Paleontological Research

Note to readers. The Palaeontological Society of Japan requested Dr. Janal to prepare a guide on citations in Paleontological Research, especially those in unfamiliar styles, e.g. classic literatures and publications/names in non-English languages. We hope this document will be helpful to authors when compiling the “References” section of their contributions.

Dense aggregations of articulated ophiuroids, in external mould preservation, were discovered in the middle Miocene Duho Formation (Yeonil Group) of Pohang City, near the southeast coast of Korea. These specimens are here described as a new species, Ophiura pohangensis, which differs from congeners in having long, slender oral papillae, and tiny quadrangular arm comb papillae. The new species constitutes the first well-identified example of the class Ophiuroidea in the fossil record of Korea. Aggregation density of the new species is similar to that of occurrences of both fossil and extant Ophiura sarsii sarsii across Japan.

Twelve species of small gastropods are extracted using the sodium tetraphenylborate method from the strongly lithified shallow marine deposits of the Barremian (Lower Cretaceous) Kimigahama Formation of the Choshi Group, central Japan. They belong to the following families and subfamilies; Eudaroniidae, Pseudomelaniidae, Ampezzopleurinae, Metacerithiidae, Procerithiidae, Nystiellidae, Metaxiinae, Stuoraxidae and Ebalinae, including six new species and one new genus. Pseudomelania yamadai sp. nov., Ampezzopleura barremica sp. nov., Choshipleura striata gen. et sp. nov., Metacerithium boshuae sp. nov., Antiphora aurora sp. nov. and Stuoraxis kasei sp. nov. are described as new species. Pseudomelania yamadai, Metacerithium boshuae and Cirsocerithium subspinosum are closely related to or identical with the species from the Lower Cretaceous in western Europe. Ampezzopleura barremica and Choshipleura striata are the first Cretaceous records of the subfamily Ampezzopleurinae that has hitherto been limited to the Triassic deposits. Antiphora aurora is the first record of the family Triphoridae from Mesozoic deposits, suggesting that the sinistral triphorids originated from the dextral ancestor. Stuoraxis kasei is the youngest occurrence of the heterostrophan family Stuoraxidae that has hitherto been reported from the Permian to Middle Jurassic deposits. The sodium tetraphenylborate method for finding the small molluscs from the strongly lithified deposits is an effective tool with which to reveal the true diversity of the fossil molluscan fauna.

The allometric relationship between suture line length and phragmocone volume was examined in 28 specimens belonging to six ammonoid species recovered from the Upper Cretaceous Yezo Group of Hokkaido, Japan. The suture perimeter was calculated by summing the distances between digitized points along the suture line in a photograph. The phragmocone volume was calculated using a modified Raup's model. The relationship between suture perimeter and phragmocone volume in each species was expressed as an allometric equation on a logarithmic scale. The exponent of ontogenetic allometry estimated for each species ranged from 0.462 to 0.626. The exponents estimated were much greater than the exponent in the case of isometry (0.333) and the value previously obtained through interspecific comparison. Calculation using a theoretical morphologic model indicates that allometric exponents for the suture perimeter of approximately 0.5 reflect positive allometry of the septal surface area with respect to body size. The present results suggest that strong positive allometry of the suture perimeter leads to a considerable positive allometry of the septal surface area resulting in satisfying Kleiber's scaling law, although its functional significance remains unclear.

We report a fossil record of Procellariidae from the Ichijiku Formation (Middle Pleistocene), Kimitsu City in Chiba Prefecture, Japan. Although this specimen is a partial sternum, we assign it to Procellariidae based on several of its osteological characteristics, such as the size, shape of the linea intermuscularis, and aspect ratio of the incisurae costales. A few marine birds that are uncommon in the area today, such as an Atlantic auk and an extinct flightless auk (i.e., Alle and Mancalla) have been reported from the Ichuijiku Formation, while the procellariid species are still common in the extant seabird fauna of the area. This new discovery suggests that not only did various marine birds exist around the Kanto area (now part of the Boso Peninsula) in the Middle Pleistocene, but also that it is important to consider about an avian faunal transition between the Pleistocene and the present.

The Triassic clam shrimp genus Aquilonoglypta Novojilov, 1958 was first erected based on a specimen collected from the Lower Triassic along the Laptev Sea coast of Russia. Its original diagnostic ornament was described as fish scale pits. Then, the genus was recovered in the Lower and Middle Triassic in the Ordos Basin in northwestern China. Because the Chinese specimens have punctate ornamentation, they were interpreted as the ancestor of the Jurassic triglyptids. In this study the diagnosis of Aquilonoglypta is revised following a re-examination of the Russian type specimens under a scanning electron microscope (SEM). In Aquilonoglypta growth bands near the umbo are ornamented with polygonal fine reticulation, which transitions to puncta on growth bands in the middle part of the carapace. The ornamentation on growth bands in the ventral part of the carapace clearly shows the transition from the puncta to a size-increasing fine reticulation pattern. This research result shows that Aquilonoglypta could not be the close link with triglyptids because of lacking of the fine reticulation on growth bands in the dorsal part of the carapace in the latter. On the contrary Triglypta Wang, 1984 could be more closely related to Punctatestheria Zhang et al., 2017 .

We describe a new specimen of physeteroid from the lower Miocene (Burdigalian) of Japan. This specimen was recovered from the Toyohama Formation, Chita County, Aichi Prefecture, Japan in 1984 and includes a finely preserved cranium with detached teeth and ear bones (periotic, tympanic bulla, and malleus). Here we refer this specimen to a new genus and species of the Physeteroidea, Miophyseter chitaensis gen. et sp. nov. Our phylogenetic analysis suggests that Miophyseter is a physeteroid more closely related to the crown Physeteroidea (Physeteridae and Kogiidae) than the macroraptorial physeteroids that flourished in middle and late Miocene times. A deep and large excavation on the ventral surface of the palatine and pterygoid in Miophyster suggests an adaptation for deep dives and/or the development of robust pterygoid muscles for active biting.

The Cambrian explosion ultimately resulted in the critical transition from microbially dominated ecosystems in the Precambrian to metazoan-dominated ecosystems in the Phanerozoic. However, the temporospatial pattern of ecosystems during the Cambrian explosion is poorly understood largely because our current knowledge is biased in metazoan evolution and redox conditions, and thus insufficient to reconstruct an ecosystem that is an integrative entirety of biotic and abiotic components. Therefore, we proposed a facies-dependent integrative approach as a working hypothesis toward a more comprehensive understanding of ecosystem evolution during the Cambrian explosion. The basis is to collect data from a rock unit with a consistent facies (or a biota) in five aspects: biodiversity, ecological network, climate, environmental trio (living, taphonomic and sedimentary conditions), and biogeochemical cycles. On the basis the temporospatial pattern can be built by tracking the spatial heterogeneity and tracing the temporal variability. Although the scenario is a general solution, not obligately applicable to the Cambrian explosion, and needs tremendous amount of work, it is a practical way, probably the only way, to understand such a global event with great complexity.