r plus 2r shorter than that of 3r + 4r and a cell height of 3r + 4r lower than 2r plus pterostigma in a forewing. To date, this is the oldest fossil record of sawflies in East Asia. Regarding genus Madygella, this is the first example found outside of the Kyrgyz Republic. This discovery provides an insight into the early evolution of the order Hymenoptera and suggests a widespread distribution of the pioneering genus Madygella during the Triassic period.