A new skull of Desmostylus hesperus Marsh, 1888 is described from the late Middle Miocene Tachikaraushinai Formation, Utanobori, Hokkaido, northern Japan. The specimen, GSJ-F7745, is a nearly complete skull and mandible, but the posterior halves of their left sides are missing. It was a juvenile individual, having part of the worn fourth deciduous molar (dp⁴) in the right upper jaw. Another specimen (GSJ-F7743) was uncovered in the same formation near the same area where GSJ-F7745 was collected. Both fossils represent nearly the same ontogenetic stage and were of the same gender.

There are two different opinions regarding the position of the external acoustic meatus of Desmostylus. The cranial cavity of specimen GSJ-7745 is observable and reveals that the meatus should be identified as being the foramen on the lateral surface of the posterior portion of the zygomatic arch.

Water temperature (T) and salinity (S) ranges for the modern distribution of relict species of cold-water ostracods in and around the Japan Sea are summarized. These results provide new information on the ecology of species in the Omma-Manganji ostracod fauna and their survival through Pleistocene environmental changes. Fourteen representative species of this fauna belonging to the three families Hemicytheridae, Cytheruridae and Eucytheridae are discussed. The summer T-S habitat requirements were divided into three species groups: (a) Japan open sea-inner bay (0–20°C, 30–341; 9 species); (b) Japan-Alaska open sea (around 5°C, 31–341; 1 species); (c) Japan open sea (0–20°C, around 341; 4 species). The winter T-S of these three species groups falls in a single range of 0–5°C and 30–341. Their summer T-S conditions are characterized by a wide range either for T or S or both. The summer T range of most species reflects the Tsushima Warm Current water in summer. The winter T range of all the species corresponds to the coldest Japan Sea Intermediate-Proper Water through the year. The large T range difference between summer and winter is a remarkable character of most species. It is clear that most of these species examined here also live in temperatures as high as 20°C, but are generally cold-water species as a whole. The winter low T (less than 5°C) is considered to be critical for the survival of all of these species. These species were interpreted as having survived the cyclic environmental changes between glacial and interglacial periods by expansion or contraction of their distribution. Group (a) species can inhabit various T-S environments in summer. Furthermore, they can probably breed and maintain their populations, even in small areas such as the restricted inner bay, when suitable open sea conditions were lost. Group (b) species have only recently migrated to the low T-S region in the Northeast Pacific, and low T regions of deeper areas of the eastern Japan Sea where only a few species live. Group (c) species invaded the newly appearing T-S condition in the shallow-open areas of the Japan Sea, and have flourished, replacing the extinct species during the Pleistocene. Their wide T-S tolerance is considered to be the most advantageous factor for survival through the Pleistocene environmental fluctuations in the Japan Sea, linked with the glacio-eustatic sea-level changes.

Eighty-seven species of molluscs were obtained from the uppermost lower-lowest middle Miocene Higashibessho Formation at Shimo-sasahara, Yatsuo Town in Toyama Prefecture, central Japan. Among them, Pagodula shojii is new to science. Judging from the autochthonous species, the Higashibessho Formation was deposited at the lower sublittoral to upper bathyal depth. Both the deep-sea and the derived shallow-water species include many warm-water dwellers. During the latest early-earliest middle Miocene, the deep-sea species migrated from the Pacific side of central Honshu to the Japan Sea through deep-sea pathways.

The Middle Triassic (Anisian) Yuqing Member of the Qingyan Formation crops out in Guizhou Province, southwestern China, and consists of storm-dominated inner and outer shelf deposits. It contains Tethyan benthic fossils that are grouped into two fossil assemblages. The allochthonous Mentzelia multi-costata-Mentzelia mentzeli assemblage is characterized by brachiopods in the inner shelf facies. The parautochthonous and allochthonous Posidonia wengensis assemblages, composed mainly of epifaunal bivalves, dominate in the inner and outer shelf facies, although some species of Posidonia generally are characteristic of deep-sea environments or low-oxygen conditions.

At least thirty-three ostracode species are reported for the first time from the Oligocene Itanoura Formation, Nishisonogi Group. This is also the first report of Oligocene ostracodes from the Japanese Islands. Fifteen samples bearing fossil ostracodes were grouped into three biofacies (A to C). Three biofacies have characteristics as follows: Biofacies A is dominated by Acanthocythereis volubilis (Liu) and Eopaijenborchella sinensis (Liu); Biofacies B is dominated by Krithe sp. associated with Palmoconcha oujiangensis (Liu) and A. volubilis; Biofacies C dominantly includes P. oujiangensis. The lithofacies, fossil molluscan assemblages and planktonic/total foraminifers ratios suggest the following habitats for the ostracodes: all ostracode species from the formation inhabited a shelf influenced by coastal water; dominant species of Biofacies A flourished in environments shallower than those of Biofacies B. Fossil ostracode assemblages from the Itanoura Formation have lower numbers of species and lower species diversity indices than other such assemblages from shelf habitats through the Neogene to Recent. These results also suggest that some genera such as Cytherella, Eopaijenborchella and Palmoconcha may differ from their Recent countertparts in their habitats, and that shallow-marine ostracodes in the northwestern Pacific might have diversified after the early Oligocene.

All species referred to Palaeograpsus Bittner, 1875, have been reevaluated, resulting in three new genera, Bittneria, Magyarcarcinus, and Litograpsus. Amydrocarcinus Schweitzer et al., 2002, and Magyarcarcinus new genus are placed within the Goneplacinae MacLeay, 1838, of the Goneplacidae MacLeay, 1838, and constitute some of the earliest occurrences of the family. Bittneria new genus, Carinocarcinus Lőrenthey, 1898, and Palaeograpsus sensu stricto are placed within the Eucratopsinae Stimpson, 1871, of the Panopeidae Ortmann, 1893, and document the first notice of the subfamily in the fossil record. The Pseudorhombilidae Alcock, 1900, and the Eucratopsinae are very difficult to differentiate from one another based upon dorsal carapace characters typically preserved in the fossil record, but the ratios of the frontal width and fronto-orbital width are shown to be useful for this purpose. Litograpsus new genus is placed within the Grapsidae MacLeay, 1838, sensu lato. Palaeograpsus guerini Via, 1959, is placed within Chasmocarcinus Rathbun, 1898. The Panopeidae displayed a Tethyan distribution pattern early in its history, and the Pseudorhombilidae has been largely restricted to the Americas since its first occurrence in the Miocene of Argentina (Glaessner, 1933).