New isotopic analyses of exceptionally well-preserved Early Cretaceous ammonoids from Madagascar reveal that delta 18O and delta 13C values in septa and simultaneously formed outer shells are not consistent. Septal delta 18O values are consistently more negative (-4.58 to-1.57%o) than those of the outer shells (-1.71 to 0.28%o), with delta 13C showing a similar trend (-13.59 to-6.86%o for septa and-1.77 to 0.93%o for outer shells). These differences cannot be fully accounted for by variations in salinity or temperature. Instead, we propose that kinetic isotope effects, particularly those occurring during rapid septal formation in juveniles, significantly influence these values. This suggests that delta 18O values in the examined ammonoid septa do not reliably represent ambient seawater temperatures. Septal isotope data should be interpreted more cautiously for palaeotemperature reconstructions, as they likely reflect a combination of kinetic, thermal, and salinity influences, at least in some ammonoid species.
The lingulide brachiopod Mergliella sp. aff. M. bechei, with an exceptionally preserved three-dimensional pedicle, is described from the upper part of the Cae'r mynach Formation (Silurian, late Ludfordian) in Wales, UK, where it occurs with a limited shelly fauna and fine plant debris. The shells of Mergliella were probably exhumed locally by a thin storm sand sheet reaching into a subtidal delta-front environment and were transported little. Microbial mats developing in the fairweather environment, limited bioturbation and a sparse shelly fauna suggest an anachronistic taphonomic environment where the soft tissue became preserved. Fossilisation in dysaerobic or euxinic conditions resulted in replacement of organic tissues by platelets of clay minerals and fine pyrite crystal growth around the shell. Soft tissue preservation in this taphonomic environment is rare in shallow subtidal environments after Proterozoic-early Cambrian times except after ecosystem disruption such as extinction events. This is the only example of soft tissue preservation in a linguliform brachiopod from the Silurian Period. square Lagerst & auml;tte preservation, Brachiopoda, Lingulida, Silurian, Wales, taphonomy.
Phosphorites of the Ediacaran Doushantuo Formation at Weng'an, South China, contain abundant and extraordinarily preserved microfossils. The nature of most of these microfossils is enigmatic and controversial, including spherical microfossils that resemble animal embryos. To elucidate the nature of these specific spherical microfossils, we analysed their mineral-organic relationships and geochemical signatures using Raman spectroscopy, micro-X-ray fluorescence (& micro;-XRF), and electron probe microanalysis (EPMA). The co-occurrence of phosphate intraclasts and fragmented and well-preserved microfossils suggests some degree ofreworking and re-deposition in the original environment, consistent with overall condensed sedimentation. The analysed microfossils exhibit similar to 800 & micro;m-sized spherical shapes covered by a similar to 10 & micro;m thick, two-layered envelope consisting of apatite and subordinated organic matter. A more detailed observation of the internal parts revealed the presence of a matrix compositionally similar to the envelope. The matrix encloses abundant, small (<= 2 & micro;m) aggregates, which show reverse proportions of apatite and organic matter (i.e., relatively more organic matter than apatite). As a whole, the observed features resemble modern microbial spheres covered by lectin-dominated extracellular polymeric substances (EPS), as exemplified by communities of anaerobic methanotrophic archaea (ANME-2) and sulphate reducing bacteria (SRB) in the euxinic Black Sea, likely as a strategy to cope with environmental stressors (e.g. varying redox conditions and substrate concentrations). Overall, our findings reinforce a microbial origin of various embryo-like microfossils preserved within phosphorites of the Ediacaran Doushantuo Formation at Weng'an, highlighting the need for further studies to assess the diversity of the palaeo-communities.
Quantitative stratigraphical methods include powerful tools for constructing strati-graphical models that maximize predictive power. Among these, Shaw's Graphic Correlation method stands out as a widely used technique that underpins many automated stratigraphical correlation tools. A key challenge in Graphic Correlation is to determine the line of correlation (LOC) in an objective manner that remains consistent with geological principles such as the law of superposition. In this study, we present a novel, graph-optimized Graphic Correlation (GOGC) approach that can automatically and quantitatively construct the LOC and generate a composite standard (CS). This method follows the qualitative rule of 'Splitting Tops and Bases', which favours the LOC that passes through the maximum number of stratigraphical events-referred to as 'Longest-path LOC' in this study. We reformulate this LOC estimation as a longest-path problem on a directed graph, which can be efficiently solved using topological sorting and dynamic programming. The results show that Longest-path LOCs are comparable to those produced by a genetic algorithm but are deterministic and more computationally efficient. The CSs derived from the Longest-path LOC exhibit high precision and are similar to those generated by Constrained Optimization (CONOP), a commonly used quantitative stratigraphical method. Additionally, our approach shows promise as a new method for applying CSs in stratigraphical correlation, refining existing CSs, and enabling the automated construction of age-depth models for stratigraphical sections or drill cores, thereby demonstrating great potential for managing large databases and facilitating quantitative stratigraphy.
Epeiric seas served as critical depositional settings for ancient carbonate successions; however, the absence of modern analogues has significantly hindered their palaeoecological reconstruction. Well-preserved Cambrian epeiric carbonates of the Zhangxia Formation crop out along the southern margin of the North China Block. An integrated sedimentological and ichnological analysis has established six facies associations in the formation, representing six distinct depositional environments, with six corresponding ichnofabrics identified to characterize biogenic-sedimentary interactions. The deep subtidal zone, near the storm wave base, lacks bioturbation structures. Intra-platform oolitic shoal and microbial reefs complex host Balanoglossites triadicus Ichnofabric. Landward marginal zones of oolitic shoal exhibit Planolites montanus-Skolithos linearis ichnofabric and Thalassinoides horizontalis ichnofabric. Open shallow subtidal settings are dominated by Arenicolites isp.-Taenidium isp. ichnofabric. The barrier island oolitic shoals show abundant Planolites montanus, whereas restricted subtidal settings behind barrier islands are characterized by dense Thalassinoides bacae. The results demonstrate that benthic metazoans had pervasively colonized the entire epeiric sea during Cambrian Miaolingian. This ecosystem-wide colonization reflects the establishment of tiered infaunal communities in the Miaolingian epeiric sea, where microenvironmental stress gradients controlled both the diversity of bioturbation styles and the dominance of r- versus K-selected trace makers. square Ichnology, carbonate platform, trace fossil, bioturbation, lithofacies.
The palaeontological record for the tundra vole Alexandromys oeconomus indicates a reduction in geographical range and population size since the Last Pleistocene. Up to four different mitochondrial haplogroups are currently identified in modern and recent historical specimens: Central European (CE), Northern European (NE), Central Asian (CA) and Beringian (BE). Here, we generated ancient mitochondrial genomes from five Late Pleistocene palaeontological samples (mandibles) from El Mir & oacute;n Cave (Cantabria, Spain), one of the last Iberian strongholds of A. oeconomus, to investigate the relationship to present-day populations. The analysis of the mitochondrial genome data obtained from the five palaeontological samples of A. oeconomus allowed the identification of a fifth novel haplogroup, currently extinct, that was present at least during the Late Pleistocene-Holocene of the Iberian Peninsula. A tentative time-calibrated phylogenetic analysis suggests that the novel haplogroup could have separated from the CE-NE haplogroups around 0.050-0.1790 Ma, probably before the separation of the CE-NE haplogroups (0.017-0.136 Ma). square Ancient DNA, mitochondrial genome, population dynamics, Iberian Peninsula, haplogroups, biodiversity
Peri-Gondwana and Baltica acritarch provinces are easily recognized during the Early-Middle Ordovician, illustrating provincialism of the global phytoplankton. However, acritarch assemblages become increasingly similar with a general cosmopolitanism towards the Late Ordovician, although acritarch assemblages from Laurentia and Baltica differ from those from peri-Gondwana. Acritarch assemblages from South America, Baltica, Iran, and Siberia, and new material from South China and Tarim, provide additional data to better understand the Late Ordovician palaeobiogeographical evolution of the phytoplankton. Sselected papers were used to build datasets for Cluster Analysis (CA), Nonmetric Multidimensional Scaling (NMDS) and Network Analysis (NA), to constrain acritarch palaeogeography. The global palaeobiogeographical distribution points to a clear acritarch provincialism during the Late Ordovician, particularly in the Katian, mainly controlled by palaeotemperature and palaeolatitude. A modified latitudinal diversity gradient shows the acritarch diversity peak moved from middle latitudes in the Early and Middle Ordovician to lower latitudes in Late Ordovician within the Southern Hemisphere. The peak of acritarch diversity correlates with strong palaeogeographical differentiation in the Katian. The proportion of cosmopolitan acritarch taxa is higher in the Hirnantian than in the Sandbian and Katian, which may be affected by the Late Ordovician Mass Extinction (LOME). Acritarch diversity in South America and North Africa increased in the Hirnantian and were less affected by the LOME, while those from the Middle East were affected moderately, and Baltica, Laurentia, Avalonia and South China were affected strongly. The different trends of the acritarch diversity changes in different palaeoplates could be linked to local environmental changes.
Records of isograptid graptolites from South America remain scarce and poorly known from Ordovician deposits at the Central Andean Basin (northwestern Argentina, Bolivia and Peru), but are widely distributed and documented in numerous stratigraphical sections in the Precordillera Argentina. Taxonomic assignations and correlations in the Puna region, northwestern Argentina, have often been regarded with uncertainty due to their poor preservation, tectonic deformation, low diversity, and isolated outcrops of difficult access. Here we document, for the first time, the presence of Isograptus divergens in the Vega de Catua section and revise previous records from the Tafna section. The age and correlation of the graptolite faunas from the Central Andean Basin are refined, contributing to the understanding of the palaeobiogeographical affinities and palaeoecology of South American isograptids. These new records allow for a more precise dating of the studied deposits to the Middle Ordovician (late Dapingian and possibly early Darriwilian), bridging the gap between the 'Isograptus victoriae' and Levisograptus austrodentatus biostratigraphical units previously proposed for the region. It also enables a more accurate global correlation of the studied Ordovician deposits with the Australian succession in which Oncograptus upsilon and Cardiograptus morsus biozones are developing, supporting the widespread (pandemic) distribution of the Isograptus genus. Furthermore, it highlights the preference of species of the genus Isograptus for deep-water palaeoenvironments of the Puna region, in contrast to the more open one of the Cordillera Oriental.
The palaeogeographical distribution of olenid trilobites shifted markedly from the Miaolingian (Guzhangian) to the Ordovician, reaching cosmopolitan range around the Cambrian-Ordovician boundary. Using genus-level occurrences, cephalic geometric morphometrics, and multivariate analyses, we examine the processes underlying this expansion. Olenids initially flourished in dysoxic, siliciclastic settings, achieving broad distribution and high morphological disparity around the Cambrian-Ordovician boundary. Their expansion was enabled by strong dispersal capacity, ecological plasticity, and environmental opportunity, allowing them to occupy habitats inhospitable to most other faunas. During the Furongian, biogeographical structure emerged, with mid-latitude siliciclastic regions hosting taxonomically and morphologically diverse assemblages, while low-latitude carbonate settings held modal morphologies, reduced disparity, and higher endemism, largely restricted to dysoxic deepwater facies. Tremadocian faunas became globally homogenized, reflecting intense late Furongian dispersal; while disparity increased, indicating broader ecological tolerance. As Ordovician ecosystems became more complex and competition intensified, olenids became increasingly restricted to stressed or marginal habitats, persisting only as minor components, except for triarthrinids, which underwent a minor Middle-Upper Ordovician radiation driven by derived ecological strategies that allowed them to persist in increasingly complex marine ecosystems. Overall, ecological dynamics-rather than palaeogeographical constraints-primarily shaped olenid evolution, governing both their expansion and decline.
Biotic immigration events significantly reshape ecosystems and community structures, yet their long-term evolutionary patterns remain understudied. One of the better studied ancient marine invasions is the Late Ordovician Richmondian Invasion in eastern Laurentia, which is expressed in both the Cincinnati and Nashville Basins. Prior studies have focused on the Cincinnati region with no previous quantitative comparisons of the invasion impacts between basins. Herein, we analyse generic occurrence data for marine invertebrates to reconstruct diversification and interaction dynamics across the Richmondian Invasion in the Nashville Basin. Origination and extinction were estimated with PyRate, and diversity-dependent interactions among native generalist, native specialist, invasive generalist, and invasive specialist groups were inferred using Multivariate Birth-Death models. Invaders, mostly generalists, first appear in the C4-C5 sequences. Despite small declines in native genera, the addition of invasive taxa increased total diversity post-invasion. Model results show strong self-suppression of origination within most groups, which is consistent with the broad ecological niches of generalists reducing opportunities for reproductive isolation and origination. For invaders, this also reflects competition between established cohorts and new arrivals. Cross-group effects indicate that invasive generalists suppress origination and elevate extinction of native generalists, both signatures of competitive interaction. Collectively, these patterns support selective turnover and tighter competitive connectivity among low-trophic invaders, not whole ecosystem collapse, which is similar to patterns reported from the Cincinnati region. Overall, the Nashville Basin records an invasion-driven reorganization that increased taxonomic richness while imposing selective losses on native taxa, illustrating how interaction networks regulate diversification during coordinated immigration events. square Laurentia, immigration, biodiversity, palaeoecology, origination, extinction, community, marine.
Insect fossils are numerous and widespread across the Phanerozoic in various states of preservation that can include colour, fully articulated specimens, and three-dimensional preservation. Due to the naturally buoyant nature of most terrestrial insects, it is surprising that so many become fossilized in lacustrine and coastal settings, and it is unclear how various processes involved in sinking differentially bias fossil insect collections. As informed by the fossil record, a series of experiments were designed to examine how salinity, disarticulation, and surface tension impact the likelihood of sinking for Teleogryllus oceanicus (oceanic house cricket), Bombus spp. (bumblebee), and their individual hindlegs and forewings. Most specimens sank readily in freshwater and saltwater when forcibly submerged; however, only cricket hindlegs sank in hypersaline water. Individual hindlegs and wings sank within hours, while whole bodies sank after days of decay. When left floating undisturbed on water surfaces, only hindlegs and cricket bodies in freshwater sank at some point within 75 days of decay. Photographed orthopteran fossils from Green River, Colorado, were categorized by body part to compare the biases in fossil collections with our experiments: isolated hindlegs comprised 20% of the categorized fossils. These results show a bias in the fossil insect record where very few isolated legs are found compared to bodies even though hindlegs sank readily in water of all salinities. square Decay experiments, insects, fossilization bias, Green River, surface tension.
This study documents fossil burrows from a new locality of the Upper Miocene-Lower Pliocene Cerro Azul Formation, from La Pampa Province, Central Argentina. This locality is distinguished by the large width of its fossil burrows (up to 2.25 m), in contrast with other tetrapod burrows found in the unit and in the worldwide Miocene record of vertebrate burrows. The 2.15-m-thick local section containing the burrows has a lower palaeosol with alfisol features and an upper calcic palaeosol. The burrows cross-cut carbonate nodules from the upper palaeosol and are easily distinguished by their laminated fill and abundant rhizoliths. Common normal grading in the burrow fill laminae suggest aqueous flows after rains entering the empty excavation and progressively filling it. Preferred occurrence of calcareous rhizoliths in the burrow fills is linked with higher moisture content than the host sediments. Some of the burrows have a horizontal elliptical cross-section which is probably linked to a large mylodontid producer. A single burrow with a subcircular cross section is probably due to roof collapse. We review the criteria for identification of significant diachronism between vertebrate burrows and host sediments and propose a new proxy for identifying potential differences between the age of deposition of the host rock and digging of large Neogene-Quaternary burrows. This proxy is based on the change in horizontal diameter of Cenozoic tetrapod burrows that roughly accompany the body fossil record of Pleistocene megafauna. For the analysed example, the possible time for burrow excavation is Middle to Late Pleistocene. square Pleistocene, megamammal burrows, taphonomy, xenarthrans, width of burrows.
The process of siliceous sponge skeleton dissolution, followed by precipitation of silica polymorphs, was part of the pre-Eocene marine Si cycle and has been linked to chert formation (so-called 'chertification'). This study was conducted to test the proposed key role of siliceous sponges as a main dissolved silica (dSi) supplier for chert formation in carbonate environments, as suggested by Maliva & Siever (1989a). The study is based on advanced mineralogical (XRD, SEM-EDS) and microtextural (SEM) analyses of fossil sponge remnants and the surrounding rocks from a Late Cretaceous marine section deposited in a similar palaeoenvironment of carbonate deposition in outer shelf of epicontinental basins. Taphonomic studies of fossil sponges, combined with mineralogical and microtextural observations of the surrounding rocks, were carried out to develop diagenetic models of opal-A sponge skeleton dissolution, silica migration, and subsequent precipitation of all mineralogical phases observed in the studied samples. The adopted approach is based on the assumption of an open system of porewaters circulating within seabed mud, in which sponge remnants were buried, and on the geochemical setting within the sediment column, which is controlled by microbial decomposition of organic matter. square Si cycle, cherts, opal-CT, taphonomy, spicule diagenesis.
Circular structures observed at the apertures of several Cornulites specimens from the earliest Silurian of China are interpreted as possible fossilized remains of a lophophore with a simple, ring-like morphology. These structures may represent partial preservation of the feeding apparatus, with the absence of tentacle preservation likely resulting from taphonomic processes. The preserved rim surrounding the circular structure likely reflects the thickness of the lophophore and its tentacles, while a neck-like extension visible in one specimen is interpreted as the basal region of the lophophore. Specimens displaying a partially extended lophophore suggest that Cornulites individuals may have been capable of retracting their lophophore entirely into the shell, between feeding episodes, although complete retraction remains speculative. These partial soft-tissue remains support the classification of cornulitids as lophophorates. However, the available evidence remains insufficient to definitively resolve whether cornulitids are more closely related to bryozoans or phoronids. As the only shelled benthic fossils in the Huangshi deposits, cornulitids seemed to have been opportunistic organisms which were able to colonize and thrive in oxygen-deficient palaeoenvironments following the Late Ordovician mass extinction.
