1,721,036 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)
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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
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 Trachyeratidae from South Canyon (central Nevada) : record, taxonomic problems and stratigraphic significance
No full textConodonts from the Ladinian-Carnian boundary beds of South Canyon, New Pass Range, Nevada, USA
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Taxonomy and stratigraphic significance of Trachyceras silberlingi n. sp., from the Lower Carnian of South Canyon (New Pass Range, central Nevada, USA
Full text linkSouth Canyon, località tipo della Zona a Desatoyense, la prima zona del Carnico nella scala
cronostratigrafica nordamericana, nel 2010 e 2011 è stata oggetto di campionamenti strato-per-strato che hanno permesso di individuare
una specie nuova di Trachyceras, che viene descritta in questo lavoro. La specie è dedicata a Norman J. Silberling (1928-2011) che per 50
anni è stato l’autorità indiscussa per la stratigrafia del Triassico marino nella parte occidentale degli Stati Uniti. Trachyceras silberlingi n.
sp. è caratterizzato da un’ornamentazione molto particolare, che consiste in due serie spirali di bullae sul fianco, una in posizione vicina al
margine ombelicale e una a circa il 70% di altezza del fianco, e da coste che spesso si congiungono a coppie alla bulla laterale.
La nuova specie è stata raccolta dal sito F, il sito stratigraficamente più alto del membro medio della Augusta Mountain Formation di
South Canyon, ove rappresenta la prima sicura presenza del genere Trachyceras Laube, 1869. Per questo motivo la nuova specie T. silberlingi
è estremamente utile per una prima revisione della Zona a Desatoyense, basata originariamente su raccolte di ammonoidi effettuate nella
parte inferiore del membro medio della Augusta Mountain Formation, senza distinzione sui livelli di raccolta. Si propone quindi la sostituzione
della Zona a Desatoyense con due unità biostratigrafiche. I Daxatina beds sono una biozona informale caratterizzata dalla presenza di
Daxatina e Frankites sutherlandi, e sono seguiti dalla biozona a Trachyceras silberlingi. Quest’ultima è una zona di distribuzione formalmente
istituita in questo lavoro, caratterizzata dalla presenza di Trachyceras. Viene delineato il significato cronostratigrafico delle due biozone, ma
il completamento della revisione del Carnico Inferiore della scala nordamericana sarà possibile solo dopo il completamento della revisione
tassonomica di tutte le faune raccolte.New intensive bed-by-bed ammonoid collecting efforts conducted in 2010 and 2011 at South Canyon, the type locality
of the lowest Carnian Desatoyense Zone of the North American chronostratigraphic scale, have lead to the recognition of a new species
of Trachyceras that is herein described. The new species is dedicated to Norman J. Silberling (1928-2011), who was widely recognized as
the leading authority on marine Triassic stratigraphy in western US for over 50 years. T. silberlingi n. sp. is characterized by a peculiar
ornamentation consisting of two spiral rows of bullae on the flank (first row on umbilical shoulder and second row at about 70% of whorl
height) and by ribs frequently looped in pairs at the lateral bulla.
The new species, from South Canyon site F, the stratigraphically highest level of the fossiliferous succession of the middle member of
the Augusta Mountain Formation, represents the first definite occurrence of the genus Trachyceras Laube, 1869 in this succession. For this
reason T. silberlingi n. sp. is of great importance for the revision of the Desatoyense Zone, a unit defined on the basis of a large collection
of ammonoids described in 1941 from the lower part of the middle member of the Augusta Mountain Formation, without regard for the
number and position of fossil bearing levels. We herein propose the subdivision and replacement of the former Desatoyense Zone with two
biostratigraphic units: the lower unit referred to as the Daxatina beds, is an informal biozone characterized by the occurrence of Daxatina
and Frankites sutherlandi, and the overlying Trachyceras silberlingi biozone is a range zone characterized by the occurrence of Trachyceras,
based on the new species. The chronostratigraphic potential of this proposed subdivision is briefly outlined, but it will be more accurately
defined upon completion of the taxonomic revision of the South Canyon ammonoid faunas
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