Outcrops of the Turonian Saku Formation in the Obira region of Hokkaido (northern Japan) have yielded two breviconic phragmocones that represent a previously unknown species of Conoteuthis, a comparatively well known genus of diplobelid coleoids. The selected holotype of Conoteuthis hayakawai sp. nov. preserves a spherical protoconch that deviates slightly from the longitudinal axis of the phragmocone and is the first record of a protoconch in Conoteuthis. Conoteuthis hayakawai sp. nov. differs only slightly from the type species Conoteuthis dupiniana from the Hauterivian-Aptian of Europe and Conoteuthis azizi Fuchs et al. from the Cenomanian of southeastern India through its weakly developed dorsal saddles. Conoteuthis hayakawai sp. nov. is the youngest report as well as the first record of the Diplobelida from the Paleopacific. This new find considerably extends the stratigraphical and geographical occurrence of the Diplobelida. Phylogenetically, the genus Conoteuthis is considered to be an isolated group within the Diplobelida. With respect to the controversial origin of the Sepiida and Spirulida, morphological comparisons have shown that the genus Conoteuthis cannot be a potential stem-group of the Sepiida and/or Spirulida.

Triassic pistosauroids are closely related to the Plesiosauria which flourished later in the Mesozoic, but their fossil record has been poor due to the fragmentary nature of the known specimens. Yunguisaurus liae Cheng et al. (2006) (Reptilia, Sauropterygia) from China was the first Triassic pistosauroid represented by an almost complete skeleton, and we provide a full description of the holotype specimen based on the result of complete preparation of the skull and postcranium. A revised diagnosis characterizes Y. liae by a mixture of primitive and derived features for sauropterygians, such as the high number of cervical vertebrae (similar to the Plesiosauria) with large zygapophyses (shared with basal sauropterygians). The holotype skeleton likely represents a juvenile individual. In a revised phylogeny, relationships among the Triassic pistosauroids are fully resolved but weakly supported; the revised phylogeny differs from the existing hypothesis on a sauropterygian relationship, likely due to the previous reliance on fragmentary taxa. The long neck and hyperphalangy give an impression that Yunguisaurus is very “plesiosaurian,” but detailed comparison revealed morphological differences in various parts of the postcranial. These differences, in combination with the revised phylogenetic hypothesis, suggest that Yunguisaurus was not necessarily comparable to the Plesiosauria in terms of body plan and mode of swimming.

A second specimen of Takahashia eureka Matsumoto, 1984, from the lowest Cenomanian in the Hobetsu area of Hokkaido (Northern Japan), is described, and the diagnosis of the taxon is revised following a careful reexamination of the holotype. The presence of partially developed, minutely crinkled ribs on the shell implies that Takahashia had a close phylogenetic relationship with the long-ranging taxon Lytoceras (upper Sinemurian-Cenomanian), and we therefore assign it to the subfamily Lytoceratidae of the family Lytoceratidae. Evolution of Takahashia from Lytoceras supports the existence of a unique fauna in the North Pacific at the Albian-Cenomanian transition.

Gaudryceras izumiense Matsumoto and Morozumi, 1980, an ammonoid of early Maastrichtian age, occurs frequently in the Izumi Group in the Izumi Mountains, Southwest Japan. Described herein are two specimens referable to this species that were recently collected from the Hakobuchi Formation of the Yezo Group in the Hobetsu area, Hokkaido and from the Matanuska Formation in the southern Talkeetna Mountains, Alaska. In the past, a precise biostratigraphic correlation of the uppermost Cretaceous in the North Pacific realm has been difficult because of the lack of common zonal-index taxa, but the discovery of G. izumiense in Hokkaido and Alaska has made it possible to correlate lower Maastrichtian strata in these localities with coeval strata in Southwest Japan. Gaudryceratid ammonoids are fairly abundant in the uppermost Cretaceous of the North Pacific realm, and consequently, they are ideal taxa for the establishment of a precise biostratigraphic correlation framework for the uppermost Cretaceous in this vast area.

Age-significant Jurassic radiolarians and other microfossils are recognized for the first time from the Kiritani Formation of the Higashisakamori Subgroup of the Tetori Group, a Middle Jurassic to late Early Cretaceous group of shallow- to nonmarine sedimentary strata in northern Central Japan. The Kiritani Formation in the Jinzu Region, eastern part of the Tetori Basin, is mainly composed of marine terrigenous clastic rocks: conglomerate, sandstone, and sandy siltstone including unlined tubelike trace fossils. Radiolarians are present only in the trace fossils, not in the surrounding sandy siltstone. The radiolarian age of the Kiritani Formation based on the European radiolarian zonation is Callovian-early Tithonian by the occurrence of Zhamoidellum ovum. The Kiritani Formation can also be correlated with the Arimine Formation, another marine formation of the Jinzu Region, which yields radiolarians of the same age.

Microfossils consist of various taxa: radiolarians, rhaxellid sponge spicules, prodissoconchs of juvenile bivalves, a charophyte gyrogonite, and a planktonic foraminifera. The radiolarian assemblages show a high ratio of spumellarians over nassellarians in the number of specimens. These microfossil assemblages suggest that the Kiritani Formation was deposited in a shallow marine environment.