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Revue de Paléobiologie
Vol. spécial 8 (2000): Résumé / Abstracts

The schlotheimiid succession across the Hettangian-Sinemurian boundary (Lower Jurassic), Taseko Lakes map area, British Columbia, Canada
Paul L. SMITH & Howard W. TIPPER

Abstract
The ammonite succession constituting the Canadensis Zone of North America is believed to span the Hettangian-Sinemurian boundary but correlation with the primary standard of northwest Europe has proved difficult because of endemism and strong Tethyan affinities. The geology and biostratigraphy of the Zone’s type area are being restudied and we present here the results of our work on the schlotheimiid succession. Five species are recognized with Angulaticeras westermanni described as new.
Four stratigraphic intervals are delineated based on the distribution of schlotheimiids: 1) The pre-Canadensis beds and the lowest part of the Canadensis Zone yield Angulaticeras cf. trapezoidale and, less commonly, A. marmoreum. 2) Angulaticeras marmoreum ranges upward and occurs alone in the lower part of the Canadensis Zone where it is relatively common. 3) After a brief interval with no schlotheimiids, most of the upper part of the Canadensis Zone is characterized by the occurrence of Angulaticeras westermanni on its own. 4) At the top of the Canadensis Zone and upwards into the post-Canadensis beds, Angulaticeras westermanni is joined by Angulaticeras pulchrum.
Schlotheimiids of the type Canadensis Zone do indeed appear to span the Hettangian-Sinemurian boundary. Schlotheimiid intervals 1 and 2 correlate with the Angulata Zone and intervals 3 and 4 with the Bucklandi Zone.
Key words: Ammonites, Schlotheimiidae, Lower Jurassic, Hettangian, Sinemurian, Canadensis Zone, Canada.

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The Podagrosiceratinae (Ammonitida) in theUpper Toarcian-Lower Bajocian (Jurassic) of Argentina
Alberto C. RICCARDI

Abstract
The Andean Podagrosiceratinae include the genera Podagrosiceras MAUBEUGE & LAMBERT, Sphaerocoeloceras JAWORSKI and Westermanniceras nov. gen. The morphological trend places the Podagrosiceratinae origin in the Late Toarcian, minute ellipto-sphaeroconic Sphaerocoeloceras, with globose phragmocone, egressing and contracted body chamber and straight primary ribs, dividing into weak secondaries that are barely interrupted on mid venter. Troughout the Aalenian (Manflasensis to Malarguensis Zones) the Podagrosiceratinae, represented by Westermanniceras nov. gen., became progressively larger, more evolute and compressed with more prominent and flexuous ribbing. This trend reached its maximum in Podagrosiceras, Malarguensis Zone, a genus with sexual dimorphism, where macroconchs were even larger and more evolute, and where ribbing became progressively obsolete on the body chamber.This mode of evolution is interpreted as hypermorphosis, i.e. a form of peramorphosis or an expression of heterochronic processes probably related to K-selective pressures.
Key words: Jurassic, Toarcian, Aalenian, Bajocian, Ammonitina, heterochrony, Argentina

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The Middle Jurassic genus Riccardiceras (Otoitidae, Ammonitina) in theWesternmost Tethys: Betic Cordillera and Lusitanian Basin
José SANDOVAL, Asunción LINARES & Maria Helena HENRIQUES

Abstract
Riccardiceras westermann, 1995, an almost pandemic genus, is common on the Aalenian/Bajocian boundary of the western Tethys, especially in the Mediterranean province, which includes the Betic Cordillera, where most of the studied specimens come from. All the Betic Riccardiceras pertain to four typical Mediterranean species: R. longalvum (vacek), R. telegdirothi (gÈczy), R. limatum (pompeckj) and R. westermanni n. sp. The genus Riccardiceras presents a well-marked dimorphism. The microconchs, formerly included by several authors in the microconchate genus Trilobiticeras buckman, 1919, have a diameter approximately seven times smaller than their corresponding macroconchs.
Morphology and the type of septal suture, together with the ontogenic development of microconchate forms, which are very similar to Otoitidae microconchs, justify the inclusion of Riccardiceras in the family Otoitidae, rather than in the families Erycitidae or Stephanoceratidae.
The analysis of the possible phylogenetic relationship shows that Riccardiceras evolved directly from the last Erycitidae, with which it has many affinities in ontogenic development, ornamentation, type of septal suture, etc. Riccardiceras can be considered a transitional form connecting the Erycitidae and the Otoitidae on the one hand, and the Otoitidae and the Stephanoceratidae, on the other. The more evolute Riccardiceras species evolved to the oldest Stephanoceratidae (Mollistephanus), whereas another species, via Docidoceras, gave rise to the more typical Otoitidae [E. (Emileia) (M) and E. (Otoites) (m)].
Key words: Ammonites, Riccardiceras, Tethys, Betic Cordillera, Lusitanian Basin, Middle Jurassic, Aalenian, Bajocian

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Lower Bathonian ammonites of Serra de la Creu (Tivissa, Catalan Basin, Spain)
Sixto Rafael FERNÁNDEZ-LÓPEZ

Abstract
The study of ammonites of the Bajocian/Bathonian boundary from Serra de la Creu (Tivissa, province of Tarragona), a locality of the Catalan Basin, allows to recognize several bio- and chronostratigraphic units commonly missing in the Iberian Basin. The Parkinsoni Zone (Upper Bajocian) and the lowermost Zigzag Zone (Lower Bathonian) established for NW Europe areas can be identified in the Catalan and Iberian basins (Spain), although the ammonite fossil assemblages are composed by Submediterranean taxa.
Key words: Middle Jurassic, Ammonoids, taphonomy, biostratigraphy, chronostratigraphy, palaeobiogeography, Iberia.

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Middle Jurassic ammonites from the island of Babar in the southern Moluccan Forearc, Indonesia
John H. CALLOMON & Graham ROSE

Abstract
This paper describes a new collection of Middle Jurassic ammonites from the island of Babar in the southern Moluccas, Indonesia. Its main element is about a dozen specimens of the bioprovincially Austral sphaeroceratid genus Satoceras, S. satoi Westermann & Callomon, found in sufficient proximity in fresh outcrop to be regarded as isochronous, in contrast to the majority of older collections described in the classical literature found loose in stream-beds. The species characterizes therefore a distinct faunal horizon recognized also elsewhere on what were the northern shelf-seas of the Australian craton, on Sula and in western Irian Jaya (western New Guinea). Its relation to other Austral faunas and its position in the faunal succession now regionally recognized are briefly discussed.
Key words: Ammonites, Middle Jurassic, southern Moluccas, Indonesia, Austral bioprovincialism, Biostratigraphy.

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Caracoliceras, a new Oxfordian (Upper Jurassic) ammonite genus from northern Chile
Axel von HILLEBRANDT, Annette KOSSLER & Manfred GRÖSCHKE

Abstract
A new Oxfordian ammonite genus of the ?Perisphinctidae, Caracoliceras n. gen., is described from northern Chile. Four taxa could be recognized within the new genus: Caracoliceras dunkeri, C. cf. dunkeri, C. sp. A, and C. sp. B. The stratigraphic distribution of these endemic ammonites is restricted to the Lower Oxfordian and the ?lowermost Middle Oxfordian. In this time period, the new genus was a dominant faunal component of the Chilean ammonite assemblages. It is very likely that the new genus evolved from the youngest Andean reineckeids.
Key words: Jurassic, Oxfordian, Ammonoidea, Perisphinctidae, South America, Chile.

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The evolutionary morphology of siphonal tube, in Spirulida (Cephalopoda, Coleoidea)
Larisa A. DOGUZHAEVA

Abstract
In Recent Spirula the inner surface of the siphonal tube bears previously unknown tiny, less than 1 mm in diameter, crater-like structures called here "rosettes". They are located on the thin irregularly calcified lamellar layer which continues in the subsequent lamello-fibrillar septal neck. This layer lines the lace-like surface of the next thicker spherulitic-prismatic layer. The latter covers about 4/5 of the septal neck length. Anteriorly it is attached to the outer surface of the succeeding septal neck and coates 1/5 of its length. In decalcified shells the ridged and folded organic lamellae of the septal neck show criss-cross fibres on the outer surface and concentric fibres on the inner surface of the septal neck.
Up to now, four genera and five species of Pre-Tertiary spirulids, and a single Miocene species of Spirula have been described. In the palaeontological record of spirulids the Stephanian Shimanskya postremus (Mapes, 1976) is the most ancient form. It is followed by the Aptian Naefia kabanovi Doguzhaeva, 1996 and Adygeya adygensis Doguzhaeva, 1996, the Santonian-Maastrichtian Naefia neogaeia, Wetzel, 1930, the Maastrichtian Groenlandibelus rosenkrantzi (Birkelund, 1956) and the Miocene Spirula mizunamiensis Tomida & Itoigawa, 1981. Judging by the slowly expanding phragmocone with the separated egg-like protoconch and sheath structure, the Eocene Belemnosis possibly also belongs to spirulids.
The analysis of the available data on the siphonal tube in spirulids leads to the suggestion that the spirulid evolution was accompanied by strengthening of the siphonal tube and its attachment to the shell wall. This tendency is probably related to the necessity to withstand higher pressures, when colonizing deeper waters.
Key words: Spirula, extinct spirulids, siphonal tube ultrastructure, evolutionary morphology.

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Geological interpretations from cephalopod habitat and implosion depth limits
Roger A. HEWITT

Abstract
The Septal Strength Index (SSI) of cephalopods with spherical septa was invented by G.E.G. WESTERMANN, 1972 and published the next year with data for 79 fossil septa; many of which were not exactly spherical. The index can be refined and tentatively extended to include the centrally fluted septa of Mesozoic ammonoids by dividing it by a term b-c based on membrane stress theory and the radii of curvature of representative septal surfaces in each sample of thickness (d) to minimum radius of curvature measurements (r). Thus the revised index SSI/b-c has the simple form (1000d/r)/(2-r/R) in synclastic surfaces with a larger radius of curvature R. Refinements can be made to increase the tensile strength assumed in smaller septa and to define Habitat Depth Limits (HDL) based on measured or average variances of the inverse stress index SSI/b-c. This is a conservative measure of the depths sometimes visited during an ontogeny reflected by shell abundances on slope facies. The maximum or Excursion Depth Limit (EDL) may be roughly defined as being a safety factor of 1.15; while the safety factor for the HDL has average values of 1.427 in anticlastic ammonoid septa and 1.429 in septa of other phragmocones. Depths in the range 50 to 100 m are deduced for Waulsortian reef cephalopod assemblages of Wenlockian age in Wisconsin and of Carboniferous age in the British Isles. Ordovician sea-levels varied by at least 415 m over South China. The largest Sinoceras individuals were able to pumb depths of about 630 m during the late Caradocian without encountering the anoxic ocean water postulated by some authorities.
Key words: Cephalopods, bathymetry, Palaeozoic, Jurassic, facies, implosion, septa.

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The relationships of color patterns and habitat for Lower Triassic Ammonoids from Crittenden Springs, Elko County, Nevada
Glen E. GARDNER, Jr. & Royal H. MAPES

Abstract
The Lower Triassic Crittenden Springs ammonoid fauna from Nevada is extremely diverse, with thirty-two species. Of the twenty-nine taxa represented in the Ohio University collection, fifteen show evidence of having color patterns or some kind of shell coloring in life.
There are three types of color patterns exhibited in the ammonoid fauna. These three types are as follows: 1) monochromatic (Preflorianites toulai, Arctoceras sp., Flemingites russelli), 2) transverse bands (Owenites koeneni, Paranannites aspensis, P. mulleri, Prosphingites slossi, Juvenites septentrionalis, and J. thermarum), and 3) longitudinal stripes (Dieneroceras knechti, D. spathi, D. subquadratum, Kashmirites sp., Wyomingites whiteanus, and Xenoceltites sp.). After the color pattern documentation, all the Crittenden Springs taxa were integrated into the WESTERMANN (1996) paleoecological ammonoid habitat model.
After integration, all of the ammonoid taxa having transverse color patterns (six taxa) clustered in the planktonic-vertical migrator habitat of the basin biofacies at depths of less than 450 meters. With one exception, all of the ammonoid taxa having longitudinal color bands (six taxa) clustered in the planktonic-drifter habitat of the inner slope and platform biofacies at depths of less than 125 meters. And, all three of the monochromatic taxa clustered in the nektonic and demersal-nektonic habitats of the inner slope and basin at depths no greater than 125 meters. The taxa without observed color patterns also clustered in these latter two habitats.
Thus, within our limited data set, the consistent distributions of species with and without color patterns provide independent support for the habitat divisions within the WESTERMANN Model. Also, the consistent similarities in coloring pattern distribution as compared to shell form and habitats indicate that type of color pattern and habitat are closely related paleobiological phenomena for Lower Triassic ammonoids.
Key words: Ammonoids, color patterns, habitat, Triassic, Nevada.

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Time-averaging and long-term palaeoecology in macroinvertebrate fossil assemblages with ammonites (Upper Jurassic)
Federico OLÓRIZ

Abstract
Time-averaging and stratigraphic completeness combine with information inherent to fossil preservation and point to the availability of long- rather than short-term palaeoecology, especially in old-fossil assemblages as those bearing ammonites. On this assumption, traditional topics such as interpretations of ammonite biogeography should be revisited and focused on long-term processes, i.e. palaeobiogeographic tracts, which in turn cannot be used to identify migration. The conceptual grounds of these hypotheses are considered.
The composition of multispecies assemblies, and therefore those containing ammonites, can inform about long- rather than short-term ecological processes. Their stratigraphic context is keystone for understanding and therefore ecostratigraphic interpretations are considered of value to approach both dynamic paleobiology and basin analysis. To exemplify, the ecological scenario for the South Iberian paleomargin during the Late Jurassic is considered and then discussed the averaged composition of Lower Kimmeridgian macrofossil assemblages. Shared trends in composition of macrofossil assemblages gathered from separate areas are identified in terms of ecostratigraphic trends, which are interpreted to show signals of paleobiological responses (results) to long-term ecological processes. In addition, an ecostratigraphic event is identified through the record of a sharp and short-term variation in the composition of macrofossil assemblages, the interpretation of which shows its relation to processes of biogeographical significance. Underlying factors forcing ecostratigraphic events and trends are presented within the context of sequence stratigraphy.
Key words: Time-averaging, ecostratigraphy, palaeoecology, palaeobiogeography, ammonites, sedimentation, Upper Jurassic.

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Hydrodynamic analysis of Late Cretaceous desmoceratine ammonites
Katsuhito SEKI, Kazushige TANABE, Neil H. LANDMAN & David K. JACOBS

Abstract
The swimming potential of Late Cretaceous desmoceratine ammonites was analyzed experimentally. Resin casts were made of well-preserved specimens representing seven species of four genera [Desmoceras (Pseudouhligella), Tragodesmoceroides, Damesites, and Hauericeras] from Hokkaido (Japan) and Sakhalin (Russia). A model of a "living" ammonite was created by attaching an artificial body extension at the shell aperture of each cast. The drag force acting on each model was measured in a flow-tank over a range of water velocities from 0.03 to 0.48 m/s. In addition, flow patterns around the models were visualized and compared between species. Based on the relationship between drag coefficient and Reynolds number, power consumption was scaled to a range of sizes and swimming velocities for each specimen. Power consumption was compared between juvenile and adult shells of the same species. Our results show that the Cretaceous Desmoceratinae have similar hydrodynamic properties to other Mesozoic ammonites with low shell-thickness ratios. Modest differences in hydrodynamic efficiency were detected among the species examined consistent with modest differences in shell geometry. In every species, the adult or subadult shell is hydrodynamically more efficient at higher swimming velocities than the juvenile shell.
Key words: Ammonites, Cretaceous, Desmoceratinae, flow-tank, shell shape, swimming, power-scaling.

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Bathymetric ranges and morphological adaptations in the Sepiidae
Peter D. WARD

Abstract
Morphological measures (sepion maximum length, septal density, and width/length) as well as maximum, minimum, and mean depth measurements from trawling data are presented from a sample of Sepia, Sepiella, Metasepia and Hemisepius (Cephalopoda). Strong correlation exists between maximum and mean habitat depths; less robust correlations are apparent between various morphological attributes of the sepion and maximum depth. These data and interpretations presented suggest that evolution of various sepion morphologies has, at least in part, been selected for by hydrostatic pressure factors.
Key words: Sepiidae, morphology, bathymetry, evolution.

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Ammonoid turnover at the Devonian-Carboniferous boundary
Jürgen KULLMANN

Abstract
The ammonoid crisis at the Devonian-Carboniferous Boundary (DCB) not only resulted in the extinction of ammonoid stocks but also in a paradigm shift of ammonoid morphotypes. During the late Famennian, below the DCB two ammonoid orders proliferated: the Clymeniida, with a dorsal siphuncle and mainly evolute and frequently ornamented conchs, and the Goniatitida, displaying an advanced involute smooth conch form. In the short "Stockum interval" immediately below the DCB, almost all prevalent stocks became extinct except for a few non-ornamented forms with evolute inner whorls. They gave rise after the DCB to smooth and ornamented Goniatitida with a triphasic mode of ontogenetic conch development and evolute ontogenetic growth stages, and to the new order Prolecanitida with discoidal evolute non-ornamented conchs. The fluctuation of ammonoid faunas in the critical interval around the DCB showed a rapid decline in diversity and a short low point with only one morphotype, and after the DCB a gradual diversification in several directions. The possible causes of this pattern are discussed.
Key words: Ammonoids, Devonian, Carboniferous, Devonian-Carboniferous boundary.

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Middle-Late Jurassic and Early Cretaceous marine fauna evolution in Eastern Russia
Irina I. SEY & Elena D. KALACHEVA

Abstract
Evolution of the Middle-Late Jurassic and Early Cretaceous marine fauna in Eastern Russia and its mixed character were determined by changes in migration pattern with the Boreal, Tethyan and Pacific realms. In the Middle Jurassic it was closely linked with the Eastern Pacific which is especially characteristic for the Russian Far East. Two ambi-Pacific provinces were formed: Beringian Province in the Aalenian-Early Bajocian and North-Pacific in the Late Bajocian-Bathonian. Since the Late Bajocian the North-East of Russia was part of the Arctic Province or Subrealm. In the Late Jurassic and Early Cretaceous the Far East was an ecotone area at the boundary between Boreal and Tethyan realms. Benthic fauna belonged to the Boreal type throughout the interval considered.
Key words: Jurassic, Cretaceous, Ammonites, Bivalves, Paleobiogeography, Eastern Russia

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Revue de Paléobiologie
Muséum d'histoire naturelle
de la Ville de Genève
2008/03