Conodont elements are components of the feeding apparatus of extinct early jawless vertebrates named conodonts. The shape of these tooth-like elements has been explored through different approaches to test whether their morphological changes through time were related to trophic ecology, environmental pressure or ontogeny. Several morphometric analyses have previously been performed on the 2D outline of P1 elements belonging to the conodont genus Palmatolepis from the Upper Devonian (381–360 Ma) of the Montagne Noire (France). These analyses showed a general decrease in breadth of P1 elements, which was interpreted as a long-term response to a change in available food resources and/or a possible change in the trophic position of this conodont. In contrast, analyses of calcium stable isotopes ratio have shown that no changes occurred in δ44/42Ca through time, suggesting that Palmatolepis did not change its trophic position despite the mentioned change in element morphology. To further investigate changes in Palmatolepis morphology through time, 3D topographic analyses were performed on Palmatolepis P1 elements spanning the Famennian. The results of this analysis highlight the first evidence of a sharpness increase over time in this genus. This covariation between the platform reduction and the increase in blade sharpness through time suggests morphofunctional changes allowing a more efficient processing of their prey. Moreover, allometric changes in Palmatolepis gracilis, the latest representative of the Palmatolepis genus, bring new insights into the palaeoecology of this species.

The Cabrières Biota from the late Floian Landeyran Formation possesses a mollusc association comprising eleven identified taxa belonging to Bivalvia, Rostroconchia, Tergomya, and Cephalopoda. The fossil record of Cabrière molluscs is impoverished compared to mollusc associations from the entire Landeyran Formation, which represents a peak in molluscan diversity in the Montagne Noire. Bivalves and rostroconchs prevail in the mollusc assemblage in Cabrières Biota with dominant Redonia michelae and Ribeiria sp., whereas gastropods are not recorded. Generally, in the Cabrières Lagerstätte, the molluscs are preserved as external and internal moulds, indicating that their original shell was dissolved. The Cabrières bivalves Babinka prima, Coxiconchia guiraudi, Redonia michelae, Thoralia languedociana and rostroconchs Ribeiria sp. and Tolmachovia sp. nov. were infaunal or semi-infaunal filter feeders. Early Ordovician bivalve taxa, including the significant genera Redonia, Babinka and Coxiconchia, were rare, geographically restricted to Gondwana and peri-Gondwanan shelves and typically favouring inshore clastic sedimentary environments. Conversely, the rostroconchs with key elements Ribeiria and Tolmachovia exhibit a widespread global distribution and reached their peak diversity during this period. Tergomyans, represented by Thoralispira laevis and Carcassonnella vizcainoi were probably semi-infaunal herbivores. They are typical taxa of the Floian Montagne Noire succession. The cephalopod assemblage is dominated by bathmoceratids and longiconic orthocones, which are interpreted as pelagic, vertical migrants known from other Gondwanan and peri-Gondwanan shelf settings. Among the Cabrières mollusc fauna, bivalves and rostroconchs show close affinities with assemblages of comparable age occurring in Morocco as well as with Middle Ordovician faunas from Perunica, Iberia and Avalonia. Tergomyans on the other hand are only shared with coeval occurrences in Morocco and Avalonia.

There is increasing evidence that hydrodynamic conditions play a crucial role in shaping the morphological evolution of marine organisms. Understanding how Ordovician graptolites changed from a benthic to a planktic lifestyle is crucial for understanding their palaeoecology and palaeobiogeography. However, interpreting the exact process of these ecological shifts is difficult due to the lack of close modern analogues or preserved soft tissues. In this study, we select and reconstruct three-dimensional (3D) life-size models of Calyxdendrum, a problematic graptolite interpreted in previous studies as an intermediate form between benthic Dendroidea and planktic Graptoloidea. By simulating the hydrodynamics of models with different nematode structures using computational fluid dynamics (CFD), we test the hypothesis that the morphological plasticity of nematode length may have played an important hydrodynamic role in acquiring the planktic lifestyle. The simulated hydrodynamic properties (velocity fields and mechanical forces) suggest that an elongated nemata at the proximal end was critical for the ecological transition from benthic to planktonic mode of life in Ordovician graptolites. A longer nemata would have provided better feeding efficiency and sufficient drag force to de-anchor the substrate, a possible pathway for initiating planktic life. Our study highlights that the transition from a benthic to a planktonic mode is a convergent adaptation that may have happened several times in the Ordovician. In addition, this study provides a more comprehensive perspective on the functional morphology of these ancient marine organisms, by integrating traditional palaeontological methods with modern computational techniques.

The study of bioerosion traces on the carapaces of Upper Jurassic turtles from Krzyżanowice, located in the northeastern margin of the Holy Cross Mountains in Poland, sheds light on the complex biotic interactions and palaeoecological dynamics of Mesozoic ecosystems. The research focuses on enigmatic pathologies observed on the turtle shells, combining histological, morphological, and palaeoenvironmental analyses to explore their origins and significance. Evidence of bone remodelling within the pathologies strongly supports their formation during the life of the turtles, suggesting interactions such as parasitism, symbiosis, and failed predation attempts. The variability in pathologies morphology—ranging from shallow, smooth-bottomed depressions to deep, irregular cavities—points to a diversity of bioeroders, including echinoids, microbial colonizers, and scavenging invertebrates. While remodelling suggests live damage in many cases, post-mortem bioerosion may have also contributed to the traces, particularly in low-energy, shallow marine environments. The findings highlight turtles as ecological hubs, playing vital roles as both substrates and participants in complex biotic interactions. Over geological time, a shift from symbiotic and parasitic traces to predation-related marks reflects changing ecological pressures and predator specialization. This study underscores the importance of turtles as indicators of palaeoenvironmental conditions and as resilient components of their ecosystems, capable of surviving repeated interactions with other organisms. By integrating modern analogs and fossil evidence, this research provides new perspectives on the evolutionary and ecological significance of bioerosion in the fossil record.

The fossil records of cyanobacteria with calcified sheaths are sparse in the Precambrian, with their first prevalence appearing in the early Cambrian. Despite diverse calcified cyanobacteria being well documented from the Cambrian Terreneuvian in the Siberian Plate, their records in the adjacent Yangtze Plate are rare. The eastern Yunnan (western margin of Yangtze Plate) is a hotspot for studying the Cambrian Explosion, with abundant small shelly fossils (SSFs) known in the Cambrian Terreneuvian. Yet, contemporaneous calcified cyanobacteria have never been described within this region. Here, we describe two calcified cyanobacteria genera and four species from the phosphorous dolomite at the base of the Yu’anshan Formation in eastern Yunnan, China. These include Girvanella problematica, G. wetheredii, G. kasakiensis, and Subtifloria delicata. We further investigate the preservational pathways of these diverse calcified cyanobacteria show that all cyanobacteria from the Yu’anshan Formation are preserved due to their original calcification and later replacement by diagenetic mineralization. Subtifloria was mainly phosphatized, whereas Girvanella might have undergone both phosphatization and aluminosilicatization. Our work confirms the presence of the Terreneuvian calcified cyanobacteria in eastern Yunnan and expands the geographical range of calcified cyanobacteria in Yangtze Plate. Compared to Siberia, the calcified cyanobacteria in Yangtze Plate are much lower in species- and genus-level biodiversity and are distributed in a quite narrow range. This disparity might be attributed to the narrow suitable ecological environment and the small volume and limited distribution of carbonate rock therein.

Outcrops in Rock Canyon (northwestern Arizona) show a Smithian (early Olenekian, Early Triassic) sedimentary succession recording a marine transgression over fluvial conglomerates and leading to several metre-thick microbial limestones. These microbial limestones are associated with a diverse sponge assemblage including keratose demosponges, halichondrids, geodiids, lyssacine hexactinellids, and presumed chaetetids, suggesting that Early Triassic sponge communities were more diverse than previously thought. A presumed chaetetid (hypercalcified demosponge) specimen, identified by its lamellar 3D structure, shows slightly raised, subcircular domal structures formed by narrow, joining tubes arranged in a bush-like pattern. Microscopic observations also reveal residual tabula and sparse spicules. Other presumed chaetetid specimens show intense recrystallization that obliterates most of their characteristic skeletal structure. Although chaetetid sponges are well-documented in the Palaeozoic, they were absent until now from the Late Permian to Late Triassic record. Occurring about 2.5 myr after the Permian-Triassic extinction, the specimens from Rock Canyon would be the first Early Triassic chaetetids and the oldest known in the Mesozoic record. The rarity of Early Triassic chaetetids may be due to sampling and taphonomic biases. Their intense recrystallization and elongated shape exhibit a morphological convergence with large fenestrae commonly found in microbial limestones. During the Early Triassic, buildups composed of microbial limestones and sponges were widespread, occuring in the Panthalassa, Neotethys and Palaeotethys oceans across various depositional settings, from saline lagoons to open marine environments of varying depths. This broad distribution questions the view that these microbial-sponge communities were confined to localized refuge settings or stressful environmental conditions in the aftermath of the Permian-Triassic crisis.

This paper reports on early Permian continental burrows from Poland. The in situ orientation of the burrows, their size, morphology, and wall margin sculpture suggest that they could have been excavated with limbs of small tetrapods. The burrow-makers likely used a technique similar to that applied by modern amphibians and reptiles with sprawled limb posture. Putative small-sized tetrapod tracks are preserved on laminae parting surfaces within the burrow-casting sediments. Their presence may suggest that some small-sized tetrapods utilized the preexisting, abandoned shelters. The purported fossorial behaviours could increase the environmental fitness of tetrapods inhabiting the environment of the circa equatorial early Permian Pangaea.

This study focuses on the siliceous microfossil preservation potential of trace fossils. To understand this potential, we studied the trace fossil Tasselia ordamensis from the Middle to Late Miocene Amatsu Formation (Miura Group), which is exposed in the Boso Peninsula, Chiba, Japan. We examined the state of preservation of radiolarian fossils within the infill of trace fossils and from the surrounding host siltstones. The following conclusions were drawn from this study. Exceptionally well-preserved radiolarian fossils with fine and delicate structures were recognized within the Tasselia ordamensis compared to those from siltstones. Furthermore, stratigraphically important radiolarian species were identified only in trace fossil samples. Thin-walled collodarian fossils, which are generally more difficult to preserve in consolidated deposits compared to spumellarian and nassellarian fossils, were found only within trace fossils. The collodarian fossils found in this study remained intact with fragile spine tips which have rarely been reported in previous studies. Finally, it is suggested here that because sediments, including microfossils, were transported into the burrows (now carbonate concretions) in a geologically extremely short period of time and were protected from burial compaction and destructive diagenesis, this led to the siliceous microfossils being exceptionally well preserved. This should be useful in elucidating the morphological diversity of radiolarians that were previously unnoticed.