Search results for "Ammonite"
showing 10 items of 96 documents
The Use of Landmarks to Describe Ammonite Shap
1999
The use of landmarks and geometrical morphometric techniques is illustrated with examples from the Harpoceratinae (Ammonitina). This approach is useful in analysing morphological variations of characters such as rib pattern or ventral shape on the scale of the genus or species. It can be used to map forms so that similarities and dissimilarities between organisms can be read and quantified directly.
Episodic deposition of the Lias in the Medianes nappe (western Switzerland): a record from mineralized ammonite-bearing beds
1992
Abstract Sinemurian and Pliensbachian depositional sequences from the starved distal northern continental margin of the Tethys are preserved in the Medianes Nappe (Western Swiss Prealps). They contain mineralized beds which include a variety of facies. The northern continental margin of the Tethys was broken into blocks, less than 50 km wide, during an extensional phase. The Sinemurian and Pliensbachian sediments in the study are vary in thickness from less than 50 m in the north to more than 200 m in the south. Although the upper Sinemurian to Pliensbachian mineralized beds are thin, between 0.10 and 0.50 m thick, they commonly contain several distinct faunal horizons stacked one upon anot…
Cladistic analysis of the Middle Jurassic ammonite radiation
2004
Cladistic analysis of the Middle Jurassic ammonite radiation shows how the Aalenian-age ancestral stock, known variously as the Hammatocerataceae or Hammatoceratinae, gave rise to numerous new groups in Bajocian times. Cladistic analysis shows this ancestral stock is not a single lineage but two: the ‘Erycites group’, which gave rise to the Stephanocerataceae, and the ‘Hammatoceras group’, from which all other Bajocian groups derived.
Ammonoid morphological signal versus sea-level changes
1997
The morphological diversity, considered as a biological signal, of a series of four Upper Callovian (Middle Jurassic) ammonite populations of Côte-d’Or (France) is quantified. These populations fall within two third-order sequences of a second-order transgression. A sampling method that adheres as closely as possible to the morphological characteristics of the populations is established. It is valuable in that it eliminates the subjectivity related to taxonomy to allow more objective comparisons between the biological signal (shell morphology) and the physical signal (eustasy).
Integrated stratigraphy of the potential candidate Oxfordian GSSP at Thuoux and Saint-Pierre d'Argençon (France).
2013
5 pages; International audience; The Thuoux and Saint-Pierre d'Argençon sections (Subalpine Basin, southeastern France) are proposed as a potential GSSP candidate for the Callovian-Oxfordian boundary. Several aspects of stratigraphy that have recently been applied in the two selected sections are discussed, including ammonite and nannofossil biostratigraphy, palynology, physical stratigraphy, and cyclostratigraphy.
First record of the enigmatic coleoid genus Longibelus from Sakhalin (Far East Russia): a contribution to our understanding of Cretaceous coleoid hab…
2021
AbstractA newly collected specimen of the enigmatic coleoid genus Longibelus is recorded from lower Turonian strata along the River Shadrinka in Sakhalin (Russian Far East). To date, this is the first record of Late Cretaceous coleoid cephalopods from the island and, in fact, from the entire Pacific coast of the Russian Federation. Lithological characteristics, coupled with published geochemical analyses (δ13C and Corg content), suggest the habitat of this coleoid taxon to have been the middle to outer (i.e. distal) shelf. Its provenance from the stratigraphical level that is known as the Scaphites Event, characterised by a mass occurrence of Scaphites and Yesoites, may be indicative of occ…
Nouvelles données biostratigraphiques sur les dépots cénomanoturoniens du Nord-Est du fosse de ia Bénoué (Nigéria)
1993
Abstract The Upper Cretaceous deposits of the Upper Benue (North-East Nigeria) record regional and local events (sea-level changes, biological successions and tectonic movements) which throw light on the Upper Cenomanian transgression. Evidence of discontinuities and sedimentary assemblages well dated by micropalaeontological data, allows the sedimentary sequence to be interpreted in the context of sequence stratigraphy. The discovery of new ammonite faunas has enabled a more precise definition of the local biostratigraphy and a correlation of this with the standard zonal scheme. In the near future, when they are better known, the ammonite successions recognized in the Upper Benue could ena…
Heterochronic differentiation of sexual dimorphs among Jurassic ammonite species
1997
Ontogenetic and then heterochronic approaches are used here to analyze sexual differentiation within two well-known Jurassic dimorphic species. This analysis compares two ways of determining the relative biological age of ammonites, one using size (diameter) and the other the number of septa as a proxy of age. The shape standard is established from factor analysis of morphological and growth parameters. Size-age-shape relationships are analyzed on the basis of a new heterochronic representation. When diameter is used as a proxy of age, microconch morphs are globally considered to be progenetic compared with macroconch morphs. When size and age are determined separately and shape is included…
Fuciniceras paradoxus nov. sp. (Harpoceratinae, Ammonitina) du Domérien portugais. Réflexion sur le sens taxonomique d’un assemblage paradoxal de car…
2002
A new ammonite (Fuciniceras paradoxus) is described here. This Lower Domerian species is based on a recently revised collections which came from the Maria Pares section (Rabacal area, South of Coimbra, Portugal). Curiously, shell of F. paradoxus bears both diagnostic traits for the genus Protogrammoceras SPATH (e.g. acute ogival ventral area) and Fuciniceras HAAS (e.g. angulirursiradiate rib). Thus, the new species can be viewed as a morphological puzzle and as a challenge for taxonomists. The amazing collection of morphological traits previously suspected as highly improbable because of biomechanical constraints (1) confirms the inadequacy of the traditional use of the genera Protogrammoce…
Existe-t-il une crise au passage Lias-Dogger chez les ammonites? Approche morphometrique par quantification de la disparite morphologique
2001
Abstract Morphological changes observed in ammonites at the Lias-Dogger (Toarcian-Aalenian) boundary are analyzed here. The study covers all known ammonites worldwide over some 2 m.y. (the last two biozones of the Toarcian: Pseudoradiosa and Aalensis and the first biozone of the Aalenian: Opalinum). Ammonite taxonomy at this boundary is still open to question, the main disagreements being over groupings at family or super-family level. The evolutionary schema developed by Tintant and Mouterde [1981] shows two main sets of Ammonitina for the time: (1) the dominant Hammatocerataceae (Graphoceratidae+Hammatoceratidae) and (2) the final representatives of the Hildocerataceae. Two conservative a…