The first scallop

Scallops (Pectinidae) are a highly diverse bivalve family with a long evolutionary history, but insufficient knowledge on the internal shell characters of initial taxa has hampered clarification of their phylogenetic roots. Here, morphological details of the shell interior of the basal pectinid Pleuronectites laevigatus from the Middle Triassic are documented for the first time. It is shown that ligament morphology, lack of internal buttresses and hinge articulation, presence of a right anterior auricular scroll, procrescent discs, and differential valve convexity of Pleuronectites link Pectinidae with Early Triassic aviculopectinoids rather than with entoliids, as recently proposed. The key adaptations of Pectinidae, i.e. the ctenolium and the alivincular-alate ligament system, probably evolved in conjunction with a marked size increase that required improvements in the shell attachment and in the system for opening the valves. Although Pleuronectites laevigatus is recognized as the earliest known member of the Pectinidae, a diphyletic origin of this family from different stocks within the Aviculopectinoidea cannot be ruled ou

Nomenclatural notes on Posidonomya clarae Emmrich, 1844, the type species of Claraia Bittner, 1901

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

Gastropods underwent a major taxonomic turnover during the end-Triassic marine mass extinction event

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

A new paleoecological look at the Dinwoody Formation (Lower Triassic, western USA): intrinsic versus extrinsic controls on ecosystem recovery after the end-Permian mass extinction

The Dinwoody Formation of the western United States represents an important archive of Early Triassic ecosystems in the immediate aftermath of the end-Permian mass extinction. We present a systematic description and a quantitative paleoecological analysis of its benthic faunas in order to reconstruct benthic associations and to explore the temporal and spatial variations of diversity, ecological structure and taxonomic composition throughout the earliest Triassic of the western United States. A total of 15 bivalve species, two gastropod species, and two brachiopod species are recognized in the study area. The paleoecological analysis shows that the oldest Dinwoody communities are characterized by low diversity, low ecological complexity and high dominance of few species. We suggest that this low diversity most likely reflects the consequences of the mass extinction in the first place and not necessarily the persistence of environmental stress. Whereas this diversity pattern persists into younger strata of the Dinwoody Formation in outer shelf environments, an increase in richness, evenness and guild diversity occurred around the Griesbachian-Dienerian boundary in more shallow marine habitats. This incipient recovery towards the end of the Griesbachian is in accordance with observations from other regions and thus probably represents an interregional signal. In contrast to increasing richness within communities (alpha-diversity), beta-diversity remained low during the Griesbachian and Dienerian in the study area. This low beta-diversity reflects a wide environmental and geographical range of taxa during the earliest Triassic, indicating that the increase of within-habitat diversity has not yet led to significant competitive exclusion. We hypothesize that the well-known prevalence of generalized taxa in post-extinction faunas is primarily an effect of reduced competition that allows species to exist through the full range of their fundamental niches, rather than being caused by unusual and uniform environmental stres

Die Muschelfauna der Nayband-Formation (Obertrias, Nor - Rhät) des östlichen Zentraliran

Auf Grundlage umfangreicher Neuaufsammlungen wird die Muschelfauna der Nayband-Formation monographisch dokumentiert, wobei die folgenden 21 Arten neu aufgestellt werden: Palaeonucula biacuta, Trigonucula goniocostata, Nuculana (Nuculana) naibandensis, Parallelodon tectum, Mysidiella imago, Gervillia (Cultriopsis) canalis, Isognomon repini, Indopecten uninodosus, Antiquilima hians, Weixiella lutensis, Gruenewaldia iranica, Gruenewaldia magna, Myophoricardium subquadratum, Praeconia matura, Coelopis (Coelopis) aurea, Opis (Trigonopis?) eumorpha, Opis (Trigonopis?) douglasi, Palaeocardita iranica, Palaeocardita stoecklini, Palaeocardita carinata und Antiquicorbula (gen. nov.) concentrica. 51 Muschelarten der Nayband-Formation werden als bereits beschriebene Arten identifiziert, 32 Taxa auf Grund unvollständiger Erhaltung in offener Nomenklatur geführt. Die höchste Diversität besitzen die Pteriomorphia mit 51 Arten (49 %), gefolgt von den Heterodonta mit 22 Arten (21,2 %), den Palaeoheterodonta und Anomalodesmata mit je 12 Arten (11,5 %) und schließlich den Palaeotaxodonta mit 7 Arten (6,7 %). In der Familie Permophoridae wird die neue Gattung Healeya, in der Familie Corbulidae die neue Gattung Antiquicorbula und in der Familie Trigoniidae die neue Untergattung Trigonia (Modestella) vorgeschlagen. Die Diagnosen der Gattungen Trigonucula, Mysidiella, Primahinnites, Indopecten, Gruenewaldia und Vietnamicardium werden revidiert. Die Gattung Primahinnites wird den Aviculopectinidae an Stelle der Prospondylidae zugeordnet, die Gattung Weixiella den Permophoridae an Stelle der Pachycardiidae. Die Familie Mysidiellidae ist u. a. auf Grund schalenmikrostruktureller Merkmale vermutlich zu den Ambonychioidea zu stellen und nicht, wie bisher meist angenommen, zu den Mytiloidea. Die von CARTER (1990) angeführten Argumente für eine Zugehörigkeit der Permophoridae zu den Modiomorphoidea werden durch das untersuchte Material bestätigt. Bei den Prospondylidae, Plicatulidae, Dimyidae und Ostreidae findet die von HAUTMANN (2001) gegebene Revision dieser Familien Anwendung, wobei die Diskussion über die taxonomische Relevanz der Schalenmikrostruktur vertieft wird. Aus funktionsmorphologischen Überlegungen, Vergleichen mit rezenten Arten und dem jeweiligen Fundzusammenhang wird die Lebensweise der einzelnen Taxa rekonstruiert. Obwohl die meisten Muschelarten der Nayband-Formation unverfestigte Substrate bewohnten, erreichte erstmals in der Erdgeschichte auch die Besiedlung von Hartsubstraten durch Muscheln eine größere Bedeutung. Die Erschließung dieses Lebensraumes gelang taxonomisch unabhängigen Gruppen mit Hilfe verschiedener Anpassungen (byssate Verankerung, Zementation, chemisches Bohren) und Besiedlungsstrategien (Begleitfauna in Korallen- und Schwammriffen, eigenständige Riffbildung, Epökie). Ein hoher Endemismusgrad insbesondere bei flachmarinen Muschelarten rechtfertigt es, die Tethys in der Obertrias als eigenes Faunenreich anzusehen. Die Stellung der Nayband-Muschelfauna innerhalb der Tethys lässt sich wegen der ungeklärten paläogeographischen Lage vieler Obertriasvorkommen nur im Rahmen einer Gesamtanalyse der Faunenbeziehungen verstehen, die ihrerseits wiederum eine unabhängige Bewertung konkurrierender plattentektonischer Modelle erlaubt. Das Verbreitungsmuster von Muschelgattungen und -arten zeigt die Existenz einer Westtethys- und einer Osttethys-Provinz auf, wobei letztere in eine Tethysnordrand- und Tethyssüdrand-Subprovinz zerfällt. Der Tethysnordrand-Subprovinz sind u. a. Iran, Yunnan, Vietnam und Burma zuzurechnen, nicht jedoch der Lhasa-Block, der enge Faunenbeziehungen zur Tethyssüdrand-Subprovinz zeigt. Die paläobiogeographische Analyse stützt damit die relativ neue These von der Existenz einer „Känotethys“ bzw. „Tethys III“, durch deren Öffnung der Lhasa-Block erst am Ende der Trias von Gondwana abgetrennt wurde. Die faunistische Eigenständigkeit des Westtethysraumes geht vermutlich auf die engräumige fazielle Gliederung dieses Gebietes zurück, durch die einerseits Faunenaustausch behindert, andererseits Speziation und damit letztlich auch die Neuentstehung höherer Taxa begünstigt wurde. Die Endemisten dieser Provinz waren vom Massenaussterben an der Trias/Jura-Grenze weit weniger betroffen als jene der Osttethys-Provinz und konnten sich mit der Unterjura-Transgression vielfach auch überregional ausbreiten. Insgesamt zeigt sich, dass für das Verbreitungsmuster obertriadischer Muscheln in der Tethys die Prozesse Artenneuentstehung, Ausbreitung und Vikarianz gleichermaßen, wenn auch mit lokal unterschiedlicher Bedeutung verantwortlich waren.The Upper Triassic (Norian-Rhaetian) Nayband-Formation of east-central Iran contains an exceptionally well-preserved bivalve fauna with more than 100 species adapted to a large spectrum of habitats. Based on new material, the present thesis provides a monographic description and taxonomic discussion of this fauna, gives a reconstruction of its mode of life and clarifies its palaeobiogeographic relations. Out of 104 documented taxa, the following 21 species are new: Palaeonucula biacuta, Trigonucula goniocostata, Nuculana (Nuculana) naibandensis, Parallelodon tectum, Mysidiella imago, Gervillia (Cultriopsis) canalis, Isognomon repini, Indopecten uninodosus, Antiquilima hians, Weixiella lutensis, Gruenewaldia iranica, Gruenewaldia magna, Myophoricardium subquadratum, Praeconia matura, Coelopis (Coelopis) aurea, Opis (Trigonopis?) eumorpha, Opis (Trigonopis?) douglasi, Palaeocardita iranica, Palaeocardita stoecklini, Palaeocardita carinata, and Antiquicorbula (gen. nov.) concentrica. A total of 51 species are already known, and 32 incompletely preserved taxa are presented in open nomenclature. The most diverse group are the Pteriomorphia with 51 species (49 %), followed by the Heterodonta with 22 species (21,2 %), the Palaeoheterodonta and Anomalodesmata with 12 species (11,5 %) each, and finally the Palaeotaxodonta with 7 species (6,7 %). On the basis of the examined material, the diagnoses of the genera Trigonucula, Mysidiella, Primahinnites, Indopecten, Gruenewaldia and Vietnamicardium are revised, and the following new genera and subgenera are proposed: Healeya within the family Permophoridae, Antiquicorbula within the family Corbulidae and Trigonia (Modestella) within the family Trigoniidae. The genus Primahinnites is transferred from Prospondylidae to Aviculopectinidae and the genus Weixiella from Pachycardiidae to Permophoridae. On grounds of morphological and shell microstructural characters, the Mysidiellidae are classified with the Ambonychioidea rather than with the Mytiloidea. The recently proposed integration of the Permophoridae within the Modiomorphoidea is confirmed by the examined material. The revision of the families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae by HAUTMANN (2001) is adopted and extended with respect to the taxonomic relevance of the shell microstructure. The mode of life of the various taxa is reconstructed on the basis of field observations, constructional morphology and comparisons with Recent species. Although most species of the Nayband-Formation occupied habitats characterized by soft substrates, colonization of hard substrates by bivalves achieved significant importance for the first time in Earth´s history. Different taxonomic groups succeeded in entering this habitat by means of various adaptations (byssal attachment, cementation, chemically boring) and settling strategies (dwelling within coral and sponge reefs, framework-constructing, epifaunal settling). A high degree of endemism, especially among shallow marine bivalves, supports categorization of the Tethys region as a separate faunal realm. Owing to the uncertain palaeogeographic position of many Upper Triassic formations, understanding the relations of the Nayband bivalves to other Tethyan bivalve faunas requires an overall analysis of the faunal connections, which, in turn, allows an independent judgement of different palaeogeographic reconstructions and plate tectonic models. The distribution pattern of bivalve genera and species suggests the existence of a western and eastern Tethys province, with the latter divided into a northern and southern subprovince. The northern subprovince comprises (among others) Iran, Yunnan, Vietnam and Burma, but not the Lhasa-block, which proved to belong to the southern subprovince. The palaeobiogeographic analysis therefore supports the hypothesis that this block was attached to Gondwana until the end of the Triassic and became separated later by opening of a "Ceno-Tethys" ocean. The faunal peculiarity of the western Tethys area is probably owing to its strongly differentiated facies pattern, which hindered faunal exchange, favoured speciation and finally led to the rise of higher taxa. Compared with the endemics of the Eastern Tethys Province, those of the Western Tethys Province were much less affected by the mass extinction event at the end of the Triassic, and many of them were able to disperse into wide areas during the ensuing Liassic transgression. The overall distribution pattern shown by the palaeobiogeographic analysis is not controlled by a single factor, but rather is the result of an interplay of speciation, dispersal and vicariance.DFG-Projekt FU131/19researc

Evidence for Factorization Breaking in Diffractive Low-Q^2 Dijet Production

We calculate diffractive dijet production in deep-inelastic scattering at next-to-leading order of perturbative QCD, including contributions from direct and resolved photons, and compare our predictions to preliminary data from the H1 collaboration at HERA. In contrast to recent experimental claims, evidence for factorization breaking is found only for resolved, and not direct, photon contributions. No evidence is found for large normalization uncertainties in diffractive parton densities. The results confirm theoretical expectations for the (non-)cancellation of soft singularities in diffractive scattering as well as previous results for (almost) real photoproduction.Comment: 4 pages, 3 figure

Dienerian (Early Triassic) ammonoids from the Candelaria Hills (Nevada, USA) and their significance for palaeobiogeography and palaeoceanography

A well-preserved ammonoid fauna of Early Dienerian age has long been known from the lower portion of the Candelaria Formation in the old Candelaria silver mining district in Mineral and Esmeralda Counties, Nevada, but for a number of reasons, this fauna has never been studied in detail nor illustrated. Previous authors assigned this ammonoid fauna to the Early Dienerian Proptychites candidus Zone of Canada. In reality, it more closely resembles the Tethyan faunas than the higher palaeolatitude Canadian faunas, thus indicating the presence of some degree of equatorial faunal exchange between opposite sides of the Panthalassic Ocean during Early Dienerian time. It also indicates the onset of a provincialism, which contrasts with the cosmopolitan Griesbachian faunas. A rigorous taxonomic analysis of the Candelaria fauna allows us to differentiate the following ten species, which include two new species and one new genus (Mullericeras nov. gen.) belonging to the new family Mullericeratidae: Ambites lilangensis (Krafft, 1909), Ambites aff. radiatus (Brühwiler, Brayard, Bucher and Guodun, 2008), Ussuridiscus sp. indet., "Koninckites” aff. kraffti Spath, 1934, Mullericeras spitiense (Krafft, 1909), Mullericeras fergusoni nov. sp., Mullericeras sp. indet., Proptychites haydeni (Krafft, 1909), Proptychites pagei nov. sp., Vavilovites sp. indet. and Parahedenstroemia kiparisovae Shigeta and Zakharov, 2009. This Early Dienerian fauna correlates with the Ambites fauna known from the base of the Ceratite Marls in the Salt Range and from the base of the "Meekoceras” beds in Spiti (northern Gondwanian margin). The fauna also permits the precise dating of a shelfal anoxic episode on the equatorial North American margin. This anoxic event correlates in time with similar palaeoceanographic changes in the southern Tethys, which indicates that the Early Triassic biotic recovery was at least partly shaped by such discrete, short events rather than by pervasive and lingering adverse environmental condition

Latest Triassic (Sevatian–Rhaetian) reef carbonates from the Northern Calcareous Alps (Austria), their mollusc dwellers, and their fate at the end-Triassic extinction event

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

Is the relative thickness of ammonoid septa influenced by ocean acidification, phylogenetic relationships and palaeogeographic position?

The impact of increasing atmospheric CO2 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 pCO2, 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 pCO2 or seawater pH, but we discovered a correlation with palaeolatitude