Paleontological Research

The late Palaeogene represents a crucial time in cetacean evolution that witnessed the origin of modern baleen and toothed whales (Neoceti) from their “archaeocete” ancestors. So far, this fundamental transition has been discussed mainly in terms of cranial morphology, whereas descriptions of postcranial material remain rare. Here, we report a small cetacean humerus from the Nichinan Group (lower Oligocene to lower Miocene), Kushima City, Miyazaki Prefecture, southern Kyushu, Japan. Our specimen resembles archaeocete humeri in being proximodistally elongate and in retaining a distinct deltoid ridge, but shares with neocetes the defining feature of an immobilised elbow joint. It resembles most Oligocene odontocetes in its small size and in lacking a notch marking the position of the distal epiphysis, and is furthermore similar to the enigmatic Microzeuglodon in having a transversely compressed shaft. A morphometric analysis based on five linear measurements, however, fails to cluster our specimen with any other known group of cetaceans, indicating that it is not easily referable to either basal mysticetes or odontocetes. Therefore, we here classify it as Neoceti incertae sedis.

This paper records the occurrence of 12 non-marine ostracod species belonging to nine genera from a new intertrappean section located at Khar in Madhya Pradesh, Central India. These are: Frambocythere tumiensis anjarensis, Gomphocythere akalypton, G. paucisulcatus, G. strangulata, Paracypretta jonesi, Stenocypris cylindrica, Zonocypris gujaratensis, Cypridopsis hyperectyphos, Eucypris intervolcanus, E. pelasgicos, Cyclocypris amphibolos and Cypria cyrtonidion. All these are assigned to previously known species from the Upper Cretaceous Lameta Group and Deccan intertrappean beds of central and western Peninsular India. The present ostracod assemblage favours a Late Cretaceous (Maastrichtian) age for the intertrappean beds of Khar and also indicates the existence of a permanent freshwater, lacustrine body during the deposition of these intertrappean beds. The lack of marine fossils in the intertrappean beds of the Narmada rift valley does not attest to any marine incursion along the Narmada rift valley, at least in the latest Cretaceous.

During Ocean Drilling Program Leg 167, Sites 1020/1021 were drilled to assess the paleoceanographic conditions within the northern region of the California Current. Radiolarian records from the upper middle Miocene to Pleistocene were obtained at Sites 1020/1021 cores in order to develop a correlation between Neogene biostratigraphic data and paleomagnetic chronostratigraphy. Of 66 radiolarian events identified during this study, 26 Pleistocene to late Miocene events were directly tied to the paleomagnetic stratigraphy, and 40 middle to late Miocene events were correlated with that result by second-order methods based on the diatom biostratigraphy. The updated ages of radiolarian bioevents were estimated based on the geologic time scale of Ogg ( 2012 ). Of these events, 12 bioevents that define low-latitude tropical radiolarian zones were either missing at Sites 1020/1021, or proved to have different ranges from those in the tropics. Using selected bioevents of the temperate and subarctic species, the studied sequences of Sites 1020/1021 were divided into fifteen radiolarian zones/subzones from the Eucyrtidium inflatum Zone to Botryostrobus aquilonaris Zone. Six new subzones were described: Hexacontium parviakitaense, Lamprocyclas hannai, Lithelius klingi, Dictyophimus splendens, Cycladophora cabrilloensis, and Collosphaera reynoldsi subzones. The Cycladophora funakawai Zone was proposed for the subarctic Northwest Pacific.

A new species of heteromorph ammonoid Eubostrychoceras valdelaxum sp. nov. is described from the Platyceramus japonicus Zone (the lowermost Campanian) of the Haboro and Mikasa areas in Hokkaido, northern Japan. The most notable characteristic of E. valdelaxum sp. nov. is its extremely longitudinally elongated helical whorls. The new species is clearly distinguished from other species by this characteristic. The shell ornamentation and whorl expansion rate of the new species resemble most closely those of E. japonicum. Considering the stratigraphic relationships, it is the most reasonable conclusion that E. valdelaxum sp. nov. evolved from E. japonicum. The variation of body chamber size in E. valdelaxum sp. nov. might be dimorphism.

A middle Permian (Wordian) brachiopod fauna, consisting of 19 species in 18 genera, is described from the lower part of the Kamiyasse Formation in Matsukawa, South Kitakami Belt, northeastern Japan. The Matsukawa fauna is a mixed Boreal—Tethyan brachiopod fauna that shows strong affinities with the middle Permian (Wordian—Capitanian) brachiopod faunas of central Japan (Hida Gaien Belt), eastern Russia (South Primorye), northeastern China (Heilongjiang), northern China (Inner Mongolia) and northwestern China (Xinjiang). The palaeobiogeographical data suggest that Proto-Japan, including South Kitakami, was part of a continental shelf along the northern and eastern margins of North China, located in the mid-latitudes of the Northern Hemisphere during the middle Permian (Wordian).

Preservations illustrating insect reproductive behaviors are much rarer in compression fossils than in amber. We discovered a copulating compression fossil of the sciarid flies from the Pleistocene Shiobara Group, Tochigi Prefecture, Japan, which is briefly described herein. The specimen represents one of the rare examples of a compression fossil showing mating dipteran insects. This finding implies that the small bodies of sciarid flies which readily fall onto the water surface may have contributed to the preservation of our copulating fossil. Moreover, the depositional environment of the paleo-Shiobara Lake was the main factor that served to preserve this specimen.

A new pectinid species, Swiftopecten djoserus sp. nov. is described from the Pliocene Zukawa Formation in Takaoka City, Toyama Prefecture in Central Honshu. This species can be distinguished from S. swiftii, the type species of the genus, by its smaller size, the fewer fine radial riblets on both valves, the wider umbonal angle and the more uneven ledges. Swiftopecten djoserus sp. nov. is an extinct species of the Omma-Manganji fauna that occurred locally in the central part of the Sea of Japan borderland during the latest Pliocene.

Eight specimens of Sphenodus have been collected from the Upper Cretaceous, Coniacian of Nakagawa Town in Hokkaido, northern Japan. They are referred to as S. cf. lundgreni and Sphenodus spp. 1 and 2, and described in detail. Nearly complete specimens of Sphenodus were previously unknown from the Cretaceous in the Pacific region, and the Nakagawa specimens are the first to exhibit distinct root morphologies, which allow comparison at the species level. A review of the occurrences of this genus reveals that their distribution concentrates in the mid- to high palaeolatitude regions. This distributional pattern of Sphenodus may represent its preference for colder water and possibly explains the extinction of this genus across the Paleocene—Eocene boundary, when the thermal maximum began.

A new genus of the Corythoecidae (Albaillellaria, Radiolaria) was recovered from the Changhsingian (uppermost Permian) Dalong Formation in Guizhou Province, South China. Qiania Ito and Feng, gen. nov., containing Q. foremanae Ito and Feng, gen. et sp. nov. and Q. uncinata (Rudenko and Panasenko), is characterized by a conical shell consisting of an apical portion and an inflated region with a lateral foramen on the ventral side. The Corythoecidae were thought to range from the Late Devonian to Guadalupian (middle Permian). Therefore, this new find suggests the presence of this family until the latest Permian. Compilation of previous occurrences of corythoecids, in addition to those of Qiania, showed that most corythoecids including Qiania occurred in phosphate-rich facies, and that Qiania occurred in deeper facies than other corythoecids.

We reinvestigated the standard calcareous nannofossil and diatom biostratigraphy zonations from Deep Sea Drilling Project (DSDP) Leg 41 Holes 366 and 369A in the eastern equatorial Atlantic Ocean in order to determine the geologic ages for the low-latitude diatom zonation. Applying the ages of nannofossil zonations to diatom ones, the ages of several diatom bioevents (first occurrence, FO) which determine the biozones of DSDP Holes 366 and 369A are evaluated as follows; FOs of Baxteriopsis brunii (ca. 38.1 Ma), Coscinodiscus excavatus (ca. 33.6 Ma), Cestodiscus reticulatus (ca. 32.9 Ma), Rocella vigilans (ca. 29.8 Ma), Rossiella symmetrica (ca. 29.5 Ma) and Bogorovia veniamini (ca. 28.3 Ma). These ages may be applicable not only for these holes but also for biostratigraphic studies of other holes which contain Paleogene diatoms. Moreover, this paper describes the taxonomy and stratigraphic ranges of marine diatom Chaetoceros resting spores from DSDP Holes 366 and 369A, including two new morpho-species (Vallodiscus truncatuhis Suto sp. nov. and Xanthioisthmus fortii Suto sp. nov.) and its allied species with synonymy lists, light microscopic observations and several key references for each taxon. As the results of counting of each diatom taxon, it was clear that the sedimentation rate and Chaetoceros resting spore abundances and diversities changed abruptly in the earliest Oligocene (ca. 32 Ma). During the separation of the South American and African continents from the Late Cretaceous to earliest Oligocene, a passage arose that acted for the transfer of Antarctic Bottom Water and modulated the bottom current velocities. The southward bottom water and the passage influenced the sedimentation rate and upwelling of nutrient-rich deeper waters stimulated marine productivity and ecology of Chaetoceros across the late Eocene to early Oligocene.