Five species of coiled nautiloids are described from a black concretionary shale (uppermost Desmoinesian; middle upper Carboniferous) of the Lost Branch Formation in northeast Oklahoma, Midcontinent North America. They include a tainoceratid, Metacoceras sp., a grypoceratid, Domatoceras collinsvillense sp. nov., a solenochilid, Solenochilus sp., and the liroceratids, Hemiliroceras reticulatum (Miller and Owen) and Peripetoceras sp. Domatoceras collinsvillense is closely similar to D. umbilicatum Hyatt, but it differs in the possession of a narrower umbilical area and more compressed whorls. New material of H. reticulatum indicates an evolute conch with a shallowly concave impressed zone, characters that warrant the present new combination. The species was previously placed in Coloceras or Liroceras. This discovery of H. reticulatum from the Desmoinesian shale extends downward the stratigraphic range of this genus from the lower Permian to the upper Carboniferous.

This paper describes the following three new species of brachiopods from the middle Permian (Wordian) of the Kamiyasse—Imo area, South Kitakami Belt, northeastern Japan: Isogramma nakamurai, Globiella kamiyassensis and Rhipidomella magna. The newly described species are regarded as additional components of the Wordian mixed Boreal—Tethyan brachiopod fauna of the South Kitakami Belt.

A late Olenekian (Early Triassic) ammonoid fauna is described from the Osawa Formation in the Utatsu area, South Kitakami Belt, Northeast Japan. The fauna comprises 14 species belonging to 13 genera: Hemilecanites discus (Arthaber), Albanites sheldoni (Kummel), Pseudosageceras? sp., Pseudokymatites tabulatus sp. nov., Columbites parisianus Hyatt and Smith, Tardicolumbites aff. tardicolumbus Guex et al., Yvesgalleticeras sp., Subcolumbites sp., Hellenites elegans Guex et al., Metadagnoceras sp., Procarnites sp., Leiophyllites wakoi sp. nov., Leiophyllites? sp., and Nordophiceratoides bartolinae Guex et al. Among them, genera Hemilecanites, Albanites, Pseudokymatites, Tardicolumbites, Yvesgalleticeras, Hellenites, and Nordophiceratoides are described for the first time from the Japanese Triassic. The generic composition of the ammonoid fauna of the Osawa Formation has thus increased to 25 genera by adding these to the 18 existing genera. This high taxonomic diversity indicates that the nektonic faunas had already recovered from the end-Permian mass extinction by the beginning of the late Olenekian in the South Kitakami Belt. The ammonoid fauna of the Osawa Formation is similar to that of the late Olenekian of Idaho, North America, and in addition, it has some faunal similarity to those in the western Tethys province. These faunal characteristics are likely to reflect the paleogeographic position of the South Kitakami Belt, which was located at the low-latitude area of the Tethys—Panthalassa border during the Triassic.

A new periotic of Numataphocoena yamashitai from the upper part of the Horokaoshirarika Formation (lower Pliocene), Numata, Hokkaido, Japan shows younger ontogenetic features in comparison to the matured holotype (NFL 7). The referred specimen of N. yamashitai is smaller (approximately 90% in size) than the physically and sexually matured holotype periotic. The holotype (NFL 7) and referred specimen (NFL 2617) show several differences owing to ontogenetic changes, such as: the holotype (NFL 7) has a more strongly swollen medial part of the anterior process, blunt anterior keel, rounded anterodorsal angle, deeper and clearer anterior incisure, more rounded pars cochlearis, deeper and narrower hiatus epitympanicus rather than a flat area, longer posterior process with an extra edge posterolaterally. N. yamashitai differs from other fossil phocoenids in having a narrower and sharper anterior part of the internal acoustic meatus and a robust anterior process. Haborophocoena toyoshimai similarly has a relatively narrow internal acoustic meatus and a robust anterior process, compared with other fossil phocoenids. Between N. yamashitai and H. toyoshimai, N. yamashitai has a narrower internal acoustic meatus and a more robust anterior process. These similarities imply a close relationship between Numataphocoena and Haborophocoena. The new specimen provides diagnostic features and insight into ontogenetic variation of N. yamashitai.

This paper describes the first record of the heteromorph ammonoid Diplomoceras cylindraceum from the uppermost Maastrichtian Kawaruppu Formation of the Nemuro Group, southeastern Hokkaido, Japan. D. cylindraceum was found in a siltstone 15 m below the Cretaceous/Paleogene (K/Pg) boundary. The stratigraphical level of the fossil is estimated to be ∼66.8 Ma, based on the time scale for the geomagnetical polarity and the K/Pg boundary. D. cylindraceum, therefore, was living at least ∼0.8 m.y. before the K/Pg boundary event in the north Pacific region.

This study investigated early to middle Miocene ostracods from the Yatsuo Group (ca. 17–15 Ma), located on the Japan Sea coast of central Japan. Ostracods from this area consist of 100 species in 60 genera, with two assemblages defined by Q-mode cluster analysis. The five most abundant genera of each assemblage are Krithe, Propontocypris?, Cytherella, Argilloecia, and Falsobuntonia in assemblage A, and Schizocythere, Cornucoquimba, Callistocythere, Neomonoceratina, and Paracytheridea in assemblage B. The depositional environment of each assemblage can be defined as (1) outer-shelf to bathyal areas (assemblage A) and (2) inner-shelf areas (assemblage B). Stratigraphic changes in the faunal composition, with changes in lithofacies, suggest a shallowing-upward phase in this sedimentary basin. These assemblages contain the same species or genera as corresponding Pacific faunas in the early to middle Miocene. The assemblage containing bathyal genera such as Cytherella and Krithe from Yatsuo at 17–16 Ma is the oldest record from the entire Japan Sea coast, and their fossil records are common to Cenozoic bathyal genera among the Pacific fauna. This fact indicates that these genera could migrate from the Pacific Ocean through the deep-sea passageway to the Japan Sea since at least around 17 Ma during the early Miocene. The shallow-water assemblage of the inner-shelf area around 15.7 Ma has only a small percentage of cold-water genera. The paleo-water temperature in the shallow-sea area around 15.7 Ma in Yatsuo would have been intermediate between warm (subtropical) and cold marine climates around 16 Ma in the Japanese Islands. The ostracod fauna from Yatsuo is significant for the paleogeography and faunal migration of benthos in the Northwest Pacific Ocean during the formation period of the Japan Sea caused by back-arc spreading.

Three species of the cirolanid isopod genus Bathynomus are reported from the Miocene deposits of central Japan. Bathynomus kominatoensis sp. nov. and an unidentified Bathynomus sp. 1 are described from the upper Miocene Amatsu Formation in the Kominato-Osawa area, Chiba Prefecture. Another large species, Bathynomus sp. 2, was obtained from the middle Miocene Negishi Formation in the Iwadono Hills area, Saitama Prefecture. The new species most resembles Bathynomus giganteus, inhabiting the deep-sea floor of the Western Atlantic and Caribbean Sea. In addition to the large-sized body, Bathynomus kominatoensis sp. nov. and Bathynomus sp. 2 are included in the supergiant species group of the genus based upon morphology of the pleotelson and uropods. Both occurrences extend the geographic and stratigraphic ranges for the supergiant species group of Bathynomus into the Miocene of central Japan, although no species of the supergiant group is distributed in modern Japanese waters.