Hiromichi Hirano

Two new extinct basal phocoenids (Cetacea, Odontoceti, Delphinoidea), from the upper Miocene Koetoi Formation of Japan and their phylogenetic significance

ABSTRACT Two new extinct porpoises—Archaeophocaena teshioensis, gen. et sp. nov., and Miophocaena nishinoi, gen. et sp. nov.—are described from the upper Miocene Koetoi Formation (5.5-6.4 Ma) of Hokkaido, Northern Japan. The holotype of the former is composed of a partial skull, whereas the holotype of the latter is composed of a partial skull, right periotic, right stylohyoid, and pelvis. Both species are assigned to Phocoenidae on the basis of a unique combination of phocoenid characters: presences of frontal bosses, nasal protuberances, premaxillary eminences, and fossae for the inferior vestibule. However, they do not have dorsally developed preorbital sinus fossae or high premaxillary eminences, unlike derived phocoenids. Furthermore, their premaxillae contact the nasals (or the right premaxilla alone contacts the right nasal), unlike all other known phocoenids except Pterophocaena. A comprehensive morphological cladistic analysis indicates that the two new extinct species are the second-most basal phocoenids next to Pterophocaena and that Phocoenidae is the sister group of Delphinidae. The cranial morphology of the two new extinct species is intermediate in form between that of phocoenids and delphinids, supporting the hypothesis of a sister relationship for the two groups. Thus, these new species fill not only the morphological gap between Phocoenidae and other families of Delphinoidea but also a temporal gap in the fossil record of phocoenids in the western North Pacific.

A new basal porpoise, Pterophocaena nishinoi (Cetacea, Odontoceti, Delphinoidea), from the upper Miocene of Japan and its phylogenetic relationships

ABSTRACT Pterophocaena nishinoi, gen. et sp. nov. (Phocoenidae), from the upper Miocene Wakkanai Formation (9.2–9.3 Ma) in Hokkaido, northern Japan, is described. This is the oldest fossil phocoenid in the western North Pacific, thus extending the fossil record of Phocoenidae an additional approximately 4 million years in the region compared with the previous record. The holotype, composed of a partial skull, with right periotic and tympanic bulla and a postcranial skeleton, has the following apomorphic characters: absence of the premaxillary eminence; posterior half of the hamular process of the pterygoids not separated by palatines; prominent dorsolaterally projecting premaxilla in the facial area; supraorbital process of the maxilla steeply sloping ventrolaterally; posteriorly protruding temporal crest; anteroventrally narrowed and inverted teardrop-shaped temporal fossa; and several short ridges on the tympanosquamosal recess of the squamosal. A comprehensive cladistic analysis (66 ingroup taxa and 278 morphological characters) indicates that Pterophocaena is the most basal phocoenid yet discovered, and that Phocoenidae and Delphinidae are closely related. The discovery of Pterophocaena leads to a review of previous hypotheses for the origin of Phocoenidae, and indicates that phocoenids had already diversified in the Pacific Ocean by late Miocene.

Carbon isotope fluctuations of terrestrial organic matter for the Upper Cretaceous (Cenomanian–Santonian) in the Obira area of Hokkaido, Japan

Stratigraphic fluctuations of carbon isotope values of terrestrial organic matter within the Upper Cretaceous (Cenomanian–Santonian) sequence in the Obira area of Hokkaido, Japan, record distinctive δ 13 C fluctuations for the Cenomanian–Turonian boundary, the Middle Turonian, the upper Turonian–lower Coniacian, and the Santonian. A biostratigraphic framework of the age-diagnostic taxa (ammonoids, bivalves and planktic foraminifers) indicates that these δ 13 C fluctuation events are comparable with those recorded in δ 13 C data of terrestrial organic matter in Japan and marine carbonates in Europe. These correlations reinforce the utility of these δ 13 C events in terms of global chemostratigraphy. In particular, the δ 13 C patterns within the overall positive interval of the Cenomanian–Turonian boundary event are highly conformable between marine and terrestrial records. The consistent nature of these different records of δ 13 C fluctuation patterns demonstrates that the terrestrial organic δ 13 C data mirror the global-scale δ 13 C patterns in the carbon reservoir of ocean–atmosphere–terrestrial biosphere during the Cenomanian–Turonian boundary event. In addition, global correlation of short-term marine and terrestrial organic δ 13 C fluctuations of the Upper Cretaceous sequence indicate that the magnitude of several terrestrial organic δ 13 C events appears more amplified than that of coeval marine carbonate δ 13 C events. This correlation is interpreted to mean that the effects of local CO 2 emission into the atmosphere by release of terrestrial methane hydrate or biomass burning of terrestrial vegetation in the hinterland of the NE Asian region have been superimposed on the global δ 13 C trend and resulted in the terrestrial organic δ 13 C records of the Yezo Group.

Eodelphis kabatensis, a new name for the oldest true dolphin Stenella kabatensis Horikawa, 1977 (Cetacea, Odontoceti, Delphinidae), from the upper Miocene of Japan, and the phylogeny and paleobiogeography of Delphinoidea

ABSTRACT The oldest reported fossil record of Delphinidae is from the late Miocene (11 Ma) of California. Reliable Miocene fossil delphinids, however, are few. Eodelphis kabatensis from the upper Miocene Mashike Formation (8.5–13.0 Ma), Hokkaido, northern Japan, is the oldest described Miocene delphinid including a skull. Therefore, this species is a significant clue to understanding the early evolutionary history of Delphinidae. The original taxonomic assignment of this species within the genus Stenella is questionable; thus, we propose a new combination for the species, Eodelphis kabatensis Horikawa, 1977. Eodelphis is a basal delphinid, and comprehensive morphological cladistic analysis, including molecular topological constraints, supported this taxonomic revision. Paleobiogeographic analyses based on the present morphological cladistic analysis and analysis under the molecular constraints suggest that the origin and early diversification of Delphinidae occurred in the middle Miocene Pacific Ocean or elsewhere, respectively.

Radiolarian-bearing conglomerate from the Hayang Group, the Kyongsang Supergroup, Southeastern Korea

Abstract The non-marine Cretaceous Kyongsang Supergroup, which is divided into the Sindong, the Hayang and the Yuchon groups, is widely distributed in southeastern Korea. Radiolarian-bearing pebbles are collected from the conglomerates of the Kumidong and the Kisadong formations of the Hayang Group. The age of radiolarian fossils range from Late Permian to Middle Jurassic. In Korea, Permian to Middle Jurassic marine chert beds are not exposed. The directions of paleocurrents of the Kumidong and the Kisadong formations are mainly from the northeast to southwest. During Cretaceous time, the Mino-Tamba Belt, within which Permian to Middle Jurassic chert beds are exposed, is suggested to have been located northeast of the Kyongsang Basin. The radiolarian faunas of the Hayang Group are similar to those of the Mino-Tamba Belt and other associated Mesozoic accretionary belts in Japan (e.g. the Ashio Belt). The provenance of the radiolarian-bearing pebbles collected from the Kumidong and the Kisadong formations is interpreted to be the Mino-Tamba Belt and other associated Mesozoic accretionary belts in Japan.

Changes in Cretaceous ammonoid diversity and marine environments of the Japanese Islands

This study surveys 902 species of Cretaceous ammonoids in Japan, and identifies species diversity changes during 29 Japanese Cretaceous substages. The species diversity, fluctuates between the peak of 92 species in upper Albian and the lowest of less than 40 species in lower and middle Albian, upper Cenomanian, lower Coniacian and upper Campanian onward. More than half of these periods of the lowest diversity except that in the lowest and uppermost Cretaceous, correlate with oceanic anoxic events/subevents indicating that species diversity of the Japanese Cretaceous ammonoids was primarily controlled by such oceanic anoxic events/subevents.

Carbon isotope stratigraphy of terrestrial organic matter for the Turonian (Upper Cretaceous) in northern Japan: Implications for ocean-atmosphere δ13C trends during the mid-Cretaceous climatic optimum

Carbon isotope data of terrestrial organic matter (δ 13 C TOM ) obtained in Hokkaido, northern Japan, from the marine Cretaceous Yezo Group along the northwestern Pacific margin elucidated a detailed chemostratigraphy for the Turonian Stage in this region of East Asia. Chemostratigraphic intra-basin correlation reveals three positive δ 13 C TOM events in the Middle–Upper Turonian of the Yezo Group. δ 13 C TOM fluctuations in these events show similar patterns in the Yezo Group, indicating that terrestrial organic matter is mixed sufficiently before deposition in the Yezo Basin. These δ 13 C TOM events are correlated with previously documented δ 13 C carbonate events in Europe (the Lulworth–Round Down, Glynde–Pewsey, and Late Turonian Events) based on global biostratigraphy. Our chemostratigraphic correlations strengthen the use of these δ 13 C events for global correlation of the Turonian marine successions. In addition, global correlation of Turonian marine and terrestrial δ 13 C events identifies changes in isotopic difference between δ 13 C TOM and δ 13 C carbonate (Δ TOM-carbonate ), which are interpreted to reflect changes in atmospheric p CO 2 levels, and climate-driven stresses of humidity and soil processes. In earlier stages of Turonian, Δ TOM-carbonate values are increased. Elevated atmospheric p CO 2 , and increased humidity and soil processes in enhanced greenhouse conditions during mid-Turonian, are interpreted to enlarge Δ TOM-carbonate values. In later stages of Turonian, Δ TOM-carbonate values are at a constant level, and the lowering of atmospheric p CO 2 or decrease of climate stress related to the diverse paleoclimatic cooling is interpreted to have restored the ocean-atmosphere δ 13 C trends.

Early Cretaceous Terrestrial Weathering in Northern China: Relationship between Paleoclimate Change and the Phased Evolution of the Jehol Biota

The Jehol Biota from lower Cretaceous deposits in northern China provides an important record of terrestrial fauna and flora, including feathered dinosaurs and one of the earliest angiosperms. This biota underwent three development phases, with a relatively limited biodiversity in the early phase that rapidly diversified in the middle phase. This study analyzes the conditions of terrestrial paleoweathering during the lower Cretaceous as inferred from the geochemistry of mudstones, with the aim of assessing the role of paleoclimate change as a background factor that led to the phased evolution of the Jehol Biota. The analysis focuses on the Dabeigou and Dadianzi formations of Hebei Province, northern China, which record the early and middle phases of the Jehol Biota, respectively. These fluviolacustrine sequences can be lithologically divided into lower and upper units. Geochemical weathering indices (e.g., W, ΣREE [total amount of rare earth elements], and ΔW) show a significant increase from the lower to the upper unit, indicating enhanced weathering of the hinterland. Based on a comparison with the W values of recent soils that developed under various climates, the obtained increase in W can be interpreted as indicating temporal increases in temperature and humidity. Therefore, the increase in hinterland weathering from the lower to the upper unit was possibly induced by a shift in the paleoclimate to a more temperate and humid state. The timing of this change in paleoclimate closely coincides with a shift in the Jehol Biota to an evolved phase. Consequently, this preliminary result indicates that paleoclimate change in terrestrial regions of northern China might have contributed to the development of the Jehol Biota.

Ammonoid biodiversity changes across the Cenomanian-Turonian boundary in the Yezo Group, Hokkaido, Japan

Ammonoid biodiversity changes from shallow to offshore environments across the Cenomanian—Turonian (C–T) boundary are reconstructed in the Yezo Group, Hokkaido, Japan. This group was probably deposited at approximately 35–45°N along a westward subduction margin in the northeastern Asian continent. Temporal changes in species richness in the Yezo Group, which show persistently high values during the middle Cenomanian and then decline stepwise from near the middle—late Cenomanian boundary, resemble those in Europe, but not those in Tunisia and the Western Interior. These differences suggest that the Cenomanian—Turonian “mass extinction” was not a global event for ammonoids but was restricted to mid-palaeolatitudinal regions (Europe and Japan). Sea level and climate changes probably influenced ammonoid faunas in the Yezo Group as well as those in Europe. However, it is unlikely that a single, simple cause led to the C—T boundary “mass extinction” because various abiotic changes in the Cenomanian—Turonian transition have been detected, and biotic and abiotic change are interrelated.

New fossil remains from the Pliocene Koetoi Formation of northern Japan provide insights into growth rates and the vertebral evolution of porpoises

Extant porpoises (Phocoenidae) are odontocetes characterized by their small size, short and wide rostrum, late (or absent) completion of epiphyseal ankylosis in the vertebral column (= physical maturity), and short life cycles, all of which are thought to have resulted from progenetic evolution. We describe a small fossil phocoenid from the lower Pliocene Koetoi Formation of Hokkaido (northern Japan), preserving a small, narrow rostrum, as well as anteroposteriorly elongate thoracic and lumbar vertebral centra with completely fused epiphyses. Physical maturity in this specimen occurred significantly earlier than in extant phocoenids, as shown by dental data indicating that the specimen died at only four years of age. The difference between the present material and extant porpoises may be attributable to different growth rates during ontogeny. The long centra and caudally inclined neural spines of the specimen from Hokkaido are primitive characters among phocoenids. By contrast, the great height of its neural spines is highly derived, even among extant species, and suggestive of a fast swimmer. In terms of its vertebral morphology, the new specimen falls within a morphological continuum defined by the archaic Numataphocoena yamashitai and the highly derived vertebral morphology of Phocoenoides dalli. Phocoenid vertebral evolution has been complex and frequently convergent, as opposed to stepwise and unidirectional. The different vertebral morphologies of the new specimen and the contemporaneous extinct taxa Numataphocoena and Piscolithax longirostris indicate that they were adapted to different environments.