Paleontological Research

The Ichinotani Formation distributed in the Fukuji area, Hida Marginal Terrane, central Japan, consists of fossiliferous bedded limestone intercalating reddish mudstone and sharpstone conglomerate with a continental margin affinity. The lower part of the formation in the studied area is subdivided into five fusuline zones from lower to upper, Eostaffella kanmerai, Pseudostaffella antiqua, Pseudostaffella kanumai, Profusulinella fukujiensis, and Profusulinella dagmarae. These five zones are probably correlated to the Visean/Serpukhovian (Venevian/Tarusian), middle part of the Bashkirian (Akavasian), middle to upper part of the Bashkirian (Askynbashian to Tashatinian), upper part of the Bashkirian (Tashatinian to Asatausian), and uppermost Bashkirian (Asatausian), respectively, of the stratotypes of the Russian Platform and the South Urals based on the biostratigraphy, faunal composition and correlation of foraminifers. There are remarkable faunal transitions between the Eostaffella kanmerai and Pseudostaffella antiqua zones. Almost coeval Pseudostaffella–Profusulinella assemblages are recognized between the upper part of the Lower Member and the lower part of the Middle Member in the type section of the Ichinotani Formation. Thirty-three species of foraminifers are paleontologically noted and compared to those mainly of the type materials and the taxa to have been described from the Ichinotani Formation.

The turbinid gastropod species Turbo (Lunella) ozawai Otuka, 1938 was described based on two opercula from the lower to middle Miocene Korematsu Formation in Southwest Japan. This inadequate proposal of the new species without the shell character information has confused subsequent taxonomic and faunal studies on the early to middle Miocene species of Turbo in Japan. For the first time, we clarify the shell characters of T. (M.) ozawai based on the type series and newly obtained materials from the Korematsu Formation in the Shobara area, Hiroshima Prefecture, and the Yoshino Formation in the Tsuyama area, Okayama Prefecture, Southwest Japan. The clarification of the shell and opercular characters of T. (M.) ozawai has enabled a taxonomic revision of the previously described four nominal species from early to middle Miocene species of Turbo (Marmarostoma) from the Honshu Arc of the Japanese Islands. Consequently, these four species are reclassified into two species, T. (M.) ozawai and T. (M.) tochiyensis Kanno, 1958 ; T. (M.) parvuloides Nomura, 1940 and T. (M.) minoensis Itoigawa, 1960 are junior synonyms of T. (M.) ozawai and T. (M.) tochiyensis, respectively. Both species are rare examples of mollusks that thrived along the Honshu Arc throughout the Miocene Climatic Optimum (∼16.9 to 14.7 Ma). The species richness of Turbo (Marmarostoma) is similar to that of the modern species in the warm water region of the Japanese Islands.

The fossil record of brittle stars, one of the five extant classes of echinoderms, is still rather poorly known. In particular for the Triassic Period, occurrences published to date are strongly biased toward Europe, with only two exhaustively described taxa recorded from the East Asian part of the Tethys Ocean. Here, we record new ophiuroids from the Carnian (Upper Triassic) of the Me area in Ninh Binh Province, Vietnam. The fossils comprise articulated disks and arm fragments preserved as external molds, all original calcite dissolved. We introduce a new genus and species, Triadoleucella meensis, for these specimens that represent the oldest known member of the order Ophioleucida. The ophiuroids were found in mudstones deposited in outer shelf environments below storm wave base. The intact articulation, combined with random orientation and intense fragmentation of individuals suggest effective burial by downslope mudflow prior to or soon after death.

The Moscovian part of the Ichinotani Formation is subdivided into six fusuline zones from lower to upper, Fusulinella kamitakarensis, Fusulina? sp., Fusulinella hanzawai–Fusulina kamensis, Fusulinella rhomboidalis–Protriticites ovatus, Beedeina lanceolata, and Fusulinella rhomboidalis–Fusulinella soligalichi. The strata underlying the first zone, previously assigned to the Moscovian, are reassigned to the upper part of the Bashkirian. Age-diagnostic species are scarce in the possibly Kashirian F. kamitakarensis Zone and are absent in the F.? sp. Zone. The third to the sixth zones are correlated to the Podolskian, Myachkovian, Podolskian, and Myachkovian of the stratotypes in the Russian Platform, respectively. The fourth zone is inferred to be fault bounded with the fifth zone. The sixth zone is overlain by the lower part of the Kasimovian Protriticites variabilis Zone. Twenty species of fusulines and five species of non-fusuline foraminifers are described. Newly proposed herein are Pseudojanischewskina titanica, Bradyinelloides paranautiliformis, and Fusulinella igoi.

The origin and early dispersion of crown groups (e.g. Cervidae and Bovidae) in pecorans are traced back to the late Oligocene or early Miocene in Eurasia. The fossil pecorans from the lower Miocene of Japan are highly fragmentary but form evidence of a zoogeographic connection between Japan and the Eurasian continent during this period. In this study, we describe dental fossils (seven specimens) from five Burdigalian formations (Nakamura Fm. ∼18.5 Ma; Hiramaki Fm. ∼18 Ma; Misawa Fm. and Kitatage/Asakawa Fm. ∼17 Ma; Kunimi Fm. ∼16 Ma), and as a result of taxonomic revision we recognize four species, including a basal species of Cervidae, Dicrocerus? tokunagai, cf. Palaeomeryx minoensis, and Amphimoschus sp. These species have the basic occlusal patterns of cheek teeth inherited from primitive pecorans (e.g. Amphitragulus), but each species displays advanced characteristics, such as full selenodonty, a weak/no external postprotocristid, and a bicuspidate third lobe of m3 (Amphimoschus). The early group of crown pecorans composed of basal cervids (Lagomerycinae or Procervulinae), Palaeomeryx s.l., and Amphimoschus, had dispersed widely in Europe (early Orleanian or MN3) and East Asia (Shanwangian), including Japan. Our findings on the Japanese fossil records demonstrate that the dispersion of a basal cervid and palaeomerycid between Japan and the Eurasian continent had been completed before 18 Ma. Further studies with additional material would reveal detailed taxonomic relationships and evolutionary process of the Japanese pecorans in the Burdigalian.

A specimen belonging to the genus Polistes (Vespidae: Polistinae) is described from the Chibanian (Middle Pleistocene) Shiobara Group, Tochigi Prefecture, Japan. The morphology of the forewing and first gastral tergum indicated a more accurate assignment of Polistes sp. This specimen is the first fossil of a paper wasp to be identified in Japan.

This study investigated the relationship between the distribution of modern ostracod biofacies and environmental factors in Lützow–Holm Bay, off Cape Darnley, and off Totten Glacier in East Antarctica. We collected study samples from water depths of 219 to 987 m by the 61st Japanese Antarctic Research Expedition. Nineteen species belonging to 13 genera and 47 species belonging to 31 genera of ostracods were found in three samples from Lützow–Holm Bay and ten samples from off Totten Glacier, respectively. We found no ostracods in the samples off Cape Darnley. Q-mode cluster analysis reveals four ostracod biofacies (A to D). Antarctiloxoconcha frigida ( Neale, 1967 ) and Australicythere polylyca ( Müller, 1908 ) were common under the influence of cold water in the upper bathyal zone (biofacies A to C). The genus Krithe was the most abundant taxon in biofacies D with low dissolved oxygen and high-water temperature (0.38°C, 34.66, and 5.0 ml/L, respectively), indicating the presence of warm deep seawater, i.e., modified Circumpolar Deep Water. Thus, we have checked the relationships between the ostracod assemblages and the environmental parameters analyzed in Lützow–Holm Bay and off Totten Glacier, and so strengthened the previous ostracod and environmental data.

Microporina articulata notoensis Sakakura, 1936 , from the Nanao Calcareous Sandstone (Middle Miocene) was restudied and raised to species rank, mainly based on the orifice morphology. Sakakura interpreted small depressions along lateral sides of the cryptocyst as additional opesiules, but it is not clear whether they function as opesiules or not, based on the SEM image. This and other Neogene to Recent Microporina species in Japan are compared, and one more species, Microporina iwayaensis sp. nov. is erected.

The Paleozoic Era experienced 4 major mass extinctions; i.e., end-Ordovician, Late Devonian, end-Guadalupian, and end-Permian episodes. As a cause of significant biodiversity decline, non-biological environmental change on global scale was inevitable; nonetheless, popular claims of bolide impact and/or large igneous province (LIP) with too many ad-hoc assumptions have not yet been accepted as common/universal explanations for the Paleozoic extinctions. Recent research on extinction causes evolved through two stages; i.e., the heyday of the bolide impact scenario in the 1980s, and the overtaking by a LIP-mantle plume scenario in the 1990–2000s. Lately, we may sense a return trend to extraterrestrial causes since the late 2000s, which is not a simple revival of the old bolide-impact model but a new proposal for a cosmoclimatological scenario relevant to extra-solar processes; i.e., supernovae explosions and relevant migration of dark clouds over the Solar System. This short article reviews the current status of extinction-related research, which emphasizes two key issues; i.e., the categorization of extinction causes and new perspectives on non-bolide extraterrestrial causes. The categorizing of extinction causes at four distinct levels is effective in separating “global triggers” on the Earth's surface from more essential “ultimate cases” within the Earth and/or on outside of the planet. Causes of extinction can be grouped into four distinct categories in a hierarchy, from small to large scale: i.e., Category 1 – direct kill mechanism for each local biota, Category 2 – background change in global environment, Category 3 – major geological phenomenon on the planet's surface, and Category 4 – ultimate cause from the interior and exterior of the planet. Recent advances in He isotope analysis for extinction-related sedimentary records suggest extraterrestrial causes, not of bolide impact but of the encounter with a dark cloud (nebula). Emerging new perspectives of cosmoclimatology leads to an alternative extinction scenario; e.g. 1) increased flux of galactic cosmic radiation (GCR) with extensive cloud cover and 2) passage of a dark cloud (nebula) enriched with micro-dusts (IDPs) enveloping the Solar System. Both meteoric cloud coverage and IDP-screen can induce lowering/shutdown of solar irradiance, which may drive global cooling and sea-level drop associated with biodiversity decline. The past star-burst events detected in the Milky Way Galaxy apparently coincide in timing with the cooling episodes associated with major extinctions of the Paleozoic, i.e., at the end-Ordovician, Late Devonian, and Late Permian. Given such astronomical processes associated with global cooling in the past, much older global freezing episodes, i.e., Proterozoic snowball Earth events developed under high atmospheric CO2 levels, can be likewise explained. The study of mass extinctions on the Earth is entering a new stage under new astrobiological perspectives.