Search results for "Ammonoidea"
showing 10 items of 29 documents
Revision of the genus Anasibirites Mojsisovics (Ammonoidea): An iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction
2016
34 pages; International audience; The family Prionitidae Hyatt represents a major component of ammonoid faunas during the Smithian (Early Triassic), and the genus Anasibirites Mojsisovics is the most emblematic taxon of this family. Its stratigraphical range is restricted to the beginning of the late Smithian (Wasatchites distractus Zone). The genus is also characterized by an unusual cosmopolitan distribution, thus contrasting with most earlier Smithian ammonoid distributions that were typically restricted by latitude. Because the late Smithian witnessed an extinction of the nekton (e.g. ammonoids, conodonts) whose amplitude is equal to or larger than that of the end-Permian crisis, the nu…
Griesbachian and Dienerian (Early Triassic) ammonoid faunas from Northwestern Guangxi and Southern Guizhou (South China).
2008
30 pages; International audience; Intensive sampling of the Luolou (northwestern Guangxi) and the Daye (southern Guizhou) Formations in South China leads to the recognition of a regional Griesbachian and Dienerian ammonoid succession for this key palaeobiogeographical area. The new biostratigraphical sequence comprises the upper Griesbachian ‘Ophiceras beds' and the lower Dienerian ‘Proptychites candidus beds', which are separated from the uppermost Dienerian ‘Clypites beds' by an unfossiliferous interval. These faunas contain some taxa with wide geographic distribution (e.g. Ambites, Pleurambites, Pleurogyronites, Proptychites candidus), thus facilitating correlation with faunal succession…
Les Ammonoïdes (Mollusca, Cephalopoda) : avancées et contributions récentes à la paléobiologie évolutive.
2009
12 pages; Les ammonoïdes qui perdurent 335 Ma constituent un modèle de choix dans l'analyse du fait évolutif. Cet article de synthèse se propose d'aborder (1) : leur place phylogénétique au sein des céphalopodes et le choix d'un modèle actuel de référence ; (2) : la construction d'espaces phénotypiques qui offrent un angle d'étude pertinent de l'évolution biologique ; (3) : les concordances et discordances entre reconstruction phylogénétique et registre fossile et (4) : les reconquêtes postcrises, modèles d'étude de l'évolution à grande échelle. Il ressort que les ammonoïdes peuvent servir d'appui à de nombreuses thématiques paléontologiques (dynamique de la biodiversité, analyse phylogénét…
Pseudoshasticrioceras bersaci nov. sp. (Ammonoidea, Gassendiceratinae), and new ammonite biohorizon for the Upper Barremian of southeastern France
2009
International audience; Research in the Feraudianus Subzone of the Sartousiana Zone of the Barremian stage led to the discovery of a new species of Pseudoshasticrioceras: P. bersaci nov. sp. Its study provides evidence concerning the developments of the latest Gassendiceratinae BERT et alii, 2006, and the relationship between the genus Pseudoshasticrioceras DELANOY, 1998, and Gassendiceras BERT et alii, 2006. In particular, this new species is derived from Pseudoshasticrioceras magnini (DELANOY, 1992) by a minor revision in the processes of ontogenesis (retardation of ornamentation - neoteny). However, the evolution towards Pseudoshasticrioceras autrani DELANOY, 1998, implies a "failure" in…
L’origine des Imerites Rouchadze, 1933 : résultat d’une innovation chez les Gassendiceratinae Bert, Delanoy et Bersac, 2006 (Ammonoidea, Ancylocerati…
2009
15 pages; La découverte récente de plusieurs spécimens remarquables d'Imerites dichotomum (Ammonoidea, Ancyloceratina) apporte de nouvelles précisions paléontologiques sur ce genre. L'étude du développement ontogénétique montre que les Imerites dérivent directement du genre Pseudoshasticrioceras. Leur origine se situe donc parmi les Gassendiceratinae et non chez les Heteroceratidae comme il était généralement admis. Par ailleurs, la cohabitation de formes macroconques et microconques au sein des espèces du genre Imerites confirme l'hypothèse du dimorphisme. Les nouvelles données paléontologiques obtenues montrent que le taxon « Crioceras » cristatus est un nomen dubium et qu'il doit être ab…
Description de Artareites landii nov. (Ammonoidea) du Barrémien supérieur de Majastre (sud-est de la France) et discussion sur les Helicancylidae Hya…
2009
25 pages; Dans le secteur de Majastre (Alpes-de-Haute-Provence, SE de la France), le domaine hémipélagique du Crétacé inférieur est exposé à la faveur du décrochement du Poil. Cette position paléogéographique et paléotectonique a permis la récolte d'une faune d'ammonites diversifiée dans le niveau à « petits Barremites ». Il est précisément daté ici pour la première fois et se place entre la base de la sous-zone à Barremense et la base du biohorizon à Breistrofferi de la biozone à Vandenheckei (base du Barrémien supérieur). Au sein de cette faune, Artareites landii nov. sp. est considéré ici, par ses caractéristiques et sa position stratigraphique, comme issu du genre Dissimilites Sarkar. L…
Globacrochordiceras gen. nov. (Acrochordiceratidae, late Early Triassic) and its significance for stress-induced evolutionary jumps in ammonoid linea…
2013
<i>Globacrochordiceras transpacificum</i> gen. et sp. nov. is an ammonoid (Ammonoidea, Cephalopoda) with a shell characterized by plicate ribbing (rounded and undulating ribs strengthening on the venter without interruption), increasing involution through ontogeny, overhanging and deep umbilical wall, absence of tuberculation, subtriangular whorl section, globose adult shape with a closed umbilicus followed by an abrupt egressive coiling, and a subammonitic adult suture line. This new taxon occurs in Nevada (USA) and in Guangxi (South China). It has its typical occurrence within the <i>Neopopanoceras haugi</i> Zone of late Spathian age (Early Triassic). The plicate r…
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…
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…
Ammonites on the Brink of Extinction: Diversity, Abundance, and Ecology of the Order Ammonoidea at the Cretaceous/Paleogene (K/Pg) Boundary
2015
We examined the stratigraphic distribution of ammonites at a total of 29 sites around the world in the last 0.5 myr of the Maastrichtian. We demarcated this interval using biostratigraphy, magnetostratigraphy, cyclostratigraphy, and data on fossil occurrences in relation to the K/Pg boundary in sections without any facies change between the highest ammonites and the K/Pg boundary. The ammonites at this time represent all four Mesozoic suborders comprising six superfamilies, 31 (sub)genera, and 57 species. The distribution of ammonites is dependent on the environmental setting. Recent data suggest that ammonites persisted to the boundary and some species may have survived for several tens of…