Michael Hautmann

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 glacioeustatic 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 UAZ3 and UAZ4. Only the association of Novispathodus pingdingshanensis with Icriospathodus crassatus can be used to unambiguously characterize the base of the Spathian.

Tropische Riffe gehören zu den vielfältigsten Ökosystemen der Erde. Die größte Diversität bzw. Artenzahl steckt allerdings weniger in den riffbildenden Organismen (z. B. Korallen, Schwämme) als in den riffbewohnenden Tieren und Pflanzen. Viele fossile Riffe hohen geologischen Alters sind massiv versteinert (lithifiziert) und ihre
Ablagerungen stark verändert (Diagenese), was u. a. Lösungsprozesse und Mineralneubildungen (Kalzitisierung und/oder Dolomitisierung) beinhaltet. Aus diesem Grund sind riffbewohnende Organismen selten gut erhalten. Sie fehlen häufig in der Dokumentation bzw. ihnen wird in wissenschaftlichen Studien keine besondere Bedeutung
beigemessen. Die Anwesenheit von Riffbewohnern in der Gesamtfauna findet dann nur kursorisch Erwähnung, die entsprechenden Arten werden in offener Nomenklatur, d. h. ohne genaue Artbestimmung, gelistet. Meistens werden solche riffbewohnenden Arten auch nicht abgebildet.
Eine neue Studie, erarbeitet von Wissenschaftlern der Bayerischen Staatssammlung für Paläontologie und Geologie München (NÜTZEL, NOSE), der Mineralogischen Staatssammlung München (HOCHLEITNER) und dem Paläontologischen Institut und Museum der
Universität Zürich (HAUTMANN), befasst sich mit fossilreichen obertriassischen Riffkalken des Rötelwand-Riffs, südöstlich Salzburg (Oberrhät-Riffkalk) und des Gosaukamms (Dachsteinkalk). Die mächtigen Kalke bauen dort, wie auch andernorts in den Nordalpen,
wesentliche Teile des Gebirges auf. Neben den sedimentologischen Aspekten zielt die Arbeit vor allem auf die Dokumentation der Riff-Fauna und hier insbesondere auf die riffbewohnenden Mollusken. Schnecken (Gastropoden) sind besonders häufig, mit z. T. auffällig großen Arten (z. B. Purporoidea moosleitneri NÜTZEL et al., 2022). Die Mollusken-
fauna ist Teil einer grobkörnigen Riffschutt-Fazies assoziiert mit kleinen Fleckenriffen, die im Falle des Rötelwand-Riffs fast ausschließlich aus grobästigen Steinkorallen (Cycliphyllia cyclica) aufgebaut sind. Gastropoden und Bivalven aus dem Oberrhät-Riffkalk finden sich in verschiedenen Museen und Privatsammlungen, wurden aber bislang
noch nicht eingehend untersucht, mit Ausnahme der Arbeiten von ZAPFE (1963, 1967). Ein weiteres Ziel dieser Studie ist die Bewertung des evolutiven Schicksals der riffbewohnenden Mollusken über das große Massenaussterben an der Trias-Jura-Grenze hinweg. Die hier vorgestellten Ergebnisse stellen eine deutschsprachige Zusammenfassung der in NÜTZEL et al. (2022) ausführlich publizierten Daten dar.

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

ABSTRACT Myophoria woehrmanni, which was erroneously identified as Cardita decussata by W OHRMANN (1889), is designated as type-species of Gruenewaldia. Gruenewaldia is separated from the morphologically similar genus Elegantinia by the lack of a posterior elongation of its central tooth (2) in the left valve. Discussion of the somewhat ambiguous character pattern of Gruenewaldia leads to corro-boration of its conventional assignment to the Myophoriidae. The development of strong pedal muscles, reflected by corresponding modifications of the shell, is an important evolutionary novelty of the Trigoniidae and a major difference to Gruenewaldia. The new findings are summarized in a revised diagnosis of Gruene-waldia. Zusammenfassung: Als Typusart der Gattung Gruenewaldia wird Myophoria woehrmanni gewahlt, die von W OHRMANN (1889) irrtiimlicherweise als Cardita decussata bestimmt worden war. Gruenewaldia unterscheidet sich von der ahnlichcn Gattung Elegantinia durch das Fehlen einer leistenformigen hinteren Verlangerung des zentralen Zahns (2) der linken Klappe. Die An-oder Abwesenheit radialer Rippen auf der Latera ist dagegen taxonomisch weniger signifikant. Bei einigen Arten der Gattung Gruenewaldia, einschlieBlich der Typusart, sind samtliche Schlosszahne gerieft, bei anderen dagegen die Zahne 3b und 4 a nur auf ihren Innen-flanken. Obwohl das Merkmalsmuster von Gruenewaldia einen gewissen Inter-pretationsspielraum laBt, ergibt sich aus Abwagung der Signifikanz der einzelnen Merkmale eine Bestatigung der konventionellen Zuordnung zur Familie Myo-phoriidae. Die Entwicklung starker Pedalmuskeln, die auch Veranderungcn in der Morphologie der Klappen mit sich brachte, wird als wichtige evolutive Neu-erwerbung der Trigoniidae angesehen, die Gruenewaldia fehlt. Die neuen Ergebnisse werden in einer revidierten Diagnose von Gruenewaldia zusammengefasst.

One 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 the 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 remains 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 compounds and acidification of seawater. Remarkably, long-term effects on marine biota were rather different between ecological groups: a nearly instantaneous recovery of level-bottom communities is contrasted by the virtual absence of reef systems for nearly 10 million years after the extinction event. Key Concepts: Nearly 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 CO2 release at the end of the Triassic is quantitatively similar to a potential release by complete combustion of the global fossil fuel reserves. A provisional prediction from the data of the fossil record is that in the marine realm level-bottom communities are able to recover much more quickly from the effects of excess CO2 than reef systems. Keywords: mass extinction; Triassic; Jurassic; volcanism; reefs; level-bottom communities; climatic change; ocean acidification

The Mysidiellidae are morphologically isolated among Triassic bivalves but share important characters with Late Paleozoic Ambonychioidea. Apart from a great similarity in the general shape of the shell, the most primitive mysidiellid genus Promysidiella resembles ambonychioids in the presence of a duplivincular-opisthodetic ligament system. Within the Mysidiellidae, this ligament type evolved into the transitional ligament system that characterizes Late Triassic Mysidiella. The phyletic polarity indicates that this evolution probably took place by paedomorphosis. New examinations of the shell microstructure of Mysidiella demonstrate the presence of simple prismatic and possibly foliated structures in the calcitic outer shell layer, which further supports an ambonychioid affinity. Therefore, the Mysidiellidae are removed from the Mytiloidea and assigned to the Ambonychioidea. The poorly known genus Protopis, which was originally included in the Mysidiellidae, probably had a parivincular ligament system and was hence a member of the Heteroconchia. Joannina, which was previously considered a junior synonym of Protopis, is re-established. The hinge margin of Joannina carries a well developed nymph but lacks teeth. These characters as well as its modioliform shape, anterior shell lobe, and pronounced diagonal carina link Joannina with the Late Triassic genus Healeya (Modiomorphoidea). Both taxa are herein placed in the new family Healeyidae, which differs from the morphologically similar Kalenteridae in the absence of elaborated hinge teeth. Protopis, as well as the recently described genera Leidapoconcha, Waijiaoella, and Qingyaniola, are tentatively assigned to the Healeyidae.

Kurzfassung  Die „Unteren Grauen Mergel“, ein wechselhaft siliziklastisch-karbonatisches Schichtglied der oberen Erfurt-Formation (Unterkeuper) des Hohenloher Landes, enthält lokal eine Fauna mit außergewöhnlich gut erhaltenen Mollusken. Zusammen mit einer Untersuchung von Museumsmaterial erlaubt das neue Material die Revision häufiger, aber bisher oft fehlinterpretierter Muschel- und Schneckentaxa. Die Muschelfauna setzt sich zusammen ausBakevellia (B.) subcostata, Myophoria transversa, Unionites brevis undU. donacinus. Schlossbau und

ABSTRACT The Early Triassic is a unique time interval during which marine biota started to recover from the end-Permian mass extinction. It is marked by recurrent high-magnitude excursions in organic and inorganic carbon isotope records, which indicate changes in global carbon cycling and perturbation of climate and of marine and ter-restrial environments (e.g. Payne et al. 2004; Galfetti et al. 2007a,c; Hermann et al. 2010). It is often assumed that recurring volcanic pulses of the Siberian Traps were responsible for the C-isotope excursions (Ovtcharova et al. 2006; Payne & Kump 2007) and cli-matic variability (Galfetti et al. 2007c) of that time. One of the few stable elements during this time interval was the palaeogeographical persistence of the supercontinent Pangaea extending almost from pole to pole (e.g. Ziegler et al. 1983). The latitudinal arrangement of the merged continents disrupted the atmospheric zonal circulation and the huge landmasses at northern and southern mid-latitudes determined climatic conditions com-bined with tropical Tethys as the moisture source (Parrish 1993). Climate models and sensitivity experiments demonstrated that Pangaean palaeogeography provided the disposition for a mon-soonal circulation with strong seasonality of temperatures and rain-fall (e.g. Kutzbach & Gallimore 1989; Parrish 1993; Gibbs et al. 2002). The main feature of this monsoon system was a strong sea-sonality with distinct northern and southern intertropical conver-gence zones (Fig. 1a). This caused rainfall maxima on the Tethyan coasts in both hemispheres during summer, and seasonal aridity in the mid-latitude continent interior during winter. Along the western Pangaea coast, strong monsoon circulation reversed the easterlies and drew moisture into the continent interior; the Pangaean tropics were arid year-round. Moist conditions prevailed in mid-and high latitudes with winter rainfall maxima in western mid-latitudes (Kutzbach & Gallimore 1989; Parrish 1993). These models are based on simplifications with respect to palaeogeography, geographical resolution, vegetation feedback and dynamic ocean– atmosphere coupling; however, they give a reasonable frame-work of the global climatic conditions during the Early Triassic (Kutzbach & Gallimore 1989; Kutzbach 1994). Models incorporat-ing mountain ranges and inland lakes simulate the same basic mon-soon circulation, although with increased humidity in the tropics and extenuated seasonal temperature extremes in the continent's interiors (as modelled for the Late Permian by Kutzbach & Ziegler 1993). A fully coupled atmosphere, land, ocean and sea-ice system model using realistic geography and topography for the latest Permian implies that elevated CO 2 levels caused significantly higher high-latitude sea surface temperatures compared with pre-sent-day data and very high land surface temperatures in dry sub-tropical regions (Kiehl & Shields 2005). Evidence for the monsoonal circulation can be inferred from various sedimentary records (e.g. Mutti & Weissert 1995). Red bed deposits have widespread occurrences (e.g. South America: Rocha-Campos 1973; Europe: Clemmensen 1979; Australia: Parrish 1993) and are assumed to indicate regions with seasonal rainfall. Ziegler et al. (2003) established a zone of high evaporation in the tropics by mapping the global distribution of evaporites, reef car-bonate, and coal deposits (see also Scotese 2001) (Fig. 1a). The Upper Permian varve deposits of the Castile Formation deposited in the Delaware Basin, near the palaeoequator of the western Pangaean coast, are interpreted to be entirely monsoonal in origin (Anderson 2010). General palaeophytogeographical considerations based on Permian floras also support the proposed climate models (Gibbs et al. 2002; Rees et al. 2002). New palaeontological and isotope data suggest that the Early Triassic climate may have been more variable than generally

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 tropic...

"A mixed siliciclastic-calcareous member ("Untere Graue Mergel") of the upper Erfurt Formation (Lower Keuper) of the Hohenlohe area locally includes a fauna with exceptionally well preserved bivalves and gastropods. The bivalves include Bakevellia (B.) subcostata, Myophoria transversa, Unionites brevis and U. donacinus. Hinge structure and muscle impressions of Bakevellia (B.) subcostata are virtually identical with those of the Permian type species of Bakevellia B. (Neobakevellia) and B. (Costibakevellia) are regarded as (younger) synonyms of Bakevellia s.s. Myophoria transversa differs from M. vulgaris not only by the greater angle between areal carina and extra-areal rib but also by the reduction of the hinge plate in the right valve and by a less clearly bifid central tooh in the left valve. New morphological find (in particular hinge morphology) suggest that Unionites belongs to the Anthracosiidae rather than to the Trigonodidae ("Pachycardiidae"). Unionites brevis has commonlybeen misidentified as U.letticus. Both taxa most probably belong even to different families. The frequent gastropods of the genus Neritaria retained their aragonitic shell and show color bands. Morphometric analysis indicates a remarkable plasticity. Taxonomic assignment, however, has to remain equivocal because of deficiencies of knowledge on the numerous mid-Triassic neritarian taxa from the Germanic Basin. Neritarian gastropodswith unusual Hologyra-type exterior morphology are described as the new species "Neritaria" interscripta n. sp."

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.

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.

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 immedi-
ate 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 sub-
sequent designation, but spelling and authorship of this species
have been controversial. This short contribution aims to clarify
these issues.

ABSTRACT Changes of community structure in response to competition usually take place on timescales that are much too short to be visible in the geological record. Here we report the notable exception of a benthic marine community in the wake of the end-Permian mass extinction, which is associated with the microbial limestone facies of the earliest Triassic of South China. The newly reported fauna is well preserved and extraordinarily rich (30 benthic macroinvertebrate species, including the new species Astartella? stefaniae (Bivalvia) and Eucochlis obliquecostata (Gastropoda)) and stems from an environmentally stable setting providing favourable conditions for benthic organisms. Whereas changes in the taxonomic composition are negligible over the observed time interval of 10–100 ka, three ecological stages are identified, in which relative abundances of initially rare species continuously increased at the cost of previously dominant species. Concomitant with the changes of dominant species is an increase in faunal evenness and heterogeneity. In the absence of both environmental and taxonomic changes, we attribute this pattern to the long-term effects of interspecific competition, which acted at an unusually slow pace because the number of competing species and potential immigrants was dramatically reduced by the end-Permian mass extinction. We suggest that these non-actualistic conditions led to decreased rates of niche differentiation and hence to the delayed rediversification of benthos that characterizes the aftermath of the greatest Phanerozoic mass extinction event. A hyperbolic diversification model is proposed, which accounts for the positive relationship between the intensity of interspecific competition and the rate of niche differentiation and resolves the conundrum of delayed rediversification at a time when niche space was largely vacated.

Model calculations predict that pathways of alpha- and beta-diversity in diversifying
ecosystems notably differ depending on the relative role of competition, predation, positive effects of
species’ interactions, and environmental parameters. Four scenarios are discussed, in which alpha- and
beta-diversity are modeled as a function of increasing gamma-diversity. The graphic illustration of this
approach is herein called a-b-c plot, in which the x-axis indicates increasing diversification rather than
absolute time. In purely environmentally controlled systems, beta-diversity maintains near-maximum
values throughout the diversification interval, whereas mean alpha-diversity increases linearly, with a
slope being reciprocal to beta-diversity. A second scenario is based on the assumption that increasing
richness will have predominantly positive effects on the addition of further species; here, alpha- and
beta-diversity increase simultaneously (though not necessarily at the same rates) and without reaching
a predictable upper limit. In ecosystems that are characterized by low competition between species,
mean alpha-diversity asymptotically approaches a saturation level, whereas the increase in betadiversity
accelerates until alpha-diversity stagnates, and then continues to rise linearly. If competition is
high, addition of species first increases beta-diversity until no further habitat contraction is possible,
followed by a period in which alpha-diversity increase through adaptive divergence becomes the
principal drive of diversification. Because there is a continuous transition between the late stage of the
low-competition model and the early stage of the high-competition scenario, both can be combined in a
single model of diversity partitioning under the premise of a diversity-dependent increase of
competition. This summary model predicts three phases of diversity accumulation: (1) a niche overlap
phase, (2) a habitat contraction phase, and (3) a niche differentiation phase. The models herein
discussed provide a potential tool to assess the question which factors primary controlled the
diversification of life over geological times.

A new Early Triassic marine fauna is described from an exotic block (olistolith) from the Ad Daffah conglomerate in eastern Oman (Batain), which provides new insights into the ecology and diversity during the early aftermath of the Permian–Triassic Boundary mass extinction. Based on conodont quantitative biochronology, we assign a middle Griesbachian age to the upper part of this boulder. It was derived from an offshore seamount and yielded both nektonic and benthic faunas, including conodonts, ammonoids, gastropods and crinoid ossicles in mass abundance. This demonstrates that despite the stratigraphically near extinction at the Permian–Triassic Boundary, Crinoidea produced enough biomass to form crinoidal limestone as early as middle Griesbachian time. Baudicrinus, previously placed in Dadocrinidae, is now placed in Holocrinidae; therefore, Dadocrinidae are absent in the Early Triassic, and Holocrinidae remains the most basal crown-group articulates, originating during the middle Griesbachian in the Tethyan Realm. Abundant gastropods assigned to Naticopsis reached a shell size larger than 20 mm and provide another example against any generalized Lilliput effect during the Griesbachian. Whereas the benthic biomass was as high as to allow the resumption of small carbonate factories, the taxonomic diversity of the benthos remained low compared to post-Early Triassic times. This slow benthic taxonomic recovery is here attributed to low competition within impoverished post-extinction faunas.

Correlation of stratigraphic sections from different continents suggests a worldwide interruption of carbonate sedimentation at the Triassic–Jurassic boundary, which coincided with one of the most catastrophic mass extinctions in the Phanerozoic. Both events are linked by a vulcanogenic maximum of carbon dioxide, which led to a temporary undersaturation of sea water with respect to aragonite and calcite and a corresponding suppression of carbonate sedimentation including nonpreservation of calcareous skeletons. Besides the frequently
cited climatic effect of enhanced carbon dioxide, lowering the saturation state of sea water with respect to calcium carbonate was an additional driving force of the end-Triassic mass extinction, which chiefly affected organisms with thick aragonitic or high-magnesium calcitic skeletons. Replacement of aragonite by calcite, as found in the shells of epifaunal bivalves, was an evolutionary response to this condition.

Ammonoids that lived in the wake of the end-Permian mass extinction are frequently encrusted by the shells of cementing bivalves, but the majority of these epizoans are too poorly preserved for a precise taxonomic identification. However, our huge collection of Griesbachian – Dienerian (Early Triassic, c. 252–251 Ma) ammonoids from east Greenland, the Salt Range (Pakistan) and Spiti (India) includes three ammonoid specimens with epizoans that can reliably be identified as oysters, based on their attachment by the left valve and the morphology of their ligament area. Some of these oysters have their right (upper) valve preserved, which shows the characteristic morphology of Liostrea. These finds predate (1) the previously known first occurrence of oysters by c. 5 Myr, (2) that of Gryphaeidae by c. 15Myr and (3) that of Liostrea by c. 20Myr. Moreover, the stratigraphic polarity indicates that Liostrea is a candidate ancestor of Gryphaea and not vice versa. The open-marine habitat of the Liostrea epizoans described herein provides an explanation for the unusual ecology of its putative descendent Gryphaea as a fully marine soft-bottom dweller with a preference for relatively deep water environments during the Triassic. The revised timing of the early phylogeny of oysters suggests that this bivalve clade underwent rapid morphological divergence during the initial phase of its evolution.

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:/...

The Schlern and Seiser Alm area (South Tyrol, Italy) is a classical locality for studies of Middle Triassic platform to basin transitions, yet details of the palaeoecology of the rich benthic faunas of this area have been insufficiently known. We present herein a detailed palaeoecological study of the fauna from the Schlernplateau beds (Late Ladinian to Early Carnian) and the more or less time-equivalent Pachycardientuffe (Late Ladinian), which is based on quantitative faunal data. Both the palaeoecology and sedimentary features suggest that the fauna of the Schlernplateau beds represents a lagoonal soft-bottom fauna. The high species richness of the fauna and the locally restricted occurrences of fossils indicate an open-lagoon setting palaeogeographically close to an ocean inlet. The high evenness of the fauna is probably a result of time-averaging. In contrast, the fauna of the Pachycardientuffe shows clear indications of transportation. Ecological features of this fauna and palaeogeographic reconstructions suggest three potential source areas: (1) the lagoon represented by the Schlernplateau beds, (2) the reef fringing this lagoon and (3) a shallow clastic coast of a nearby volcanic island and/or submarine high. A comparison between diversities of selected Early and Middle Triassic lithological units revealed the increasing species richness of all major benthic taxa during the Middle Triassic and a shift from bivalve-dominated Early Triassic faunas to gastropod-dominated faunas.

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.