Taphonomy and ichnology of cephalopod shells in a Maastrichtian chalk from Western Australia

The post-mortem history of a prolific Maastrichtian ammonite and nautiloid fauna preserved as phosphatic steinkerns in chalk of the upper Miria Formation of Western Australia is described. Sediment infilling of phragmocones, required for their fossilisation, was accomplished by means of perforations in the shell wall induced by the activity of abundant endoliths. These include borings ascribed to clionid sponges (Entobia), thallophytes, polychaete worms (including Caulostrepis and probable Maeandropolydora), phoronids (Talpina and Gnathichnus) and others of conjectural origin. Sediment infilling by this mechanism is considered to be more applicable to the taphonomy of phragmocones in general than sediment entry through the siphuncle and to be indicative of low sedimentation rates for the hosting strata. Nonheteromorph ammonites, and the nautiloid Cimomia, are preserved almost exclusively as phragmocones in the upper Miria Formation, and are numerically subordinate to the heteromorph Eubaculites which, together with Glyptoxoceras, is preserved predominantly as body chambers. This phragmocone/body chamber preservational contrast is attributed to the influence of shell shape on pre-burial mechanical abrasion. The apparent dominance of Eubaculites is considered to be largely a preservational artifact and ascribed to the ease with which body chambers were infilled, and thereby favoured for steinkern formation, relative to phragmocones. Phragmocones, or parts thereof. not filled with sediment were eliminated from the fossil record by diagenetic aragonite dissolution. Many ammonites with open umbilici have the early whorls missing. This we attribute to the trapping of sediment in the umbilicus prior to burial, preventing endolith attack whereby the early whorls avoided a sediment infilling. However, the protected inner whorls of involute ammonites and Cimomia, which have closed umbilici, and the inner whorls of evolute ammonites where a cemented umbilical plug supported the mouldic cavity left by shell dissolution, were preserved and were commonly infilled with calcite spar later in diagenesis. The dearth of cephalopod fossils in chalk underlying the upper Miria Formation is ascribed to diagenesis in which aragonite dissolution was not preceded by cementation.     

Sclerotic Rings in Mosasaurs (Squamata: Mosasauridae): Structures and Taxonomic Diversity

Mosasaurs (Squamata: Mosasauridae) were a highly diverse, globally distributed group of aquatic lizards in the Late Cretaceous (98–66 million years ago) that exhibited a high degree of adaptation to life in water. To date, despite their rich fossil record, the anatomy of complete mosasaur sclerotic rings, embedded in the sclera of the eyeball, has not been thoroughly investigated. We here describe and compare sclerotic rings of four mosasaur genera, Tylosaurus, Platecarpus, Clidastes, and Mosasaurus, for the first time. Two specimens of Tylosaurus and Platecarpus share an exact scleral ossicle arrangement, excepting the missing portion in the specimen of Platecarpus. Furthermore, the exact arrangement and the total count of 14 ossicles per ring are shared between Tylosaurus and numerous living terrestrial lizard taxa, pertaining to both Iguania and Scleroglossa. In contrast, two species of Mosasaurus share the identical count of 12 ossicles and the arrangement with each other, while no living lizard taxa share exactly the same arrangement. Such a mosaic distribution of these traits both among squamates globally and among obligatorily aquatic mosasaurs specifically suggests that neither the ossicle count nor their arrangement played major roles in the aquatic adaptation in mosasaur eyes. All the mosasaur sclerotic rings examined consistently exhibit aperture eccentricity and the scleral ossicles with gently convex outer side. Hitherto unknown to any squamate taxa, one specimen of Platecarpus unexpectedly shows a raised, concentric band of roughened surface on the inner surface of the sclerotic ring. It is possible that one or both of these latter features may have related to adaptation towards aquatic vision in mosasaurs, but further quantitative study of extant reptilian clades containing both terrestrial and aquatic taxa is critical and necessary in order to understand possible adaptive significances of such osteological features.     

Pelagic neonatal fossils support viviparity and precocial life history of Cretaceous mosasaurs

Mosasaurs were large marine squamates that inhabited all of the world's oceans during the Late Cretaceous. Their success as apex predators has been attributed to their rapid acquisition of aquatic adaptations, which allowed them to become fully pelagic. However, little is known about the breeding biology of derived, flipper‐bearing mosasaurs, as the record of neonatal mosasaur fossils is extremely sparse. Here, we report on the fragmentary cranial remains of two neonatal mosasaurs from the Niobrara Formation, referred to Clidastes sp. Comparison with other preliminary reports of neonatal mosasaurs reveals that these specimens are among the smallest individuals ever found and certainly represent the smallest known Clidastes specimens. The recovery of these extremely young specimens from a pelagic setting indicates that even neonatal mosasaurs occupied open oceanic habitats and were likely born in this setting. These data shed new light on the ecology of neonatal mosasaurs and illustrate the degree to which size‐related taphonomic and collection biases have influenced our understanding of the early life history of these iconic marine reptiles.     

Sudden origin of ribbing in Jurassic Paracenoceras (Nautiloidea) and its bearing on the evolution of ribbing in post‐Triassic Nautiloids

Ribs appeared cryptically in the Middle Jurassic nautiloid Paracenoceras. These ribs were produced by crowding of growth lirae as a corollary of change in body size during paedomorphic evolution. Initially, they had no direct functional significance. Some other contemporary genera are found to have similar ribbing patterns, partially developed on either the flanks or venter of the adult body chamber.

Subsequently in nautiloid phylogeny, ribs spread all around the whorl, becoming analogous to those of contemporary ammonites. Shell rugosity is observed to occur with increasing frequency in post‐Triassic nautiloids, paralleling the trend in ammonites. This is believed to be an outcome of the ‘arms race’ known as the Mesozoic marine revolution. Ribbing that was not at first adaptive in these nautiloids was subsequently co‐opted as a defensive adaptation. The evolution of this structure is a good example of exaptation.     

Taphonomy and systematics of a new Late Cretaceous verrucid barnacle (Cirripedia,Thoracica) from Canterbury,New Zealand

Abstract: Cirripede remains (Thoracica, Verrucomorpha), found associated with the mosasaur Prognathodon waiparaensis  Welles and Gregg, 1971 in glauconitic sands of the Late Cretaceous Conway Formation exposed along the Waipara River bank (mid‐Canterbury, New Zealand), are identified as a new species, Verruca sauria sp. nov. On the basis of taphonomy, it is deduced that these verrucids grew on a postmortem accumulation of mosasaur bones under very quiescent conditions. The current amphitropical distribution of the earliest known verrucids, i.e. V. sauria sp. nov., V. prisca  Bosquet, 1854 , V. pusilla  Bosquet, 1857 and V. tasmanica  Buckeridge, 1983 , is rationalized in the light of Tethyan palaeogeography.     

Convergent Evolution in Aquatic Tetrapods: Insights from an Exceptional Fossil Mosasaur

Mosasaurs (family Mosasauridae) are a diverse group of secondarily aquatic lizards that radiated into marine environments during the Late Cretaceous (98–65 million years ago). For the most part, they have been considered to be simple anguilliform swimmers – i.e., their propulsive force was generated by means of lateral undulations incorporating the greater part of the body – with unremarkable, dorsoventrally narrow tails and long, lizard-like bodies. Convergence with the specialized fusiform body shape and inferred carangiform locomotory style (in which only a portion of the posterior body participates in the thrust-producing flexure) of ichthyosaurs and metriorhynchid crocodyliform reptiles, along with cetaceans, has so far only been recognized in Plotosaurus, the most highly derived member of the Mosasauridae. Here we report on an exceptionally complete specimen (LACM 128319) of the moderately derived genus Platecarpus that preserves soft tissues and anatomical details (e.g., large portions of integument, a partial body outline, putative skin color markings, a downturned tail, branching bronchial tubes, and probable visceral traces) to an extent that has never been seen previously in any mosasaur. Our study demonstrates that a streamlined body plan and crescent-shaped caudal fin were already well established in Platecarpus, a taxon that preceded Plotosaurus by 20 million years. These new data expand our understanding of convergent evolution among marine reptiles, and provide insights into their evolution''s tempo and mode.     

Biostratigraphy of the Peri-Gondwana Cambrian trilobite fauna (northern Kerman,Iran) and correlation with other countries

Polymeroid trilobite fauna from two stratigraphic sections (Godbondar and Kuhbanan) of the Kuhbanan Formation in northern Kerman (central Iran) were studied and subjected to biostratigraphic analysis. Eleven genera and species are recognised from the latest Early Cambrian and Middle Cambrian Peri-Gondwanian successions of the study sections. The recognised fauna includes Afghanocare lategenatum, Blountia blountia, Iranoleesia sp., Iranoleesia pisiformis, Kermanella kuhbananensis, Kermanella lata lata, Kermanella lata minuta, Kermanella sp., Redlichia chinensis, Redlichia noetlingi and Redlichia sp. Based on trilobite distribution, three trilobite biozones were recognised in the study sections, namely Redlichia noetlingi biozone, Kermanella kuhbananensis biozone and Iranoleesia pisiformis biozone. The age of the study sections is late Early Cambrian to late Middle Cambrian based on the recognised trilobite biozones. The recognised late Early Cambrian trilobite assemblages (especially Redlichia and Kermanella) from northern Kerman are similar to those found from some other parts of Gondwana or Peri-Gondwana terrains (north India, Pakistan, northwestern Kashmir, Tajikistan, South Australia, South China and Afghanistan) and show affinities with fauna found in some other parts of Iran (Alborz, northern Iran; Tabas, eastern Iran; southeast Karman).     

Pennsylvanian shark-cephalopod predation: a case study

A well-preserved portion of a body chamber of a coiled nautiloid (taxon uncertain) from the Kendrick Shale (Lower Pennsylvanian) of Floyd County, Kentucky, U.S.A., exhibits three comparatively large, nearly circular punctures and a circular indentation in the shell. These punctures are interpreted as representing an attack on the nautiloid by a cladodontid shark, most likely by the large symmoriid shark, Symmorium reniforme. We conclude that the punctures in the nautiloid body chamber were inflicted by three teeth in a single tooth file in the lower jaw of a specimen of 5. reniforme that was approximately 2.5 meters long. This nautiloid specimen is the first Paleozoic record of a chondrichthyan-cephalopod/ predator-prey relationship. We suggest, however, that this relationship was perhaps a common one and that other examples probably exist in collections of late Paleozoic ccphalopods. ?Paleozoic, Pennsylvanian, Symmorium reniforme, cephalopod. predation.     

Turtle Shell Impression in a Coprolite from South Carolina,USA

Coprolites (fossilized feces) can preserve a wide range of biogenic components. A mold of a hatchling turtle partial shell (carapace) referable to Taphrosphys sulcatus is here identified within a coprolite from Clapp Creek in Kingstree, Williamsburg County, South Carolina, USA. The specimen is the first-known coprolite to preserve a vertebrate body impression. The small size of the turtle shell coupled with the fact that it shows signs of breakage indicates that the turtle was ingested and that the impression was made while the feces were still within the body of the predator. The detailed impression could only have survived the act of defecation if the section of bony carapace was voided concurrently and remained bonded with the feces until the latter lithified. Exceptionally, the surface texture of the scutes is preserved, including its finely pitted embryonic texture and a narrow perimeter of hatchling scute texture. The very small size of the shell represented by the impression makes it a suitable size for swallowing by any one of several large predators known from this locality. The coprolite was collected from a lag deposit containing a temporally mixed vertebrate assemblage (Cretaceous, Paleocene and Plio-Pleistocene). The genus Taphrosphys is known from both sides of the Cretaceous–Paleogene (K–Pg) boundary so, based on the size of the coprolite and the locally-known predators, the juvenile turtle could have been ingested by a mosasaur, a crocodylian, or a theropod dinosaur. Unlike mosasaurs and theropod dinosaurs, crocodylian stomachs have extremely high acid content that almost always dissolves bone. Therefore, the likely predator of this turtle was a mosasaur or a (non-avian or avian) theropod dinosaur.     

Three-dimensionally preserved integument reveals hydrodynamic adaptations in the extinct marine lizard Ectenosaurus (Reptilia, Mosasauridae)

The physical properties of water and the environment it presents to its inhabitants provide stringent constraints and selection pressures affecting aquatic adaptation and evolution. Mosasaurs (a group of secondarily aquatic reptiles that occupied a broad array of predatory niches in the Cretaceous marine ecosystems about 98-65 million years ago) have traditionally been considered as anguilliform locomotors capable only of generating short bursts of speed during brief ambush pursuits. Here we report on an exceptionally preserved, long-snouted mosasaur (Ectenosaurus clidastoides) from the Santonian (Upper Cretaceous) part of the Smoky Hill Chalk Member of the Niobrara Formation in western Kansas, USA, that contains phosphatized remains of the integument displaying both depth and structure. The small, ovoid neck and/or anterior trunk scales exhibit a longitudinal central keel, and are obliquely arrayed into an alternating pattern where neighboring scales overlap one another. Supportive sculpturing in the form of two parallel, longitudinal ridges on the inner scale surface and a complex system of multiple, superimposed layers of straight, cross-woven helical fiber bundles in the underlying dermis, may have served to minimize surface deformation and frictional drag during locomotion. Additional parallel fiber bundles oriented at acute angles to the long axis of the animal presumably provided stiffness in the lateral plane. These features suggest that the anterior torso of Ectenosaurus was held somewhat rigid during swimming, thereby limiting propulsive movements to the posterior body and tail.     

Unusual histology and morphology of the ribs of mosasaurs (Squamata)

We report the presence of two previously unrecognized features in the dorsal ribs of mosasaurs: first, the presence of extremely dense, pervasive extrinsic fibres (anchoring soft tissue to bone, sometimes called Sharpey's fibres); and second, high intraspecific variation in costal bone compactness. Extensive extrinsic fibres are developed in the dorsal ribs of the mosasaurs Tylosaurus proriger and Eonatator sternbergi. The dorsal ribs of these mosasaurs are also characterized by a longitudinally ridged texture that almost completely covers the bone. Pervasive extrinsic fibres and ridged textures are absent in the mosasaur Selmasaurus russelli as well as the dorsal ribs of extant semi‐aquatic reptiles (e.g. crocodyliforms) and mosasaurs' close extant relatives and analogues (e.g. snakes and varanids). Similar ridged textures characterize the dorsal ribs of several other mosasaur taxa but are developed to a lesser extent (e.g. Mosasaurus, Clidastes, Platecarpus and Ectenosaurus), but in no other taxa have pervasive extrinsic fibres been reported. We interpret these osteohistological features in T. proriger and E. sternbergi as evidence of tendinous attachment of extensive and highly differentiated axial musculature capable of producing great stresses, most likely related to stabilization of the trunk relative to contralateral movements of the tail during carangiform locomotion. We also report the compactness indices (percentage of space occupied by bone rather than cavities) for these large mosasaur ribs, which are much higher than previously reported. This suggests high intraspecific variation in bone compactness that complicates its use in reconstructing mosasaur palaeoecology.     

Revision of <Emphasis Type="Italic">Actinastrea</Emphasis>, the most common Cretaceous coral genus

The very common and species-rich Scleractinian genus Actinastrea (family Actinastraeidae, suborder Archeocaeniina) is revised on the basis of the type material of its type species and additional material from the type locality. A lectotype is designated for the type species. It was discovered that Jurassic to Early Cretaceous corals currently assigned to Actinastrea do not fit into the concept of this genus. These species belong to the genus Stelidioseris, which is also revised on the basis of the type of the type species, including designating a lectotype. These two genera are distinguished by various characteristics: septal external parts are swollen in Actinastrea but not in Stelidioseris, the costae are confluent in Stelidioseris but not in Actinastrea, the coenosteum is granulated in Actinastrea but narrow than in Actinastrea and only with costae in Stelidioseris. Actinastrea is restricted to the Late Cretaceous (Late Turonian—Maastrichtian), whereas Stelidioseris originates in the Jurassic and reaches into the Late Cretaceous, but is less common from the Turonian on.     

Mode of life and habitat of scaphitid ammonites

Scaphitid ammonites (scaphites) are among the most common ammonites in the Upper Cretaceous of the U.S. Western Interior. We have examined species of Hoploscaphites from the Campanian and Maastrichtian Pierre Shale and Bearpaw Shale for clues about their mode of life and habitat. Like most other ammonites, scaphites exhibit determinate growth. The “morphogenetic countdown” begins at the point at which the shell departs from the spiral coil and develops into a shaft and recurved hook. This is accompanied by a reduction in the spacing of ribs and tubercles on the hook and the formation of a constriction and varix at the aperture. Internally, this coincides with a decrease in septal spacing. The common association of scaphites and benthic fossils (e.g., Inoceramus) is interpreted as reflecting oxygen-rich episodes in the history of the Western Interior Seaway. Habitat depths are estimated at less than 100 m, based on faunal associations and studies of the mechanical strength of the septa and siphuncle. Analyses of the isotopic composition of the shells suggest that the animals lived near the sea floor. The high angle of orientation of the aperture at maturity (approximately 100°) seems incompatible with a nektobenthic mode of life. The constricted aperture ending in a thin lip may also have restricted unimpeded movement of long, muscular arms protruding from the aperture. Adults were probably poor swimmers, based on a comparison of their musculature (as inferred from their muscle scars) with that of nautilus (assuming that such a comparison is valid). The lack of a hyponomic sinus on the midventer would have prevented the animal from extending its hyponome below the shell in order to swim forward. As a consequence, scaphites may have been limited in their movement to swimming backward or downward, and may have exploited a low-energy lifestyle, remaining at a single site for an extended period of time. They may have consumed small prey in the water column, which is consistent with the presence of an aptychus-type lower jaw.     

Late Viséan foraminifers and algae from the Cataloturan Nappe, Aladag Mountains, eastern Taurides, southern Turkey

The Aladag Mountains at the western end of the eastern Taurides, southern Turkey, are composed of nappe structures imbricated in the Late Cretaceous by ophiolite emplacement. The Cataloturan Nappe contains Mississippian (i.e., Early Carboniferous) deep-water (basinal-lower slope) facies in the lower part and shallow-water (shelf edge) facies in the upper part. These Mississippian strata belong to the Nohutluk Formation. The main outcrop occurs at Nohutluktepe where it is 460 m thick. Eighty taxa of algae, foraminifers, and calcareous microproblematica permit dividing the upper part of the formation into three informal assemblage biozones: (1) Howchinia bradyana longa - Lituotubella magna - Koktjubina (?) sp. biozone (late Viséan Cf6γ1), (2) Bradyina rotula - Euxinita tauridiana biozone (Cf6γ2), (3) Janischewskina typica - Biseriella aff. parva biozone (upper Cf6δ). The genus Euxinita is discussed and a new species E. tauridiana nov. sp. is described. A paleobiogeography, based on Euxinita, Koktjubina (?), Vissarionovella, Janischewskina and Hortonella, is reconstructed, where the Taurides are juxtaposed to the northwestern border of the Paleotethys, with possible direct connections with Russia, Kazakhstan, western Europe, and Morocco.     

<Emphasis Type="Italic">Dentalium saturni</Emphasis><Emphasis Type="SmallCaps">Goldfuss</Emphasis>, 1841 (Eifeliari: Mollusca): complex issues from a simple fossil

The specimen commonly thought to be the holotype ofDentalium saturni Goldfuss, 1841, does not match the published drawings and is presumed to be spurious. That fossil is incomplete and lacks critical detail to demonstrate that it is a member of the class Scaphopoda, for its curvature and fine longitudinal ribbing can be duplicated among nautiloid Cephalopoda; the relatively thin shell of the specimen suggests Support for that possible reassignment. The drawing of the type has widely spaced, coarse lirae, but also does not show features which conclusively link it to the Scaphopoda. This Ornament is similar to that of livingDentalium, but is equally similar to that of several Carboniferous nautiloid genera. The homeomorphy between a broken scaphopod and a broken body Chamber of a curved nautiloid indicates the danger of too precise assignment of poor specimens. It is concluded that there is no satisfactory proof of the occurrence of Scaphopoda in the Devonian.      

The influence of prey behaviour on prey selection of the carnivorous plant Utricularia vulgaris

The mechanisms underlying differential prey selection of two microcrustaceans by the common bladderwort (Utricularia vulgaris) were studied in the laboratory. Functional response experiments with single prey showed that Utricularia had a higher attack rate coefficient and a longer handling time coefficient with the cladoceran Polyphemus pediculus than with the cyclopoid copepod Eucyclops serrulatus. Observation of predation rate, defined as number of prey eaten per unit time, from direct behavioural observation on single prey species, showed a higher predation rate with Polyphemus than on Eucyclops, at low prey densities. The opposite pattern was found at high prey density. When the two prey were presented simultaneously to the predator, Eucyclops was preferred over Polyphemus. Results from the situation with two prey and some of the results from the direct behavioural observations support field data on the diet of Utricularia, which shows that cyclopoid copepods are selected more frequently than Polyphemus.     

Foraging behaviors and the interaction of alewife,Alosa pseudoharengus,and bloater,Coregonus hoyi

Synopsis Alewife, Alosa pseudoharengus, and bloater, Coregonus hoyi, are common planktivores in Lake Michigan. Both alewife and bloater use a variety of feeding modes. Alewives can filter, gulp and particulate feed; bloaters can only gulp and particulate feed. We examined handling time per prey and probability of capture for alewife and bloater particulate feeding on Mysis relicta. Using these estimates and available data for filtering alewives, cost curves were derived for alewife and bloater particulate feeding and for alewife using all three modes of feeding. Alewives filter small prey relative to their own body size and particulate feed on larger prey. Feeding mode appears to be dependent on prey size and density and shifts in feeding mode are apparently based on maximizing biomass eaten per time. The ability to filter confers a competitive advantage on alewife when small prey are abundant as they were in the mid 1960s in Lake Michigan. If the zooplankton are large, bloater young-of-year do not suffer this relative disadvantage. In fact, large bloaters can consume prey on the bottom not available to alewife. This shifting competitive balance may explain, in part, the observed dynamics of alewife and bloater.     

Comparative Study of Functional Response of Common Hemipteran Bugs of East Calcutta Wetlands,India

The common and abundant hemipteran water bugs Anisops bouvieri, Diplonychus rusticus, D. annulatus, of the wetlands of East Kolkata are known predators of a wide range of aquatic insects including the mosquito larvae. In the laboratory their predation were assessed in respect to short term and long term periods using the larvae of Culex quinquefasciatus to reveal their possible role in regulating the dipteran population in nature. The attack rate (a) and handling time (T_h ) of these predators varied with respect to the prey size. For the backswimmers A. bouvieri the values for a and T_h for the small prey were 5.47 L and 18.72 min respectively, while in case of the belostomatid bugs, the values for the same were 5.37 L and 8.64 min (for D. rusticus), 5.81 L and 20.16 min (for D. annulatus). The predation rate varied with prey and predator densities for both the prey sizes. It was revealed that on an average A. bouvieri can kill and consume 10–82 and 6–44, D. rusticus 10–118 and 10–84 and D. annulatus 10–70 and 10–138 small and large sized prey per day, respectively. However the mutual interference (m) values of the three predators varied with the prey size and ranged between 0.053–0.326 for A. bouvieri, 0.0381–0.066 for D. rusticus and 0.0556–0.115 for D. annulatus, respectively. In the long term experiments A. bouvieri killed between 6–119 small preys and 3–31 large preys, D. rusticus killed 50–94 small preys and 50–96 large preys and D. annulatum were found to kill between 14–74 small prey and 50–131 large prey per day, respectively. The clearance rates were found to be proportional to the predator density as well to the prey size and density, and differed between the predator species significantly. These data are supportive of qualifying the water bugs, A. bouvieri, D. rusticus, and D. annulatus as potential biological resources in regulating the population of mosquito larvae in the wet‐lands. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Feeding habits and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in a shallow lake,central China

The diet and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in Lake Xiaosihai along the middle reach of the Yangtze River were studied through stomach content analysis. A total of 401 specimens (91–539 mm total length) were collected in 2007. The diet was dominated by topmouth gudgeon Pseudorasbora parva, sharpbelly Hemiculter leucisculus, redfin culter Cultrichthys erythropterus, and crucian carp Carassius auratus, with significant seasonal and ontogenetic differences. Ontogenetic variation in diet was apparent that larger prey items such as crucian carp and redfin culter became more common, while smaller prey such as topmouth gudgeon, bitterlings and shrimps gradually declined in the larger fish. Mandarin fish total length (TL) was strongly related to mouth gape width (GW) and gape height (GH). Mandarin fish TL and prey fish TL as well as mandarin fish GW and prey fish body depth (BD) were positively and linearly related for sharpbelly, redfin culter and crucian carp. Strong size selectivity for topmouth gudgeon, sharpbelly and redfin culter as prey indicated that the piscivorous mandarin fish can have potential impact on the population size structure of the three prey fish.     

Microfacies and sequence stratigraphy of the Amapá Formation, Late Paleocene to Early Eocene, Foz do Amazonas Basin, Brazil

On the basis of thin-section studies of cuttings and a core from two wells in the Amapá Formation of the Foz do Amazonas Basin, five main microfacies have been recognized within three stratigraphic sequences deposited during the Late Paleocene to Early Eocene. The facies are: 1) Ranikothalia grainstone to packstone facies; 2) ooidal grainstone to packstone facies; 3) larger foraminiferal and red algal grainstone to packstone facies; 4) Amphistegina and Helicostegina packstone facies; and 5) green algal and small benthic foraminiferal grainstone to packstone facies, divisible locally into a green algal and the miliolid foraminiferal subfacies and a green algal and small rotaliine foraminiferal subfacies. The lowermost sequence (S1) was deposited in the Late Paleocene–Early Eocene (biozone LF1, equivalent to P3–P6?) and includes rudaceous grainstones and packstones with large specimens of Ranikothalia bermudezi representative of the mid- and inner ramp. The intermediate and uppermost sequences (S2 and S3) display well-developed lowstand deposits formed at the end of the Late Paleocene (upper biozone LF1) and beginning of the Early Eocene (biozone LF2) on the inner ramp (larger foraminiferal and red algal grainstone to packstone facies), in lagoons (green algal and small benthic foraminiferal facies) and as shoals (ooidal facies) or banks (Amphistegina and Helicostegina facies). Depth and oceanic influence were the main controls on the distribution of these microfacies. Stratal stacking patterns evident within these sequences may well have been related to sea level changes postulated for the Late Paleocene and Early Eocene. During this time, the Amapá Formation was dominated by cyclic sedimentation on a gently sloping ramp. Environmental and ecological stress brought about by sea level change at the end of the biozone LF1 led to the extinction of the larger foraminifera (Ranikothalia bermudezi).