Aptychi microstructure in Late Cretaceous Ancyloceratina (Ammonoidea)

The microstructure of aptychi (bivalved calcareous coverings on lower jaws) of three genera of Late Cretaceous Ancyloceratina, Baculites, Polyptychoceras and Jeletzkytes is described for the first time on the basis of well-preserved and in situ material from the Western Interior of the USA and Hokkaido, Japan. Optical and scanning electron microscope observations of aptychi on polished median and cross-sections reveal some variation in their relative size, shape and microstructure among the three genera. The aptychus of Baculites is composed of two calcitic layers: one with tilted lamellae and the other one with horizontal lamellae, whereas those of Polyptychoceras and Jeletzkytes consist of a thin layer with horizontal lamellae. Comparison with aptychi (e.g. Laevaptychus) of Jurassic Ammonitina shows that the aptychi of Ancyloceratina differ from those of Jurassic Ammonitina in the smaller number of layers and the absence of a sponge-like structure. We propose for the first time growth models for a sponge-like aptychus of Jurassic Ammonitina and the lamellar aptychus of Cretaceous Ancyloceratina. The remarkable microstructural variation of aptychi observed in Mesozoic Ammonoidea is probably related to the diversity of their modes of feeding and the secondary function of the lower jaws as opercula.     

Ammonite aptychi: Functions and role in propulsion

Seven previous proposals of aptychus (sensu stricto) function are reviewed: lower mandible, protection of gonads of females, protective operculum, ballasting, flushing benthic prey, filtering microfauna and pump for jet propulsion. An eighth is introduced: aptychi functioned to actively stabilize the rocking produced by the pulsating jet during forward foraging and backward swimming. Experiments with in-air models suggest that planispiral ammonites could lower their aperture by the forward shift of a mobile cephalic complex. In the experiments, the ventral part of the peristome is lowered from the lateral resting (neutral) position by the added “ballast” of a relatively thin Laevaptychus to an angle < 25° from horizontal with adequate stability to withstand the counter-force produced by the jet of the recurved hyponome. However, of the shell forms tested, only brevidomes with thick aptychi, e.g., the Upper Jurassic Aspidoceratidae with Laevaptychus and average whorl expansion rates, were stable enough to swim forward by jet propulsion at about Nautilus speed (∼ 25 cm/s). We propose that aptychus function most commonly combined feeding (jaw, flushing, filtering) with protection (operculum), and, more rarely, with locomotion (ballast, pump, diving and stabilizing plane). Aptychi may thus have been multi-functional.     

Shell microstructure and mineralogy of the Littorinidae: ecological and evolutionary significance

An examination of the shell microstructure and mineralogy of species from 30 of the 32 genera and subgenera of the gastropod family Littorinidae shows that most species have a shell consisting of layers of aragonitic crossed-lamellar structure, with minor variations in some taxa. However, Pellilitorina, Risellopsis and most species of Littorina have partly or entirely calcitic shells. In Pellilitorina the shell is made entirely of calcitic crossed-foliated structure, while in the other two genera there is only an outer calcitic layer of irregular-prismatic structure. A cladistic analysis shows that the calcitic layers have been independently evolved in at least three clades. The calcite is found only in the outermost layers of the shell and in species inhabiting cooler waters of both northern and southern hemispheres. Calcium carbonate is more soluble in cold than warm water and, of the two polymorphs, calcite is about 35% less soluble than aragonite. We suggest that calcitic shell layers are an adaptation of high latitude littorinids to resist shell dissolution.     

Systematic revision and palaeobiogeography of Perisphinctes Waagen (Ammonoidea) from the Oxfordian of Kutch,India: Stratigraphic and evolutionary implications

Perisphinctes Waagen, 1869 is an important genus of the Oxfordian. In many areas the taxon has been excessively and subjectively split. Based on the material collected in Kutch (India), including the type specimens, we have grouped eight species previously described as distinct into one biological species, Perisphinctes indogermanus Waagen, 1875. It is characterized by strong sexual dimorphism. Macroconch shows high intraspecific variability. Microconch is previously described from Kutch in different generic names. Thirteen species of Dichotomosphinctes Buckman, 1926, Perisphinctes Waagen, 1869 and Lithacoceras Hyatt, 1900 are considered here as microconch which is lappeted. The precise age of P. indogermanus is disputed. A detailed stratigraphic analysis of several sections in this study suggests that the species ranges from early to middle Oxfordian. Perisphinctes indogermanus is distinct from other contemporary species of the world and abundant in the Indo-Madagascan Province. Kutch population of P. indogermanus has developed virgatotome style of ribbing in juvenile stage. During the middle Oxfordian marine transgression, the species along with many other ammonites of deeper habitat of the mainland basin reached the shallow shelf of eastern fringe of the Kutch Sea. Being peripherally isolated, it soon underwent an adaptive radiation that resulted in the origination of a new family Ataxioceratidae Buckman, 1921 whose members have neotenously retained the virgatotome ribbing in adult stage. The ataxioceratids later migrated to Europe and flourished during the Kimmeridgian.     

Aptychen als Kieferelemente der Ammoniten

The jaws of the ammonite generaEleganticeras, Hildoceras, Normannites, Scaphites, Physodoceras, andQuenstedtoceras (ofQuenst. lower jaws only) are described. Lower jaws and aptychi of these genera are shown to be identical. They consist of an inner layer of organic material, which corresponds to the complete anaptychi of liassic ammonites, and an outer layer of calcitic material deposited on both flancs of the lower jaw, giving rise, after decay of the organic layer, to the aptychi. Previously published interpretations of aptychi as opercula or hoods are discussed and rejected. It is concluded that they certainly functioned as jaws or possibly shovel-like devices.     

Double function of aptychi (Ammonoidea) as jaw elements and opercula

Lehmann, U. & Kulicki, C. 1990 10 15: Double function of aptychi (Ammonoidea) as jaw elements and opercula. Lethaia , Vol. 23, pp. 325–331. Oslo. ISSN 0024–1164.
Aptychi are calcitic coverings on the outer surface of organic ammonite lower jaws. They are similar in shape to that of the corresponding ammonite apertures. This observation and additional features of many aptychi are in harmony with their former interpretation as protective opercula. We suggest that they served as opercula in addition to functioning as jaws. The primary function of the lower jaws was thus secondarily extended to that of protective shields when they acquired their calcitic covering, while as lower jaws their importance dwindled to that of a more passive abutment. Phylogenetically, this seems to have started slowly in some anaptychi and became obvious with the first aptychi. ▭ Ammonites, aptychus, operculum, jaw apparatus, evolution, function .     

Litho- and biostratigraphy of the Upper Jurassic Mozduran Formation,Kopet-Dagh,Iran, and its paleoenvironmental implications

The Upper Jurassic Mozduran Formation at Baghak section, Kopet-Dagh area northeast Iran, characterized by multiple units of carbonates and evaporates intercalated with siliciclastic deposits, yielded benthic foraminifera, calcareous algae, and crustacean coprolites, including Alveosepta jaccardi, Charentia aff. nana, Deloffrella quercifoliipora, Marinella cf. lugeoni, Favreina, and Solenopora sp. The almost consistent occurrence of Alveosepta jaccardi in the studied section, i.e., the Alveosepta jaccardi Zone, indicates late Oxfordian to the Kimmeridgian in age. Facies analysis of the formation reveals depositional settings of a peritidal zone, a lagoon, and a high-energy shoal of a carbonate ramp. Terrigenous and evaporites are found in eastern parts of Kopet-Dagh, representing a more proximal sedimentary environment. These siliciclastic inputs are associated with tectonic events during Oxfordian to Tithonian in the region.     

Oxfordian perisphinctid ammonites from Chacay Melehué, Argentina

A significant assemblage of Oxfordian perisphinctids was collected at Chacay Melehué, Neuquén, Argentina. It is composed of well preserved specimens belonging to the family Perisphinctidae:Perisphinctes aff.promiscuus Bukowski (Perisphinctinae),Tenuisphinctes herreroduclouxi (Leanza) (Perisphinctinae), andSubvinalesphinctes pseudokranaus n. sp. andS. prophetae (Gygi & Hillebrandt) (Vinalesphinctinae). The family Ataxioceratidae is represented byLithacosphinctes aff. janus (Choffat) (Ataxioceratinae). The subfamily VinalesphinctinaeMeléndez & Myczynski, 1987 is discussed and organized into three genera:Subvinalesphinctes Wierzbowski,Vinalesphinctes Spath andCubasphinctes Judoley & Furrazola, which seems to cover the whole of the subfamily, ranging, at least, from the lowerplicatilis to the lowerbifurcatus zones, Middle Oxfordian in Cuba, part of Mexico, Chile and Argentina. The root of the subfamily is most likelyS. pseudokranaus n. sp. The paleobiogeographic affinites are mainly Tethyan, and Tethyan-Caribbean during the Middle Oxfordian.     

Turiasauria-like teeth from the Upper Jurassic of the Lusitanian Basin,Portugal

Turiasauria is a clade of eusauropods with a wide stratigraphic range that could extend from the Bathonian to the lower Aptian including Turiasaurus, Losillasaurus, Zby and putatively, Galveosaurus, Atlasaurus and isolated remains from Middle Jurassic-to-Lower Cretaceous. Some are characterised by the presence of heart-shaped teeth. Several tooth occurrences from the Portuguese Upper Jurassic with this type of morphology (SI: 1.1–1.8) are reported and discussed. If this morphology is regarded as synapomorphic of Turiasauria, the teeth will be tentatively related to this clade. From a sample of 43 teeth, three main morphotypes are described. Three hypotheses might explain the morphological variation: (1) the range of tooth morphologies indicates variation in the jaw, (2) the range of tooth morphologies indicates taxonomic variation or (3) a combination of both. The general wear pattern in morphotypes I and II starts with a distal facet, then the appearance of mesial/apical facet and finally a ‘V’-shaped facet. In morphotype III, the wear begins with a mesial facet. The variability observed for Portuguese Upper Jurassic specimens is congruent with the morphological variability along the tooth row shown by other sauropods with spatulate/spoon-shaped teeth and it is considered the most parsimonious hypothesis to explain it.     

On the occurrence of the ammonite aptychi Lamellaptychus cf. rectecostatus (Peters, 1854) from the Ogrodzieniec quarry (southern Poland)

The largely Kimmeridgian-Tithonian (Late Jurassic) aptychus Lamellaptychus rectecostatus (Peters, 1854) is considered to represent the jaw apparatus of the ammonite superfamily Haploceratoidea (Family Oppeliidae). However, here, from the Ogrodzieniec quarry (southern Poland), we present its unusual allochthonous occurrence embedded in a perisphinctid, Perisphinctes (Kranosphinctes) sp., and co-occurring with a late early Oxfordian Cordatum Subzone (Cordatum Zone) ammonite assemblage. The assemblage includes Cardioceras (Cardioceras) cf. cordatum (Sowerby), Neocampylites delmontanus (Oppel), Lissoceratoides erato (d’Orbigny), Bukowskites distortus (Bukowski), Trimarginites cf. arolicus (Oppel), Glochiceras sp., Holcophylloceras zignodianum (d’Orbigny) and Euaspidoceras (Euaspidoceras) perarmatum (Sowerby).     

First records of brachiopods of the family Discinidae (Class Lingulata) from the Upper Jurassic of West Siberia

The organophosphatic brachiopods of the superfamily Discinoidea, family Discinidae are described from the Upper Jurassic of West Siberia. The protegulum (embryonic shell) preserved in adult shells is for the first time discovered in Mesozoic discinids. The shell microstructure is studied. A new species, Discinisca undata Smirnova, sp. nov., is established.     

New Data on the Upper Jurassic (Middle–Upper Oxfordian and Middle Volgian) Foraminifers in the East of the Moscow

The Middle–Upper Oxfordian foraminifera were studied from the borehole section drilled in the east of the Moscow Region (Russia). The foraminiferal zones were distinguished in Oxfordian clays: Opthalmidium strumosum–Lenticulina brestica and Lenticulina russiensis–Epistomina uhligi. It was established that the distribution of foraminiferal assemblages varies throughout the Moscow Region.     

Spatial distribution patterns of calcareous nannofossils across the Callovian–Oxfordian transition in the French Subalpine Basin

Callovian–Oxfordian calcareous nannofossils are documented from four sections distributed along a proximal–distal (slope to central basin) transect in the French Subalpine Basin (south-eastern France). The sections were dated and correlated using integrated ammonite, dinoflagellate and nannofossil biostratigraphies. The nannofossil assemblages are constantly dominated by Watznaueria britannica. However, significant spatial changes in nannofossil assemblage composition are recorded. Nannofossil assemblages recovered in slope and slope-to-basin transition sections are characterized by high abundances, lowest diversities, highest percentages of smallest-sized morphotypes of W. britannica, subordinated W. britannica/manivitiae (a morphotype described in this study), and are indicative of turbulent, unstable and/or eutrophic conditions. Towards the central part of the basin, as the nutrient content and turbulence declined and paleoenvironmental stability increased, the nannofossil assemblages become more diverse and characterized by lower relative abundances of W. britannica but higher contribution of larger morphotypes and higher relative abundances of W. barnesiae/fossacincta, Biscutum dubium and Zeugrhabdotus erectus. These latter small coccoliths, markers of high surface-waters fertility for the Cretaceous, were probably not competitive with respect to smaller-sized W. britannica in unstable and eutrophic surface waters for the Jurassic. An increase in the surface water productivity is recorded both in proximal and distal sections at the Callovian–Oxfordian transition, and is demonstrated both by an increase in nannofossil total abundances and in the relative abundances of taxa adapted to high-trophic levels. Thermal minimum in surface waters, as indicated by an increase in the percentages of the cool-water nannofossil taxa, is associated to increased productivity. Further studies will be necessary to demonstrate whether surface-water productivity changes, already recorded in the eastern Paris Basin, were global.     

Coprolite morphotypes from the Upper Cretaceous of Sweden: novel views on an ancient ecosystem and implications for coprolite taphonomy

Eriksson, M.E., Lindgren, J., Chin, K. & Månsby, U. 2011: Coprolite morphotypes from the Upper Cretaceous of Sweden: novel views on an ancient ecosystem and implications for coprolite taphonomy. Lethaia, Vol. 44, pp. 455–468. Coprolites (fossilized faeces) are common, yet previously unreported, elements in the Campanian (Upper Cretaceous) shallow‐marine strata of Åsen, southern Sweden. They are associated with a diverse vertebrate fauna and comprise at least seven different morphotypes that suggest a variety of source animals. Their faecal origin is corroborated by several lines of evidence, including chemical composition (primarily calcium phosphate), external morphology and nature of the inclusions. Preservation in a fossil coquina, interpreted as a taphocoenosis, suggests early lithification promoted by rapid entombment. This would have prevented disintegration of the faecal matter and facilitated transportation and introduction to the host sediment. The coprofabrics can generally be correlated to specific gross morphologies, supporting a morphology‐determined coprolite classification. Moreover, having been deposited under presumably comparable taphonomic conditions, variations in coprofabrics infer differences in diet and/or digestive efficiency of the host animal. Size and morphology of the coprolites imply that most, if not all, were produced by vertebrates and the largest specimens infer a host animal of considerable size. Two spiralled coprolite morphotypes yield bone fragments and scales of bony fish, suggesting that the producers were piscivorous sharks. Other coprolites contain inclusions interpreted as the remains of shelled invertebrates, thus indicating that they may have derived from durophagous predators and/or scavengers. The occurrence of small scrapes, tracks and traces on several specimens suggest manipulation of the faeces by other (presumably coprophagous) organisms after deposition. The collective data from the Åsen coprolites provide new insights into a shallow‐water Late Cretaceous marine ecosystem hitherto known solely from body fossils. □ Coprolites, vertebrates, coprofabrics, taphonomy, trophic levels, Upper Cretaceous, Sweden.     

A new genus of cardioceratids (Ammonoidea) from the Upper Callovian-Lower Oxfordian of northern Siberia

A new genus, Anabariceras, and two new species, A. meledinae and A. aspectabile, are described from the Upper Callovian-Lower Oxfordian boundary beds from the Anabar River basin. Based on analysis of the ontogenetic development of major characters (suture, shell shape, and ornamentation), the affinity of this genus to the subfamily Quenstedtoceratinae is substantiated.     

<Emphasis Type="Italic">Tuberosciponoceras</Emphasis>: a new dimorphic ammonoid genus from the Upper Albian of Patagonia,Argentina

Tuberosciponoceras insolitum n. gen., n. sp. is a single dimorphic species in the Upper Albian of the Austrat Basin, southern Patagonia. The short-lived genus was characterized by distinct ventral tubercles on all ribs and a deep, trifid internal lobe.     

Growth of modern branched columnar stromatolites in Lake Joyce,Antarctica

Modern decimeter‐scale columnar stromatolites from Lake Joyce, Antarctica, show a change in branching pattern during a period of lake level rise. Branching patterns correspond to a change in cyanobacterial community composition as preserved in authigenic calcite crystals. The transition in stromatolite morphology is preserved by mineralized layers that contain microfossils and cylindrical molds of cyanobacterial filaments. The molds are composed of two populations with different diameters. Large diameter molds (>2.8 μm) are abundant in calcite forming the oldest stromatolite layers, but are absent from younger layers. In contrast, <2.3 μm diameter molds are common in all stromatolites layers. Loss of large diameter molds corresponds to the transition from smooth‐sided stromatolitic columns to branched and irregular columns. Mold diameters are similar to trichome diameters of the four most abundant living cyanobacteria morphotypes in Lake Joyce: Phormidium autumnale morphotypes have trichome diameters >3.5   μm, whereas Leptolyngbya antarctica, L. fragilis, and Pseudanabaena frigida morphotypes have diameters <2.3   μm. P. autumnale morphotypes were only common in mats at <12 m depth. Mats containing abundant P. autumnale morphotypes were smooth, whereas mats with few P. autumnale morphotypes contained small peaks and protruding bundles of filaments, suggesting that the absence of P. autumnale morphotypes allowed small‐scale topography to develop on mats. Comparisons of living filaments and mold diameters suggest that P. autumnale morphotypes were present early in stromatolite growth, but disappeared from the community through time. We hypothesize that the mat‐smoothing behavior of P. autumnale morphotypes inhibited nucleation of stromatolite branches. When P. autumnale morphotypes were excluded from the community, potentially reflecting a rise in lake level, short‐wavelength roughness provided nuclei for stromatolite branches. This growth history provides a conceptual model for initiation of branched stromatolite growth resulting from a change in microbial community composition.     

Evolutionary trend of Zoophycos morphotypes from the Upper Cretaceous–Lower Miocene in the type pelagic sections of Gubbio,Italy

About 200 Zoophycos specimens, including 90 specimens studied in detail, have been analysed in the continuous Upper Cretaceous–Lower Miocene pelagic sedimentary type sections of the Gubbio area (the Contessa Highway, Contessa Quarry and Bottaccione sections, Northern Apennines). The sediments are reddish to grey limestones and marls of the Scaglia Group and marls with volcaniclastic deposits of the Bisciaro Formation. The aim was to examine the evolutionary trend of what is probably the most debated trace fossil of all time, from the Upper Cretaceous to Lower Miocene. Despite having been found in beds ranging from the Cambrian to the present, no consensus has been reached regarding mode of construction, tracemaker or ethological explanation for Zoophycos. Four Zoophycos morphotypes are recognized at Gubbio showing variations of major and minor lamellae, apex, lobes and whorls: the Cretaceous–Eocene cone‐shaped type 1, the Upper Eocene–Middle Oligocene helicoidal type 2, the Oligocene lobate type 3 and the Upper Oligocene–Lower Miocene flat type 4. The very high ichnodensity in some beds (hundreds of specimens in discrete levels of the Bisciaro Formation, now destroyed by quarrying) seems to find explanation in abnormal concentrations of phytodetritus and organic matter on the seafloor in some periods. This very high abundance in discrete levels reflects a change in sedimentation and seafloor conditions at pre‐flysch deposition. Due to such high ichnodensity, many adjacent specimens display deformed outer margins. Taphonomic analysis shows a variation of whorls, laminae and U‐shaped lobes, reflecting ontogenetic development of the tracemaker(s) (?sipunculid worms).     

Paterimitra pyramidalis from South Australia: scleritome,shell structure and evolution of a lower Cambrian stem group brachiopod

The tommotiid Paterimitra pyramidalis Laurie, 1986, is redescribed based on well‐preserved material from the lower Cambrian Wilkawillina, Wirrapowie and Ajax limestones of the Flinders Ranges, South Australia. The material shows that the scleritome of Paterimitra pyramidalis includes three sclerite morphotypes (S1, S2 and L). Detailed shell microstructure studies show striking similarities with both the paterinid brachiopod Askepasma toddense and the tommotiid Eccentrotheca helenia, which strengthens the suggested evolutionary link between tommotiids and brachiopods. Based on the partly articulated specimens and similarities in shell microstructure and sclerite morphology with Eccentrotheca, Paterimitra pyramidalis is reconstructed as a tube‐dwelling, epifaunal, sessile, filter‐feeder with an organic pedicle‐like attachment structure. The proposed reconstruction of the scleritome comprises a basal unit composed of one S1 and one S2 sclerite, as well as an unresolved number of L sclerites lining a coniform tubular structure.     

Origin and expansion of foliated microstructure in pteriomorph bivalves

The ultrastructure of the calcitic prisms of the prismatic shell layers of pteriomorph bivalves was examined by scanning electronic microscopy and diffraction techniques. Results indicate that the internal structure of the prisms is noticeably different among taxa. In species belonging to the families Pinnidae, Pteriidae, and Isognomonidae (Pterioida), prisms are built up with nanometric calcite crystals. On the other hand, Pectinidae, Propeamussliidae, Anomiidae (order Pectinoida) and the Ostreidae (Ostreoida) have prisms constituted by calcitic laths with micrometric size. These laths are indistinguishable from those constituting the foliated microstructure. In almost all cases, there is mineral continuity from the prisms to the underlying foliated layer, as confirmed by X-ray texture analyses. These findings corroborate a previous assumption that the foliated microstructure derived from calcitic prisms, particularly from those with internal foliated structure. The appearance of the foliated microstructure facilitated drastic mineralogical and microstructural changes in pteriomorph shells-for example, the development of rigid shell margins and the production of largely calcitic shells. Such changes have, no doubt, contributed to the evolutionary success of the groups, which have shown a pronounced diversification over time.