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Bert D.,Reserve naturelle nationale geologique de Haute Provence | Bert D.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites Gpa | Bert D.,French National Center for Scientific Research | Courville P.,French National Center for Scientific Research
Annales de Paleontologie | Year: 2016

The outstanding discovery of two heteromorph ammonites in Late Callovian and Early Oxfordian deposits, where such ammonites were deemed absent, substantially reduce the interval without heteromorph ammonite known into the Jurassic. A new species is described for the Early Oxfordian: Acuariceras acucostis sp. nov.; the Late Callovian Parapatoceras cf. tuberculatum is also studied. These latter expands our knowledge of the latest Parapatoceratinae and complete their stratigraphic distribution. The evolution of ornamentation between A. acuarius/. Paracuariceras incisum and A. acucostis sp. nov., from which it is derived, tends toward a net reinforcement of the ribs at least on the body chamber. Without the preservation of the suture lines however, it is difficult to know the relationships maintained between the new species and the genera Acuariceras and Paracuariceras. It is not excluded that these two genera, which are distinguished only on the basis of relatively discrete suturing criteria, could be synonymous. © 2016 Elsevier Masson SAS. Source


Bert D.,French National Center for Scientific Research | Bersac S.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites Gpa
Carnets de Geologie | Year: 2014

The Late Barremian Hemihoplitidae (Ancyloceratina, Ammonoidea) are widely known in the northern Tethyan Margin and the Essaouira-Agadir Basin (Morocco). Their rapid evolution and diversification make them one of the key groups for that period, but their origin remains poorly known and several competing hypotheses have been published. These hypotheses are tested here with cladistic analysis in order to reject those receiving the least support and discuss those well supported. The analysis discards the Crioceratitidae, Emericiceratidae (Emericiceras and Honnoratia) and Toxancyloceras as stem-groups of the Hemihoplitidae (Gassendiceras). The Toxancyloceras appear instead to be a sister-taxon of the Moutoniceras, so we propose the latter to be classified with the Ancyloceratidae rather than with the Heteroceratidae. The best supported hypothesis assumes that the Hemihoplitidae first appeared suddenly in the Essaouira-Agadir Basin at the end of the Early Barremian from small populations of Boreal Paracrioceras. These latter could have migrated southward episodically before invading the northern Tethyan margin at the beginning of the Late Barremian. As a consequence, the Paracrioceratidae fam. nov. is proposed to include the Boreal groups Fissicostaticeras/Paracrioceras/ Parancyloceras, and Gassendiceras essaouirae sp. nov. is proposed as a new name for the Moroccan endemic "Barrancyloceras" maghrebiense sensu COMPANY et al., 2008, non IMMEL, 1978. © 2014, Carnets de Geologie. All rights reserved. Source


Bert D.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites Gpa
Annales de Paleontologie | Year: 2014

The homogeneity of a large sample of Gassendiceras alpinum is tested statistically. The quantitative analysis did not reject the null hypothesis and the homogeneity of the sample is accepted. As a result, the different taxa used in the literature (G. alpinum, "Barrancyloceras barremense", Leroyiceras mascarellii and Spinocrioceras sauvanae) all fall into the variability of a single species, although some doubt subsist for L. dolloi. Taxonomically, by the priority principle the only name that should be used is G. alpinum. The results and other examples about the intraspecific variability confirm the importance of the Westermann's laws in ammonites, but they show that there are other important sources of covariation. In Gassendiceras the variability is tripolar (both the classic robust-slender poles of the Westermann's laws plus a third morphological pole with thick section and not so robust ornamentation), which implies that the intraspecific variability is not always uniform or consistent from one group to another, or in any case do not necessarily respond to the same factors in equivalent proportions. Heterochronies, erasing of the ornamentation and uncoiling of the heteromorph ammonites are also considered as factors of the intraspecific variability. © 2013 Elsevier Masson SAS. Source


Bert D.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites Gpa | Bersac S.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites Gpa | Delanoy G.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites Gpa | Delanoy G.,University of Nice Sophia Antipolis | Canut L.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites Gpa
Acta Geologica Polonica | Year: 2013

Bed-by-bed sampling of twelve Barremian sections in southeastern France from pelagic basin (Vocontian Basin) to neritic platforms (Arc of Castellane, Arc of Nice and Provencal Domain) has enabled the collection of isochronous samples of the ammonite genus Gassendiceras. Three poorly known species of the Toxancyloceras vandenheckei Zone (Upper Barremian) are revised: G. alpinum, G. multicostatum and G. hoheneggeri; two new species are described (G. rebouleti nov. sp. and G. bosellii nov. sp.). The intraspecific variability of particular species was recognised. This variability is between slender peramorphic and robust paedomorphic extreme morphologies, with the presence of all intermediates. Source

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