Paleontological Research

The Triglypta–Qaidamestheria clam shrimp assemblage, widely known from the non-marine Jurassic deposits in northern China, is important for biostratigraphic correlation of the fossil bearing strata. Qaidamestheria Wang, 1983 , an essential component of the assemblage, was originally described from the upmost oil shale member of the Dameigou Formation at the northern margin of the Qaidam Basin, northwest China. Though the original description of the genus Qaidamestheria was based on SEM microscopy, the published pictures of the type specimens are unclear, and the type specimens were lost. We collected new specimens of the type species Qaidamestheria dameigouensis Wang, 1983 from the 7^th unit of the Dameigou Formation in the Dameigou section, where the holotype of the species was originally collected. The examination of the specimens under SEM has revealed three critical taxonomic features for the genus: the fine reticulation (mesh diameter 7–18 µm) on the larval valve and several adjacent growth bands; the transitional (reticulated-punctate) ornamentation on the middle–ventral part of the carapace; and linearly arranged puncta appearing only on growth bands near the antero-ventral margin of the carapace, puncta never clustered.

We collected samples from the middle part of the Tetori Group and obtained diverse spores (28 species) and gymnosperm pollen (8 species) from the Barremian Itsuki and Kuwajima formations. This is the first report of Barremian palynofloras from the Tetori-type floristic province in Japan and we compared them to coeval ones from the Ryoseki-type floristic province. These palynofloras include various cyathealean spores and cheirolepidiaceous pollen, indicating that floristic differences between the Tetori- (Inner Zone) and Ryoseki-type (Outer Zone) provinces are not so distinct during the Barremian in Japan. They also show similarities with floras of the Sindong Group of the Gyeongsang Basin, southeast Korea and Shitouhezi Formation in northeast China, thus indicating that some Ryoseki-type elements may have extended their distribution northward in the Barremian.

We report a single whale bone associated with many molluscan fossils from the Omma Formation, Lower Pleistocene shallow marine deposits, along the Sai-gawa River, Kanazawa City, in central Japan. Most molluscan species which are commonly found in the Omma Formation show disarticulated and/or damaged shells, indicating semi-autochthonous or allochthonous modes of occurrence. However, the assemblage contained chemosynthetic bivalves, such as lucinid, solemyid and thyasirid bivalves, which are rare in the Omma Formation. The lucinids and solemyids show a high articulation ratio, along with some predatory and scavenging gastropods, such as naticids, nassariids and borsoniids whose well-preserved shells indicate an autochthonous mode of occurrence. In addition, most of the lucinid bivalves show an umbo-upward position similar to the life position of Recent species. Recent lucinid, solemyid and most thyasirid bivalves harbor chemosymbiotic bacteria in their gills and are well known members of the chemosynthetic community. These lines of evidence indicate that the community, mainly comprising lucinid bivalves and other autochthonous molluscan species associated with the whale bone, is an ancient whale-fall community. This shallowest fossil whale-fall community differs from deep-water cases in the dominance of infaunal bivalves, such as lucinids, and in the lack of epifaunal and semi-infaunal chemosynthetic bivalves, such as bathymodiolins and vesicomyids. This community supports a previous suggestion that the difference in characteristic species of the whale-fall communities depends on the water depth.

The ammonoid-bearing limestone blocks at the classic Crittenden Springs ammonoid site belong to the lower part of the Lower Triassic Thaynes Group. These 0.5–1.2 m thick blocks, consisting mainly of bioclastic floatstone and rudstone, contain abundant macro- and micro-fossils such as ammonoids, gastropods, bivalves and scaphopod shells, as well as conodont elements, fish and echinoid remains. Ammonoid and conodont assemblages obtained from three blocks are utilized for biostratigraphical analysis. Twelve informal Smithian ammonoid biostratigraphic intervals from a previous study are condensed into four ammonoid beds, based on the range of age-diagnostic taxa, in ascending order: Meekoceras millardense-M. aff. olivieri beds, Owenites koeneni beds, Anasibirites multiformis bed, and Condensoceras youngi bed. Conodonts recovered from the three blocks consist of 30 species distributed among 15 genera, including one newly described taxon, i.e., Guangxidella minuta Maekawa and Jenks sp. nov. The blocks are divided into two conodont interval zones, i.e., the Novispathodus ex gr. waageni Interval Zone and Nv. pingdingshanensis Interval Zone, based on the first occurrences of their eponymous taxa. Additionally, four conodont range zones, i.e., the Paullella meeki Range Zone, Guangxidella bransoni Range Zone, Scythogondolella milleri Range Zone, and Borinella buurensis Range Zone are recognized, based on the ranges of these four index species. Conodonts within these interval and range zones vary in age from middle Smithian to latest Smithian. The presence of key ammonoid and conodont taxa regarding the Smithian-Spathian boundary (SSB) such as the AW (Anasibirites and Wasatchites) and GXP (Glyptophiceras, Xenoceltites and Pseudosageceras) ammonoid assemblages and the conodonts B. buurensis, Nv. pingdingshanensis and S. milleri demonstrate that the study area is an important reference site for the SSB in the eastern Panthalassa area.

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, 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 successions. 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 occurs 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 environments 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. The extinction of Bellerophontoidea before the beginning of the late Smithian suggests that the group may have been more sensitive to global warming and related harmful events than other organisms.

Linguliformean brachiopods often exhibit a clustered occurrence. Because there has been no detailed analysis of whether these clusters represent death or living assemblages, we exemplified the burial processes of the Middle Permian discinid brachiopods from the Hoso-o Formation with the systematic descriptions of Orbiculoidea verum sp. nov. and Discinidae gen. et sp. indet. There were three types of discinid occurrences: 1) articulated Orbiculoidea in a ventral-side-down orientation, 2) disarticulated valves of both species in a convex-up orientation, and 3) disarticulated ventral valves of the Orbiculoidea in a convex-down orientation. The articulated specimens occurred in laminated mudstone and must have been autochthonous, while the disarticulated specimens with a convex-up orientation were para-autochthonous, resulting from turbiditic or storm flow. The specimens with convex-down ventral valves always occurred at the base of the sandstone beds with their ventral apexes slightly penetrating the underlying mudstone. This is the argument for an autochthonous ventral valve, whereby only the dorsal valve was transported after death. The distribution of epibionts suggests that the life posture of the Orbiculoidea was a ventral-side-down orientation, with its anterior half slightly higher than the sediment-water interface, which was advantageous for the feeding flow and the clearance of sediments around the posterior margin. Although dense monospecific assemblages of Orbiculoidea occur only as disarticulated valves, the exclusive occurrence of articulated individuals in the underlying mudstone suggest that the animal inhabited the specific environments opportunistically, which has never been explored in other fossilised organisms.

We describe two well-preserved mandibles of Stegolophodon pseudolatidens (Mammalia, Proboscidea, Stegodontidae) discovered from the lower Miocene (ca. 16.9–16.6 Ma) in Northeast Japan. The mandible of Sl. pseudolatidens is primitive within the Stegodontidae in having a short symphysis with lower tusks, tetralophodont lower molars, and a mandibular canal with the large dorsoventral diameter in the anterior segment. It is characterized by a perpendicular mandibular ramus (forming an almost right angle between the anterior margin of the mandibular ramus and the dorsal horizontal surface of the corpus), and many scratches in mesial direction on the occlusal surface of m3, implying that Sl. pseudolatidens appears to have acquired a proal jaw movement during mastication. While the mandibular morphology of Sl. pseudolatidens is comparable to that of other species of the genus that of Stegolophodon cf. stegodontoides from the upper Miocene of Myanmar differs from that of these species in having a shorter symphysis, which is a derived condition.

Biostratigraphy of conodonts is widely used for age assignment of Permian strata. In this paper, we report conodonts from the limestone of the Nabeyama Formation deposited on a pelagic seamount in 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 that 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 pelagic Panthalassa during the late Kungurian.

A preliminary description is provided of a new assemblage of small, three-dimensional and charcoalified mesofossils from the Tamagawa Formation (late Turonian–middle Santonian; Upper Cretaceous) of the Kuji Group in northeastern Japan. The new mesofossils yield excellent structural details and include well-preserved circinate shoots of ferns together with conifer leafy-shoots, seeds and probable pollen cones, and variety of angiosperm fruits and seeds, including fruits of Cornales and seeds of Nymphaeales. The new mesofossil assemblage is complementary to the previously published macrofossil flora from the Kuji Group.

In this study, a new late Campanian (Late Cretaceous) heteromorph ammonoid, Didymoceras morozumii Misaki and Tsujino sp. nov., from the Hiketa Formation, Izumi Group, southwestern Japan, is described. It is characterized by a loose helical post-embryonic early whorl and relatively tight helical middle whorls, followed by a retroversal hook with a highly elevated apertural end, and two rows of irregular tubercles. Didymoceras morozumii sp. nov. occurs in the upper part of the Didymoceras sp. Zone, which is overlain by the Didymoceras awajiense Zone. Didymoceras awajiense-bearing beds of the Hiketa Formation in the study area is correlated to the lower part of that of the Toyajo Formation in the Kii Peninsula on the basis of the shell forms of D. awajiense. Didymoceras morozumii sp. nov. and D. awajiense have similar characteristics, and it is thought that D. awajiense evolved from D. morozumii sp. nov. As indicated in the descendants, some specimens of D. morozumii sp. nov. are also encrusted by anomiid bivalves.