Cretaceous Research – incoming editorial
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Mid-Cretaceous ammonoid assemblages are newly identified from four localities in the Aridagawa area, Wakayama, southwest Japan. They consist of Middle to Upper Albian ammonoids such as Desmoceras (Pseudouhligella) dawsoni shikokuense, Puzosia subcorbarica, Mojsisoviczia sp., Oxytropidoceras sp., Mortoniceras sp., etc., and Mantelliceras japonicum, which indicates the Lower Cenomanian stage. The Albian ammonoids were found for the first time from the Chichibu Belt of Kii Peninsula. The discovery of these ammonoids indicates a considerably wide distribution of the mid-Cretaceous deposits in the Aridagawa area, and the necessity of a large revision of the previous stratigraphic division of the Cretaceous strata in the area. The mid-Cretaceous deposits in the Aridagawa area and their abundant molluscan fossils are important for reconstruction of the mid-Cretaceous paleoenvironment and tectonics in the eastern margin of Asia.
Cenomanian
Ammonoidea
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Low latitude
High latitude
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Sequence (biology)
Section (typography)
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Late Cretaceous heteromorph ammonoids, Ainoceras kamuy and Ainoceras paucicostatum, were discovered for the first time from the Futakawa Formation in the Aridagawa area, Wakayama, southwestern Japan. Other molluscan fossils such as Eupachydiscus sp., Gaudryceras aff. striatum, “Gigantocapulus” transformis, Sphenoceramus nagaoi, Sphenoceramus orientalis and Inoceramus balticus also cooccur with Ainoceras, and together they indicate the lower Campanian Stage. Recently, the middle Turonian—Santonian and upper lower Campanian—Maastrichtian litho- and biostratigraphy in the Aridagawa area was established. Therefore, the lower Campanian strata in the study area fill the gap between them and supplement the Upper Cretaceous stratigraphy in the Aridagawa area. The results of this study advance the biostratigraphy and correlation of the marine Cretaceous strata in the northwestern Pacific region.
Ammonoidea
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Abstract Pliosaurid marine reptiles played important roles in marine food chains from the Middle Jurassic to the middle Cretaceous, frequently as apex predators. The evolution of pliosaurids during the later parts of the Early Cretaceous has recently been illuminated by discoveries from Russia (Hauterivian) and Colombia (Barremian). However, knowledge of pliosaurids representing the Jurassic–Cretaceous transition (late Tithonian – Valanginian), is still largely incomplete, especially during the earliest Cretaceous. As such, the effect on pliosaurids of hypothesized faunal turnover during the Jurassic–Cretaceous boundary interval is poorly understood. We report pliosaurid teeth from the upper Volgian (Tithonian, Upper Jurassic) of the Kheta river basin (Eastern Siberia, Russia), to the Berriasian and Valanginian (Lower Cretaceous) of the Volga region (European Russia). These assemblages have yielded a series of distinct tooth morphotypes, including the first reports of conical‐toothed pliosaurids from the latest Jurassic and earliest Cretaceous. This challenges the hypothesis that only one lineage of pliosaurids crossed the Jurassic–Cretaceous boundary. It appears that conical‐toothed pliosaurids co‐existed with their trihedral‐toothed relatives for at least 25 million years during the latest Jurassic and earliest Cretaceous. In fact, our quantitative analyses indicate that pliosaurids reached their maximal dental disparity during this interval, showing little evidence of turnover associated with the Jurassic–Cretaceous transition. Instead, disparity decreased later in the Early Cretaceous, with the disappearance of trihedral‐toothed forms in the Barremian.
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The Jurassic-Cretaceous (J/K) and Cretaceous-Paleogene (K/Pg) boundaries/transitions are found in Pakistan especially well exposed on the western continental margin of the Indo-Pakistan plate (part of Gondwana) like Kirthar, Sulaiman and Kohat and Potwar basins. Its lithology is variable both lateral and also vertical. The J/K and K/Pg transitions are represented by terrestrial and marine strata like laterite, bauxite, vary colored shale, sandstones and conglomerates and rare limestone beds. Mesozoic vertebrates found so far belong to archosaurs like poripuchian titanosaurs (sauropods), theropods, mesoeucrocodiles, pterosaurs, snake and bird are briefly overviewed here.
Paleogene
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Cenomanian
Aptian
Ammonite
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Dinoflagellate
Lithology
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