Volumes & issues:
20, 4(2016); http://dx.doi.org/10.2517/2015PR037View Description Hide DescriptionAbstract.
Dental fossils of an indeterminate small cervoid (Ruminantia, Artiodactyla, Mammalia) from the lower Miocene Koura Formation of southwestern Japan are described. The examined specimens of Cervoidea fam., gen. et sp. indet. consist of selenodont lower molars with plesiomorphic characteristics of early cervoids: a strong external postprotocristid (or Palaeomeryx-fold), a deep groove on the lingual wall of the internal postmetacristid, and opening posterior cristids between the postentocristid and the posthypocristid. The lower molars are similar in shape and size with those of Miocene Cervidae rather than Moschidae or Palaeomerycidae because the present specimens are comparable to those of Dicrocerus tokunagai, which is one of the lower/ middle Miocene cervids from northeastern Japan, and D. grangeri from the middle Miocene of China. The lower Miocene Nakamura Formation (ca. 19 Ma) of central Japan also yielded a small cervoid species sharing the lower molar characteristics with Cervoidea fam., gen. et sp. indet. from the Koura Formation, suggesting a faunal or biostratigraphical correlation between the two formations.
Osmium Plasma Coating for Observation of Microfossils, Using Optical and Scanning Electron Microscopes20, 4(2016); http://dx.doi.org/10.2517/2016PR002View Description Hide DescriptionAbstract.
A scanning electron microscope (SEM) is a very common instrument to observe fossil specimens. Although a low-vacuum SEM is now getting to be a common tool, still a conductive coating is required for observation of specimens at higher magnification. For SEM images of nonconductive fossil specimens, the specimens are usually coated with metals such as gold and platinum. The metal sputter coating method has a problem that the coating reduces the transparency of the fossil specimens when observed under a transmitted optical microscope. Therefore, the metal coating may not be suitable for observation of types in museum research collections. We applied an osmium plasma coating to the SEM preparation of microfossil specimens and found that the osmium coating neither shades transmitted light through the specimens nor masks the internal structures of the specimens. Also this method allowed us to observe specimens at high magnification. The osmium coating has an advantage over the metal sputter coating since it enables one to observe specimens using both SEM and optical microscopes.
LA-ICP-MS Zircon U—Pb Dating of Acidic Tuff from the Eocene Akasaki Formation, Amakusa, Kumamoto Prefecture, Western Kyushu, Japan: Implications for the Age of the Land Mammal Fauna in Japan20, 4(2016); http://dx.doi.org/10.2517/2016PR001View Description Hide DescriptionAbstract.
We obtained zircon U—Pb ages using LA-ICP-MS for an acidic tuff bed in the upper part of the Akasaki Formation, a basal unit of the Eocene sequence in the Amakusa area, Kumamoto Prefecture, Japan. The U—Pb age of 49.1±0.4 Ma (95% confidence interval) suggests a late early Eocene age. Our result is important for biochronological assessment of the land mammal fauna of the Akasaki Formation. The new age date supports the correlation of the Akasaki mammal fauna with the Bridgerian North American Land Mammal Age.
20, 4(2016); http://dx.doi.org/10.2517/2016PR022View Description Hide DescriptionAbstract.
One of the commonest explanations for the evolutionary radiation of animals during the Cambrian and Ordovician periods (about 541 to 443 million years ago) is the predation hypothesis. According to this widely cited but untested idea, the first rise of predatory animals would have accelerated evolution, and so diversification, by increasing natural selection on preys and starting predator-prey coevolutionary arms races. This predation-diversification hypothesis is here tested for the first time for the Cambrian—Ordovician radiation, by comparing the pace of origination of marine invertebrates and the dynamics of the predator ratio in fossil communities, at the local scale and genus level, focusing on the open shelf habitat (reefs excluded). Overall, origination rates decreased whereas the median predator ratio first increased up to a maximum at the middle—late Cambrian and then decreased more or less gradually during the Ordovician. Time-series analysis, using data differencing and detrending, shows that there is no positive correlation between origination rate and synchronic predator ratio over the Cambrian and Ordovician. Thus, the results do not provide evidence of any acceleration of origination rate driven by the rise of predation. Predatory animals might have contributed to the start of the Cambrian—Ordovician radiation by promoting defensive exoskeletons and infaunal lifestyles, but the results suggest they did not facilitate diversification in any other way.
Middle and Late Campanian (Late Cretaceous) Ammonoids from the Urakawa Area, Hokkaido, Northern Japan20, 4(2016); http://dx.doi.org/10.2517/2016PR004View Description Hide DescriptionAbstract.
Twelve species of middle and late Campanian (Late Cretaceous) ammonoids, of which one is a newly described species, are reported from the Chinomigawa Formation of the Yezo Group in the Urakawa area, southern central Hokkaido, northern Japan. Furthermore, two ammonoid biozones, the Metaplacenticeras subtilistriatum and Baculites subanceps in ascending order, are recognized. Zircon radiometric ages reveal that the ages of tuffs immediately below the B. subanceps Zone are 75.1±0.9 Ma and 76.0±1.3 Ma respectively, which infer an early late Campanian age. Therefore, the Metaplacenticeras subtilistriatum and Baculites subanceps zones correlate with the upper middle Campanian and lower upper Campanian, respectively. The latter zone is probably a correlative of the lower part of the Didymoceras sp. Zone of the Izumi Group in Southwest Japan because of the discovery of the herein newly described species, Didymoceras hidakense Shigeta sp. nov. Since Didymoceras and Baculites subanceps flourished in other regions during late middle Campanian time, their occurrence in the Urakawa area suggests that they extended their geographic distribution from other areas to the Northwest Pacific region in early late Campanian time.
A Kungurian (early Permian) Brachiopod Fauna from Ogama, Kuzu Area, Central Japan, and Its Palaeobiogeographical Affinity with the Wolfcampian—Leonardian (early Permian) Brachiopod Fauna of West Texas, USA20, 4(2016); http://dx.doi.org/10.2517/2016PR012View Description Hide DescriptionAbstract.
This paper describes a Kungurian (early Permian) brachiopod fauna consisting of 16 species in 16 genera from the lower part of the Nabeyama Formation of Ogama in the Kuzu area, Ashio Mountains (Mino Belt), central Japan. The fauna includes a new species, Acritosia ogamensis. The Ogama fauna is a tropical Panthalassan fauna showing strong affinity with the Wolfcampian—Leonardian (early Permian) fauna of West Texas, USA.
Nipponomaria, a New Pleurotomarioidean Gastropod Genus (Mollusca) from the Permian Akasaka Limestone, Central Japan20, 4(2016); http://dx.doi.org/10.2517/2016PR023View Description Hide DescriptionAbstract.
Pleurotomaria yokoyamai Hayasaka is a remarkably large gastropod commonly found in the middle Permian allochthonous Akasaka Limestone of central Japan. Its supraspecific systematics have however been unsettled. Examination of a museum collection and newly obtained material reveal previously unreported shell characteristics such as the presence of a long labral slit in the outer lip and a slit-like umbilicus surrounded by an accretionally growing callus pad. On the basis of these and previously known shell characters, a new genus Nipponomaria is proposed. We include Pleurotomaria? anatolica Enderle from the Permian anthracolithic limestone of northwestern Turkey as a member of this new genus.
Morphologic Variation and Microspheric Forms of Parafusulina japonica from Tamanouchi, Itsukaichi-Ome Area, West Tokyo, Japan20, 4(2016); http://dx.doi.org/10.2517/2016PR013View Description Hide DescriptionAbstract.
Specimens of Parafusulina japonica (Gümbel), middle Permian (late Wordian) Fusulinoidea from a small, exotic limestone block within the Middle Jurassic Kamiyozawa Formation exposed at Tamanouchi, west Tokyo, Japan, show considerable morphologic variation and include microspheric forms. The megalospheric specimens vary greatly in the shape and size of their tests, expansion of their tests, and in the shape and size of their proloculi. Two microspheric specimens are about twice the size of the megalospheric specimens and show early whorls to be schubertellid-like. The presence or absence of an initial one or two endothyroid whorl is not established. The shape of septal folds seems distinctive as they have slightly wider, flattened or slightly rounded dome-shaped tops both in megalospheric and microspheric forms. Cuniculi are absent in early whorls and quite poorly developed in later whorls where they are low inconspicuous features, suggesting a relatively early evolutionary stage in the Parafusulina lineage. The features of the megalospheric specimens have led some authors to place this species in the genus Parafusulina (Skinnerella) or even as a separate genus, Skinnerella. However, the microspheric specimens are much more typical of the genus Parafusulina (Parafusulina), and so P. japonica will be placed in the unsubdivided genus Parafusulina.
20, 3(2016); http://dx.doi.org/10.2517/2016PR007View Description Hide DescriptionAbstract.
The apparatuses of Triassic ellisonid conodonts: Cornudina breviramulis, Hadrodontina aequabilis, and Staeschegnathus perrii gen. et sp. nov. from the Taho Formation in Higashiuwa-gun, Ehime Prefecture, Southwest Japan and Furnishius triserratus from the Iwai Formation in Nishitama-gun, Tokyo were reconstructed on the basis of the multielement structure of natural assemblages previously reported. Ellisonia triassica was remarked on this occasion. These species well agree with the general septimembrate apparatus structure containing 15 elements: angulate or pastinate P1, angulate P2, breviform digyrate M, alate S0, extensiform digyrate S1 and S2, and bipennate S3 and S4 elements. Having compared the morphologic features of apparatus elements of the Ellisonidae, I propose herein the new subfamily Hadrodontinae within it. Among the Ellisonidae and other taxa of the Prioniodinina, a phylogenetic relationship is recognized only between E. triassica and Upper Devonian Hibbardella angulata. Other species of the Ellisonidae are more closely related to ozarkodinides with “ozarkodiniform” angulate P1 element than any previously reported prioniodininids with “oulodiniform” extensiform digyrate and carminate P1 elements.
20, 3(2016); http://dx.doi.org/10.2517/2015PR030View Description Hide DescriptionAbstract.
Radiolarian assemblages in 69 surface sediment samples from the Japan Sea were moderately diversified, consisting of about 100 taxa in total, although only a few species accounted for a large proportion of most assemblages. First, the assemblages were often dominated by deep-dwelling species: Cycladophora davisiana, Actinomma leptodermum, A. boreale, A. langii, and adult forms of Larcopyle buetschlii. These species were restricted to great depths and were characteristic of the cold, oxygen-rich deep water that fills deep basins of this marginal sea, the so-called Japan Sea Proper Water. Second, although the observed Japan Sea assemblages included some subtropical elements, such as the Dictyocoryne and Euchitonia groups, Didymocyrtis tetrathalamus and the Tetrapyle octacantha group, many of the major temperate and subarctic elements of the North Pacific were essentially excluded. The semi-enclosed topography of the Japan Sea is most likely responsible for the dominance of certain subtropical surface dwellers as well as for the near-absence of transitional and cool water species from corresponding latitudes of the North Pacific. Q-mode cluster analyses of the relative abundance data of the radiolarian species distinguished three faunal provinces that reflect the modern surface water circulation and the distributions of the upper water masses, including the Tsushima warm current and the Liman cold current. These results suggest that the radiolarian assemblages are strongly related to the present hydrography of the Japan Sea and can therefore be used as environmental proxies in this region.