Late Campanian–early Maastrichtian heteromorph-dominated ammonoid assemblages of the Nakaminato Group, central Honshu, Japan: biostratigraphic and paleontological implications

Masukawa, Genya; Ando, Hisao

doi:10.1016/j.cretres.2018.06.018

Cited by 5 publications

(13 citation statements)

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“…The Upper Cretaceous Nakaminato Group is distributed along a ~3.5 km north-south stretch of wave-cut benches facing the Pacific coast at Hitachinaka, Ibaraki, Japan (Figure 3; e.g., Ando, 2006;Saito, 1958Saito, , 1959Saito, , 1961Saito, , 1962. The Nakaminato Group is subdivided into the offshore mudstone of the Hiraiso Formation and the overlying sandstone and sandy turbidite of the Isoai Formation (Figure 4; Tanaka, 1970;Ando, 2006;Masukawa & Ando, 2018). The Hiraiso Formation is subdivided into five lithostratigraphic units: Hl1-Hl3 and Hu1-Hu2; the Isoai Formation is subdivided into eight units: Is1-Is8 (Masukawa & Ando, 2018;Tanaka, 1970).…”

Section: Geological Settingmentioning

confidence: 99%

“…The Nakaminato Group is subdivided into the offshore mudstone of the Hiraiso Formation and the overlying sandstone and sandy turbidite of the Isoai Formation (Figure 4; Tanaka, 1970;Ando, 2006;Masukawa & Ando, 2018). The Hiraiso Formation is subdivided into five lithostratigraphic units: Hl1-Hl3 and Hu1-Hu2; the Isoai Formation is subdivided into eight units: Is1-Is8 (Masukawa & Ando, 2018;Tanaka, 1970). The Hiraiso and Isoai Formations were deposited under sedimentary environments as basin plain (Hl1) to lower submarine fan facies (Hl2-Hl3) and mid to upper submarine fan facies (Hu1-Is8) .…”

Section: Geological Settingmentioning

confidence: 99%

“…Heteromorph ammonoids, represented by nostoceratids and diplomoceratids, are numerically dominant among the ammonoid assemblages from the lower-middle parts of the Hiraiso Formation and from a few horizons in the Isoai Formation (Masukawa & Ando, 2018). Although several vertebrate remains, such as a mosasaur vertebra, costals and a humerus of trionychid turtles, and shark teeth, have been found in the Isoai Formation (Figure 4;Saito, 1962;Kato et al, 2017Kato et al, , 2019Kato, Miyata, et al, 2020;Kato, Sonoda, et al, 2020), no vertebrate remains had been reported from the Hiraiso Formation previously.…”

Section: Geological Settingmentioning

confidence: 99%

“…Although several vertebrate remains, such as a mosasaur vertebra, costals and a humerus of trionychid turtles, and shark teeth, have been found in the Isoai Formation (Figure 4;Saito, 1962;Kato et al, 2017Kato et al, , 2019Kato, Miyata, et al, 2020;Kato, Sonoda, et al, 2020), no vertebrate remains had been reported from the Hiraiso Formation previously. Masukawa and Ando (2018)…”

Section: Geological Settingmentioning

confidence: 99%

“…INM-4-15694 was found in situ from the lower part of the unit Is3 of the Isoai Formation. This horizon is considered to be a lower Maastrichtian deposit (Masukawa & Ando, 2018). The centra are procoelous.…”

Section: Locality and Horizonmentioning

confidence: 99%

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Advanced mosasaurs from the Upper Cretaceous Nakaminato Group in Japan

et al. 2021

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Plotosaurus is a highly aquatically adapted mosasaur, which is supposed to inhabit the deep ocean basin. The geographic occurrence of this genus has been limited only to the west coast of North America. In this study, two Plotosaurus-type mosasaur caudal vertebrae derived from the Upper Cretaceous Nakaminato Group in Ibaraki Prefecture, Japan, are described with discussion on the paleobiogeographic significance of the Late Cretaceous mosasaur fauna in the Northwestern Pacific region. The two specimens are an intermediate caudal vertebra found in a beach cobble, which presumably originated from the Hiraiso Formation (upper Campanian), and a terminal caudal vertebra found in situ in the lower Isoai Formation (lower Maastrichtian). Because their relative centrum lengths (ratio of centrum length/centrum height, ~0.7) are very close to that of Plotosaurus, the specimens are referred to cf. Plotosaurus sp. The two specimens provide the first evidence that highly specialized Plotosaurus-type mosasaurs inhabited the Northwestern Pacific Ocean, suggesting that such forms had a wider distribution than previously recognized and might have existed since the late Campanian in the Northwestern Pacific Ocean.

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Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Locality and Horizonmentioning

confidence: 99%

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Advanced mosasaurs from the Upper Cretaceous Nakaminato Group in Japan

et al. 2021

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Evolutionary process of extremely twisted heteromorph ammonites from the Upper Cretaceous of Japan

Misaki,

Okamoto,

Maeda

2023

Papers in Palaeontology

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The heteromorph ammonite Pravitoceras sigmoidale with extremely twisted retroversal hook and its probable ancestors, Didymoceras awajiense and D. morozumii, occur mainly in the Upper Cretaceous Izumi and Sotoizumi groups in southwest Japan. Their morphological characteristics were investigated in this study. Morphotypes I–II were recognized in D. morozumii. Morphotypes III–V were recognized in D. awajiense. Morphotypes VI–VIII were recognized in P. sigmoidale. Moreover, all morphotypes were recognized in both the dextral and sinistral forms of these three species. Based on the morphological and stratigraphic relationships, it is considered that the evolutionary process of these species is divided into three steps: (1) shift from morphotypes I–II to III; (2) increase in variation from morphotypes III to III–V; and (3) shift from morphotypes III–V to VI–VIII. By comparing these morphotypes based on the ‘growing tube model’ belonging to the moving frame analysis, it is seen that there are no significant gaps of coiling patterns in the evolutionary processes of this lineage. Meanwhile, morphotypes III–V of D. awajiense have a larger morphological variation than morphotypes I–II of D. morozumii and morphotypes VI–VIII of P. sigmoidale. These results, and the radiometric ages from previous studies, suggest that D. awajiense, with considerable variation between ancestor and descendant species, existed in a short interval. It seems that P. sigmoidale occurred after the continuous but rapid and drastic morphological evolution from D. morozumii via D. awajiense.

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New records of Diplomoceras (Ammonoidea, Diplomoceratidae) from Koryak Upland, North-West Pacific Province: taxonomic, biostratigraphical and palaeogeographical implications

Jagt-Yazykova,

Zolina,

Golovneva

2024

Netherlands Journal of Geosciences

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The geographical and stratigraphical distribution of the heteromorph ammonite genus Diplomoceras within the North-West Pacific Province is briefly reviewed. Although Diplomoceras ranks amongst the more important, globally distributed taxa during the latest Cretaceous, its precise stratigraphical range still is uncertain. Moreover, the status of the various species assigned to this genus is a matter of debate; for instance, two commonly cited forms, Diplomoceras cylindraceum and D. notabile, are considered to be conspecific by some authors, but treated as discrete taxa by others. The majority of records of species of Diplomoceras are from Maastrichtian strata; however, several late Campanian finds bring some discrepancy into the discussion about their biostratigraphical significance. Here we record new specimens from the upper Maastrichtian Kokuy Unit, refer them to Diplomoceras cylindraceum and briefly consider the geographical, biostratigraphical and taxonomic issues surrounding the genus Diplomoceras.

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Late Campanian–early Maastrichtian heteromorph-dominated ammonoid assemblages of the Nakaminato Group, central Honshu, Japan: biostratigraphic and paleontological implications

Cited by 5 publications

References 21 publications

Advanced mosasaurs from the Upper Cretaceous Nakaminato Group in Japan

Advanced mosasaurs from the Upper Cretaceous Nakaminato Group in Japan

Evolutionary process of extremely twisted heteromorph ammonites from the Upper Cretaceous of Japan

New records of Diplomoceras (Ammonoidea, Diplomoceratidae) from Koryak Upland, North-West Pacific Province: taxonomic, biostratigraphical and palaeogeographical implications

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