Tanaka, Y. and Taruno, H., in press: The first cetacean record from the Osaka Group (Middle Pleistocene, Quaternary) in Osaka, Japan. Paleontological Research. doi:10.2517/2018PR016. オンライン公開日2018年07月13日. PDF
A new partial skeleton consisting of a left mandible and five caudal vertebrae, OMNH-QV 282 from the Osaka Group (Middle Pleistocene, about 0.3 million years ago) of Osaka City is reported as the first cetacean record from the Group. The skeleton is identified as Balaenopteridae gen. et sp. indet. based on the combination of mandibular characters, such as having a small mandibular foramen, reflected neck in dorsal view and lack of satellite process of the mandible. OMNH-QV 282 expands diversity for the local fauna, and also adds an evidence of existence for large sized balaenopterids from the poorly known epoch, the Middle Pleistocene.
Tanabe, K., Misaki, A., Ikeda, T., Izukura, M. and Moriya, K., in press: Taxonomic relationships and paleoecological significance of two exceptionally large lower jaws of Late Cretaceous ammonoids from Japan . Paleontological Research. doi:10.2517/2018PR015. オンライン公開日2018年07月09日. PDF
Two exceptionally large cephalopod jaws collected from the Upper Cretaceous marine deposits of the Hidaka area, Hokkaido (Yezo Group), and Awaji Island, Southwest Japan (Izumi Group), respectively, are described. Further, their taxonomic relationships and functional morphologic aspect for feeding are discussed. Based on a comparison to counterparts of modern and extinct cephalopods, they were identified as the lower jaws of ammonoids. Owing to the development of a thick calcareous tip in the large outer chitinous lamella, the lower jaw from the Yezo Group is classified as a rhychaptychus-type known from the Cretaceous Lytoceratina and Phylloceratina. The lower jaw from the Izumi Group lacks a sharply pointed calcareous tip and is characterized by a posteriorly elongated outer chitinous lamella, whose outer surface is sculptured by a median furrow in the anterior portion. These features categorize it as an intermediate-type lower jaw shared by the Cretaceous Desmoceratoidea. As determined from the co-occurring ammonoids and the relationship between the dimensions of in situ lower jaws and conchs for ammonoids previously described, the two lower jaws from the Yezo and Izumi groups were, respectively, thought to belong to large gaudryceratid and pachydiscid specimens, both of which have shell diameters greater than 40 cm. The overall shape and structure of the two lower jaws suggest a scavenging-predatory feeding habit for the gaudryceratid and a passive microphagous habitat for the pachydiscid.
Kitamura, N., in press: Features and paleoecological significance of the shark fauna from the Upper Cretaceous Hinoshima Formation, Himenoura Group, Southwest Japan . Paleontological Research. doi:10.2517/2018PR013. オンライン公開日2018年07月08日. PDF
The shark fauna of the Upper Cretaceous Hinoshima Formation (Santonian: 86.3–83.6 Ma) of the Himenoura Group (Kamiamakusa, Kumamoto Prefecture, Kyushu, Japan) was investigated based on fossil shark teeth found at five localities: Himedo Park, Kugushima, Wadanohana, Higashiura, and Kotorigoe. A detailed geological survey and taxonomic analysis was undertaken, and the habitat, depositional environment, and associated mollusks of each locality were considered in the context of previous studies. Twenty-one species, 15 genera, 11 families, and 6 orders of fossil sharks are recognized from the localities. This assemblage is more diverse than has previously been reported for Japan, and Lamniformes and Hexanchiformes were abundant. Three categories of shark fauna are recognized: a coastal region (Himedo Park; probably a breeding site), the coast to the open sea (Kugushima and Wadanohana), and bottom-dwelling or near-seafloor fauna (Kugushima, Wadanohana, Higashiura, and Kotorigoe). The shark fauna of the Hinoshima Formation is similar to that of the Yezo and Futaba groups, and also fauna from Angola, Australia, and Antarctica. However, based on the composition of taxa, the fauna differs from that of the Upper Cretaceous shark fauna of the Western Interior Seaway and Europe. The Upper Cretaceous shark fauna of Japan, including the Hinoshima Formation, contained active pelagic (Squalicorax and Cretoxyrhina mantelli) and bentho-pelagic (e.g. Notidanodon, Chlamydoselachus, Sphenodus) predators. These taxa probably coexisted, as they occupied different ecological niches. The characteristics of the Late Cretaceous shark fauna in Japan are similar to those of the contemporaneous Southern Hemisphere fauna (e.g. Angola, Australia, and Antarctica). This shows that the characteristic shark fauna (e.g. Notidanodon, Chlamydoselachus, Sphenodus) of the Southern Hemisphere had spread to the middle latitudes of the Northern Hemisphere by the Late Cretaceous.
Aiba, D., in press: A possible phylogenetic relationship of two species of Hyphantoceras (Ammonoidea: Nostoceratidae) in the Cretaceous Yezo Group, northern Japan. Paleontological Research. doi:10.2517/2018PR010. オンライン公開日2018年06月05日. PDF
A possible phylogenetic relationship of two species of Hyphantoceras (Ammonoidea: Nostoceratidae) was proposed, based on the newly found specimens with precise stratigraphic occurrences in the Kotanbetsu and Obira areas, northwestern Hokkaido. Two closely related species, Hyphantoceras transitorium and Hyphantoceras orientale, were recognized in the examined specimens from the Kotanbetsu and Obira areas. Specimens of H. transitorium show the wide intraspecific variation in the whorl shape. The stratigraphic occurrences of two species indicate that they occur successively in the Santonian–lowermost Campanian, without stratigraphic overlapping. The similarity of their shell surface ornamentations and the stratigraphic relationships possibly suggest that Hyphantoceras orientale was derived from Hyphantoceras transitorium. The presumed lineage is likely indigenous to the northwestern Pacific realm in Santonian–earliest Campanian. Hyphantoceras venustum and H. heteromorphum might be out of a lineage of Hyphantoceras transitorium¬–Hyphantoceras orientale, judging from differences of their shell surface ornamentations.
Handa, N., in press: Reassessment of a Pleistocene rhinocerotid (Mammalia, Perissodactyla) from Aira, Kagoshima, southwestern Japan. Paleontological Research. doi:10.2517/2018PR009. オンライン公開日2018年05月21日. PDF
This study describes right upper postcanaine teeth of a single individual of Pleistocene rhinocerotid (Mammalia, Perissodactyla) from the lower to lower middle Pleistocene Kamo Formation of the Kokubu Group in Aira City, Kagoshima Prefecture, southwestern Japan. These teeth are heavily worn and are identified as P2–M2 with missing M1. They are identified as an indeterminate genus and species of the Rhinocerotidae, although they were previously named as Rhinoceros aff. sinensis. These dental fossil specimens and the rhinocerotid footprints from the lower to lower middle Pleistocene of Japan indicate that rhinocerotid certainly existed in Japan during the early to early middle Pleistocene.
Johnson-Ransom, E. D., Popov, E. V., Deméré, T. A. and Shimada, K., in press: The Late Cretaceous chimaeroid fish, Ischyodus bifurcatus Case, 1978 (Chondrichthyes: Holocephali), from California, USA, and its paleobiogeographical significance. Paleontological Research. doi:10.2517/2018PR004. オンライン公開日2018年05月11日. PDF
A nearly complete right mandibular tooth plate of Ischyodus bifurcatus Case (Holocephali: Chimaeroidei) is reported from the Point Loma Formation (upper Campanian) of the Upper Cretaceous Rosario Group in southern California, USA. The individual is estimated to have measured nearly 1 m in total body length. Remains of I. bifurcatus have been reported from marine rocks deposited in epicontinental seas and continental shelf paleoenvironments of temperate latitudes in the Northern Hemisphere. Previous records of the species consist of specimens from Santonian to Maastrichtian strata of the US (Delaware, New Jersey, North Carolina, Georgia, Alabama, Arkansas, Montana, and Wyoming), Sweden, and European Russia. The tooth plate described herein is the first verifiable record of I. bifurcatus from California, and more significantly, represents the only known definite Mesozoic record of Ischyodus from the entire North Pacific region.
Ishida, Y., Fujita, T., Kohtsuka, H., Manabe, M. and Ohara, M., in press: A new example of the trace fossil Asteriacites quinquefolius from Japan and the process of production as revealed by observations of an extant sea star. Paleontological Research. doi:10.2517/2018PR003. オンライン公開日2018年04月19日. PDF
A star-shaped trace fossil here assigned to Asteriacites quinquefolius (Quenstedt) was found in the Miocene Shirahama Formation, Wakayama Prefecture. This is the first report in Japan and stratigraphically youngest record for the ichnospecies. The fossil has five distinct arms and wide striations on both lateral sides of each arm, and the shape is bilaterally symmetrical. To clarify the fossil producing process, we conducted burial experiments of extant asteroids in aquarium and in situ for the first time. Asteroids buried themselves in the substratum using the tube-feet, and when asteroids were covered with thin sand, they escaped slantingly upward onto the sand tilting their body in a bilaterally symmetrical posture. As a result, the remaining trace was very similar to the fossil of A. quinquefolius from the Shirahama Formation. Accordingly, the results suggest the present fossil was formed by the behavior of escaping from thin sand cover by asteroids.
Inose, H., Furuuchi, K., Ito, T., Sashida, K. and Agematsu, S/, in press: Radiolarian fossils from conglomerate layers of the Upper Cretaceous Nakaminato Group exposed along the Pacific coast of Ibaraki Prefecture, central Japan: Staged denudation of the mid-Mesozoic accretionary complexes in the Kanto District. Paleontological Research. doi:10.2517/2017PR026. オンライン公開日2017年12月05日. PDF
The Upper Cretaceous Nakaminato Group, which contains the Chikko, Hiraiso, and Isoai formations in ascending order, crops out along the Pacific coast of Ibaraki Prefecture, central Japan. This group is composed mainly of sandstone, siltstone, and sandstone-siltstone alternations, with intercalated conglomerate layers at several levels. The siltstone of the Hiraiso and Isoai formations has yielded ammonites and inoceramid bivalves indicating a middle Campanian to Maastrichtian age. Some conglomerate layers in the Isoai Formation reach 1 m in thickness and mostly consist of pebbles and cobbles of rhyolite, dacite, chert, siliceous siltstone, siltstone, sandstone, and hornfels. We obtained late Paleozoic to Late Jurassic radiolarians from pebbles of argillaceous rock and chert from four levels of the conglomerate layers within the Isoai Formation. We describe the radiolarians systematically herein. The probable provenance of the radiolarian-bearing pebbles is interpreted as the Ashio and Yamizo terranes, which consist of Late Jurassic to Early Cretaceous accretionary complexes. We propose that there were two denudation stages of the accretionary complexes in the Kanto District, stages α (Barremian–) and β (Campanian–).
Sato, T, Hanai, T., Hayashi, S. and Nishimura, T., in press: A Turonian polycotylid plesiosaur (Reptilia; Sauropterygia) from Obira Town, Hokkaido, and its biostratigraphic and paleoecological significance. Paleontological Research. doi:10.2517/2017PR024. オンライン公開日2017年12月05日. PDF
The Polycotylidae are short-necked plesiosaurs known from theCretaceous in various parts of the world, but only a few occurrences have beendocumented in Japan where elasmosaurid remains are much more common. Anindeterminate polycotylid specimen from the Upper Cretaceous in Obira Town,Hokkaido, is described. Characteristics of the vertebrae and clavicular archsupport its taxonomic affinity. The Turonian occurrence of the specimen indicatesthe continuous presence of the Polycotylidae across the Cenomanian-Turonianboundary in the northwestern Pacific. Macroscopic osteological features of thevertebrae and clavicular arch indicate an advanced stage of ossification, and thereare histological characteristics suggesting slowed growth. The osteoporotic-likecondition implies a high degree of aquatic adaptation.
Tanaka, Y., Furusawa, H. and Barnes, L. G., in press: Fossil herpetocetine baleen whales (Cetacea, Mysticeti, Cetotheriidae) from the lower Pliocene Horokaoshirarika Formation at Numata, Hokkaido, northern Japan. Paleontological Research. doi:10.2517/2017PR025. オンライン公開日2017年12月01日. PDF
Two mandibles of fossil mysticetes from the early Pliocene, upper part of the Horokaoshirarika Formation at Numata Town, Hokkaido, Japan, belong to the archaic, extinct cetotheriid baleen whale, Herpetocetinae, gen. et sp. indet. by having an elongated angular process projecting posteriorly beyond the mandibular condyle. The new materials of the Herpetocetinae represent the northernmost occurrence in the North Pacific.
Maekawa, T., Komatsu, T., Tanaka, G., Williams, M., Stocker, C. P., Okura, M. and Umayahara, A., in press: Missourian (Kasimovian, Late Pennsylvanian) conodonts from limestone boulders, Mizuboradani Valley, Gifu Prefecture, central Japan. Paleontological Research. doi:10.2517/2017PR023. オンライン公開日2017年11月21日. PDF
Two Late Pennsylvanian conodont species, Gondolella sublanceolata Gunnell and Idiognathodus sulciferus Gunnell, were extracted from limestone boulders in the Mizuboradani Valley, Fukuji district, central Japan. These provide the first evidence of Missourian (Kasimovian) cosmopolitan conodonts in the Akiyoshi and Hida Gaien belts, Inner Zone of Japan. The limestone boulders might be derived from the Ichinotani Formation and/or from limestone clasts in conglomerates of the Permian Sorayama Formation that crop out in the Mizuboradani Valley.
Yamashita, D., Kato, H., Onoue, T. and Suzuki, N., in press: Integrated Upper Triassic conodont and radiolarian biostratigraphies of the Panthalassa Ocean. Paleontological Research. doi:10.2517/2017PR020. オンライン公開日2017年10月31日. PDF
The Late Triassic conodont biostratigraphy of two pelagic chert sections (sections N and Q) in the Inuyama area, central Japan, was investigated to calibrate the Triassic radiolarian zonation proposed by Sugiyama in 1997 with the conodont zones and the standard Triassic timescale. Based on the stratigraphic distributions of marker species, six conodont zones were defined: the Paragondolella? tadpole interval Zone, the Quadralella tuvalica interval Zone, the Epigondolella quadrata interval Zone, the E. triangularis interval Zone, the Mockina postera interval Zone, and the M. bidentata Zone. These conodont zones are comparable to the standard Carnian and Norian conodont zones of North America and the Tethys. The Carnian-Norian boundary in the sections studied is tentatively placed between the last occurrence of a Carnian species (Q. tuvalica) and the first occurrences of Norian species (E. quadrata and E. spatulata). The intercalibrated conodont–radiolarian biostratigraphy from the sections we studied accurately calibrates the radiolarian zones in Japan with standard chronostratigraphic stages and substages.
Suzuki, H., in press: Fossil evidence of the Hammerjaw fish, Omosudis sp. (Teleostei, Aulopiformes) from the Middle Miocene Yokoo Formation in Nagano Prefecture, central Japan. Paleontological Research. doi:10.2517/2017PR019. オンライン公開日2017年10月26日. PDF
A fossil palatine of an alepisauroid fish collected from the Middle Miocene Yokoo Formation in Nagano Prefecture, central Japan is described as Omosudis sp. Although the palatine is preserved as a fragment, the palatine teeth arranged in a single row are well-preserved. In fact, the palatine tooth characteristics are adequate as diagnostic at generic level identification. The fossil appears to be assignable to the genus Omosudis belonging to the family Alepisauridae by having the following characteristics: enormously large, posteriorly inclined teeth with each sharply pointed apex, apico-basal striations, a nearly straight to arcuate anterior cutting edge, a wide pulp-cavity surrounded by a thin dentine layer and a fang-like outline due to a basally elongated postapical barb. The Yokoo specimen represents the first reliable fossil record of the genus from the Middle Miocene in Japan and appears to mark the earliest occurrence of this recent genus in the Northwest Pacific region.
Sato, T., Konishi, T., Nishimura, T. and Yoshimura, T., in press: A basal mosasauroid from the Campanian (Upper Cretaceous) of Hokkaido, northern Japan. Paleontological Research. doi:10.2517/2017PR018. オンライン公開日2017年09月13日. PDF
A basal mosasauroid specimen, including a rib and a vertebra from middle to posterior portion of the trunk, is reported from the lower Campanian Inoceramus (Platyceramus) japonicus zone in Obira Town, northern Hokkaido, northern Japan. It is the second occurrence of basal mosasauroids sensu lato in Japan after the halisaurine Phosphorosaurus ponpetelegans, but represents a larger individual than the P. ponpetelegans holotype. The Obira specimen predates the early Maastrichtian P. ponpetelegans by about 10 million years, indicating colonization by basal mosasauroids of the northwestern Pacific by at latest the early Campanian age. While the overall morphology of the Obira specimen agrees well with that of a halisaurine vertebra, the presence of well-developed zygantra (zygosphenes missing postmortem if present) on the vertebra and its inclined condyle uniquely align the specimen with Pannoniasaurus inexpectatus, a Santonian-aged basal mosasauroid from freshwater deposits in Hungary.
Yamada, in press: Plant fossils from the Arimine Formation (Oxfordian, Jurassic) of the Tetori Group in Arimine, Toyama Prefecture, Central Japan. Paleontological Research. doi:10.2517/2017PR017. オンライン公開日2017年08月27日. PDF
Ptilophyllum sp. and Zamites brevipennis are newly described from the middle Oxfordian Arimine Formation in 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.
Jenkins, R. G., Kaim, A., Amano, K., Sakurai, K. and Matsubara, K., in press: A new Miocene whale-fall community dominated by bathymodiolin mussel Adipicola from Hobetsu area, Hokkaido, Japan. Paleontological Research. doi:10.2517/2017PR006. オンライン公開日2017年06月23日. PDF
We report the fourth record of a fossil whale-fall community in Japan. The new material consists of a single whale bone associated mainly by small bathymodiolin mussels, Adipicola sp., found in the Karumai Formation (late middle Miocene–early late Miocene) in the Hobetsu area of Hokkaido, Japan. This association of whale bone and Adipicola sp. and its mode of occurrence resembles the description of some other ancient whale-fall communities dominated by small mussels from the Olympic Peninsula in Washington State (early Oligocene), Shosanbetsu in Hokkaido (early middle Miocene) and Carpineti in northern Italy (middle Miocene) and constitutes an example of a chemosynthesis-based community sustained by whale–fall decay in the Miocene deep sea. The new example extends the Miocene distribution of bathymodiolin dominated whale-fall communities to the northwestern Pacific Ocean.
Wang, Y. and Wang, Y., in press: Globusphyton Wang et al., an Ediacaran macroalga, crept on seafloor in the Yangtze Block, South China. Paleontological Research. doi:10.2517/2017PR005.. オンライン公開日2017年06月21日. PDF
The Ediacaran genus Globusphyton Wang et al., only including one species G. lineare Wang et al., is a eukaryotic macroalga in the Wenghui biota from black shale of the upper Doushantuo Formation (ca. 560–551 Ma) in northeastern Guizhou, South China. It was assigned as one of significant fossils in the assemblage and biozone divisions in the middle-late Ediacaran Period. Morphologically, Globusphyton is composed of several structural components, displaying that it had tissue differentiation to serve various bio-functions. Its prostrate stolon, a long ribbon bundled by unbranching filaments, crept by holdfasts on the seafloor. Its pompon-like thalli, the circular to oval thallus-tuft composed of many filamentous dichotomies, may have served for photosynthesis. The fusiform ribbon-tubers, the caked and expanded segments of the ribbon, may have served to sustain the growth of the thalli and the possible holdfasts. The zigzag-shaped stolon and pompon-like thalli of Globusphyton, in a relatively low-energy environment,were crept on the surface of the muddy sediments and suspended in water column, respectively. When water current occurred occasionally, all or part of its body was probably suspended in the water column to be deformed as a variable pattern.