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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 ammo- noids? 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.

Palaeogeographers, geographers and structural geologists use different well-defined terms to designate continental and tectonic units, whereas biogeographers, palaeobiogeographers and palaeontologists use a wide range of subjective terminologies to describe biogeographical and palaeobiogeographical units. The absence of clear definitions and of rules or guidelines for palaeobiogeographical nomenclature has resulted in frequent misunderstandings and general confusion, in particular when applied to ancient time periods, such as the Palaeozoic. Palaeogeographical and palaeobiogeographical terminology used in Palaeozoic geology and palaeontology is reviewed, and recent attempts to standardize palaeobiogeographical nomenclature summarized. We make a number of proposals for future use of terms to avoid confusion and misunderstandings.

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 discussed.

The siliciclastic, up to 4,000 m thick Upper Triassic–Bajocian Shemshak Formation is widespread across the Iran Plate, especially in the Alborz Mountains of northern Iran. In contrast to its lower, generally non-marine part, the upper part is marine. Based on the Tazareh section of the eastern Alborz, an integrated analysis of this marine interval is presented. The 1,700 m thick marine sedimentary succession records a gradual deepening from inner to mid and outer shelf environments from the Middle Toarcian to early Late Aalenian. During the Late Aalenian–Early Bajocian, the trend was reversed and infilling of the basin by a large delta system occurred. This general facies development reflects a nearly symmetrical transgressive–regressive (T–R) megacycle, terminated by the inter-regional mid-Cimmerian tectonic event. A renewed transgression in the early Late Bajocian initiated a subsequent sedimentary megacycle. The bioturbated mid and outer shelf sediments contain a low to moderately diverse benthic fauna dominated by deep burrowing bivalves, often preserved in the growth position. A hierarchy of four orders of sedimentary cycles can be recognized (parasequences, parasequence sets, unconformity-bounded third-order depositional sequences, and the 13 ma long second-order T–R megacycle). A regional correlation with the Jajarm area (200 km to the east) shows a very similar temporal facies pattern of the upper Shemshak Formation. The eastern Alborz T–R cycle is completely out-of-phase with other (eustatic) sea-level curves, suggesting regional tectonic control. Rough estimates of subsidence rates give an average value of 126 m/ma. However, much higher values for the Aalenian (230 m/ma), particularly the Late Aalenian (700 m/ma), indicate a distinct increase in subsidence rate towards the Early Bajocian mid-Cimmerian tectonic event. These high subsidence rates suggest that the sediments of the Shemshak Formation of the eastern Alborz formed in a (young) rift basin.

The genus Metastreblitesis a rare taxon that was represented by seven specimens reportedfrom two localities of the Mediterranean Tethys. Recently, this genus has been discovered in the Rocca Drago section (western Sicily, Italy) in a neptunian-dyke containing an Early Kimmeridgian ammonite fauna of the Metahaploceras strombeckiZone. Two species have been recognized: M. praesemiformisOlórizand M. oloriziSarti. The striking morphologic similarities between Metastreblitesand the younger, almost homeomorphic, Early Tithonian Semiformiceras semiforme(Oppel) are analysed. It has been possible to point out the differences between these forms, particularly the ontogenetic development of the ventral area. The iterative development of Streblitinae characterized by an elliptically coiled body chamber seems to be related to their palaeobiogeographic distribution in distal, epioceanic areas of the Mediterranean Tethys.

An integrated stratigraphic, palaeontological, and geochemical study has been carried out across the uppermost Hauterivian Faraoni Level of the Fiume Bosso section in the Umbria-Marche Apennines, Italy. This level represents a first, prominent sign of the global changes that led to the widespread deposition of mid-Cretaceous organic-rich facies. Marked changes in the organic geochemical record and microfloral and micro- and macrofaunal assemblages occur within the interval. They are characteristic for short-term deposition in strongly dysoxic bottom conditions. Such changes probably reflect climatic variation which, in turn, induced variations in the palaeoceanographic regime.

Le dimorphisme au sein du genre RichterellaAvramest confirmé sur la base d'un matériel récolté en Ardèche (Le Pouzin, Broyon), principalement dans les niveaux de la zone à Fallauxi. Le microconque, R. richteri(Oppel), est dépourvu d'oreillettes latérales mais un rostre ventral, dû à la forte inflexion vers l'avant des côtes secondaires, est présent. Le macroconque correspond à «Lemencia praerichteriDonze& Enay. Ces deux formes sont donc réunies dans la même espèce, R. richteriet a fortiori, dans le même genre, Richterella. Le microconque, généralement mieux conservé que le macroconque dans le matériel étudié, montre une variabilité de l'ornementation plus importante que celle admise jusqu'ici. Les formes ardéchoises montrent plus d'affinités avec celles d'Espagne qu'avec celles de Roumanie. Le cadre stratigraphique et le contexte faunique de Richterellaen Ardèche, sont discutés.

Il sottordine polifiletico Ancyloceratina ebbe un considerevole successo evolutivo nel corso del Cretaceo. La radiazione delle Protancyloceratidae ebbe inizio nel Titoniano mentre quella delle Crioceratitinae (progenitrici di tutte le altre Ancyloceratina cretacee) alla fine del Valanginiano. Questi due gruppi si originarono dalle Perisphinctacea ma da famiglie diverse ed in tempi diversi. Poiché lo svolgimento dei giri è un carattere sviluppato alla fine della crescita di molte ammoniti ad avvolgimento planospiralato, si ipotizza l’effetto di un processo eterocronico di accelerazione nello sviluppo di questo carattere a stadi di crescita sempre più precoci. Le forme che svilupparono conchiglie svolte furono avvantaggiate, a cavallo tra i periodi Giurassico e Cretaceo, dalle nuove opportunità trofiche che si crearono a seguito di importanti cambiamenti paleogeografici e paleoambientali su scala globale. Viene respinta l’ipotesi del ruolo delle variazioni eustatiche quale fattore dell’evoluzione di queste forme.

Cccca, F. 1992 07 15: Ammonite habitats in the Early Tithonian of Western Tethys. Habitats of Early Tithonian ammonites of Western Tethys are inferred from analysis of faunal spectra, functional morphology. facies characteristics and palaeogeography. Phylloceratina and Lytoceratina are included in a pelagic group characterized by taxa which could reach bathyal depths. This group is very abundant and dominant in some localities. A neritic nektobenthic group, relatively abundant in the Cmbria‐Marche Apennines only. is composed of taxa characterired by species bearing simple sutures (some Simoceratidae and Pseudolissoceras). probably living at shallower depth. The habitat of Haplplocerasand some Oppeliidae. is interpreted to be close to the shelf margin/continental slope. Perisphinctids. Aspidoceratidae and some other Oppeliidae are provisionally included in an ‘indeterminate’ group including deep and shallow taxa. Quantitative studies of assemblage composition and comparison of faunal spectra successions from different pelagic regions allow the characterization of different pelagic environments. Bathymetric hypotheses by means of ammonites are discussed. Z Ammonoidea. habitats. facies, faunal spectra. Jurassic, Tithonian. Tethys.