Search results for "Ammonoidea"
showing 10 items of 29 documents
Apparition d'une morphologie scaphitomorphe par miniaturisation chez une ammonite oxfordienne : Scaphitodites scaphitoides ()
1997
The pyritized fossil-bearing marls of the Jura (Lower Oxfordian) contain an ammonite that is remarkable because of its tiny adult size (less than 16 mm) and of the scaphitoidal coiling of its body chamber, which is similar to that of certain Cretaceous Scaphitaceae. Anatomical and ontogenetic analysis demonstrates that these individuals, which are ascribed to Scaphitodites scaphitoides (Coquand, 1853), formed a single species. We argue that the genus Scaphitodites derived from Taramelliceras by a complex process of progenesis (sensu Landman et al., 1991).
Late Carnian-Early Norian ammonoids from the GSSP candidate section Pizzo Mondello (Sicani mountain, Sicily).
2012
A small collection of ammonoids from the Upper Triassic Scillato Formation at Pizzo Mondello (Agrigento, Sicily) is studied. The specimens were collected in a framework of a project aimed at providing an integrated high-resolution bio-chronostratigraphic support to the Upper Carnian-Norian magnetostratigraphic scale defined at this site, that is located in an historical area from which G.G. Gemmellaro collected the Upper Triassic of ammonoids monographed at the beginning of the XX century. The specimens from Pizzo Mondello were bed-by-bed sampled and represent the first collection of Upper Triassic ammonoids described from Sicily since Gemmellaro time. Quite several levels of the Pizzo Mond…
Faunal invasions as a source of morphological constraints and innovations? The diversification of the early Cardioceratidae (Ammonoidea; Middle Juras…
2005
Abstract Multivariate analysis of shell characters and quantification of morphological diversity (morphospace occupation and disparity) are used here to investigate the modes of morphological diversification of ammonites. We define five events in early cardioceratid history that connect geographical changes causing emigration or immigration phases with biodiversity dynamics: (1) the initial colonization of the Arctic Basin by the Cardioceratidae at the end of the Bajocian, Middle Jurassic; (2) the first appearance of the Kosmoceratidae clade in the Boreal Realm during the Bathonian; (3) the ensuing expansion phase of this clade in the Boreal Realm; (4) the first phase of migration of the Ca…
Ammonite Faunal Dynamics Across Bio-Events During the Mid-and Late Cretaceous Along the Russian Pacific Coast
2012
The present paper focuses on the evolutionary dynamics of ammonites from sections along the Russian Pacific coast during the mid-and Late Cretaceous. Changes in ammonite diversity (i.e., disappearance [extinction or emigration], appearance [origination or immigration], and total number of species present) constitute the basis for the identification of the main bio-events. The regional diversity curve reflects all global mass extinctions, faunal turnovers, and radiations. In the case of the Pacific coastal regions, such bio-events (which are comparatively easily recognised and have been described in detail), rather than first or last appearance datums of index species, should be used for glo…
High-resolution dynamics of Early Jurassic marine extinctions: the case of Pliensbachian–Toarcian ammonites (Cephalopoda).
2010
Abstract: The Pliensbachian–Toarcian interval was marked by major environmental disturbances and by a second-order mass extinction. Here, we reappraise the taxonomic, spatiotemporal and selective dynamics of extinctions over the whole interval, by analysing a high-resolution dataset of 772 ammonite species from NW Tethyan and Arctic domains. On average, 40–65% of ammonite species disappeared during each subchronozone, but higher extinction pulses (reaching 70–90%) prevailed from the Margaritatus to the Dispansum Chronozone. The main extinctions, corresponding to the Gibbosus, Pliensbachian–Toarcian boundary, Semicelatum, Bifrons–Variabilis, and Dispansum events, differed in their dynamics, …
Ammonite faunas from condensed Cenomanian-Turonian sections (‘Tourtias’) in southern Belgium and northern France
2011
AbstractIn southern Belgium (Mons Basin and Tournai region) and northern France (area between Lille, Valenciennes and Maubeuge), condensed sequences have been referred to as ‘tourtias’ since the start of the nineteenth century. These levels correspond to a succession of trangressive systems tracts and generally appear as dark green, glauconitic and microconglomeratic facies. They are distributed all along the base of the more important transgressive systems tracts of the Cenomanian and basal Turonian from the Boulonnais (northwest France) to the Mons Basin (southern Belgium), through the Artois and Douaisis. Their age can now be determined more accurately by identification of their ammonite…
Les ammonites du Sinémuriensupérieur du Jebel-Bou-Hamid (Haut-Atlas central, Rich, Maroc). Approches paléontologique et biostratigraphique
1998
Resume L'etude des faunes d'ammonites - plus de 25 taxons - et de leur succession biostratigraphique dans unecoupe exceptionnellement complete et fossilifere du Haut-Atlas central de la region de Rich (Maroc) a permis la mise en evidence de 10 unites biochronologiques elementaires (=assemblages) pour une periode debutant au sein de la partie terminale du Sinemurien inferieur et s'achevant avec le Sinemurien superieur. Pour les zones a Oxynotum et Raricostatum, il s'agit des premieres donnees biostratigraphiques collectees avec une telle precision dans le Nord de l'Afrique. Pour le Sinemurien inferieur et la zone a Obtusum, les nombreuses donnees nouvellement acquises, completent, precisent …
Les ammonites du sinémurien supérieuret du carixien inférieur a moyen du gisement de lefterochori (Albanie méridionale). Témoin exceptionnel des faun…
2000
Resume L'exploitation du gisement de Lefterochori situe pres de Delvina a l'Est de Saranda (Zone ionienne, Albanie meridionale) a permis l'etude d'une riche faune d'ammonites datant du Sinemurien terminal et du Carixien inferieur a moyen. Une cinquantaine de taxons ont ete reconnus et trois especes nouvelles decrites (Lytoceras platypleura, Tropidoceras sulcatum et Protogrammoceras ionicum). Il s'agit en fait d'un materiel exceptionnel, tant en quantite qu'en qualite, car a l'exception de rares specimens isoles, les peuplements helleniques (Albanie et Grece) etaient jusqu'ici inconnus pour la periode consideree. Ces faunes presentent un maximum d'affinites avec celles de l'Apennin central e…
Les ammonites traditionnellement regroupées dans la sous-famille des Bouleiceratinae (Hildoceratidae, Toarcien) : aspects phylogénétiques, biogéograp…
2003
Resume Les genres d’ammonites, traditionnellement regroupes dans la sous-famille des Bouleiceratinae, appartiennent en fait a des lignees differentes de la famille des Hildoceratidae. Une approche utilisant des arguments paleogeographiques, stratigraphiques et morphologiques d’une part et une approche cladistique d’autre part ont permis de distinguer 3 groupes se succedant au cours du temps et a repartitions paleogeographiques differentes : • les Bouleiceratinae s.s. (genres Bouleiceras, Nejdia et Kohaticeras) du Toarcien inferieur ; • les Leukadiellinae (genres Leukadiella et Renziceras) du Toarcien moyen ; • et les Paroniceratinae (genres Frechiella, Paroniceras et Oxyparoniceras) du Toar…
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…