Biogeographic evolution of Permian ammonoids

The distribution of Permian ammonoids within the five major biogeographic provinces (Arctic, Uralian, American, Tethyan, and Australian) is discussed. Changes in the taxonomic and biogeographic structure of assemblages according to stages in the evolution of Permian ammonoids are considered for each region. It is shown that the geographical distributions and taxonomic diversity of ammonoids changed continuously throughout the Late Permian.     

Ostracodes from the Upper Permian Khivach formation in Kolyma-Omolon Basin

Ostracodes Healdianella splendida Belousova, Paraparchites ganelini sp. nov., Paraparchites? hivachensis sp. nov. and Arcibairdia vodopadniensis sp. nov. are described from the Upper Permian deposits of the Khivach Formation (Kolyma-Omolon Basin, Eastern Siberia). Paraparchites species most closely resemble ancient Paleozoic ostracodes of the Boreal province. Valve morphology of Healdianella and Acribairdia points to their similarity to ostracodes from the upper levels of the Upper Permian of the Tethyan realm.     

Permian ammonoids: Biostratigraphic,biogeographical, and ecological analysis

This monograph analyzes all available data on the biostratigraphic and biogeographical distribution of Permian ammonoids and the ecological interpretation of morphological changes in this group. Ammonoid assemblages of various regions at successive stages of the Permian are examined. Four major stages are substantiated in the evolution of Permian ammonoids. The most contentious stages in the Permian evolution of the group are extensively discussed.     

New species of Dzhulfian (Late Permian) ammonoids from the Hambast Formation of Central Iran

New ammonoid species of the genus Araxoceras (A. abarquense sp. nov. and A. iranense sp. nov.) are described from the Early Dzhulfian (Early Wuchiapingian) beds of the Hambast Formation of Central Iran (Abade). The data on the distribution of Paraceltites (Paraceltites sp.) and Vedioceras (V. umbonovarum Ruzhencev), for the first time discovered in the Dzhulfian beds of Abade, and of Eoaraxoceras are provided. The correlation of the Late Permian assemblages of ammonoids of Iran and Transcaucasia is amended.     

Quantitative biochronology of Devonian ammonoids from Morocco and proposals for a refined unitary association method

Monnet, C., Klug, C., Goudemand, N., De Baets, K. & Bucher, H. 2011: Quantitative biochronology of Devonian ammonoids from Morocco and proposals for a refined unitary association method. Lethaia, Vol. 44, pp. 469–489. Based on a rich dataset, the biostratigraphy of the late Emsian and the Eifelian (Early–Middle Devonian) ammonoids from the Moroccan Tafilalt is re‐evaluated. We processed this dataset (comprising 53 species from 15 sections) with the unitary association method (UAM), by means of the UA‐graph freeware. This led to the construction of a sequence of 17 UAs (maximal sets of actually or virtually coexisting taxa), which are grouped into 10 laterally reproducible association zones. This biostratigraphical subdivision of this interval is in some parts finer than the classically used empirical stratigraphical scheme and than a previous graphic correlation analysis. It enabled us to measure regional ammonoid diversity of this interval in detail. The UAM is a powerful biochronological method, which benefits from complementary tools to analyse conflicting inter‐taxon stratigraphical relationships inherent to complex biostratigraphical datasets. In cases of under‐constrained superpositional relationships between the taxa, the UAM can yield results, which are not parsimonious in terms of reconstructed virtual coexistences. We suggest several additions to complement the algorithmic steps of the method. The most important is the exhaustive or heuristic reconstruction of possible solutions resolving the observed biostratigraphical contradictions (conflicting inter‐taxon superpositional relationships and cycles between maximal cliques) and the selection among the solutions of the most‐parsimonious one(s) in terms of reconstructed virtual coexistences. Multiple equivalent results may then be processed with standard consensus techniques. Finally, the robustness of the results can be tested by bootstrapping methods to provide confidence estimates on the ranges and associations of studied taxa. □Ammonites, Anti‐Atlas, biostratigraphy, correlation, zonation, diversity.     

Ecological structure of Paleozoic ammonoids

Ecological specialization of Paleozoic ammonoid orders is discussed along with changes in the ecological structure of the ammonoid assemblages in the Early Devonian-Late Permian. Two large cycles of change in the ecological structure, Devonian and Carboniferous-Permian are recognized.     

Life-cycles of some Devonian ammonoids

Whorl expansion rates of six representative ammonoid genera from late Emsian and Eifelian strata of Morocco were calculated for each whorl. The corresponding body chamber lengths and the orientations of the apertures were computed based on these values. The resulting body chamber length and orientation of the aperture graphs were compared with other conch features, ecology of Recent cephalopods, and sedimentological data of the host rocks in the Tafilalt (eastern Anti-Atlas, Morocco). A subdivision of the ontogeny of these ammonoids was achieved comprising the early and late embryonic periods, the juvenile period, the preadult, and the adult growth period. All growth periods are defined by specific changes in growth, conch morphology, and mode of life. According to this reconstruction, hatchlings were probably already capable of active movements. Differentiation in two main modes of life of the examined taxa occurred in the late juvenile or early preadult period. As preadult animals, most of the Mimagoniatitoidea and Agoniatitoidea became active swimmers (Nektonic), whereas the representatives of the Anarcestoidea were capable of slow movements only (Planktonic). As adults, most representatives of the three superfamilies had an approximately horizontally oriented aperture, allowing active swimming and possibly active choice of spawning sites. Additionally, the new ammonoid taxon Rherisites tuba gen. nov., sp. nov. from the late Emsian is introduced.     

Morphospace occupation of ammonoids over the Devonian-Carboniferous boundary

In a case study, a stratophenetic analysis of the succeeding ammonoid faunas of the latest Devonian and earliest Carboniferous cephalopod limestones of the Rhenish Massif has been made. This investigation concentrated on the development of the whorl expansion rate (WER), a character very important for ammonoids since it indicates the body chamber length and hence the orientation in the water column as well as mobility. The study leads to the conclusion that the Hangenberg Event caused an almost complete change in the morphospace adopted by ammonoids. All clymenüds as well as tornoceratids became extinct at or immediately after the Hangenberg Event, and the morphospace left behind by these Devonian groups was reoccupied only incompletely by the surviving prionoceratid ammonoids.     

Cystic echinococcosis and the Mediterranean Region: a long-lasting association

Cystic echinococcosis (CE) is an important zoonosis in Italy and in the whole Mediterranean Region, as confirmed by the work by Ettore Biocca, whose contributions to the subject are reported in a summarised annex to the bibliography. The contribution to the understanding and control of CE are presented, with special emphasis on the socio-economic impact, on factors affecting the maintenance of CE in the Mediterranean Region, on the epidemiological situation and control measures, on the present status of epidemiological surveillance, on the control problems in normal and emergency situations, on health education and training. Also, the justifications of combined control programmes are discussed, which may be applied only in situations of peace and well-being.     

The mode of life in ammonoids

The following structural features clearly indicate that ammonoid shells were adapted to withstand considerably higher hydrostatic pressures thanNautilus shells: (1) the corrugated and marginally fluted septa gave the shell wall efficient support against implosion; (2) the secondary connecting rings could grow a great deal in thickness; and (3) the last formed chambers remained full of liquid which supported the last septum. On the basis of the following characters it is concluded that ammonoids were incapable of swimming efficiently by jet-propulsion: (1) the retractor muscles were weakly developed; (2) the life position was unstable and highly variable; and (3) in animals with a ventral apertural rostrum the hyponome was probably absent. Ammonoids are considered here as having been pelagic cephalopods which lived in the upper 1000 m of the oceans, and which probably undertook considerable diurnal vertical migrations, similar to those inSpirula. Only some groups may have adopted a life in shallow epicontinental seas. In the late Mesozoic, ammonoids have been replaced by modern oceanic squids which are extremely numerous in the corresponding pelagic environment.     

Changed number of the collection of Permian ammonoids from Novaya Zemlya housed in the cited collection repository of the Borissiak Paleontological Institute,Russian Academy of Sciences

The development of views on the phylogeny of the family Cyclolobidae Zittel, 1895 is discussed. The generic composition is emended, phylogenetic links are indicated, a new version of the phylogenetic scheme is proposed, and phylogeny of the key genera is traced at species level. The sutural ontogeny of the genus Mexicoceras is examined, its placement in the family Cyclolobidae is supported, and its position in the phylogenetic reconstruction of the family is determined.     

On Frasnian ammonoids of the New Siberian Islands

Ammonoids from the basal beds of the Nerpalakh Formation (Lower Frasnian) of Belkovsky Island (New Siberian Archipelago) are systematically studied. Taxonomically, the assemblage studied (Manticoceras insulare sp. nov., Tornoceras typum (Sandberger, 1851), and T. contractum Glenister, 1958) is similar to the Early Frasnian ammonoid assemblage of South Timan, from which its is distinguished by the absence of the genera Timanites and Komioceras. The same beds contain conodonts of the Palmatolepis transitans Zone (= MN 4 Zone of the Montagne Noire standard succession), which allow the correlation of the beds studied with the Timanites keyserlingi and Komioceras stuckenbergi ammonoid zones of South Timan. The Early Frasnian ammonoids could supposedly have entered the region of the New Siberian Archipelago from the southwest at the time of a major transgression, which facilitated the distribution of the genera Manticoceras and Tornoceras. A new species of the genus Manticoceras is described.     

Role of heterochronies in the morphogenesis of paleozoic ammonoids

Various types of evolutionary changes related to shifts in the appearance or order of formation of characters, i.e., heterochronies are shown. The most common such changes in Paleozoic ammonoids was the appearance of mosaic forms combining conservative and advanced characters resulting from recapitulation and paedomorphosis. These phenomena are related to certain phylogenetic stages in each group: the growth stage predominantly showed recapitulations; the diversification stage showed the appearance of many mosaic forms; the decline stage commonly shows paedomorphosis connected with retardation.     

Tuberculate micro-ornament on the juvenile shell of Middle Jurassic ammonoids

In two genera of Callovian Ammonitina of distinct superfamilies, the juvenile shell displays a tuberculate micro-ornament in addition to growth lines. In contrast to the circular micro-tubercles of the ammonitella shell, post-embryonic tubercles are oval to longish in outline. They are arranged in rows running parallel to the growth lines in Kosmoceras (Spinikosmoceras) and cross the growth lines in Binatisphinctes.     

Phylogenetic relationships of Early Triassic ammonoids (new data on the inner shell structure of some Olenekian ammonoids of Southern Primorye)

The inner shell structure for several ammonoid taxa (Inyoceras singularis, Anasibirites simanenkoi, A. nevolini, Yvesgalleticeras proximus, and Koninckitoides popovi) from the Olenekian of Southern Primorye is studied. The family-group level taxonomy of ammonoids is discussed.     

Thriving at high hydrostatic pressure: the example of ammonoids (extinct cephalopods)

Ammonoids are a group of extinct mollusks belonging to the same class of the living genus Nautilus (cephalopoda). In both Nautili and ammonoids, the (usually planospiral) shell is divided into chambers separated by septa that, during their lifetime, are filled with gas at atmospheric pressure. The intersection of septa with the external shell generates a curve called the suture line, which in living and most fossil Nautili is fairly uncomplicated. In contrast, suture lines of ancient ammonoids were gently curved and during the evolution of the group became highly complex, in some cases so extensively frilled as to be considered as fractal curves. Numerous theories have been put forward to explain the complexity of suture ammonoid lines. Calculations presented here lend support to the hypothesis that complex suture lines aided in counteracting the effect of the external water pressure. Additionally, it is suggested that complex suture lines diminished shell shrinkage caused by water pressure, and thus aided in improving buoyancy. Understanding the reason for complex sutures in ammonoids represents an important issue in paleobiology with potential applications to the problem of the resistance of hollow mechanical structures subjected to high pressure.