Tetori Group Research Articles

New goniopholidid specimens from the Lower Cretaceous Kitadani Formation, Tetori Group, Japan

New crocodyliform fossils have been discovered from the Lower Cretaceous Kitadani Formation of the Tetori Group, Fukui, Japan. They include skull elements (premaxilla, maxilla, parietal, quadrate and dentary), postcranium elements (dorsal vertebra, caudal vertebra, femur and osteoderm) and isolated teeth, and are described as goniopholidid crocodyliforms. Phylogenetic analysis resulted in nesting the Kitadani goniopholidid at the basal position of Goniopholididae and one autapomorphy is recognized: presence of the parietal sagittal crest. In addition, the narrow snout and a heterodont dentition in jaws of this goniopholidid is a unique combination of rostral morphology among Goniopholididae. Generally, the basal taxa bear a narrow snout with homodont dentition, and the heterodont dentition is seen in derived broad-snouted taxa. Judging from those rostral shape and dentitions, the Kitadani form possessing acute caniniform and blunt teeth tends to be more opportunistic as foraging strategy than other basal narrow-snouted goniopholidids with only acute caniniforms throughout. Our new discovery is the first osteological report of Japanese Cretaceous crocodyliform. Siamosuchus phuphokensis from the Early Cretaceous Sao Khua Formation, Khorat Group also shows combination of basal and derived cranial characters. Transitional species from Asia suggest allopatric speciation of goniopholidid in geographically intermediate Asian area.

Molluscan Faunal Changes from Brackish to Freshwater Deposits in the Lower Cretaceous Itsuki Formation of the Tetori Group, Japan

This paper focuses on the molluscan faunal changes in the nonmarine deposits of the Lower Cretaceous (Barremian) Itsuki Formation of the Tetori Group, central Japan. In the lower part of the Itsuki Formation, the transition from brackish to freshwater environments is recognized by lithofacies, sedimentary structures, and fossil indices of molluscs and plant remains. The molluscan assemblages include eleven gastropod species and six bivalve species, and one new gastropod species, Probaicalia okurai sp. nov., is described. The brackish habitats in the delta-front were dominated by Myrene tetoriensis, which usually formed shell beds. The newly founded freshwater habitats on the fluvial environments were populated by Campeloma onogoense and Sphaerium coreanicum as pioneer immigrants. With the development of the fluvial floodplain, a variety of aquatic and semiaquatic microenvironments formed, thereby providing various habitats suitable for small gastropods.

A Three-Dimensionally Preserved Frog (Amphibia, Anura) from the Lower Cretaceous Kuwajima Formation, Tetori Group, Ishikawa Prefecture, Japan

The Early Cretaceous Kuwajima Formation, Tetori Group, Japan has yielded various aquatic and terrestrial vertebrates, but lissamphibian records are limited to albanerpetontids and an isolated longbone of a frog. Here we provide the first report of an associated frog specimen from the Tetori Group. The specimen is composed of a few skull elements and several postcranial bones, including the femur, ilium, and vertebrae. This new Tetori frog is distinguished from the previously reported Early Cretaceous Asian genera, Liaobatrachus from China, and Hyogobatrachus and Tambabatrachus from Japan, in having hatchet-shaped sacral diapophyses and a posteriorly tapering urostyle with a weakly developed dorsal crest. Phylogenetic analysis of this new material places it as a non-neobatrachian frog that may be related to previously described Chinese and Japanese taxa, but more complete material would be needed to establish its affinities with confidence.

Morphometric and Cladistic Analyses of a Theropod Tooth from the Itsuki Formation of the Tetori Group in the Kuzuryu District, Ono City, Fukui Prefecture, Japan

An isolated theropod tooth was found in the Hauterivian–Barremian Itsuki Formation of the Tetori Group in the Kuzuryu district, Ono City, Fukui Prefecture, central Japan. The present specimen, OMFJ V-1, shows a thick lanceolate basal cross-section and small mesial and distal denticles. A cladistic analysis based on the dental characters suggested that OMFJ V-1 be classified as belonging to Allosauroidea or Tyrannosauroidea. Principal component and linear discriminant analyses also suggested that OMFJ V-1 belongs to either of these two theropod clades. The posterior probabilities obtained in the linear discriminant analyses indicated that the confidence of the classification as Allosauroidea is slightly higher than that for Tyrannosauridae. However, because these analyses also supported possibilities of OMFJ V-1 belonging to other theropod clades to lesser extents, its taxonomic referral remains ambiguous. If OMFJ V-1 belongs to Tyrannosauroidea, it would indicate that a medium-sized tyrannosauroid already appeared in central Japan during the Hauterivian–Barremian age. On the other hand, if OMFJ V-1 belongs to Allosauroidea, it would indicate that at least two medium-to-large-sized theropods, allosaurids and tyrannosaurids, lived almost coevally in this region. The third possibility is that OMFJ V-1 belongs to Megaraptora. If such affinities are established, it would represent the oldest record of this clade of theropods.

Pterophyllum pachyrachis (Bennettitales) from the Upper Jurassic to Lower Cretaceous Tetori Group, Fukui Prefecture, Central Japan

We designate the lectotype of Ptilophyllum pachyrachis Oishi (1940), collected from the Upper Jurassic (Tithonian) to Lower Cretaceous (Berriasian) Ashidani Formation of the Tetori Group exposed in Mochiana, Ohno City, Fukui Prefecture, Central Japan. We further propose a reclassification of this species to the genus Pterophyllum. We found that Oishi's (1940) syntypes included one Ptilophyllum specimen that reflected Eurosinian-type vegetation, contrary to the widely accepted idea that typical Siberian-type vegetation flourished in the Tetori Group region during the Tithonian to Berriasian.

Relationship among paleosol types, depositional settings, and paleoclimates in Tetori group (Lower Cretaceous, central Japan)

AbstractOne of the key areas and periods for dinosaur evolution is considered to be Early Cretaceous East Asia, of which paleoclimate, that affected dinosaur diversity, needs to be accurately estimated. This study reconstructed paleoenvironmental information from two paleosol sections of the Lower Cretaceous Tetori Group in Hokuriku province, Japan. Elemental and isotopic compositions indicate that the two sections (Sections K5 and T1) formed under similar mean annual temperature (MAT) and mean annual precipitation (MAP) but exhibit significantly different paleosol colors (red in the Section K5, and gray in the Section T1) and mineralogy of carbonate nodules (dolomite–siderite in the Section K5, and dolomite–calcite in the Section T1). In addition, the oxygen isotopic ratio of carbonate minerals in the Section K5 was significantly low. The differences in sedimentary features and isotopic composition were considered to reflect the differences of seasonal climatic factors (e.g., monsoon) and local settings (e.g., drainage condition) despite the two sections exhibiting similar MAT and MAP. The results of this study suggest that the northeastern margin of East Asia, where the Tetori Group was deposited, had temperate and humid climate with monsoonal contrast in humidity during Aptian to Albian.

The Tetori Group Exposed at Yunotani, Upstream on the Tedori River in Southwestern Mt. Hakusan

The Tetori Group Exposed at Yunotani, Upstream on the Tedori River in Southwestern Mt. Hakusan

Sedimentary Environments and Basin Development of the Middle Jurassic–Early Cretaceous Tetori Group in Its Main Area, Central Japan

Sedimentary Environments and Basin Development of the Middle Jurassic–Early Cretaceous Tetori Group in Its Main Area, Central Japan

Palynofloras from the Itsuki and Kuwajima Formations of the Tetori Group and their Correlation with Paleofloristic Provinces of Eastern Asia

We collected samples from the middle part of the Tetori Group and obtained diverse spores (28 species) and gymnosperm pollen (8 species) from the Barremian Itsuki and Kuwajima formations. This is the first report of Barremian palynofloras from the Tetori-type floristic province in Japan and we compared them to coeval ones from the Ryoseki-type floristic province. These palynofloras include various cyathealean spores and cheirolepidiaceous pollen, indicating that floristic differences between the Tetori- (Inner Zone) and Ryoseki-type (Outer Zone) provinces are not so distinct during the Barremian in Japan. They also show similarities with floras of the Sindong Group of the Gyeongsang Basin, southeast Korea and Shitouhezi Formation in northeast China, thus indicating that some Ryoseki-type elements may have extended their distribution northward in the Barremian.

Depositional environments and taphonomy of the bone-bearing beds of the Lower Cretaceous Kuwajima Formation, Tetori Group, Japan

Thebone-bearing beds of the Lower Cretaceous Kuwajima Formation (Tetori Group) are described. Three facies of bone-bearing beds (Facies I: carbonaceous sandstones; Facies II: dark grey fine-grained silty sandstones; Facies III: dark greenish-grey mudstones) are present in inter-channel deposits that originated on a floodplain. The grain size of the sediments, and plant and molluscan fossils occurring in each bone-bearing bed, indicate that Facies I was deposited in a peat marsh, Facies II in a shallow lake, and Facies III in a vegetated swamp. Isolated small bones and teeth are the most abundant vertebrate fossils. Common elements in Facies II are aquatic vertebrates such as fishes and turtles. Facies III is characterized by the occurrence of terrestrial lizards, tritylodontid synapsids and mammals. Vertebrate fossil assemblages in Facies II and III are not mixed with each other even though they both represent parautochthonous assemblages. In contrast, Facies I is allochthonous, and is composed mostly of reworked sediments from Facies II. Depositional environments of the bone-bearing beds are strongly correlated with the composition of their fossil assemblages, indicating that different facies preserve the original faunal differences that existed between the shallow lake and vegetated swamp environments.

Early Cretaceous freshwater fishes from the Tetori Group, central Japan

Early Cretaceous freshwater fishes from the Tetori Group, central Japan

A Reexamination of Dinosaur Trackmakers Based on Three-Dimensional Quantitative Data from the Lower Cretaceous Tetori Group of the Oshirakawa Area, Gifu Prefecture (Japan)

Researchers disagree on the identity of dinosaurs that left footprints in the Lower Cretaceous Tetori Group of the Oshirakawa area (Japan). To clarify these identities, we quantitatively analyzed footprint data obtained from three-dimensional laser scanning technology. From these data, we identified six tracks belonging to dinosaurs. These six tracks were bipedal with a tridactyl morphology, which we could differentiate into large theropods (the ichnofamily Eubrontidae) and large ornithopods (similar to Amblydactylus-type). Our results indicate that the ichnofauna of the Oshirakawa site is richer than previously thought. Additionally, the cooccurrence of large theropod and Amblydactylus-type ornithopod footprints in the Oshirakawa area is the oldest in the Tetori Group (although a similar assemblage was identified in the Kitadani Formation, which is the uppermost part of the Tetori Group). Thus, quantitatively assessing dinosaur footprints using 3D digital data is an effective approach to identify dinosaur footprints.

Boreal Molluscan Records Around the Jurassic–Cretaceous Boundary in East Asia Provide Clues for the Paleobiogeographical Reconstruction in the Mid-Latitudes of the Northwest Pacific

Studying marine paleobiogeographical conditions in the mid-latitudes of the Northwest Pacific around the Jurassic–Cretaceous boundary would be expected to contribute to a better understanding of the paleoclimatic and/or paleoenvironmental background of the evolution of the Late Mesozoic terrestrial ecosystem in East Asia. However, uncertainty about the paleogeography of the eastern margin of the Asian Continent has meant difficulties for paleobiogeographical discussion. In this paper, the strata containing Boreal faunal elements, Buchia, and cylindroteuthidid belemnites in East Asia (Far East Russia, Heilongjiang in northeastern China, and Japan) and their tectonic settings are reviewed. The Uda and Torom (northern Sikhote-Alin), Suibin (Heilongjiang), and Tetori (northern Central Japan) regions were located from north to south in the eastern margin of the already amalgamated Asian Continent around the Jurassic–Cretaceous boundary and can be considered the “fixed points for paleobiogeographical reconstruction.” On the other hand, Buchia-bearing strata in the Komsomolsk (northern Sikhote-Alin) and Dong'an (Heilongjiang) regions can be considered to have been deposited in the fore-arc basin or trench slope basin on the accretionary complex along the East Asian continental margin. The strata around the Jurassic–Cretaceous boundary in the Partizansk Basin (southern Sikhote-Alin) contain both Buchia and Tethyan ammonoids and were deposited on the Paleozoic continental basement or block (Sergeevka Belt). The paleo-position of these three regions around the Jurassic–Cretaceous boundary is highly debated.The Tethyan–Pacific ammonoids, Boreal belemnites, and Tetori bivalve fauna, showing some similarities with those in the Boreal Realm and Early Cretaceous strata in Heilongjiang, are present in the late Tithonian–Berriasian Mitarai Formation of the Tetori Group in the Tetori Region. This unit, deposited in the eastern margin of the North China Block, provides evidence that Boreal faunal elements reached the mid-latitudes of the Northwest Pacific. The position of the ecotone of the Boreal and Tethys realms in the Northwest Pacific can be discussed based on the comparison of the faunal elements among almost coeval strata in the Tetori Region (fixed point), the Sergeevka Belt, and the South Kitakami Belt (Pacific side of Northeast Japan), which is usually correlated with the Sergeevka Belt but contains only Tethyan faunal elements. Further studies of the records of Tethyan and Boreal taxa in the “fixed points” and other localities could provide clues to reveal the paleoclimatic and/or paleoenvironmental background of the evolution of the terrestrial and marine ecosystems in East Asia around the Jurassic–Cretaceous boundary.

New belemnite records from the Mitarai Formation, Tetori Group, Japan: Delimitation of the Jurassic-Cretaceous boundary in the Japanese Islands

Traditional faunal elements for zoning the uppermost Jurassic‒lowermost Cretaceous stratigraphic interval in Tethyan regions, i.e., ammonites and calpionellids, are either lacking in the boreal regions at that time, or are of generally low diversity and endemic compositions. Consequently, recognition of Jurassic-Cretaceous boundary interval sections has been hindered in many areas of the boreal regions, as well as some lower latitude intermediate areas, such as the Japanese Islands.Strata of the Mitarai Formation of the Tetori Group of central Japan have previously provided ammonites suggesting a broadly Tithonian–Berriasian age for the formation, but the Jurassic-Cretaceous boundary, nor the boundary interval, have never been precisely identified in it, due to the poorly preserved nature of the faunas and their endemic nature. We have recognized a fauna of belemnites from a locality of the Mitarai Formation, including Cylindroteuthis knoxvillensis Anderson, C. knoxvillensis?, C.? sp., Arctoteuthis tehamaensis (Stanton), A. cf. tehamaensis, A. cf. repentina Saks & Nal'nyaeva, and Acroteuthis? sp. Collectively, this belemnite assemblage of the Mitarai Fm indicates the interval of the Jurassic-Cretaceous boundary, as recognized at northern Siberia (Russia) and northern California (USA), and is thus the first certain identification of this boundary in the Japanese Islands. The Mitarai Fm belemnite assemblage can be used to establish the presence of the Jurassic-Cretaceous boundary interval in other areas of the Japanese Islands.

石川県白峰地域における手取層群赤岩層の凝灰岩から得られたジルコンLA-ICP-MS U-Pb年代

石川県白峰地域における手取層群赤岩層の凝灰岩から得られたジルコンLA-ICP-MS U-Pb年代

Early Cretaceous plants from the Itsuki and Nochino formations of the Tetori Group in the Kuzuryu area, central Japan and their paleoclimatic implications

Early Cretaceous plants are widely distributed in a number of localities and horizons in the Tetori Group in central Japan. However, the stratigraphical occurrences and diversity patterns of some plant groups and their palaeoclimatic implications are not well understood. In this study, we report the diverse fossil plants recently collected from the Lower Cretaceous Itsuki and Nochino formations of the Tetori Group in the Kuzuryu area, central Japan. The plant assemblage from the lower and middle part of the Itsuki Formation has no Ryoseki-type floral element, whereas the assemblage from the Nochino Formation has some Ryoseki-type floral elements such as microphyllous conifers. The occurrence of Ryoseki-type floral elements is consistent with floral change that conifers are more diverse in the Nochino Formation than in the Itsuki Formation, and a warming and drying climate trend from the Itsuki Formation to the Nochino Formation is recognized. The Early Cretaceous warming and drying trend recorded in floral assemblages of the Tetori Group is considered to reflect the paleoclimate transition represented by drastic shrinking of the Hadley circulation in the mid-latitudes of East Asia, thus providing evidence for understanding the climatic switch pattern during the Early Cretaceous.

A diverse theropod footprint assemblage from the Lower Cretaceous Kitadani Formation, Tetori Group, central Japan

Theropod footprints occupy more than 50% of dinosaur footprints from the Lower Cretaceous Kitadani Formation of the Kitadani Dinosaur Quarry in Fukui, central Japan. However, ichnotaxonomical description of these footprints has never been carried out. In this study, five different ichnotypes, which are the ichnofamilies Grallatoridae, Eubrontidae, and Ornithomimipodidae, and the ichnogenera Asianopodus, and Minisauripus, are described. Among them, morphological variation between the ichnofamilies Grallatoridae and Eubrontidae, and the ichnogenus Asianopodus show the same pattern with the Grallator–Anchisauripus–Eubrontes plexus, which is suggested as an ontogenetic or phylogenetic phenomenon. Occurrence of the ichnogenus Minisauripus indicates that the theropod ichnofauna of this quarry has a strong correlation with those of South Korea, Shandong Province, and Sichuan Province. In addition, discovery of the ichnofamily Ornithomimipodidae from this quarry is the second report of this ichnofamily from Asia and extends its distribution. This report adds important information for better interpreting the paleobiology, paleoecology, and paleogeography of the Kitadani Dinosaur Quarry, and it is also important for those of Asia Continent during the Early Cretaceous time.

Land-Ocean Linkage: Pelagic Cherts in Mesozoic Neritic-Terrestrial Sequences in East Asia

Chert clast-bearing epi-continental neritic-terrestrial Jurassic and Cretaceous sequences are sporadically distributed in southwestern Japan. Typical and geological entities are the Torinosu Group and Tetori Group. Radiolarian dating of chert clasts enables us to discuss denudation stages of mid Mesozoic accretionary complexes. Chert clast-dominated conglomerate can be used for identifying marine beds within terrestrial sequences.

Plant Fossils from the Arimine Formation (Oxfordian, Jurassic) of the Tetori Group in Arimine, Toyama Prefecture, Central Japan

Ptilophyllum sp. and Zamites brevipennis are newly described from the middle Oxfordian Arimine Formation in the Arimine area, Toyama Prefecture, Central Japan. These two species characterize the vegetation of the Eurosinian paleophytogeographic province where a climate with dry season(s) prevailed. This finding, as well as the presence of a Kaizara Flora, suggests that Eurosinian-type vegetations continuously flourished during the late Bathonian to Oxfordian on the land of the Tetori Group. We also infer that Tetori-type floras first appeared during the Tithonian in the Tetori Group.

Stratigraphy of the Lower Cretaceous Tetori Group and stratigraphic implication of plant assemblages in the border area between Ishikawa and Fukui Prefectures, central Japan

Stratigraphy of the Lower Cretaceous Tetori Group and stratigraphic implication of plant assemblages in the border area between Ishikawa and Fukui Prefectures, central Japan