Search results for "Ammonitina"
showing 9 items of 9 documents
Problems in the identity of "Crioceras" barremense Kilian, 1895 (Ancyloceratida, Late Barremian), and their proposed resolution
2010
17 pages; The study of "Crioceras" barremense KILIAN was undertaken as a part of the revision of the Hemihoplitidae. This species was considered "classic" and has been used as the index of an Upper Barremian subzone; this usage raises a number of problems. The type specimen from Tyrol was a fragment described and illustrated by UHLIG as Crioceras sp. ind. aff. roemeri. This specimen could not be retrieved, and a topotype could not be collected. Our study revealed that there is both a biostratigraphic hiatus and important differences between conceptions of this species: (1) that ascribed UHLIG's type specimen (Upper Barremian, Tyrol), (2) KILIAN's concept of the specimen he found and named "…
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…
Les Gregoryceras (Ammonitina) de l'Oxfordien moyen terminal et supérieur téthysien : révision systématique, biostratigraphie et évolution.
2009
43 pages; Les Gregoryceras Spath, 1924 (Ammonitina, Peltoceratina) de la fin de l'Oxfordien moyen (sous-zone à Rotoides) et de la base de l'Oxfordien supérieur (zone à Bifurcatus) sont révisés. Les coupes ayant fourni la plupart des spécimens de ce travail (Espagne et Maghreb) sont décrites et datées sur la base de comparaisons fauniques entre les domaines téthysien et subtéthysien. Le meilleur outil pour ces corrélations est la présence du genre Gregoryceras. La succession des espèces de Gregoryceras est identique pour les deux domaines suscités, ce qui permet de compléter l'échelle biostratigraphique proposée antérieurement et parallèle à la zonation standard. Les espèces reconnues et red…
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.
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…
World distribution of middle Jurassic ammonites (Upper Aalenian to Middle Bathonian): relationships between biodiversity and palaeogeography
2004
Abstract The break up of the Pangea takes place in the Jurassic; the palaeoceanographic consequences are the opening of seaways, particularly at the place of the future Atlantic and Indian oceanic areas. During the Toarcian, and from the late Aalenian to the middle Bathonian, the so-called “Hispanic corridor” (or “Atlantic seaway”) exists between the “western Tethys” and the “American Pacific border”, through the “Caribbean Tethys”. Two additional seaways which play as by-passes of the Pangea are proposed, one along the northern border of Laurasia (Boreal sea), and a second along the southern border of Gondwana (South Pacific Sea); however, if these two last could be effectively used for fa…
Leptechioceras (Neomicroceras) Donovan, 1966 (Ammonitina, Echioceratidae, Sinémurien, Europe du Nord-Ouest): Taxon progénétique ou microconque?
1992
Resume Des faunes d'ammonites inedites collectees banc par banc dans des series epaisses a dominante argileuse duSinemurien terminal du Bassin parisien (Cher, France) sont decrites. Certains des peuplements etudies sont esentiellement constitues d'ammonites de petite taille attribuees au sous-genre Leptechioceras (Neomicroceras) ; le rattachement de ces formes aux Echioceratidae, alors qu'elles etaient initialement interpretees comme des Eoderoceratidae, est base sur des arguments cladistiques et est confirme par les observations stratigraphiques. Une nouvelle espece, la plus tardive du sous-genre, Leptechioceras (Neomicroceras) sparsicosta est decrite. L'originalite en termes d'heterochron…
Modalités évolutives du genre bullatimorphites (Ammonitina) au Bathonien-Callovien (Jurassique moyen) en Europe occidentale
1999
Abstract The genus Bullatimorphites, (macroconchs Bullatimorphites, Kheraiceras; microconchs Bomburites, Schwandorfia, Spbaeroptycbius, Treptoceras), is characterized by an ontogenesis with three morphologic phases: serpenticone, sphaerocone and ellipticone. Within the successive populations, the relative development of these morphologies allows the defined species to be placed in an evolutive and stratigraphic lineage. The history of the genus comprises five steps: 1) emergence (Early Middle Bathonian), 2) first gradual evolution (Middle-Upper Bathonian), 3) first morphological diversification (Uppermost Bathonian), 4) second gradual evolution, 5) second morphological diversification and e…
Le Toarcien inférieur et moyen du Quercy méridional études stratigraphique, sédimentologique et paléoécologique d’après la nouvelle coupe de Caylus (…
2017
The study of a new section around Caylus (Tarn-et-Garonne) allows new biostratigraphic and sedimentological observations on the terms of passage from the Upper Pliensbachian (Formation of the Barre à Pecten) to the Toarcien (Formation de Penne) of the Quercy (France). The Schistes cartons member (Lower Toarcian, Serpentinum zone) is particularly remarkable.Four taxa of brachiopods and eleven taxa of Toarcian ammonites from the Tenuicostatum, Serpentinum and Bifrons zones, sub-zone to Sublevisoni are the subject of the following paleontological study.