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Bert D.,Reserve naturelle nationale geologique de Haute Provence | Bert D.,CNRS Geosciences Laboratory of Rennes | Bert D.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites | Bersac S.,Laboratoire Du Groupe Of Recherche En Paleobiologie Et Biostratigraphie Des Ammonites | And 2 more authors.
Cretaceous Research | Year: 2017

Field sampling data in the Vocontian Basin (southeastern France) and Mallorca (Spain), at the transition between the lower and upper Barremian (upper Moutoniceras moutonianum Zone and lower Toxancyloceras vandenheckei Zone), provides new information about the early representatives of the ammonite family Ancyloceratidae. Several successive species of the genera Moutoniceras and Toxancyloceras are identified. A review of the history of the acquisition of the Astier collection by the Natural History Museum of London, which contains the holotype of the type-species T. vandenheckei, clarifies some misinterpretations which this species previously suffered. T. vandenheckei and M. eigenheeri are revised, and a new species is described: T. canuti sp. nov. With respect to an evolutionary perspective under biostratigraphic control, their phylogeny is considered (M. eigenheeri -> T. canuti sp. nov. -> T. vandenheckei). The hypothesis of the origin of the genus Toxancyloceras within the Moutoniceras is strengthened; this link is consistent both stratigraphically and morphologically. Moutoniceras appears to be the oldest known representative of the Ancyloceratidae, which is rooted in the early Barremian. The ontogenetic and evolutionary patterns of the phyletic lineage Moutoniceras/. Toxancyloceras are twofold: the first concerns the ornamental changes (itself determined by three imbricated patterns) and the second involves the adult size. Both patterns determine two evolutionary phases through time: (1) the giant Moutoniceras and the progressive disappearance of the tubercles through heterochrony (paedomorphosis), and (2) the drastic size reduction and the reappearance of the tubercles from the "small" Moutoniceras to the Toxancyloceras (through heterochrony, with peramorphosis and a combination of pseudo-dwarfism, acceleration and graduaptation). The oscillation in disappearance and reappearance of the tubercles demonstrates a possible case of evolutionary reversibility where heterochrony helped by the progenesis impact, favours character repeatability in the evolutionary patterns. The results for the genera Moutoniceras and Toxancyloceras have significant biostratigraphic implications for the Tethyan Barremian. The status of T. vandenheckei as a zonal and subzonal index species (basal upper Barremian) is reinforced, and three new ammonite horizons are defined: the Moutoniceras eigenheeri, Toxancyloceras canuti and T. vandenheckei horizons. The stratigraphic distribution of all their index species is very restricted, indicating a well established evolutionary context. © 2017 Elsevier Ltd.


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.

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