Tanaka, Y., Ohara, M. and Kimura, T., in press: A fossil dolphin from the Oi Formation, Ichishi Group (late early Miocene) in Japan. Paleontological Research. doi:10.2517/2020PR021. オンライン公開日2020年07月02日. PDF
A narrow dolphin mandible with an elongate mandibular symphysis from the Ichishi Group, Oi Formation (late early Miocene) of Tsu City, Mie Prefecture, Japan is reported. The specimen shows different morphologies from “Eurhinodelphis” minoensis and Ninjadelphis ujiharai, which were reported from late early Miocene sediments of the same region. This new record expands our knowledge of lower Miocene odontocetes from Japan and indicates that at least three odontocetes are represented in the Mizunami and Ichishi Groups.
Muto, S., Okumura, Y. and Mizuhara, T., in press: Late Kungurian conodonts of the pelagic Panthalassa from seamount-capping limestone in Ogama, Kuzuu, Tochigi Prefecture, Japan. Paleontological Research. doi:10.2517/2020PR012. オンライン公開日2020年06月17日. PDF
Biostratigraphy of conodonts is widely used for age assignment of Permian strata. In this paper, we report conodonts that occurred from the limestone of the Nabeyama Formation deposited on a pelagic seamount in the Panthalassa, which is an oceanic realm where Permian conodont data are scarce compared to other oceanic realms. Samples collected from the lower part of the Nabeyama Formation yielded Mesogondolella idahoensis (Youngquist, Hawley and Miller) and Sweetognathus hanzhongensis (Wang), which indicate a late Kungurian age. Previous studies and fusulinids obtained in this study indicate the studied samples belong to the Parafusulina yabei biozone. Therefore, the Parafusulina yabei Zone includes the uppermost Kungurian. Mesogondolella idahoensis and Sweetognathus hanzhongensis are respectively regarded as cool and warm water species. Hence, the distribution of cool and warm water conodont species may have overlapped in the pelagic Panthalassa during the late Kungurian.
Setiyabudi, E., Kurniawan, I., Insani, H. and Takahashi, A., in press: Late Pleistocene fossil record of Cuora amboinensis (Testudines: Geoemydidae) from the Wajak site, East Java, Indonesia, and its paleozoogeographic and archeozoological implications. Paleontological Research. doi:10.2517/2020PR007. オンライン公開日2020年06月15日. PDF
A Late Pleistocene fossil represented by an incomplete right hypoplastron of Cuoraamboinensis was recovered from the Wajak site (ca. ka–29 ka: Late Pleistocene) in East Java, Indonesia. The fossil constitutes the first certain prehistoric record of this species from Java, which implies that the current conspecific population in this island is indigenous to the region rather than artificially introduced from the Southeast Asian continent in historic times. The specimen has four small distinct impact pits on the hypoplastron in dorsal view, which were possibly caused by a pointed stone artifact or a bone tool. The presence of such percussion marks suggests that this turtle was consumed by the Wajak people.
Tokuda, Y AND Ezaki, Y. , in press: Microskeletal structures suggest taxonomic distinction between subgenera of azooxanthellate scleractinian Flabellum. Paleontological Research. doi:10.2517/2019PR021. オンライン公開日2020年06月15日. PDF
Recent molecular analyses have challenged the traditional classification of scleractinian corals at almost all taxonomic levels, suggesting a requirement of new morphological characters for classification. Microskeletal characters have shown great potential to support the classification of the molecular-based clades of the scleractinian corals. Flabellum (Family Flabellidae) is the fifth largest genus and contains two subgenera, F. (Flabellum) and F. (Ulocyathus). The genus is very important in deciphering flabellid evolution, as phylogenetic relationship is still ambiguous in this family. In particular, little is known of the microstructural features of Flabellum species. Here we discuss the microskeletal structures of F. (F.) magnificum and F. (U.) deludens. Rapid accretion deposits (RADs) on the walls of F. (F.) magnificum show dome-shaped strands ca. 50–100 μm wide, which are composed alternatively of microcrystalline and fibrous parts. In contrast, the RADs on the walls of F. (U.) deludens consist of strands (50–100 μm long and 20–30 μm wide) made up of very short fibers (ca. 0.5–5 μm long) or microcrystallines with meniscus structure and dome-shaped fibrous layers. Thickening deposits (TDs) on the walls of both species are characterized by three qualities: (1) layered bundles consisting of fibrous crystals; (2) shingle-like TDs composed of small crystals and microcrystallines; and (3) shingle-like TDs comprised of larger fibers. In particular, in F. (U.) deludens, the TD of the calicular side of the wall is mainly formed of shingle-like TDs. The walls of F. (U.) deludens and F. (F.) magnificum thus differ completely in terms of the RAD (digitated strand and dome-shaped fibrous layers vs. continuous dome-shaped alternation) and TD characteristics. These kinds of microskeletal differences could support the molecular phylogenetic distinction between the F. (U.) spp. cluster and the F. (F.) clusters.
Maekawa, T., Kiyokawa, S., Maeda, H., Tanaka, G., Costa, J. E. F., and Freitas, A. T., in press: First report of early Permian albaillellarian radiolarians from East Timor. Paleontological Research. doi:10.2517/2020PR009. オンライン公開日2020年06月15日. PDF
Two early Permian radiolarians, Pseudoalbaillella postscalprata Ishiga, 1983 and Pseudoalbaillella sakmarensis (Kozur, 1981), are described from a calcareous nodule of the Permian siliciclastic succession distributed in north-central East Timor. The association probably indicates the Sakmarian (early Cisuralian) in age. This is a first report of age-diagnostic Permian radiolarians from East Timor and demonstrates a potential source of well-preserved radiolarians of the Permian siliciclastic succession.
Shigeta, Y., Kumagae, T., Zakharov, Y.D., Popov, A.M., in press: Timing of bellerophontoid (Gastropoda) demise in the Early Triassic of South Primorye, Russian Far East. Paleontological Research. doi:10.2517/2020PR020. オンライン公開日2020年06月14日. PDF
The stratigraphic distribution and modes of occurrence of Early Triassic Bellerophontoidea (Gastropoda) are studied at seven sections in South Primorye, Russian Far East, where depositional environments ranging from nonmarine, via shoreface, to distal basin plain settings are recorded. Warthia zakharovi and Dicellonema abrekensis are abundant in Induan (Griesbachian and Dienerian) fine- to medium-grained, hummocky cross-stratified (HCS) sandstone beds occasionally intercalated with wavy-mudstone layers, whereas they are absent in coarser-grained cross-stratified succession. This observation suggests that bellerophontoids inhabited a lower shoreface environment above the storm wave base and possibly an inner shelf environment as well during this particular stage. Olenekian (Smithian and Spathian) bellerophontoids have not been found in the storm-induced sandstone beds, but W. zakharovi does occur in the lower Smithian sandstone beds of distal turbidites intercalated in the laminated mudstone. This mode of occurrence strongly suggests that W. zakharovi inhabited a deeper environment than lower shoreface, most probably an inner shelf environment, and after death, its shells were transported from their habitat to the basin-floor by sediment gravity flow. Bellerophontoids have not been found in middle Smithian and younger strata in South Primorye, and the timing of this disappearance is synchronous with other areas of the world. Bellerophontoids were distributed over wide-ranging areas from the equator to the high latitudes during Induan time, but they disappeared from the lower latitude areas and the shallower marine environment of middle latitude South Primorye during the early Smithian, before eventually becoming extinct during middle Smithian time. Such a step by step demise strongly implies that the severe global warming and related harmful events that occurred during the Smithian may have had a serious effect on bellerophontoids. This suggests that because the Bellerophontoidea went extinct before the beginning of the late Smithian, the group may have been more sensitive to global warming and related harmful events than other organisms.
Mori H. and Miyata K., in press: Early Plotopteridae specimens (Aves) from the Itanoura and Kakinoura Formations (latest Eocene to early Oligocene), Saikai, Nagasaki Prefecture, western Japan. Paleontological Research. doi; 10.2517/2020PR018. オンライン公開日2020年06月14日. PDF
Plotopterids, commonly known as "penguin-like birds", are wing-propelled diving birds known from the latest Eocene to middle Miocene in the eastern and western Pacific Rim. Here, we describe two new specimens of the family Plotopteridae, a right femur from the Itanoura Formation (latest Eocene to earliest Oligocene), and a distal half of a right tibiotarsus from the Kakinoura Formation (early Oligocene), both at the lower part of the Nishisonogi Group, Saikai City, Nagasaki Prefecture, Kyushu, southwestern Japan. The femur is slightly younger than or potentially as old as the earliest plotopterid known from Japan and the U.S.A. CT scanning revealed that it has a dense cortical bone, justifying its taxonomic assignment to the family Plotopteridae. It resembles the femur of Olympidytes, which is endemic to North America previously, in its femoral neck, well developed trochanter femoris, and straight facies articularis antitrochanterica, but is not assignable to any known genus. The tibiotarsus resembles that of Olympidytes in the presence of a well-developed trochlea catilaginis tibialis, a large embossment lateral to the pons supratendineus, and a deep incisura intercondylaris, and therefore referable to Olympidytes. The possibility of hindlimb-propelled diving in the family Plotopteidae was also discussed. These new specimens suggest the early diversity of the family in Japan was higher than previously thought.
Kodama, S., Takayanagi, H., Yoshii, K., Ha, T.T.N, Asami, R., Abe, O. and Iryu, Y., in press: Carbon and oxygen isotope records of Tridacna squamosa shells from two different latitudes in the Ryukyu Islands. Paleontological Research. doi:10.2517/2020PR003. オンライン公開日2020年02月25日. PDF
We report carbon (δ13C) and oxygen (δ18O) isotope records of two modern giant clam (Tridacna squamosa) shells from two sites (Ishigaki-jima and Okinoerabu-jima) at different latitudes in the Ryukyu Islands, Japan. The δ13C profiles of samples from the inner shell layer on cross-sections along the maximum growth axis display no ontogenetic trends or seasonal variations. This finding suggests that the calcification site is likely to be unaffected by CO2 uptake and release resulting from the metabolic activity of the molluskan host and algal symbionts. The δ18O profiles show distinct seasonal cycles. After accounting for the influence of seawater δ18O, the time-series variations are consistent with variations in sea surface temperature, and the temperature dependency of oxygen isotope fractionation is nearly identical to previously published δ18O–temperature relationships for biogenic and synthetic aragonite. We conclude that δ18O records from pristine fossils of this species will enable accurate paleoenvironmental reconstructions at high temporal resolution.
Parent, H., Bejas, M., Greco, A., in press: Shell area-to-volume ratio in ammonoids. Paleontological Research. doi:10.2517/2019PR013. オンライン公開日2019年06月18日. PDF
The external area-to-volume ratio of the ammonite shell has been held to be related to morphology but never evaluated quantitatively. A dimensionless ratio, the Vogel number, was computed for large samples of Devonian to Cretaceous ammonites with a new method based on the ADA-model. The estimated ratios range from 2.4 to 3.4. The highest values are exhibited by uncoiled serpenticone ammonites, lowering in the sequence serpenticone-oxycone-spherocone. It is shown that the area-to-volume relationships are controlled by the involution (degree of overlapping) and the relative width of whorl section. The typical evolutionary trends serpenticone–spherocone and/or serpenticone–oxycone, broadly documented through the history of the Ammonoidea could have been driven, at least in part, by the lowering of the area-to-volume ratio.
Yabumoto, Y. and Nazarkin, M. V., in press: Clupea hanishinaensis nomen novum, a replacement name for the Miocene clupeid fish Clupea macrocephala Yabumoto and Nazarkin, 2018 from Nagano, Japan. Paleontological Research. doi:10.2517/2019PR011. オンライン公開日2019年05月10日. PDF
Isaji, S. and Okura, M., in press: Microgastropods from the late Carboniferous limestone in Fukuji, Gifu Prefecture, central Japan. Paleontological Research. 10.2517/2019PR010. オンライン公開日2019年04月10日. PDF
This paper describes microgastropod fossils from the Kasimovian (late Carboniferous) limestone floats collected from the Mizuboradani Valley, Fukuji, Okuhida-onsengou, Takayama City, Gifu Prefecture, central Japan. The microgastropod assemblage consists of a diversity of larval and/or early juvenile shells and represents late Palaeozoic cosmopolitan taxa, including Euomphalidae, Pleurotomarioidea, Anomphalidae, Naticopsidae, Trachyspiridae, Goniasmatidae, Orthonematidae, Pseudozygopleuridae, Subulitidae, Meekospiridae and Streptacididae. The microgastropod assemblage bears some resemblances to those from the early Carboniferous of New South Wales, Australia, and those from the latest Permian of Guangxi Province, China.
Handa, N., in press: Reappraisal of a rhinocerotid (Mammalia, Perissodactyla) from the lower Miocene Yotsuyaku Formation, Northeast Japan, with an overview of the early Miocene Japanese rhinocerotids. Paleontological Research. 10.2517/2019PR009. オンライン公開日2019年04月10日. PDF
A fragmentary femur of the Rhinocerotidae (Perissodactyla, Mammalia) from the lower Miocene Yotsuyaku Formation of the Shiratorigawa Group, Ichinohe, Iwate Prefecture, Northeast Japan is redescribed, and the fossil record of Japanese early Miocene rhinocerotids, including footprints, is briefly reviewed. The femur is identified as belonging to an indeterminate species of rhinocerotid, cf. Aceritherini, in having the distal portion of the base of the lesser trochanter situated near the apex of the third trochanter and a less projected third trochanter than in most rhinocerotids. Since ca. 20 Ma, rhinocerotids have inhabited and been widely distributed in Japan, which formed an eastern margin of continental East Asia at that time.