THE LATE ALBIAN GENUS SEMENOVICERAS (HOPLITIDAE, AMMONITINA): PALAEONTOLOGIC STUDY OF A FAUNA OF THE SEMENOVICERAS LITSCHKOVI ZONE FROM MANGYSHLAK (WEST KHAZAKSTAN)

The ammonites collected during an expedition to Mangyshlak in September, 1995,, are described. Three ammonitiferous levels were sampled in an arenaceous formation characterised by ferruginous, phosphatic metric concretions. The six species recognised in the two older levels belong to the genus Semenoviceras Wright, 1996 (pro Semenovites Glazunova, non  Tarbinskii, 1932), which was widespread in Central Asia mainly during the Late Albian. The third level yielded only a specimen of the mid-Cenomanian genus Cunningtoniceras, which will not be described. The second Semenoviceras -bearing level contained an extremely rich fauna of the S. litschkovi zone, S. pseudocoelonodum subzone, defined in the former Soviet Union and correlated with the Diploceras cristatum zone of western Europe. The present study allowed the intraspecific variability of Semenoviceras pseudocoelonodum (Semenov) to be defined, since the holotype was originally established on the basis of a single fragment. Furthermore, the subdivision in the subgenera Semenoviceras s. str. and Planihoplites is maintained.   &nbsp

THE APPEARANCE OF THE GENUS DESHAYESITES (KAZANSKY, 1914, AMMONOIDEA) IN THE LOWERMOST APTIAN (LOWER CRETACEOUS) OF LA BÉDOULE (SE FRANCE)

New palaeontological and biostratigraphic investigations were carried out at La Bédoule (SE France), which is the stratotype-area of the Bedoulian (Lower Aptian). The levels that directly overlie the last Barremian Pseudocrioceras-bearing bed revealed the occurrence of a fauna characterized by previously undescribed macroconchs of the genus Deshayesites, that we included in Deshayesites bedouliensis n. sp. and in D. aff. consobrinus (d’Orbigny). These forms are associated with the species Deshayesites antiquus Bogdanova, D. oglanlensis Bogdanova, D. cf. weissiformis Bogdanova, D. aff. weissiformis Bogdanova in Delanoy, D. cf. planicostatus Bogdanova, and D. aff. normani Casey. These ammonites characterize the basal Aptian Deshayesites tuarkyricus Zone. This Zone was defined in Turkmenistan but its recognition in the Mediterranean Tethys is confirmed by the present study. Contrary to previous assertions, the genus Prodeshayesites (which pre-dates Deshayesites in northern Germany and southern England), whose FAD was taken to mark the base of the Aptian, is absent at La Bédoule. Prodeshayesites is absent also in Turkmenistan and in all other Mediterranean localities. The FAD of the genus Deshayesites is taken to mark the base of the Aptian in the Mediterranean area.&nbsp

THE APTIAN STRATIGRAPHY OF SOUTHERN TUARKYR (NW TURKMENISTAN, CENTRAL ASIA)

The ammonite successions of Turkmenistan, particularly those of the Greater Balkhan and Tuarkyr areas, are considered references for the Aptian Stage. Six sections across the uppermost Barremian - basal Upper Aptian interval were studied in the Tuarkyr desert in October 1997,and ammonites and bivalves were collected. Data are compared with those from a section sampled by a Russian team in 1959. The stratigraphic distribution of the faunas in the sections is discontinuous, as the fossiliferous levels intercalate with terrigenous sediments. The ammonite faunas, at least in the intervals sampled, show low diversity and are dominated by the genus Deshayesites in the lower Aptian and the genus Epicheloniceras, associated with the less common Caspianites, in the basal upper Aptian. The Turkmenistan sections contain species present also in the Caucasus, England, Germany, France and Switzerland, indicating that the Turkmenian faunas reflect impoverishement rather than geographic isolation. The chronologic equivalence between the Turkmenian Epicheloniceras subnodosocostatum Zone and the Epicheloniceras martinioides Zone in England seems questionable because the Epicheloniceras-bearing beds of the Tuarkyr correspond to the upper part of the E. martinioides Zone, i. e. the Epicheloniceras buxtorfi Subzone. The bivalve fauna consists mainly of pteriids, Exogyrinae oysters and trigoniids. These groups undoubtedly indicate a very shallow, fairly warm and fully marine environment, typical of the Tethyan Lower Cretaceous. The heterodonts are too rare to give further bathymetric indications. None of the taxa indicate deep burrowing and all are assumed to be ?? littoral. The bivalve fauna shows strong affinities with that of the English Lower Greensand.&nbsp

LATE BARREMIAN-EARLY APTIAN AMMONITES FROM THE MAIOLICA FORMATION NEAR CESANA BRIANZA (LOMBARDY BASIN, NORTHERN ITALY)

The ammonite faunas collected in three marly interbeds of the Maiolica limestone exposed near Cesana Brianza (Como province, Lombardy) are described in this paper. The age of the first and second interbeds is Late Barremian. In particular the first is tentatively ascribed to the sartousi zone and the second to the feraudi/giraudi zones. The new specíes Toxoceratoides sudalpinus sp. n. has been collected in the second level. The fauna of the youngest interbed does not allow us to recognize a specific ammonite zone, although it can be ascribed to the Barremian-Aptian boundary or even the basal Aptian. It is characterized by the occurrence of Leptoceratoidinae which were not reported before from this stratigraphic level

Ammonites from the latest Aalenian-earliest Bathonian of La Baume (Castellane area, SE France): palaeontology and biostratigraphy

Middle Jurassic strata are naturally exposed around the village called La Baume, near Castellane (Alpes de Haute Provence, SE France). We have realized both a detailed log and a bed-by-bed sampling for ammonite biostratigraphy in a 68 metres thick succession of subpelagic marls and limestones ("Calcaires à Zoophycos”) that spans the Middle Jurassic from uppermost Aalenian to lowermost Bathonian. The subpelagic succession can be roughly subdivided into three members. Ammonites from the Upper Aalenian Concavum Zone, all Lower Bajocian Zones (Discites Zone, Laeviuscula Zone including Ovale Subzone, Humpriesianum Zone), one Upper Bajocian Zone (Parkinsoni Zone) and probably one lower Bathonian Zone (Zigzag Zone) were found. A major gap of both the Niortense Zone and the Garantiana Zone, which was not previously described, was detected at the boundary between members 2 and 3. The main palaeontological interest of the ammonite fauna from La Baume is the richness and diversity of the family Sonniniidae, which is the subject of a systematic study and figurated along with some biostratigraphically significant forms. Biostratigraphical results and open problems are discusse

La dimension biogéographique de l'évolution de la vie

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La dimension biogéographique de l’évolution de la Vie

Le rôle de la composante biogéographique dans les mécanismes de l’évolution biologique fait l’objet de discussions entre les évolutionnistes. Dans ce travail, les idées de Darwin dans le contexte de la biogéographie sont discutées après avoir rappelé le rôle de l’élément géographique dans les processus de spéciation et résumé les notions de base et les modèles théoriques classiques de la biogéographie. Le modèle de Darwin, ou de la dispersion à partir d’un « centre d’origine », fut proposé lorsque les preuves de la mobilité continentale n’étaient pas encore concluantes. Le modèle de la vicariance, qui s’oppose à celui de la dispersion, est maintenant soutenu par la dérive continentale et l’expansion des fonds océaniques. Ces deux modèles classiques de la biogéographie pourraient s’appliquer dans les cas de convergence et divergence biogéographique, en relation avec des changements paléogéographiques.The role that biogeography plays in the mechanisms of biological evolution is strongly debated. Darwin’s ideas are discussed in the present paper on the basis of a short review of the role of the geographic dimension in speciation processes, and of the basic concepts and classic models of biogeography. Darwin’s model of dispersal from a “centre of origin” was proposed when proofs of continental motion were not yet conclusive. The vicariant model, opposed to the dispersal one, is now supported by plate tectonics and ocean floor expansion. These two classic models of biogeography could correspond to cases of biogeographic convergence and divergence, which are related to palaeogeographic changes.</p

Ammonites du Pliensbachien supérieur (Jurassique) du Lac de Charmes (Haute-Marne, France) : systématique, biostratigraphie et paléobiogéographie

Cet article présente la description d’une faune riche et bien préservée d’ammonites du Pliensbachien supérieur collectée dans deux affleurements bordant le lac de Charmes (Haute-Marne, France). En termes de zonation, la faune indique les chronozones à Margaritatus et à Spinatum. Pour la première fois dans cette région, la plupart de leurs subdivisions ont été reconnues. Nous proposons une corrélation avec les biozonations établies dans les régions avoisinantes (Allemagne et Sud de la France). Nos résultats confirment la possibilité de subdiviser plus finement la zonule à Solare, ce qui avait été précédemment suggéré par d’autres auteurs. Nous reconnaissons un premier intervalle avec seulement Pleuroceras solare (Phillips, 1829) et un second où cette espèce présente plusieurs sous-espèces et où apparait Pleuroceras spinatum (Bruguière, 1789). Un point de vue est donné à propos de Amaltheus gr. margaritatus Montfort, 1808 et Pleuroceras gr. solare (Phillips, 1829) ainsi qu’à propos de l’espèce Pleuroceras transiens (Frentzen, 1934).The present paper deals with the systematic description of a rich and well-preserved ammonite fauna of the Late Pliensbachian, collected in two outcrops near the “Lac de Charmes” (Haute-Marne, France). In terms of ammonite zonation, the studied faunas indicate the Margaritatus and Spinatum Chronozones. Most of their subdivisions (subchronozones and zonules) have been recognized for the first time in this region. We propose a correlation with zonations established in close areas (Germany, Southern France). As already suggested on the literature, the possibility to further subdivide the Solare zonule in finner intervals is confirmed by our data. Within this zonule, we recognize a first interval with only Pleuroceras solare (Phillips, 1829), and a second one where this species occurs with several subspecies and where Pleuroceras spinatum (Bruguière, 1789) appears. Our results also confirm the possibility to subdivide more finely the Solare zonule firstly suggested by some authors. We recognize a first part with only Pleuroceras solare and a second one where this species present various subspecies and where Pleuroceras spinatum appears. Some points of view are given about Amaltheus gr. margaritatus Montfort, 1808, Pleuroceras gr. solare (Phillips, 1829) and the species Pleuroceras transiens (Frentzen, 1934).</p

Appendix 1: List of cladistic characters published on ammonites

The file here provided, is the list of all characters that have been used in cladistic analysis on ammonoids published so far. It constitutes the base of a study which investigates practices in characters establishment. Find here after the abstract of the article that is associated to this file. Cladistics appears as one of the most useful method to reconstruct phylogeny of fossil taxa. However, ammonoids workers tend to sulk this method. The capital step of cladistic analysis is the recognition of homology hypothesis as clue to reconstruct monophyletic clades based on the sharing of derived traits. Previous authors have suggested that coding schemes are usually direct transcription of original taxa description. However, establishing a list of characters (i.e. a matrix taxa /characters) is a very different work compared to a compilation of diagnoses. How morphology is coded in ammonoids? How coding schemes are influenced by traditional descriptions / characters? Here, we review all cladistic analyses of ammonoids published in the literature to compare characters and the way authors have dealt with the treatment of continuous characters, polymorphism and ontogeny. Several barriers are usually invoked to justify that cladistics cannot be applied to reconstruct ammonoids phylogenies. We show that an appropriate use of improvements both on ammonoids' knowledge and cladistics methodology may overcome limitations usually invoked to perform cladistic analysis on ammonoids