Marine Micropaleontology最新文献

The Middle Eocene Climatic Optimum (MECO; ca. 40 Ma) was a prominent global warming event that lasted 400 kyr and was characterized by a 4–6 °C rise in high latitude surface and deep-water temperatures. As the radiolarian plankton response to this warming event is practically unknown, whole assemblage quantitative analyses were undertaken on well-preserved radiolarian assemblages from ODP Site 1051 (western North Atlantic). Although radiolarians have apparently benefited at this site from increase in oceanic fertility induced by the MECO, this event does not appear to have had a severe impact on subtropical radiolarian fauna. No prominent faunal turnover was found in the studied interval, suggesting that subtropical radiolarians are relatively resilient to transient warming events. Likewise, variations in radiolarian assemblage composition establish that ocean warming induced only a weak ecological response. One of the most striking faunal changes associated with the MECO is the clear increase in radiolarian diversity (taxic richness), as a result of the northward migration of warm tropical radiolarian species. Similarly, several typical middle Eocene tropical species are found to be more abundant in the warmest interval. In addition to these poleward migrations, we identified three radiolarian clusters composed of warm-water or cool-water species, as well as two abundant artostrobiid species which may represent nutrient opportunists.

Conodonts are a group of extinct marine organisms widely used in Paleozoic and Triassic biostratigraphy. The genus Siphonodella comprises ozarkodinid conodonts from the latest Famennian to the middle Tournaisian. The phylogenetic model of this genus plays an important role in biostratigraphy. This study is based on the authors' and published data on 31 species of siphonodellids of cosmopolitan and East European groups. A new phylomorphogeny of Siphonodella is proposed on the basis of known mechanisms of morphological transformations of siphonodellid P₁ elements during speciation processes, presence of interspecies transitional forms, and data on ontogeny. The main morphogenetic pathways in the evolution of siphonodellids are the following: formation and transformation of the rostrum, transformation of the platform outline, transformation of the platform ornamentation, transformation of the keel, and histological transformations. In the process of modeling the phylomorphogeny of Siphonodella, some taxonomic problems are solved: a new species S. thompfelli is described, a new variant of the division of S. lobata (Branson and Mehl) into morphotypes is proposed, the validity of S. plana (Huddle), S. praeplana Bardasheva, Bardashev, Weddige and Ziegler, and S. gladia Zhuravlev and Plotitsyn is clarified, and the knowledge of the morphospace of most representatives of the genus is extended. The phylogeny of siphonodellids provides a basis for the new phylogenetic zonal sequences based on the conodont phylogenetic-zone concept.

The flourishment of conodont diversity through the Paleozoic is evidenced by the strong diversification of the shape of the elements composing their feeding apparatus. Among the different elements that compose the feeding apparatus, the platform elements (P1) are the most robust. However, the P1 elements also represent the most posterior dental elements of the apparatus, performing therefore the ultimate stage of food processing before ingestion of the food bowl. Thus, characterizing the shape of these elements across various species of conodonts could be relevant to decipher the diversity of feeding behavior among this group. Here we use topographic indices initially developed for the description of teeth relief (RFI, Slope), orientation (OPCr) and sharpness (ARC, DNE) to discriminate quantitatively P1 element shapes among conodont communities of the Late Famennian from the Montagne Noire Area (south France). We evidence methodological considerations such as voxel size impact on topographic indices that should be imperatively considered before conducing these methods on conodonts. Under several homogeneous conditions, this quantification of shape diversity, even on poorly damaged specimens, could bring new clues for the understanding of P1 elements kinematics and feeding strategies among conodonts.

Triassic strata in the Drežnica section, Bosnia and Herzegovina have been examined biostratigraphically. The limestone and dolostone strata were deposited in deep pelagic environment. The conodont faunas are marked by prevailing elements of the genus Pseudofurnishius including clusters that enabled to distinguish the huddlei (lower Longobardian) and murcianus (upper Longobardian–?Cordevolian) Zones, the later fauna is characterized by the presence of Budurovignathus with rare representation of Gladigondolella and Paragondolella. This is the first report on recovery of Pseudofurnishius in the region.

A conodont fauna of late Tremadocian to early Floian age (Early Ordovician) is documented from the Yinchufu Formation of Zhejiang Province, South China. It is characterized by the occurrence of two species of Prioniodontidae, a new species of Prioniodus and Acodus triangularis. Prioniodus antiquus sp. nov. may represent the most primitive species of Prioniodus, which is one of the earliest conodont genera with a ramiform—pectiniform apparatus. Based on the review of nearly 200 species originally assigned to Prioniodus, six multielement species are confirmed to belong to this genus. Morphological changes of these six species shows that they form an evolutionary lineage directly evolved from an adentate species, likely Acodus triangularis which has been reported from South China, Australia and from the Precordillera of western Argentina. Origination of the ramiform—pectiniform apparatuses as represented by the appearances of Prioniodus through late Tremadocian to Floian of the Early Ordovician might be a major response of the 'conodont animals' to occupy and adapt to the increasingly diversified environments in the shelf and slope settings. The biofacies distribution of the six Prioniodus species indicates that Prioniodus might have originated in deep-water slope settings and progressively spread into distal and then interior shelves in the late Tremadocian and diversified in the Floian, with Prioniodus amadeus possibly representing a relict species that survived into the Middle Ordovician and was restricted to shallow water environments.

Benthic and planktonic foraminifera faunal and stable isotopic (δ¹⁸O and δ¹³C) analyses on foraminiferal tests were carried out on a piston core, collected from the Campos Basin slope at a water depth of 1475 m. The core location is in front of Cape São Tomé and exhibits landslide scars features. Benthic foraminifera biofacies with ecological indexes and statistics, lithological facies, biostratigraphy and stable isotopic analysis were used to understand the paleoenvironmental evolution of the region by comparison with modern foraminiferal assemblage. Six biofacies were identified between Marine Isotope Stage (MIS) 7 to MIS 1. The main ecological factors controlling the modern assemblages are: bottom currents, slope stability, oxygen concentration, and nutrient input. However, the last two factors are linked to oceanic processes associated with the Paraíba do Sul river, the influence of which has changed in the past. In particular, Biofacies 3, contains infaunal species, points to dysoxic or anoxic periods in the environment, which are interpreted as periods of increased river influence. Changing environmental conditions were observed as the dominant benthic foraminifera species varied down the core, from Epistominella exigua that thrives in stressful conditions, such as sea level oscillations to Globocassidulina crassa, that prefers mild environments during periods of sea level stability.

A new radiolarian image database was used to train a Convolutional Neural Network (CNN) for automatic image classification. The focus was on 39 commonly occurring nassellarian species, which are important for biostratigraphy.

The database consisted of tropical radiolarian assemblages from 129 middle Eocene samples retrieved from ODP Holes 1258A, 1259A, and 1260A (Demerara Rise). A total of 116 taxonomic classes were established, with 96 classes used for training a ResNet50 CNN. To represent the diverse radiolarian assemblage, some classes were formed by grouping forms based on external morphological criteria. This approach resulted in an 86.6% training accuracy.

A test set of 800 images from new samples obtained from Hole 1260A was used to validate the CNN, achieving a 75.69% accuracy. The focus then shifted to 39 well-known nassellarian species, using a total of 15,932 images from the new samples. The goal was to determine if the targeted species were correctly classified and explore potential real-world applications of the trained CNN.

Different prediction threshold values were experimented with. In most cases, a lower threshold value was preferred to ensure that all species were captured in the correct groups, even if it resulted in lower accuracies within the classes.

The genus Pseudooneotodus (Drygant, 1974) is a genus of small and conical elements widely distributed from the Middle Ordovician to the Early Devonian throughout the world. Because of its unusual shape, Pseudooneotodus has long been considered enigmatic, and only in the late nineties of the last century the genus has been finally placed within conodonts according to histological data.

This study investigates possible similarities between Pseudooneotodus and Eurytholia (Sutton et al., 2001), an incertae sedis genus of enigmatic plates with a phosphate composition. An association of over one hundred specimens of Pseudooneotodus beckmanni and Eurytholia bohemica was analyzed from conodont residues in two distinct geographical areas: the Prague Basin (Požáry and Mušlovka sections, Bohemia, Czech Republic) and the Carnic Alps (Rauchkofel Boden section, Austria). Through an investigation that combines the use of optical and electron microscopy (including focused ion beam scanning electron microscopy), X-ray microdiffraction, and trace element (HFSE) analysis by mass spectrometry, differences between these fossil groups were observed and compared with data resulting from typical conodonts (Dapsilodus obliquicostatus, Panderodus unicostatus and Wurmiella excavata) recovered from the same samples.

In this paper we compare the diversity of Floian (Lower Ordovician) conodonts from the Precordillera with that of the Cordillera Oriental, Argentina. The comparative analysis is restricted to the middle Floian Stage Slice (Fl2) from correlative intervals: Oepikodus evae Zone (Juanognathus variabilis Subzone) in the Precordillera and the Gothodus andinus Zone in the Cordillera Oriental. For the comparative analysis, absolute frequency tables of the conodont data from published articles and collections under study, were prepared. These include four sections of the Precordillera with 13 samples recovered from the middle section of the carbonate San Juan Formation, and six sections of the Cordillera Oriental with 28 samples from the middle-upper section of the shaly Acoite Formation. Diversity patterns and indices were generated from absolute frequencies using the software PAST 4.03. Remarkable differences in the species richness and diversity between coeval communities of referred basins are displayed. Comparisons with other basins elsewhere suggest that the paleolatitudinal gradient is not a major factor controlling changes in diversity, which may be due to a response to the complex interaction of biological and physico-chemical factors.

Benthic foraminifers living in euphotic coastal and shelf environments commonly occur in association with macrophytes (macroalgae and seagrasses), and many lineages have evolved morphologic adaptations to thrive in such habitats. Species that did not occur in the Mediterranean Sea prior to recent centuries, commonly known as “introduced” or “alien” species, are now widespread, and some are so abundant that they are altering coastal habitats. With accelerating climatic change and warming of Mediterranean surface waters, recognizing how invasive algal and foraminiferal species are affecting sedimentation and microenvironments has become increasingly urgent. This project examined 18 sets of sediment samples collected in the Abu Qir coastal area east of Alexandria for comparison with a previous assessment of live assemblages within the macroalgae. Overall, 68 foraminiferal species were identified, of which sixteen species were categorized as epiphytic. The hyaline epiphytic Elphidium crispum was the most common species found in sediments from the platform, while the porcelaneous free-living Quinqueloculina auberiana dominated sediments from the small bay. Eleven introduced foraminiferal species were recorded, one of which, Amphistegina lobifera, was commonly found, especially in the platform sediment samples. Taxa recorded live (stained) in platform sediments were predominantly (>10% each) Peneroplis, Amphistegina and Elphidium, while bay sediments were dominated by Quinqueloculina, followed in order by Elphidium, Amphistegina and Peneroplis. The assemblage differences from previously reported live assemblages associated with macralgae, compared with live and dead assemblages in sediments, appear to reflect hydrodynamic influence of sediment sorting and resistence of larger taxa to physical degradation.