Tetori Group Research Articles

O-308 手取層群分布域南東部の石徹白亜層群の礫岩から産出した放散虫化石とその地質学的な意義

O-308 手取層群分布域南東部の石徹白亜層群の礫岩から産出した放散虫化石とその地質学的な意義

"手取層群"の新しい見方―時代論の見直しと細分提案―

"手取層群"の新しい見方―時代論の見直しと細分提案―

REVIEW OF MICROFOSSIL-BEARING CLASTS WITHIN LATE MESOZOIC STRATA IN EAST ASIA: STAGED DENUDATION OF MID-MESOZOIC ACCRETIONARY COMPLEXES

Late Mesozoic neritic-continental strata of East Asia show intercalations of conglomerates including microfossil-bearing clasts. Some clasts are presumed to have originated in mid-Mesozoic accretionary complexes (ACs) of East Asia. Microfossils ( e.g ., radiolaria, conodonts) in these clasts can provide age constraints. Relationships between rock facies and age in sequences of the mid-Mesozoic ACs have been clarified in previous studies; therefore, the rock facies and the age of the clasts offer a clue about denudation history and provenance of the mid-Mesozoic ACs. This study compiles previous studies of microfossil-bearing clasts within the Late Mesozoic in the Outer and Inner Zone of Southwest Japan and in the Gyeongsang Supergroup in the southeastern Korean Peninsula. The compilation, at present, recognizes three denudation stages (Stages A, B, and C) of the mid-Mesozoic accretionary complexes. Stage A (Oxfordian-Hauterivian) is characterized by an initial and narrow denudation. The denudation of the mid-Mesozoic ACs started at some point in this stage, but it was of limited extent. Stage B (Barremian-early Albian) is characterized by wide denudation: the mid-Mesozoic ACs became largely exposed. Afterwards, some younger geologic bodies of the mid-Mesozoic ACs, which were structurally underlying, were exposed and denuded. Stage C (late Albian–) is characterized by denudation of almost all the mid-Mesozoic accretionary complexes. This denudational evolution might be related to some tectonic and igneous events in East Asia, such as the uplift of the Tetori Group in late Hauterivian-early Barremian and the initiation of the granitic magmatic activity in middle Albian.

Late Mesozoic bivalve faunas from the Tetori Group, Japan

The Tetori Group of Japan ranks amongst the more important Upper Mesozoic strata in East Asia, with common animal and plant fossils throughout and is well suited for analyses of the links between environmental changes and the various animal and plant fossil assemblages. Three marine transgressions (i. e., Bathonian–Oxfordian, Tithonian–Berriasian and Hauterivian–Barremian in age) have been recognized in the Tetori Group, based on ammonite index taxa. These pulses are also reflected in bivalve faunas which comprise, 81 species in 65 genera (marine taxa) and 16 species in 13 genera (non-marine taxa). Many of these are considered as endemic species to the Tetori Group. In view of the fact that the occurrence of non-marine taxa was primarily controlled by environmental conditions, these do not constitute chronological indices. The faunal composition of the first marine transgressive phase is similar to that found elsewhere in southeast Asia, while that of the second one resembles both that of southeast Asia and of northeast China and Far East Russia. Assemblages of the third phase are similar to those of Heilongjiang, northeast China. Currents from the equator and high-latitudes explain these similarities.

Black-colored silica-rich veins in the Tetori Group from the southern Ishikawa Prefecture, Japan

Black-colored silica-rich veins in the Tetori Group from the southern Ishikawa Prefecture, Japan

Fauna and flora of Early Cretaceous Tetori Group in Central Japan: The clues to revealing the evolution of Cretaceous terrestrial ecosystem in East Asia

The Early Cretaceous Tetori Group in northern Central Japan was deposited in the eastern margin of the Asian Continent at mid-latitudes. It consists of two depositional stages: DS2 (Berriasian–late Hauterivian; mainly brackish environment with intercalations of marine horizons) and DS3 (Barremian–Aptian; freshwater environments only). Review of their faunal and floral compositions reveals that (1) two vertebrate fossil localities in DS3: Kaseki-kabe (upper part of the Kuwajima Formation) and Kitadani Dinosaur Quarry (Kitadani Formation) are assigned to the Barremian and the Aptian, respectively, and probably coeval to the Jehol Group in the Liaoning, northern China; (2) abundant freshwater bivalves occur in DS3, and the Trigonioides–Plicatounio–Nippononaia (TPN) assemblage is present only in the Kitadani Formation; and (3) stratigraphic change of plant assemblages in DS3 indicates that climatic change (warmer and dryer) occurred around the Barremian–Aptian boundary, which is concordant with the faunal change inferred from the choristodere-bearing assemblage in the Okurodani and Kuwajima formations to the crocodyliform-bearing assemblage in the Kitadani Formation. Vertebrate and invertebrate faunal as well as floral compositions of the Tetori Group are distinct from those of the Jehol Group. Paleoclimatic and/or paleogeographical conditions were probably different between two regions, and thus paleobiogeographical differentiation in East Asia is suggested in the Early Cretaceous.

Radiolarian assemblage and ammonoid age in the Middle Jurassic Kaizara Formation, Kuzuryu Subgroup, Tetori Group distributed in Ono City, Fukui Prefecture, Central Japan

Radiolarian assemblage and ammonoid age in the Middle Jurassic Kaizara Formation, Kuzuryu Subgroup, Tetori Group distributed in Ono City, Fukui Prefecture, Central Japan

Sedimentary environments and study of fossil woods of the Tetori Group in Shokawa, Gifu Prefecture, central Japan

Sedimentary environments and study of fossil woods of the Tetori Group in Shokawa, Gifu Prefecture, central Japan

A new Early Cretaceous tritylodontid (Synapsida, Cynodontia, Mammaliamorpha) from the Kuwajima Formation (Tetori Group) of central Japan

ABSTRACTWe describe tritylodontid remains from the Lower Cretaceous Kuwajima Formation (Tetori Group) in central Japan as representing a new genus, Montirictus kuwajimaensis, gen. et sp. nov. Montirictus is a medium-sized tritylodontid genus characterized by upper cheek teeth having the cusp formula 2-2-2 with subequal cusps, buccal and lingual cusps retaining a crescentic shape with both buccal and lingual ridges anteriorly, and ‘V’-shaped buccolingual cross-sections of two anteroposterior grooves between the three cusp rows. Tentative dating of the Kuwajima Formation to the Barremian–Aptian makes it the stratigraphically youngest representative of a long-lived, globally distributed and abundant mammaliamorph lineage and extends the known geographic range of tritylodontids.http://zoobank.org/urn:lsid:zoobank.org:pub:DE3038A4-6C14-4214-9618-BF9F097A4DD4Citation for this article: Matsuoka, H., N. Kusuhashi, and I. J. Corfe. 2016. A new Early Cretaceous tritylodontid (Synapsida, Cynodontia, Mammaliamorpha) from the Kuwajima Formation (Tetori Group) of central Japan. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1112289.

A bizarre theropod from the Early Cretaceous of Japan highlighting mosaic evolution among coelurosaurians.

Our understanding of coelurosaurian evolution, particularly of bird origins, has been greatly improved, mainly due to numerous recently discovered fossils worldwide. Nearly all these discoveries are referable to the previously known coelurosaurian subgroups. Here, we report a new theropod, Fukuivenator paradoxus, gen. et sp. nov., based on a nearly complete specimen from the Lower Cretaceous Kitadani Formation of the Tetori Group, Fukui, Japan. While Fukuivenator possesses a large number of morphological features unknown in any other theropod, it has a combination of primitive and derived features seen in different theropod subgroups, notably dromaeosaurid dinosaurs. Computed-tomography data indicate that Fukuivenator possesses inner ears whose morphology is intermediate between those of birds and non-avian dinosaurs. Our phylogenetic analysis recovers Fukuivenator as a basally branching maniraptoran theropod, yet is unable to refer it to any known coelurosaurian subgroups. The discovery of Fukuivenator considerably increases the morphological disparity of coelurosaurian dinosaurs and highlights the high levels of homoplasy in coelurosaurian evolution.

New fossil anurans from the Lower Cretaceous Sasayama Group of Hyogo Prefecture, Western Honshu, Japan

We describe two well-preserved and articulated fossil anurans excavated from the Lower Cretaceous Sasayama Group in Hyogo Prefecture, Western Honshu, Japan, as new taxa on the basis of unique combinations of character states. We performed a phylogenetic analysis that included these new taxa, as well as Mesozoic and archaic anurans. This analysis strongly supports the monophyly of each of the two new taxa, both of which are placed in more derived positions than extant leiopelmatids or Liaobatrachus from the Lower Cretaceous in China. Anuran specimens from the Tetori Group of Japan are not assigned to the two new taxa, suggesting that at least three anuran taxa were present in Japan during the Early Cretaceous. These Japanese representatives are not closely related to known fossil anurans from Eastern Eurasia, unlike recently described Cretaceous lizards from these two regions.

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

New specimens of two non-therian (non-tribosphenidan) mammals are described from the Lower Cretaceous Kitadani Formation in the upper part of the Tetori Group, Katsuyama, Fukui Prefecture, Japan. Despite their poor preservation, these specimens represent undescribed species from Japan, suggesting additional mammalian diversity in the Tetori Group. Previously, four mammal taxa had been formally described from this rock unit: a spalacotheriid ‘symmetrodont’, two eobaatarid multituberculates and a eutriconodont mammal. One of the new specimens is a damaged left p4 of a ‘plagiaulacidan’ grade multituberculate assignable to the family Eobaataridae. The Kitadani eobaatarid is a large species distinguished from the two previously described eobaatarids, Tedoribaatar and Hakusanobaatar, which are known from the stratigraphically lower Kuwajima Formation of the Tetori Group, Hakusan, Ishikawa Prefecture, Japan. It also differs from Sinobaatar, Heishanobaatar and Liaobaatar described from the Early Cretaceous of China. Another specimen, a partial right dentary with a faint Meckelian groove, is assigned to a eutriconodontan that is larger than and morphologically distinguishable from the eutriconodont Hakusanodon from the Kuwajima Formation. The Kitadani eutriconodontan is potentially related to the family Triconodontidae. The additional specimens from the Kitadani Formation shed new light on Early Cretaceous mammalian faunal change and dispersal in East Asia.

Ornithischian dinosaur material from the Kuwajima Formation (Tetori Group: Lower Cretaceous) of Ishikawa Prefecture, Japan

The Kumajima Formation (Lower Cretaceous: ?Hauterivian–Barremian) of Ishikawa Prefecture, central Honshu, Japan, has yielded a diverse vertebrate fauna that includes a variety of dinosaur taxa. Here, we describe teeth and cranial elements that are referable to an indeterminate styracosternan iguanodontian, an additional unnamed small ornithischian (represented by an isolated maxilla) that is distinct from Albalophosaurus, and other indeterminate ornithischian remains that may belong to the unnamed taxon, Albalophosaurus or another ‘basal’ ornithischian taxon. Iguanodontian specimens are numerically dominant in the available sample of dinosaur material. The Kuwajima Formation has yielded the most diverse dinosaur fauna from Japan and provides a useful point of comparison with other better-known East Asian dinosaur faunas, such as that of the Chinese Jehol Biota.

Water quality estimated basal on the fossils of Planorbidae (Gastropoda) and Characeae (Charophyceae) from the Kitadani Formation of the Tetori Group in Katsuyama City, Fukui Prefecture

Water quality estimated basal on the fossils of Planorbidae (Gastropoda) and Characeae (Charophyceae) from the Kitadani Formation of the Tetori Group in Katsuyama City, Fukui Prefecture

An assemblage of lizards from the Early Cretaceous of Japan

© Palaeontological Association July 2015. The Early Cretaceous deposits of the Tetori Group of western Japan have yielded a diverse wetland vertebrate fauna including both aquatic and terrestrial components. The latter include several lizards, three of which have been named and described in detail: Kaganaias hakusanensis, a long-bodied aquatic lizard; Kuwajimalla kagaensis, a herbivorous borioteiioid; and Sakurasaurus shokawensis, a relative of the Chinese Jehol genus Yabeinosaurus. Here we describe lizard material from the Shiramine locality representing five or six additional taxa, three of which are named herein: a small lizard represented by two associations, but of unresolved phylogenetic position; a slightly larger lizard with tricuspid teeth that is related to borioteiioids; and a bizarre lizard with bicuspid teeth represented by a single, but morphologically unique, jaw. The three additional lizard morphotypes are unnamed. One has bicuspid teeth but unspecialised jaws. The second has small unicuspid teeth in a dentary bearing a deep coronoid process and resembling the dentary of the enigmatic Late Cretaceous Mongolian Myrmecodaptria microphagosa. The third morphotype is represented by a single fragmentary specimen and has small teeth in a deep jaw. Together, the Kuwajima lizards form a phylogenetically and morphologically diverse assemblage.

Sinamia kukurihime, a New Early Cretaceous Amiiform Fish from Ishikawa, Japan

Abstract. A new species of the genus Sinamia of the family Sinamiidae of the order Amiiformes, S. kukurihime is described on the basis of a hyomandibula and many isolated bones and scales found from the Lower Cretaceous freshwater deposits of the Kuwajima Formation, Itoshiro Subgroup, Tetori Group in Kuwajima, Hakusan City, Ishikawa Prefecture, Japan. The new species is distinguished from other congeners by the forms of the hyomandibular, frontal, dermopterotic, maxilla, gular plate, preopercle, supracleithrum and scales. Among the genus Sinamia, S. kukurihime sp. nov. is considered to be closest to S. liaoningensis. This is the first record of the genus Sinamia from Japan. The presence of a new species of the genus from Japan demonstrates the wide distribution and diversity of the genus during the Cretaceous in East Asia.

Bathonian/Callovian (Middle Jurassic) ammonite biostratigraphy of the Kaizara Formation of the Tetori Group in central Japan

Bathonian/Callovian (Middle Jurassic) ammonite biostratigraphy of the Kaizara Formation of the Tetori Group in central Japan

手取層群の分布域東部（富山・岐阜県境）の層序の再検討と神通層群（新称）の提案

富山-岐阜県境に分布する中生界を手取層群と神通層群（新称）に区分した．そして，手取層群を下位より真川層と有峰層，有峰層に対比される桐谷層に，神通層群を庵谷峠層，猪谷層，白岩川層に岩相層序区分し，層レベルの分布を地質図として示した．手取層群はジュラ紀のアンモナイトを産する海成層が認められるが，その上位に不整合で重なる神通層群は主として陸成層で，化石の産出が乏しく地質時代の解釈が難しかった．神通層群猪谷層の凝灰質砂岩に含まれるジルコンのフィッション・トラック（FT）年代は複数の年代母集団からなり，各試料に含まれる若い年代母集団はアプチアン～アルビアンを示し，猪谷層は白亜紀前期のアプチアン～アルビアン以後に堆積したことが示された．神通層群の猪谷層はFT年代からアプチアン～アルビアン以後が示されたが，白山区の手取層群はアンモナイトによりアプチアン以後を示す地層が認められない．

The first record of a long-snouted choristodere (Reptilia, Diapsida) from the Early Cretaceous of Ishikawa Prefecture, Japan

A longirostrine choristoderan reptile is described from the Early Cretaceous Tetori Group on the basis of an associated specimen from the Kuwajima Formation, Ishikawa Prefecture. This is the first report of Neochoristodera from Japan. However, the brevirostrine Monjurosuchus has already been reported from the same deposit, and the long-necked Shokawa was recovered from the Okurodani Formation, which is a lateral equivalent of the Kuwajima Formation. This new material demonstrates that the three known choristoderan morphotypes (short-necked longirostrine, short-necked brevirostrine and long-necked brevirostrine) were all present in the Early Cretaceous deposits of the Tetori Group. Until now, the Jiufotang Formation of China was the only deposit where all three were known to have co-occurred.

Discovery of latest Jurassic ammonoids from the Ono area of the Kuzuryu district, Fukui Prefecture in Central Japan and a proposal for division of the Tetori Group in this district

Discovery of latest Jurassic ammonoids from the Ono area of the Kuzuryu district, Fukui Prefecture in Central Japan and a proposal for division of the Tetori Group in this district