196,104 research outputs found
Towards the definition of the GSSP of the Norian stage: report on the ongoing activities of the Italian working group.
No full textDiscovery of upper Ladinian ammonoids at the type locality of the lower Carnian desatoyense zone (South Canyon, New Pass Range, Nevada)
No full textCymbospondylus vertebrae (Ichthyosauria, Shastasauridae) from the Upper Anisian Prezzo Limestone (Middle Triassic, Southern Alps) with an overview of the chronostratigraphic distribution of the group.
No full textFour vertebral centra from the well known fossil-bearing Prezzo Limestone (Upper Anisian, Middle Triassic) of the new locality Piazza Brembana (Bergamo) are described. The four bones were originally articulated and exposed on bed surface. Despite the incompleteness of three centra due to the erosion, the fairly good preservation allowed their study and their attribution to a shastasaurid ichthyosaur; the diapophysis reaching the cranial margin of the centrum are considered as diagnostic for the genus Cymbospondylus Leidy, 1868 (Sander 1997; Maisch & Matzke 2000).
The new finding comes from an ammonoid-bearing facies, as usual for ichthyosaurs. The bio-chronostratigraphic position of Piazza Brembana bones is well constrained by ammonoids from the lowest part of the Paraceratites trinodosus Zone (Illyrian, Middle Triassic). The record of Cymbospondylus in the Southern Alps and the Germanic Basin is summarized and all the previous occurrences of the genus are bio-chronostratigraphically calibrated by using the rich ammonoid literature available. The genus spans from the Pelsonian (late Middle Anisian) to the Longobardian (Late Ladinian) and its stratigraphic distribution is strictly controlled by the development of the basins. Within the basins the distribution of the specimens seems to include relatively protected and shallow waters. Such a distribution is consistent with the mode of life of this group of ichthyosaurs, suggested by morphofunctional analysis. Cymbospondylus probably was an undulatory swimmer, better manoeuvrer but slower than their Jurassic forthcomer
In the search for a “golden” event to define the GSSP of the Norian Stage (Upper Triassic): bivalve events and their ammonoid calibration
No full textThe Italian journal of geosciences is increasing its appeal among geoscientists
No full textThis is an Editorial of the new Editorial Board of the Italian Journal of Geosciences, composed by Marco Balini (Milan), Hugo Bucher (Zürich), Simonetta Cirilli (Perugia), Laura Crispini (Genoa), Maurizio Mazzucchelli (Modena), and Giulio Ottonello (Genoa), which underlines the progress in the appeal of the journal among Geoscientists
Taxonomic revision, stratigraphic significance and phylogeny of the Bithynian ammonoid genus Kocaelia Fantini Sestini, 1990 (Anisian, Middle Triassic)
No full textThe potential of the integrated study of historical type specimens and newly collected (bed-by-bed) topotypes towards a much improved definition of modern, population-based and phylogeny-oriented taxonomy is here demonstrated by our case study of Kocaelia FANTINI SESTINI, 1990 and Semibeyrichites KRYSTYN & TAZTREITER, 1991.The systematic relationship of these two Middle Anisian Beyrichitidae has been a matter of considerable debate for the past three decades.
Our study of the type specimens of Aspidites toulai ARTHABER, 1914, type species of Kocaelia, collected from Gebze (NW Turkey), reveals that this species was incorrectly figured by Arthaber in 1914. The ventral side of this species is subtabulate instead of rounded as reported in the original figuration. As a result, the original definition of Kocaelia by Fantini Sestini, based mainly on its subtabulate venter, is indeed correct. Thus, Semibeyrichites KRYSTYN & TATZREITER, 1991, also based on a subtabulate venter and typified by S. ruttneri KRYSTYN & TATZREITER, 1991 from Aghdarband (NE Iran), becomes a junior synonym of Kocaelia. The study of the type specimens of Semibeyrichites ruttneri allows us to demonstrate that this species is congeneric with K. toulai, differing by its thicker whorl section.
Most of the type specimens of K. toulai share a subtabulate venter, while their ammonitic suture lines differ only in the depth of the external lobe E from specimen to specimen. Unfortunately, the type specimens of K. toulai and K. ruttneri were collected without information as to their stratigraphic position in the section; consequently the specimens cannot be studied utilizing a populationistic and stratigraphic (stratophenetic) approach in order to test the significance of the slight difference in suture lines. However, such a study is possible with the Assereto collection, which was formerly studied by FANTINI SESTINI in the 1980s. Assereto amassed his collection from the exact same locality (Gebze, Turkey) where the ammonoids studied by Arthaber were found. Our study of this collection is focused on the suture line, which is well preserved in some tens of specimens. A comparison of specimens collected from the same beds with those from stratigraphically higher beds, reveals the existence of three main components in the variation of the suture line. The most interesting one is stratigraphic and consists of a gradual deepening of the external lobe E as exhibited by specimens from the Nicomedites osmani chronozone as compared to those of the overlying Aghdarbandites ismidicus chronozone. Both chronozones, originally defined at Gebze, are therefore revised as to their boundaries and scope. Stratophenetic comparison of bed-by-bed collected topotypes of Kocaelia toulai, with bed-by-bed topotypes of Nicomedites osmani TOULA and Aghdarbandites ismidicus (ARTHABER), species both originally described from Gebze, has enabled us to establish the first reconstruction of the phylogeny of the early Tethyan Beyrichitidae, mainly based on their suture lines. In the Tethys Realm this family developed in the Middle Anisian a first lineage Nicomedites-Kocaelia, whereas Aghdarbandites, in part coeval with Kocaelia, bears no relationship with the latter. Evidence for the ancestor/descendant relationship of Nicomedites and Kocaelia is found in the ammonitic suture line with its shallow external lobe, and in the shell ornamentation. Aghdarbandites and Nicomedites share a subammonitic suture line with a shallow external lobe, but the former differs by its stronger ribbing and the presence of three rows of nodes on the flank. Further investigation is necessary to clarify the possible relationships between Aghdarbandites and Nicomedites
The Trachyeratidae from South Canyon (central Nevada) : record, taxonomic problems and stratigraphic significance
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