It has been proposed that the extant bivalve family Plicatulidae was derived from Prospondylidae during the Triassic, but the repeated evolution of species with transitional morphologies makes the differentiation between the two families difficult. Based on new material from the Hettangian Germig Formation of southern Xizang (Tibet), a new subgenus Persia (Nyalamia) and a new species Eoplicatula nianduoensis are proposed. P. (Nyalamia) is closely allied to the prospondylid Persia s.s. in shell outline and external ornamentation, but it is distinguished by the presence of resilial teeth and stronger crura, which enhances the mechanical strength of the hinge region. Hence, P. (Nyalamia) is phylogenetically linked to Prospondylidae but evolved character traits that are more typical of Plicatulidae. We suggest that the evolution of additional hinge elements was an evolutionary response to increased predation pressure during the initial Mesozoic marine revolution, which fostered iteration in the evolution of strongly interlocking hinges in cementing bivalves. Whether Early Jurassic Harpax evolved from Eoplicatula or from P. (Nyalamia) is currently unresolved, but if the latter option is confirmed, the taxonomy of Plicatulidae would be further complicated. This study reveals the complex evolutionary relationship between the two families and highlights the role of intensified predation pressure during the Mesozoic in promoting increased structural complexity of the hinge systems in cementing bivalves. (c) 2026 Nanjing Institute of Geology and Palaeontology. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

A predictive ecological response to both the present and past climate crises is that marine ectotherm species will become smaller before going extinct or fluctuate in abundance and size with environmental conditions. The problem with studying past climate events with high rates and magnitude of warming, which may serve as analogues for projected climate change, is that very few species, or even genera, survived such events. Here, we utilized one of the few records of marine bivalves that spans the Permian-Triassic climate crisis with specimen-level data and at a high resolution. These measurements come from the Bellerophon and Werfen formations of the Dolomites in Italy, representing relatively shallow marine environments. At the species-level, there is almost a complete turnover, and the newly evolved species are typically significantly smaller, but not unusually small, whereas the three surviving species do not show a significant body size change. Our results indicate that the observed temporary size reduction at the genus-level is primarily driven by the preferential evolution of smaller species after the extinction, rather than, as often assumed, by a size decrease within existing species; this challenges the universal validity of the “Lilliput effect” in the sense of direct intra-species dwarfing, but confirms it as a consequence of faunal turnover. Subsequently, there are two pulses of genus-level body size recovery caused by different mechanisms. The first phase (late Griesbachian) is driven by the size-increase of the existing species, whereas the second phase (early Spathian) is also due to the evolution of larger species. The effects of abiotic and biotic factors in controlling these body size dynamics are superimposed during the Early Triassic. These results suggest a mechanism to explain size reductions during climate crises, but does not find a species-level body size reduction to be a forecastable response to extreme climate warming.

Traditional approaches to studying paleontological biodiversity have focused on richness, that is, the number of taxa at a given level in the Linnaean hierarchy. While valuable, this approach does not capture the phylogenetic dimension of biodiversity as reflected by its taxonomic structure. This paper introduces a novel perspective in the study of past biodiversity by applying taxonomic distinctness (TD) metrics, average taxonomic distinctness (AvTD) and variation in taxonomic distinctness (VarTD), to investigate the rediversification of marine bivalves following the Permian-Triassic mass extinction. Using a dataset of 59 fossil faunas, we explore the dynamics of the taxonomic tree during the Triassic and along paleolatitudinal gradients. Subtropical assemblages show higher AvTD and lower VarTD than tropical ones, suggesting ecological and biogeographic influences on the taxonomic structure. In the temporal dimension, our data reveal an Early Triassic decrease in AvTD and an increase in VarTD, followed by a long-term trend of increasing AvTD and decreasing VarTD that persisted until the Norian. This pattern suggests that vacant ecospace after the end-Permian mass extinction did not stimulate the immediate appearance of a disproportional number of supraspecific taxa, possibly due to the unusual biotic and abiotic environment of the early postextinction time. In contrast, the long-term increase in AvTD that followed this Early Triassic lag phase indicates a low but steady surplus of supraspecific taxa relative to newly evolved species. This observation supports macroevolutionary scenarios in which evolutionary rates correlate with ecological opportunity. However, the long duration of this phase is unexpected, particularly when compared with conventional indicators for "complete" recovery. Based on TD metrics, recovery from the greatest Phanerozoic mass extinction went on at least until the end of the Norian, nearly 50 Ma after the crisis.

The Qiangtang Basin, Tibetan Plateau, is a Mesozoic marine basin characterised by well-developed Jurassic marine sedimentary systems. The South Qiangtang Basin, being closer to the Bangong-Nujiang suture zone, exhibits more localised and complex Jurassic strata compared to the North Qiangtang Basin. This study focuses on the Middle Jurassic 114 Daoban Formation in the South Qiangtang Basin, which consists of marine siliciclastic and carbonate rocks with abundant bivalve fossils, particularly Liostrea birmanica. We analyse the taxonomy, shell microstructure, and palaeoecology of L. birmanica. Based on its shell morphology and sedimentary context, we suggest that L. birmanica adopted a reclining lifestyle on soft substrates, representing an adaptation to soft substratum environments. The microstructure of the shells, composed mainly of irregularly foliated layers, distinguishes Liostrea from morphologically similar genera. The occurrence of monospecific shell beds of L. birmanica across a broad area suggests their potential as regional marker beds for refining the Jurassic stratigraphic framework in the South Qiangtang Basin. This research contributes to a better understanding of the palaeoecology and biostratigraphy of Jurassic marine systems in the Tibetan Plateau.

We report 79 species of gastropods and five species of scaphopods from the Early Pliocene Kairuku Limestone on Yule Island, Papua New Guinea. All scaphopods are described in open nomenclature. The gastropod fauna comprises 39 families, with 40 species identified to species level, some tentatively (using 'aff.'). Of these, 30 are extant, three were first reported from the Miocene, and seven from the Pliocene. Among the extant taxa, seven range back to the Miocene and 21 to the Pliocene. Four species are here documented for the first time in the fossil record: Nerita costata Gmelin, 1791, Ministrombus aff. caledonicus Maxwell, 2022, Labiostrombus aff. epidromis (Linnaeus, 1758), and Aliculastrum aff. debile (Pease, 1860). The architectonicid Stellaxis nitens (Noetling, 1901) is identified as the geologically youngest member of this otherwise predominantly Eocene genus. Many species from the Kairuku Limestone had wide geographic distributions within the Indo-West Pacific region during the Pliocene. This suggests that any biogeographic separation between northern and southern sectors of the Coral Triangle biodiversity hotspot, inferred for the Late Miocene, had largely diminished by Early Pliocene time

The phylogeny of the highly diverse bivalve order Venerida can be traced back to the Triassic, thanks to the well-understood evolution of its hinge system. I here suggest that the Early or Middle to Late Triassic genus Pseudocorbula is at the root of this phylogenetic lineage. The hinge of Pseudocorbula is primitive relative to the Early Jurassic Eotrapezium in the lack of a chevron-shaped AII-2b complex below the umbo of the left valve. However, both Pseudocorbula and Eotrapezium lack cardinal tooth 3a in the right valve. It is suggested that this lack stimulated the evolution of cardinal tooth 1, which first appeared as a small tubercle at the posterior end of lateral tooth AI that fits below the AII-2b complex; this early stage evolved into the well-known veneroid hinge with a differentiated cardinal tooth 1 in the pivotal position below the umbo of the right valve and the 2a-2b pair of cardinal teeth in the left valve. Pseudocorbulinae new subfamily is proposed for taxa that represent the earliest stage of veneroid hinge evolution, which is placed in Isocyprinidae. This phylogenetic hypothesis extends the roots of Venerida back to the Early or early Middle Triassic, a time that also saw the first appearance of oysters and modern scallops.UUID: http://zoobank.org/1ba1e7c4-a6c1-4fb2-9e4c-2c1097649365

A fossil assemblage of small bivalves and gastropods from the latest Triassic (Rhaetian) K & ouml;ssen Formation at the Brauneck Mountain in the Bavarian Alps is reported. It consists of the bivalve species Pseudocorbula alpina (Winkler, 1859) and at least three gastropod species including Ampezzopleura brauneckensis sp. nov. and Jurilda stoppanii (Winkler, 1861) comb. nov. The fossils are well-preserved including protoconch preservation in the gastropods and preserved hinges in the bivalves. The gastropod genera Ampezzopleura and Jurilda are reported from the Rhaetian for the first time. Both genera are also known from pre-Rhaetian and post-Triassic strata and hence they survived the end-Triassic mass extinction event. Their occurrence in the Rhaetian fills a gap in their stratigraphic distribution and removes them from the list of Rhaetian Lazarus taxa. The new material of Pseudocorbula alpina (Winkler, 1859) demonstrates a dentition of the AI, AIII, 3b, PI, PIII / AII, AIV, 2, 4b, PII type, which was possibly ancestral to the isocyprinid hinge of early veneroids. Therefore, Pseudocorbula alpina provides insights into the early evolution of the Venerida, which are among the most specious bivalve clades today.

This paper provides a palaeoecological analysis and interpretation of benthic marine communities from the first two stages of the Jurassic in southern Germany, based on quantitative data that represent more than 1,000 individuals from six samples. Alpha-diversity of these samples varies from eight to 48 species, with a tendency towards higher richness in the stratigraphically younger samples. Dominance (Simpson D) was relatively low in all samples, ranging from 0.06 to 0.24. In most samples, bivalves are the richest and most abundant taxon. The presence of gastropods is variable, ranging from complete absence to dominance in one sample (Betakalkbank; Sinemurian). Accessory taxa include brachiopods, crinoids and echinoids. The number of guilds varies from two to eleven; the most common guilds are epibyssally attached suspension feeders, semi-infaunal suspension feeders, reclining suspension feeders and locally epifaunal grazers/detritivores. Local factors that controlled the faunal composition include substratum, water depth and energy, and possibly oxygen content. However, cluster analysis also revealed a strong stratigraphic signal, which outweighs lithological similarities. We interpret this stratigraphic signal as a superordinated macroevolutionary pattern, which reflects the evolutionary changes that were associated with the recovery from the endTriassic mass extinction. Based on the data from this paper, recovery lasted at least to the Sinemurian, which is in accordance with bivalve diversity data from the UK. Globally, data on benthic recovery are still scarce, but it seems that there were notable differences among palaeogeographic regions. In comparison to the recovery from the end-Permian mass extinction, we found a less extreme change in richness and dominance, with neither a long lag phase nor an explosive diversification thereafter. We interpret this difference as a result of the lower extinction magnitude, which did not shatter the structure of marine benthos to the same extent than the end-Permian event did 50 Ma earlier.

Claraia Bittner, 1901 is a prominent extinct bivalve genus of the Permian-Triassic transition (Newell and Boyd, 1995). Although it first appeared in the Wuchiapingian (Late Permian; Fang Zong-Jie, 2010), its massive proliferation in the immediate wake of the end-Permian mass extinction makes it the archetype of a cosmopolitan and eurytopic disaster species and a hallmark of the base of the Triassic (e.g., Schubert and Bottjer, 1995). Diener (1923, p. 38) fixed “Posidonomya Clarai Emmrich (1844)” as the type species of Claraia by subsequent designation, but spelling and authorship of this species have been controversial. This short contribution aims to clarify these issues.

Some 2.7 myr after the Permian-Triassic boundary mass extinction, a stepwise extinction of the nekton (ammonoids and conodonts) ended at the Smithian-Spathian boundary (SSB) during an episode of climate cooling. SSB records from continental shelves are usually affected by an unconformity, suggesting a forced regression of glacio-eustatic origin. Here, we document a new 30-m-thick SSB section from Jebel Aweri (Batain Plain, Oman) that provides an exceptionally complete and expanded record preserved in an exotic block. Most of this SSB section consists of microbial boundstone build-ups with a framework of metazoan bioclasts that formed in shallow water on an offshore seamount. In Wadi Musjah (Hawasina nappes, Oman), another exotic block records the SSB in a deeper water setting represented by Hallstatt-type facies. These two sections provide a unique perspective on the early Spathian rapid re-diversification of conodonts. They led to a thorough revision of conodont taxonomy around the SSB and to the construction of the highest resolution biochronological scheme for this time interval in the Tethys. A total of five SSB sections from Oman representing both offshore seamounts and lower slope deposits were included in a high-resolution, quantitative unitary associations (UA) analysis. The resulting 8 conodont biozones are intercalibrated with ammonoid zones and with the carbonate carbon isotope record ultimately placing the SSB in the interval of separation between UAZ(3) and UAZ(4). Only the association of Novispathodus pingdingshanensis with Icriospathodus crassatus can be used to unambiguously characterize the base of the Spathian.

Based on an exhaustive database of gastropod genera and subgenera during the Triassic-Jurassic transition, origination and extinction percentages and resulting diversity changes are calculated, with a particular focus on the end-Triassic mass extinction event. We show that gastropods suffered a loss of 56% of genera and subgenera during this event, which was higher than the average of marine life (46.8%). Among molluscs, gastropods were more strongly affected than bivalves (43.4%) but less than ammonoids, which were nearly annihilated. However, there were also pronounced differences among gastropod subclasses. The most strongly affected subclass was the Neritimorphia, which lost 72.7% of their Rhaetian genera; on the other extreme, the Heterobranchia remained nearly unaffected (11% loss). We analysed this extinction pattern with respect to larval development, palaeobiogeography, shell size, and anatomy and found that putative feeding of the pelagic larval stage, adaptation to tropical-temperate water temperatures, and flexibility of the mantle attachment were among the factors that might explain extinction resilience of heterobranchs during the end-Triassic crisis. Among molluscs, extinction magnitude roughly correlates with locomotion activity and thus metabolic rates. We suggest three potential kill mechanisms that could account for these observations: global warming, ocean acidification, and extinction of marine plankton. The end-Triassic extinction of gastropods therefore fits to proposed extinction scenarios for this event, which invoke the magmatic activity of the Central Atlantic Magmatic Province as the ultimate cause of death. With respect to gastropods, the effect of the end-Triassic mass extinction was comparable to that of the end-Permian mass extinction. Notably, Heterobranchia was relatively little affected by both events; the extinction resilience of this subclass during times of global environmental changes was therefore possibly a key aspect of their subsequent evolutionary success.

The impact of increasing atmospheric CO 2 and the resulting decreasing pH of seawater are in the focus of current environmental research. These factors cause problems for marine calcifiers such as reduced calcification rates and the dissolution of calcareous skeletons. While the impact on recent organisms is well established, little is known about long-term evolutionary consequences. Here, we assessed whether ammonoids reacted to environmental change by changing septal thickness. We measured the septal thickness of ammonoid phragmocones through ontogeny in order to test the hypothesis that atmospheric p CO 2 , seawater pH and other factors affected aragonite biomineralisation in ammonoids. Particularly, we studied septal thickness of ammonoids before and after the ocean acidification event in the latest Triassic until the Early Cretaceous. Early Jurassic ammonoid lineages had thinner septa relative to diameter than their Late Triassic relatives, which we tentatively interpret as consequence of a positive selection for reduced shell material as an evolutionary response to this ocean acidification event. This response was preserved within several lineages among the Early Jurassic descendants of these ammonoids. By contrast, we did not find a significant correlation between septal thickness and long-term atmospheric p CO 2 or seawater pH, but we discovered a correlation with palaeolatitude.

A reef-associated mollusc fauna (gastropods and bivalves) and its facies context are described from latest Triassic (Sevatian–Rhaetian) reef carbonates of Austria (Rötelwand reef at Gaissau and Gosaukamm near Hallstatt). The studied carbonates from the Rötelwand reef consist of mollusc-rich rudstones, partly boundstones, which contain branched corals ( Cycliphyllia and Retiophylia, Pinacophyllum ), whereas coralline sponges are absent. The rich foraminiferid fauna that is associated with the reef builders consists of 11 genera; eight of these genera became extinct until the end of the Rhaetian. Associated with small patch reefs was a rich mollusc fauna with 19 gastropod species and 8 epifaunal bivalve species. The gastropod fauna is dominated by Microschiza rhaetica , Trochotoma praecursor , and the large growing Purpuroidea moosleitneri . Six gastropod species are new to science: Angulomphalus senowbarii sp. nov., Stuorella zapfei sp. nov., Hologyra callosa sp. nov., Microschiza rhaetica sp. nov., Angularia corallina sp. nov., and Purpuroidea moosleitneri sp. nov. Four Triassic gastropod species are placed in other genera (new combinations): Tylotrochus diversicostatus Wolff, 1967 and Eucycloscala epitoniformis Nützel and Senowbari-Daryan, 1999 are placed in Sadkia, Praelittorina sepkoskii Nützel and Erwin, 2004 in Microschiza , and Purpuroidea ? minioi Leonardi, 1935 in Angularia Koken, 1892. Reversal of precedence is proposed for Angularia Koken, 1892 (Gastropoda) and Angularia Busk, 1881 (Bryozoa) under ICZN Art. 23.9. Although reefs suffered a catastrophic decline at the end of the Triassic, most of the studied reef-associated bivalve and gastropod genera survived into the Jurassic, indicating a considerable ecological plasticity of these groups. Only 12 out of 47 reef-associated mollusc genera became extinct (25.5%). This observation is at variance with earlier suggestions that taxa that were associated with reefs and carbonate substrata had a significantly higher extinction risk than level-bottom dwellers. However, extinction at the species level appears more severe; only three bivalve species but no gastropod species recorded in this fauna have records from the Jurassic.

Soft-tissue preservation in molluscs is generally rare, particularly in bivalves and gastropods. Here, we report a three-dimensionally preserved specimen of the limid Acesta clypeiformis from the Cenomanian of France that shows preservation of organic structures of the adductor muscles. Examination under UV-light revealed likely phosphatisation of organic remains, which was corroborated by EDX-analyses. We suggest that the parts of the adductor muscles that are very close to the attachment are particularly resistant to decay and thus may be preserved even under taphonomic conditions usually not favouring soft-tissue fossilisation.

The mass extinction characterizing the Permian/Triassic boundary (PTB; ~ 252 Ma) corresponds to a major faunal shift between the Palaeozoic and the Modern evolutionary fauna. The temporal, spatial, environmental, and ecological dynamics of the associated biotic recovery remain highly debated, partly due to the scarce, or poorly-known, Early Triassic fossil record. Recently, an exceptionally complex ecosystem dated from immediately after the Smithian/Spathian boundary (~ 3 myr after the PTB) was reported: the Paris Biota (Idaho, USA). However, the spatiotemporal representativeness of this unique assemblage remained questionable as it was hitherto only reported from a single site. Here we describe three new exceptionally diverse assemblages of the same age as the Paris Biota, and a fourth younger one. They are located in Idaho and Nevada, and are taxonomic subsets of the Paris Biota. We show that the latter covered a region-wide area and persisted at least partially throughout the Spathian. The presence of a well-established marine fauna such as the Paris Biota, as soon as the early Spathian, indicates that the post-PTB biotic recovery and the installation of complex ecosystems probably took place earlier than often assumed, at least at a regional scale.

We describe two new genera of Triassic Aviculopectinoidea: Cristaflabellum n. gen., which is biconvex and has a strongly plicate shell, and Globodiscus n. gen., which is equiconvex and externally smooth or nearly so. Globodiscus contains the new species G . kiliani n. gen. n. sp. and G . vinzenti n. gen. n. sp. In order to make the taxonomic concept of the superfamily Aviculopectinoidea more consistent with that of its sister group Pectinoidea (scallops), we use tribes rather than families or subfamilies for accommodating the new taxa. Cristaflabellum is placed in the tribe Antijanirini (previously family Antijaniridae), whereas Globodiscus is made the type genus of the new tribe Globodiscini. Both tribes are placed within the family Aviculopectinidae, which is revised to include both equiconvex and inequiconvex taxa. We suggest that tribes are a more appropriate taxonomic rank for many of the previously erected species-poor families and subfamilies of Aviculopectinoidea. UUID: http://zoobank.org/d143663a-9016-459f-8e24-660102adcf6a

The recovery of marine life from the end-Permian mass extinction event provides a test-case for biodiversification models in general, but few studies have addressed this episode in its full length and ecological context. This study analyses the recovery of marine level-bottom communities from the end-Permian mass extinction event over a period of 15 Ma, with a main focus on the previously neglected main phase during the Middle Triassic. Our analyses are based on faunas from 37 lithological units representing different environmental settings, ranging from lagoons to inner, mid- and outer ramps. Our dataset comprises 1562 species, which belong to 13 higher taxa and 12 ecological guilds. The diversification pattern of most taxa and guilds shows an initial Early Triassic lag phase that is followed by a hyperbolic diversity increase during the Bithynian (early middle Anisian) and became damped later in the Middle Triassic. The hyperbolic diversity increase is not predicted by models that suggest environmental causes for the initial lag phase. We therefore advocate a model in which diversification is primarily driven by the intensity of biotic interactions. Accordingly, the Early Triassic lag phase represents the time when the reduced species richness in the wake of the end-Permian mass extinction was insufficient for stimulating major diversifications, whereas the Anisian main diversification event started when self-accelerating processes became effective and stopped when niche-crowding prevented further diversification. Biotic interactions that might drive this pattern include interspecific competition but also habitat construction, ecosystem engineering and new options for trophic relationships. The latter factors are discussed in the context of the resurgence of large carbonate platforms, which occurred simultaneously with the diversification of benthic communities. These did not only provide new hardground habitats for a variety of epifaunal taxa, but also new options for grazing gastropods that supposedly fed from microalgae growing on dasycladaceans and other macroalgae. Whereas we do not claim that changing environmental conditions were generally unimportant for the recovery of marine level-bottom communities, we note that their actual role can only be assessed when tested against predictions of the biotic model.

AbstractOne of the five greatest mass extinction events in Earth's history occurred at the end of the Triassic,c. 200 million years ago. This event ultimately eliminated conodonts and nearly annihilated corals, sphinctozoan sponges and ammonoids. Other strongly affected marine taxa include brachiopods, bivalves, gastropods and foraminifers. On land, there is evidence for a temporal disturbance of plant communities but only few plant taxa finally disappeared. Terrestrial vertebrates also suffered but timing and extent of this extinction remain equivocal. The cause of the end‐Triassic mass extinction was probably linked to the contemporary activity of the Central Atlantic Magmatic Province, which heralded the breakup of the supercontinent Pangaea. Possible kill mechanisms associated with magmatic activity include sea‐level changes, marina anoxia, climatic changes, release of toxic elements and compounds and ocean acidification. Recovery from the extinction event was remarkably fast for marine level‐bottom faunas but delayed for reef communities, possibly because reef organisms were more co‐evolved and suffered higher losses during the extinction.Key ConceptsNearly half of all marine genera and a smaller but still significant proportion of terrestrial taxa went extinct at the end of the Triassic period,c. 200 million years ago.The end‐Triassic mass extinction took place during a geologically short time interval, which coincided with the onset of massive magmatic extrusions along fracture zones of the disassembling supercontinent Pangaea.A cause‐and‐effect relationship between magmatic activity and mass extinction is indicated by the accordance of predicted extinction patterns and observed data from the fossil record.Ocean acidification as a kill mechanism in marine ecosystems is confirmed by preferential extinction of taxa with thick aragonitic skeletons.The end‐Triassic mass extinction event provides a test case for studying evolutionary responses to major environmental disturbances on the global scale and over geological time.Although there are differences in emission rates, the massive magmatic CO2release at the end of the Triassic is quantitatively similar to a potential release by complete combustion of the global fossil fuel reserves.A prediction from data of the fossil record for marine ecosystems is that level‐bottom communities are able to recover much more quickly from the effects of excess CO2than reefs.