Article

Selective extinction among end-Triassic European bivalves

January 1995
Geology 23(2):102-104

January 1995
23(2):102-104

DOI:10.1130/0091-7613(1995)023<0102:SEAETE>2.3.CO

Authors:

State University of New York College at Cortland

Bivalve data from Lombardia (Italy), Northern Calcareous Alps (Austria and Germany), and northwest Europe (England and Wales) provide the biologic signal of selective extinction to compare two competing extinction hypotheses: (1) sea-level change and associated anoxia and (2) reduced primary productivity. The end-Triassic extinction was independent of body size and geographic distribution. Species from the three regions show a significantly greater proportion of infaunal bivalve extinction. The greater survival of epifaunal bivalves is correlated to their more efficient feeding. The pattern is consistent with a reduction of primary productivity. -from Authors

Macroevolutionary drivers of extinction and quantitative stratigraphy of graptolites

Thesis

Full-text available

Aug 2018

James T Boyle

The last few decades have seen rapid expansion of large-scale paleontological databases that have allowed a much more methodologically rigorous approach to macroevolutionary patterns over geologic timescales. Studies have included insights into extinction, speciation, geographic range, ecological diversification, and the effects of climate change among others. However, these databases are heavily biased towards benthic shelly invertebrates, no doubt a reflection of their proportional contribution to the fossil record as a whole. Because of this it has not been clear how general observed patterns are to other groups, particularly planktic organisms which may face very different evolutionary pressures. Here, I examined some common correlates of extinction risk identified previously, apply them to a group of planktic organisms, graptolites, and compare the significance and effect size to results from benthic taxa. Of the properties associated with extinction risk geographic range is the most widely used and consistent. This property can be measured in a variety of ways that may impact results but there is relatively little published literature comparing different methods of measuring geographic range despite its widespread use. I explore how six measures of geographic range respond to changes in sample size as well their utility as correlates of extinction risk in the context of three disparate datasets. Finally, graptolites are of practical use in biostratigraphy and form the bulk of the global geologic timescale for the Ordovician and Silurian periods. Automated techniques have been developed to incorporate ever larger biostratigraphic datasets but the uncertainty in results has been difficult to characterize. I use a graptolite occurrence dataset assembled from the literature to build a novel ordinal composite for the Middle to Late Ordovician with the recently developed Horizon Annealing (HA) technique. From this composite I explore the limits and advantages of HA, with a particular focus on characterizing the uncertainty within and across the solution space of the ordinal composite. Analyses of 1114 graptolite species with general linear models found that all factors commonly associated with extinction risk in benthic taxa were also significant in this planktic clade. However, the magnitude of the effect of geographic range was much lower than typically reported. This is most likely because the relationship between geographic range and extinction risk is non-linear with the greatest gains in extinction risk between taxa with small geographic range values and those with moderate ranges. As graptolites generally have large geographic ranges, even substantial increases in geographic range only provide a modest decrease in extinction risk. Different measures of geographic range also varied substantially in their explanatory power, and unidimensional measures were particularly poor. When the covariance among factors was accounted for by the use of partial least squares regression the strongest correlate of extinction risk was overall commonness, which reflects the interdependent effects of sampling and geographic range. Among analyses overall commonness explained 12-30% of the total variance in extinction risk. Because these two properties reinforce one another they are essentially impossible to disentangle in fossil datasets where the number of occurrences per taxon is typically low. After taking account of the correlation geographic range and sampling, the individual contributions of either variate alone were either very low (<5%) or not significant at all. The second strongest correlates of extinction risk were clade and age cohort, which are strongly correlated in graptolite evolutionary history. These two variates individually explained as much as an additional 18% of the variance. While all individual measures of geographic range were significant correlates of extinction risk in graptolites their individual magnitudes varied substantially. To explore the cause of these differences I examined how six measures of geographic range (minimum spanning tree distance, convex hull area, maximum pairwise great circle distance, latitudinal range, longitudinal range, and equal area cell count) responded to sample size using three datasets: a simulated dataset with two differently shaped distributions of equal area, a fossil dataset of 381 brachiopod genera from the Paleobiology Database, and a set of 1152 modern bird species from the eBird database. Results showed that measures could be classified into two groups based on how their accuracy and precision responded to sampling. Group 1 measures (maximum pairwise distance, latitudinal range, and longitudinal range) rapidly became accurate and precise as sample size increased while Group 2 measures (minimum spanning tree, convex hull, and cell count) became accurate at a much slower rate, with one notable exception. In one of the simulated distributions the convex hull, as expected, became more precise as sample size increased, but unexpectedly, became less accurate at the same time. Group 2 measures also often showed a humped pattern where the lowest precision occurs at low, but not the lowest, sample sizes. This feature reflects the fact that variance at very small sample sizes is limited by either the method (cell count) or clustering of occurrences (minimum spanning tree and convex hull). Whereas the rank order of the value taxon geographic ranges was robust to variation in sample size across all measures, Group 1 measures had lower values at the smallest sample sizes. I further examined the six measures as correlates of extinction risk in the PBDB dataset using both logistic regression and general linear models. Logistic regression of the duration of generic survival beyond their stage of first occurrence showed that all measures of geographic range were significant and relatively robust to differences in how large versus small ranges were classified. General linear models of extinction risk also found that all measures of geographic range were significant but that the magnitude of effects varied significantly. Group 1 measures were relatively poor correlates of extinction risk in comparison to Group 2 measures. The relatively poor performance of Group 1 measures probably reflects that fact that these measure are not able to capture the complex nature of real distributions and because of methodological biases in these measures that make them vulnerable to outlier points and make some values more likely than others. The convex hull also suffers from vulnerability to outlier points and consistently overestimates geographic range. The minimum spanning tree method performs well as a correlate of extinction risk but is computationally expensive while equal area cell count performs even better and is not computationally expensive. For these reasons I advise the use of equal area cell count as a measure of geographic range in most cases, with minimum spanning tree as a supplement if the number of point occurrences is not too great. I also advise against the use of Group 1 measures and CH as measures of geographic range for extinction risk analyses. Finally, although previous automated biostratigraphic methods of ordination have proven powerful, the amount of uncertainty in solutions remains unclear, partially because such characterization is time-consuming. This is especially true for the Horizon Annealing (HA) approach, which uses more data than other methods. I examined how HA performed using a large dataset of 109 stratigraphic sections containing 136 graptolites species, one event bed, and three K-bentonites across 1549 horizons. The resulting composite generally agrees with published biozonations and independently developed composites affirming HA scales up effectively. To test for a previously hypothesized methodological bias (greater influence of first appearances than last appearances on determining the ordination of events in the composite), I ran the solution in reverse but did not find any evidence of this bias in the system. To reduce the initial burn-in time of searching in HA, I tested the use of a quasi-Bayesian scaffolding approach that starts the solution closer to traditional biozonations and found that it did significantly improve the penalty score of the solution, without any apparent bias. I further examined how effective the different ways of mutating the composite solution were at improving the solution during the search procedure. Mutations that allow changes in the spacing of collection levels within sections relative to the composite were much more effective than those that did not. I characterized uncertainty in the solution with three methods (vice, jackknife, and an island search). Vice was the fastest and most conservative measure, and it indicates an uncertainty range of 40 horizons on average, which corresponds to a temporal resolution of ~373 Kya. Finally, I characterized the uncertainty based on differences between three independent runs and found that although the global first and last occurrences of taxa were robust, the position of individual horizons varied more than was implied by any of the within-run uncertainty metrics. This result suggests that using HA composites to test dynamics based on patterns of occurrence within the temporal range of individual taxa should be done with caution. Although the accelerating pace of quantitative approaches to macroevolution have yielded more robust results than was previously possible there are substantial gaps in taxonomic coverage and methodological issues which have often been downplayed. The studies presented here attempt to address some of those issues. First, a large proportion of macroevolutionary studies have been based on patterns in shelly benthic invertebrates and the results then treated as if they apply to all groups of organisms. I demonstrate that while the same factors are often significant between these shelly benthic invertebrates and planktic graptolites the magnitude of relationships vary substantially. These contrasts in magnitude are reflective of the groups’ ecological strategies and can provide further insight into macroevolutionary processes that uniquely effect each one. Therefore, studies should be careful to interpret their results with regard to the ecology of the particular organisms being examined and to not be overly broad in claims about how generalizable a pattern is. Second, the treatment of geographic range in macroevolutionary studies has been inconsistent and the field of macroevolution would be well-served by some standardization. Here I found that unidimensional measures of geographic range, particularly the commonly used maximum pairwise distance, should not be used due to serious biases and limitations. More complex methods, minimum spanning tree distance and equal area cell count, were found to have the most desirable qualities as measures of geographic range and should be used in most macroevolutionary analyses. Finally, the use of ordinal composite built from biostratigraphic data for analyses of turnover, extinction, colonization, or other patterns requires a knowledge of the uncertainty in the system that was lacking. I demonstrated three methods of quantifying uncertainty in an ordinal composite as well as refining search methods that should allow for this powerful approach to be more widely utilized and understood.

The impact of geographic range, sampling, ecology, and time on extinction risk in the volatile clade Graptoloida

Article

Feb 2017

James T Boyle

Although extinction risk has been found to have a consistent negative relationship with geographic range across wide temporal and taxonomic scales, the effect has been difficult to disentangle from factors such as sampling, ecological niche, or clade. In addition, studies of extinction risk have focused on benthic invertebrates with less work on planktic taxa. We employed a global set of 1114 planktic graptolite species from the Ordovician to lower Devonian to analyze the predictive power of species’ traits and abiotic factors on extinction risk, combining general linear models (GLMs), partial least-squares regression (PLSR), and permutation tests. Factors included measures of geographic range, sampling, and graptolite-specific factors such as clade, biofacies affiliation, shallow water tolerance, and age cohorts split at the base of the Katian and Rhuddanian stages. The percent variance in durations explained varied substantially between taxon subsets from 12% to 45%. Overall commonness, the correlated effects of geographic range and sampling, was the strongest, most consistent factor (12–30% variance explained), with clade and age cohort adding up to 18% and other factors <10%. Surprisingly, geographic range alone contributed little explanatory power (<5%). It is likely that this is a consequence of a nonlinear relationship between geographic range and extinction risk, wherein the largest reductions in extinction risk are gained from moderate expansion of small geographic ranges. Thus, even large differences in range size between graptolite species did not lead to a proportionate difference in extinction risk because of the large average ranges of these species. Finally, we emphasize that the common practice of determining the geographic range of taxa from the union of all occurrences over their duration poses a substantial risk of overestimating the geographic scope of the realized ecological niche and, thus, of further conflating sampling effects on observed duration with the biological effects of range size on extinction risk.

Marine extinction risk shaped by trait–environment interactions over 500 million years

Article

Jul 2015
GLOBAL CHANGE BIOL

Perhaps the most pressing issue in predicting biotic responses to present and future global change is understanding how environmental factors shape the relationship between ecological traits and extinction risk. The fossil record provides millions of years of insight into how extinction selectivity (i.e., differential extinction risk) is shaped by interactions between ecological traits and environmental conditions. Numerous paleontological studies have examined trait-based extinction selectivity; however, the extent to which these patterns are shaped by environmental conditions is poorly understood due to a lack of quantitative synthesis across studies. We conducted a meta-analysis of published studies on fossil marine bivalves and gastropods that span 458 million years to uncover how global environmental and geochemical changes covary with trait-based extinction selectivity. We focused on geographic range size and life habit (i.e., infaunal vs. epifaunal), two of the most important and commonly examined predictors of extinction selectivity. We used geochemical proxies related to global climate, as well as indicators of ocean acidification, to infer average global environmental conditions. Life-habit selectivity is weakly dependent on environmental conditions, with infaunal species relatively buffered from extinction during warmer climate states. In contrast, the odds of taxa with broad geographic ranges surviving an extinction (>2500 km for genera, >500 km for species) are on average three times greater than narrow-ranging taxa (estimate of odds ratio: 2.8, 95% confidence interval = 2.3-3.5), regardless of the prevailing global environmental conditions. The environmental independence of geographic range size extinction selectivity emphasizes the critical role of geographic range size in setting conservation priorities. © 2015 John Wiley & Sons Ltd.

Volcanism of the Central Atlantic magmatic province as the trigger of environmental and biotic changes around the Triassic-Jurassic boundary

Article

Full-text available

Sep 2014

In the last decade, major advances have been made in our understanding of the end-Triassic mass extinction, related environmental changes, and volcanism of the Central Atlantic magmatic province. Studies of various fossil groups and synoptic analyses of global diversity document the extinction and subsequent recovery. The concomitant environmental changes are manifested in a series of carbon isotope excursions (CIE), suggesting perturbations in the global carbon cycle. Besides the earlier-recognized initial and main negative anomalies, a more complex picture is emerging with other CIEs, both negative and positive, prior to and following the Triassic-Jurassic boundary. The source of isotopically light carbon remains debated (methane from hydrate dissociation vs. thermogenic methane), but either process is capable of amplifying an initial warming, resulting in runaway greenhouse conditions. Excess CO2 entering the ocean causes acidification, an effective killing mechanism for heavily calcified marine bio

Within-and among-genus components of size evolution during mass extinction, recovery, and background intervals: A case study of Late Permian through Late Triassic foraminifera

Article

Full-text available

Sep 2012

One of the best-recognized patterns in the evolution of organismal size is the tendency for mean and maximum size within a clade to decrease following a major extinction event and to increase during the subsequent recovery interval. Because larger organisms are typically thought to be at higher extinction risk than their smaller relatives, it has commonly been assumed that size reduction mostly reflects the selective extinction of larger species. However, to our knowledge the relative importance of within-and among-lineage processes in driving overall trends in body size has never been compared quantitatively. In this study, we use a global, specimen-level database of foraminifera to study size evolution from the Late Permian through Late Triassic. We explicitly decompose size evolution into within-and among-genus components. We find that size reduction following the end-Permian mass extinction was driven more by size reduction within surviving species and genera than by the selective extinction of larger taxa. Similarly, we find that increase in mean size across taxa during Early Triassic biotic recovery was a product primarily of size increase within survivors and the extinction of unusually small taxa, rather than the origination of new, larger taxa. During background intervals we find no strong or consistent tendency for extinction, origination, or within-lineage change to move the overall size distribution toward larger or smaller sizes. Thus, size stasis during background intervals appears to result from small and inconsistent effects of within-and among-lineage processes rather than from large but offsetting effects of within-and among-taxon components. These observations are compatible with existing data for other taxa and extinction events, implying that mass extinctions do not influence size evolution by simply selecting against larger organisms. Instead, they appear to create conditions favorable to smaller organisms.

Revision of the British Lower Jurassic Astartinae (Bivalvia)

Article

Jun 2024
J MOLLUS STUD

The Astartidae (Bivalvia) are a common benthic fossil in the British Lower Jurassic and as such it is important to understand their taxonomy so as to use them as a study system with which to consider environmental change through, and extinction events in, this epoch. The majority of the species of the Astartidae from the British Lower Jurassic are taxa within the subfamily Astartinae, encompassing the genera Neocrassina, Coelastarte and Oxyeurax. There has been some question as to whether those shells attributed to Neocrassina could be further split, with two species assigned to this genus having some characters that are atypical. We prefer to retain the atypical species within ?Neocrassina, the genus with which they have the greatest affinity, rather than erect another genus. This study assigns the suite of British Lower Jurassic fossil bivalves attributed to Nicaniella to Oxyeurax, based on the presence of a poorly defined 3a tooth and form of commarginal ridge ornament. Differentiation at the species level in Astartinae is complicated; the subfamily exhibits generally low disparity compared with other bivalves, compounded by ecomorphological effects and, in some cases, sexual dimorphism. We show that the Neocrassina lineage exhibits gradual changes in shape, as well as hinge plate development and complexity, through the Lower Jurassic, and identify potential sexual dimorphism in species of Oxyeurax. The temporally overlapping species of Oxyeurax display varying degrees of ornamental development which may well be environmentally controlled and are used in this study to define distinct new species. This study recognizes 12 distinct species of Astartinae from the British Lower Jurassic. Nine are established taxa (Neocrassina elegans, N. expansa, N. gueuxii, N. lurida, N. phaedra, ?N. camertonensis, ?N. dentilabrum, Oxyeurax duplicata, O. striatosulcata), whilstthree are new species (Coelastarte wardenensis, O. mickletonensis and Oxyeurax thompsoni). Only two of the British Lower Jurassic Astartinae species appear to have survived the global Early Toarcian extinction event as represented in British successions; one Neocrassina and one Oxyeurax. However, the lack of fossiliferous, high energy near shore environments in the early Toarcian may bias this observation, especially for Oxyeurax.

Mid-Norian to Hettangian record and time-specific oolites during the end-Triassic Mass Extinction at Wadi Milaha, Musandam Peninsula, United Arab Emirates

Article

Full-text available

Jun 2023
J Southeast Asian Earth Sci

The end-Triassic Mass Extinction (ETME) is generally regarded as a consequence of the environmental changes associated with the emplacement of the Central Atlantic Magmatic Province (CAMP) and ranks among the 'big five' mass extinctions in Earth history. A notable feature of the ETME is a halt in marine carbonate deposition followed by the formation of unusual facies such as carbonate cement fans and oolites in the early aftermath of the event. The ETME time interval has been well studied over the last few decades, in contrast to a few minor extinction events that preceded it, among them the extinctions associated with the Norian-Rhaetian boundary (NRB). This study provides new insights into these extinction events with complete mid-Norian to Hettangian δ 18 O carb and δ 13 C carb record from a key section at Wadi Milaha (Ras Al Khaimah Emirate, United Arab Emirates). Ooids are important proxies for palaeoenvironmental reconstruction. The post ETME oolite horizon is documented providing morphological classification as well as a detailed modal analysis of rock components and different types of coated grains. Through a multi-technique approach, we argue for the stability of the carbon cycle across the NRB extinction event and the existence of a hiatus at the TJB (Triassic-Jurassic Boundary) in Wadi Milaha. Our new morphological classification of post-extinction ooids is compatible with a major role for seawater geochemistry with respect to sedimentological processes, by example in the peculiar way ooids diversify and alternate with other kinds of coated grains.

Marine redox change and extinction in Triassic–Jurassic boundary strata from the Larne Basin, Northern Ireland

Article

Full-text available

Apr 2022
PALAEOGEOGR PALAEOCL

The de‑oxygenation of marine environments is thought to have played a significant role in many of Earth's major mass extinction events. This includes the end-Triassic mass extinction event (ETME), which witnessed the disappearance of conodonts, the near extinction of ammonoids and the most significant reef crisis across the entirety of the Phanerozoic. However, there are few high-resolution redox studies across the ETME, including across the main pulse of marine extinction, and few studies that directly correlate marine redox conditions with the biotic record in the same sedimentary succession. Here we present a high-resolution multi-proxy redox record from an expanded Triassic–Jurassic boundary section (Carnduff-2 borehole) from the Larne Basin, Northern Ireland. Redox conditions within the Larne Basin during the latest Triassic and earliest Jurassic were oxic to suboxic with suboxia being mainly restricted to sedimentary pore fluids. Such conditions differ from the photic zone euxinia reported from this time in other basins. Despite the Larne Basin being relatively oxygenated during the latest Triassic (Rhaetian) to earliest Jurassic (Hettangian), subtle pulsed marine redox changes within the Larne Basin had a profound effect on infaunal marine organisms. Suboxia within the Larne Basin coincided with the disappearance of 62.5% of bivalve species, of which 90% were infaunal, and the temporary absence of bioturbation.

Phylogeny, paleobiogeography, and paleophysiology of the Triassic dicynodonts (Therapsida, Anomodontia) : contributions of the Laotian and Moroccan forms

Thesis

Feb 2020

Chloe Olivier

Dicynodonts represent an emblematic Permian-Triassic (P-Tr) taxa to survive the big crisis at the end of Permian. The evolution of Triassic dicynodonts and their recovery conditions are still unclear. This work focused on the Laotian and Moroccan forms. The post-crisis recovery of dicynodonts would appear to be earlier as supported by the description of two new Laotian species (Counillonia superoculis and Repelinosaurus robustus) in Early Triassic. Despite their non-consensual phylogenetic relationships, they support the survivorship of multiple lineages across the P-Tr boundary. Paleophysiological models inferred high metabolism in Permian and Triassic studied dicynodonts, refuting the hypothesis of a high metabolism to mainly explain differential survival beyond the crisis. They also highlighted a unique acquisition of the endothermy in Synapsida occurring at least in middle Permian at the Neotherapsida node. Considering the age and the terrestrial lifestyle of dicynodonts, a terrestrial connection between the Indochina Block and Pangea could thus be interpreted at least in late Permian-Early Triassic. A new dicynodont postcranial material discovered in Morocco was studied and a taxonomic revision of the Moroccan forms was made. Moghreberia nmachouensis was considered as valid and clearly distinguished from Placerias. The restudy of the cranial material of Azarifeneria did not allow distinguishing it from other Triassic genera. In addition to Moghreberia, a second morphotype, more robust, could be noticed in the postcranial material. The large size of Moghreberia and of the second big morphotype confirmed an increase of the body size in dicynodonts during the Triassic.

Bivalve body-size distribution through the Late Triassic mass extinction event

Article

Jan 2022
PALEOBIOLOGY

L. Felipe Opazo

The synergic relationship between physiology, ecology, and evolutionary process makes the body-size distribution (BSD) an essential component of the community ecology. Body size is highly susceptible to environmental change, and extreme upheavals, such as during a mass extinction event, could exert drastic changes on a taxon's BSD. It has been hypothesized that the Late Triassic mass extinction event (LTE) was triggered by intense global warming, linked to massive volcanic activity associated with the Central Atlantic Magmatic Province. We test the effects of the LTE on the BSD of fossil bivalve assemblages from three study sites spanning the Triassic/Jurassic boundary in the United Kingdom. Our results show that the effects of the LTE were rapid and synchronous across sites, and the BSDs of the bivalves record drastic changes associated with species turnover. No phylogenetic signal of size selectivity was recorded, although semi-infaunal species were apparently most susceptible to change. Each size class had the same likelihood of extinction during the LTE, which resulted in a platykurtic BSD with negative skew. The immediate postextinction assemblage exhibits a leptokurtic BSD, although with negative skew, wherein surviving species and newly appearing small-sized colonizers exhibit body sizes near the modal size. Recovery was relatively rapid (~100 kyr), and larger bivalves began to appear during the pre-Planorbis Zone, despite recurrent dysoxic/anoxic conditions. This study demonstrates how a mass extinction acts across the size spectrum in bivalves and shows how BSDs emerge from evolutionary and ecological processes.

Anthropogenic-scale CO2 degassing from the Central Atlantic Magmatic Province as a driver of the end-Triassic mass extinction

Article

Full-text available

Dec 2021
GLOBAL PLANET CHANGE

The climatic and environmental impact of exclusively volcanic CO2 emissions is assessed during the main effusive phase of the Central Atlantic Magmatic Province (CAMP), which is synchronous with the end-Triassic mass extinction. CAMP volcanism occurred in brief and intense eruptive pulses each producing extensive basaltic lava flows. Here, CAMP volcanic CO2 injections into the surface system are modelled using a biogeochemical box model for the carbon cycle. Our modelling shows that, even if positive feedback phenomena may be invoked to explain the carbon isotope excursions preserved in end-Triassic sedimentary records, intense and pulsed volcanic activity alone may have caused repeated temperature increases and pH drops, up to 5 °C and about 0.2 log units respectively. Hence, rapid and massive volcanic CO2 emissions from CAMP, on a similar scale to current anthropogenic emissions, severely impacted on climate and environment at a global scale, leading to catastrophic biotic consequences.

Palaeoecology of Late Triassic marine assemblages from the proto-Atlantic Basin (Ayamonte, SW Spain)

Article

Dec 2021
P GEOLOGIST ASSOC

The Triassic represents a critical period that attests to the diversification of marine ecosystems. This paper analyses the stratigraphy of the easternmost Mesozoic series of the Algarve Basin in the Ayamonte sector (SW Spain). Two sets forming this series are described. The first, mainly siliciclastic, was deposited in continental contexts represented by fluvial and lacustrine environments with bioturbation associated with swamp-like environments (Taenidium) or with plain alluvial sediments (Labyrintichnus terrerensis, Planolites). This ichnoassemblage corresponds to the ichnofacies of Scoyenia. The second set, is carbonate-dominated and shows a remarkable palaeontological content comprising bivalves and gastropods, which made it possible to review our current knowledge of the regional stratigraphy of the Triassic in this area. Trigonodus-Isocyprina form this association for bivalves and Coeslostylina and Coeslostylina-Spirostylus-Mathilda for gastropods allowing to infer a Late Triassic (Carnian-Rhaetian) age for the Ayamonte area. The characteristic trace fossils of the carbonate sections are represented by Thalassinoides Treptichnus pollardi and Helminthoidichnites tenuis, which belong to the proximal expression of the Cruziana ichnofacies. Shallow marginal, low energy, and brackish and locally lacustrine conditions are inferred for this carbonate-dominated set, alternating with episodes of normal salinity, and towards the top, with punctuated episodes of higher energy. This palaeoenvironmental context is congruent with the palaeogeographical scenario conditioned by the existence of a threshold of major order that would indicate the initial breaking of Pangea and the opening of the Tethys in the eastern Mediterranean.

Extinction: End‐Triassic Mass Extinction

Chapter

Full-text available

Jul 2021

Michael Hautmann

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 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 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 CO 2 release 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 CO 2 than reefs.

Flood Basalts and Mass Extinctions

Article

Full-text available

May 2019

Flood basalts were Earth's largest volcanic episodes that, along with related intrusions, were often emplaced rapidly and coincided with environmental disruption: oceanic anoxic events, hyperthermals, and mass extinction events. Volatile emissions, both from magmatic degassing and vaporized from surrounding rock, triggered short-term cooling and longer-term warming, ocean acidification, and deoxygenation. The magnitude of biological extinction varied considerably, from small events affecting only select groups to the largest extinction of the Phanerozoic, with less-active organisms and those with less-developed respiratory physiology faring especially poorly. The disparate environmental and biological outcomes of different flood basalt events may at first order be explained by variations in the rate of volatile release modulated by longer trends in ocean carbon cycle buffering and the composition of marine ecosystems. Assessing volatile release, environmental change, and biological extinction at finer temporal resolution should be a top priority to refine ancient hyperthermals as analogs for anthropogenic climate change. Expected final online publication date for the Annual Review of Earth and Planetary Sciences Volume 47 is May 30, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Dasycladacean alga Palaeodasycladus in the northern Tethys (West Carpathians, Poland) and its new palaeogeographic range during the Early Jurassic

Article

Feb 2018

The green alga Palaeodasycladus was recognized in Lower Jurassic shallow-marine high-energy calcarenites of the Choč Nappe (Hronicum Domain) in the Tatra Mts in Poland. This occurrence indicates the most Northern record of Palaeodasycladus as it is known mostly from the southern part of the Western Tethys. The stratigraphic range of Palaeodasycladus (Norian, Sinemurian–Pliensbachian) and the upper Pliensbachian age of the overlying calcarenites (previous data on the basis of brachiopods) suggest that the studied part of the section was deposited during the Sinemurian–early Pliensbachian. The previous and current reports on occurrences of Palaeodasycladus allowed determination of a new northern palaeogeographic range of the shallow-marine Mediterranean biota during the Early Jurassic time.

A new Rhaetian δ 13 C org record: Carbon cycle disturbances, volcanism, End-Triassic mass Extinction (ETE)

Article

Full-text available

Jan 2018
EARTH-SCI REV

The links between large-scale volcanism, carbon cycle perturbations and the biotic crises at the End-Triassic Extinction event (ETE) are not well understood. The ETE seems to be marked by three carbon isotope excursions (CIEs) likely triggered by different eruptive phases of the Central Atlantic Magmatic Province (CAMP). These three CIEs appear to occur during the late Rhaetian, close to the Triassic/Jurassic boundary (TJB), but the relative timing connecting the volcanism, carbon perturbations and extinctions is still subject to debate resulting from: i) the difficulties in long-distance biostratigraphic correlations of Rhaetian successions due to the step-like extinction pattern characterizing the ETE, and to the lack of globally correlatable key-fossil group(s) across the system boundary; ii) the limit of coverage of available δ¹³C profiles to the system boundary interval, rather than the entire Rhaetian; iii) the inherent difficulties in correlating CIEs without clear biostratigraphic markers. Here we present a δ¹³Corg curve from the Lombardy Basin which covers for the first time the entire Rhaetian. Using this chemostratigraphy, we propose two possible correlations (option 1 and option 2) with other late Rhaetian to early Hettangian successions worldwide. These two possible correlations rely on a combination of paleontological (ammonoids, pollens, conodonts), lithostratigraphic and geochemical constraints. Option 2 in particular has important implications for the causality and geochronology of the ETE events by suggesting that the sharp negative peak usually considered to be the “initial” CIE in the Lombardy might represent a carbon perturbation within the negative trend of the “main” CIE. This implies that a reconsideration of the succession of biotic events occurring during this time interval is required.

Dataset-Daxiakou PTB China

Data

Full-text available

Nov 2017

Changes in terrestrial floras at the Triassic-Jurassic Boundary in Europe

Article

May 2017
PALAEOGEOGR PALAEOCL

One of the biggest mass extinctions took place at the Triassic-Jurassic Boundary. It affected both marine and terrestrial ecosystems, and caused the disappearance of many animal taxa, mostly marine ones. Its influence on floral changes has been widely discussed, with arguments offered for the sudden mass extinction of plants over vast areas, or, alternatively, for slow, less extensive changes. The aim of this study was to statistically verify changes in terrestrial plant composition during the TJB in Europe, and to examine the type and extent of these changes. Data from Polish localities, an interesting new addition to the floristic data from the TJB, were compared with those from other selected localities in Europe. The database contains 311 macroflora taxa from 106 localities (16 Polish) in 13 countries, grouped into 29 regions; and 571 microflora taxa from 105 localities (29 Polish) in 11 countries, grouped into 37 regions. The analysed data cover the period from the Anisian to the Toarcian stages.

Orbital pacing of the Early Jurassic carbon cycle, black shale formation and seabed methane seepage

Article

Full-text available

Sep 2016
SEDIMENTOLOGY

The Early Jurassic (ca 201 to 174 Ma) was marked by a series of rapid perturbations in climate, the environment and global geochemical cycles, which have been linked to volcanic outgassing and the release of biogenic or thermogenic methane into the ocean–atmosphere system. The state of the global carbon cycle and prevailing climatic and environmental conditions that existed at this time are, however, poorly constrained. Here, mudrocks of the Lower Sinemurian Arietites bucklandi ammonite Biozone at coastal exposures at Kilve, Somerset, UK, have been studied. This succession includes laminated organic-rich black shales, which are present throughout the Bristol Channel Basin, and coincides with a 2 to 3‰ negative carbon-isotope excursion, distinct changes in inferred land vegetation, and abundant marine prasinophytes (green algae). The event itself does not represent a single perturbation of the regional environment, but follows in a sequence of eccentricity-modulated, precession-paced perturbations that occur throughout the preceding Hettangian stage, with the periodic formation of organic-rich laminated black shales in the Bristol Channel Basin. However, the Early Sinemurian event studied herein is more extreme in nature, with sedimentary total organic carbon values of 5 to 11% persisting over about 2 m, representing ca 100 kyr, possibly in phase with short (ca 100 kyr) and long (ca 405 kyr) eccentricity forcing. The formation of methane seep carbonate cemented mounds took place relatively soon after the deposition of laminated black shales. Biogenic methane probably formed in response to microbial methanogenesis in the organic-rich black shale, which was subsequently channeled to the sediment–water interface approximately 5 m above the source bed, and ca 200 kyr after cessation of formation of the black shale.

Body Size Evolution Across the Geozoic

Article

Full-text available

Jun 2016

The Geozoic encompasses the 3.6 Ga interval in Earth history when life has existed. Over this time, life has diversified from exclusively tiny, single-celled organisms to include large, complex multicellular forms. Just how and why this diversification occurred has been a major area of interest for paleontologists and evolutionary biologists for centuries. Here, we compile data on organism size throughout the Geozoic fossil record for the three domains of life. We describe canonical trends in the evolution of body size, synthesize current understanding of the patterns and causal mechanisms at various hierarchical scales, and discuss the biological and geological consequences of variation in organismal size.

Paleoecological succession of Norian (Late Triassic) benthic fauna in eastern Panthalassa (Luning and Gabbs formations, west-central Nevada)

Article

Apr 2016

The Norian Stage of the Late Triassic represents a long interval from which the benthic faunal succession is poorly understood, particularly from eastern Panthalassa. Fossiliferous bulk samples of shallow marine carbonates were collected from the Luning and Gabbs formations in west-central Nevada to evaluate the changes in faunal composition and paleoecological structure during the Norian Stage. Stationary epifauna dominated the early Norian faunal assemblages but gradually became less common by the late Norian, with the exception of cementing bivalves, which were common in the middle and late Norian. After the early Norian, mobile infauna also became increasingly abundant and diverse. These paleoecological trends are similar to those observed in Tethyan level-bottom carbonate deposits from the Lombardian Basin in northern Italy. Reclining epifauna remained uncommon in the local area until the Early Jurassic, and this Mesozoic decline in recliners preceded the end-Triassic mass extinction in Nevada.

2015-Wei-etal-ESR

Data

Full-text available

Feb 2016

Trophic group and the end-Cretaceous extinction: Did deposit feeders have it made in the shade?

Article

Dec 1996
PALEOBIOLOGY

Jeffrey Levinton

It has been suggested that a sudden event at the end of the Cretaceous period caused a major extinction that was felt disproportionately by creatures in the water column. It also has been argued that benthic deposit feeders, being relatively independent of abundance of organic particles in the water column, should have survived the crisis more readily than suspension feeders, which depended more upon feeding upon phytoplankton. I argue that the hypothesis of relative immunity of deposit feeders is insufficient, because deposit feeders by and large depend upon a supply of organic matter from the water column and would have succumbed to food shortage nearly as rapidly as suspension feeders, possibly within a maximum of three to six months. This near simultaneity of extinction would have been especially true of continental shelf environments. Even in some parts of the deep sea, it is likely that a dependence upon the water column above might have caused deep-sea deposit feeders to succumb rapidly. Therefore, deposit feeders would not necessarily have outsurvived suspension feeders during a crisis of depleted water-column phytoplankton, increased shading by inert particles, or poisoning of the water column and killing of phytoplankton. The relatively lower rate of extinction of nuculoid bivalves may relate instead to their presence in deeper-water refuge habitats, their apparent relative ability to diversify in higher latitudes, or their resistance to factors other than food shortage.

Palaeoecological insights into the Changhsingian–Induan (latest Permian–earliest Triassic) bivalve fauna at Dongpan, southern Guangxi, South China

Article

Full-text available

Nov 2015

The Talung Formation (latest Permian) and basal part of Luolou Formation (earliest Triassic) of the Dongpan section have yielded 30 bivalve species in 17 genera. Eight genera incorporating 11 species are systematically described herein, including three new species: Nuculopsis guangxiensis, Parallelodon changhsingensis and Palaeolima fangi. Two assemblages are recognized, i.e., the Hunanopecten exilis-Euchondria fusuiensis assemblage from the Talung Formation and the Claraia dieneri-Claraia griesbachi assemblage from the Luolou Formation. The former is characterized by abundant Euchondria fusuiensis, an endemic species, associated with other common genera, such as Hunanopecten, which make it unique from coeval assemblages of South China. A palaeoecological analysis indicates that the Changhsingian bivalve assemblage at Dongpan is diverse and represented by various life habits characteristic of a complex ecosystem. This also suggests that redox conditions were oxic to suboxic in deep marine environments of the southernmost Yangtze Basin during the late Changhsingian, although several episodes of anoxic perturbations and declines in palaeoproductivity saw deterioratation of local habitats and altered the taxonomic composition or population size of the bivalve fauna.

Comparative size evolution of marine clades from the Late Permian through Middle Triassic

Article

Full-text available

Nov 2015

The small size of Early Triassic marine organisms has important implications for the ecological and environmental pressures operating during and after the end-Permian mass extinction. However, this “Lilliput Effect” has only been documented quantitatively in a few invertebrate clades. Moreover, the discovery of Early Triassic gastropod specimens larger than any previously known has called the extent and duration of the Early Triassic size reduction into question. Here, we document and compare Permian-Triassic body size trends globally in eight marine clades (gastropods, bivalves, calcitic and phosphatic brachiopods, ammonoids, ostracods, conodonts, and foraminiferans). Our database contains maximum size measurements for 11,224 specimens and 2,743 species spanning the Late Permian through the Middle to Late Triassic. The Permian/Triassic boundary (PTB) shows more size reduction among species than any other interval. For most higher taxa, maximum and median size among species decreased dramatically from the latest Permian (Changhsingian) to the earliest Triassic (Induan), and then increased during Olenekian (late Early Triassic) and Anisian (early Middle Triassic) time. During the Induan, the only higher taxon much larger than its long-term mean size was the ammonoids; they increased significantly in median size across the PTB, a response perhaps related to their comparatively rapid diversity recovery after the end-Permian extinction. The loss of large species in multiple clades across the PTB resulted from both selective extinction of larger species and evolution of surviving lineages toward smaller sizes. The within-lineage component of size decrease suggests that only part of the size decrease can be related to the end-Permian kill mechanism; in addition, Early Triassic environmental conditions or ecological pressures must have continued to favor small body size as well. After the end-Permian extinction, size decrease occurred across ecologically and physiologically disparate clades, but this size reduction was limited to the first part of the Early Triassic (Induan). Nektonic habitat or physiological buffering capacity may explain the contrast of Early Triassic size increase and diversification in ammonoids versus size reduction and slow recovery in benthic clades.

Temperature and salinity shaping life-history traits and long-term population stability of Mesodesma donacium in the Humboldt Upwelling System

Article

Full-text available

Jan 2009

Environmental controls on marine ecosystem recovery following mass extinctions, with an example from the Early Triassic

Article

Oct 2014
EARTH-SCI REV

The recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity. The pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors. Here, we present an analysis of changes in marine conditions following the end-Permian mass extinction with the objective of evaluating the role of environmental factors in the protracted (~ 5-Myr-long) recovery of marine ecosystems during the Early Triassic. Specifically, our study examines changes in weathering, productivity, and redox proxies in three sections in South China (Chaohu, Daxiakou, and Zuodeng) and one in northern India (Mud). Our results reveal: 1) recurrent environmental perturbations during the Early Triassic; 2) a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early Griesbachian, late Griesbachian, mid-Smithian, and (more weakly) the mid-Spathian; 3) increases in marine productivity during the aforementioned intervals except for the early Griesbachian; and 4) stronger and more temporally discrete intervals of environmental change in deepwater sections (Chaohu and Daxiakou) relative to shallow and intermediate sections (Zuodeng and Mud). Our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity, within-community (alpha) diversity, infaunal burrowing, and ecosystem tiering. We infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the Early Triassic. These perturbations were associated with elevated weathering and productivity fluxes, implying that nutrient and energy flows were key influences on recovery. More regular secular variation in deepwater relative to shallow-water environmental conditions implies that perturbations originated at depth (i.e., within the oceanic thermocline) and influenced the ocean-surface layer irregularly. Finally, we compared patterns of environmental disturbance and ecosystem recovery following the other four “Big Five” Phanerozoic mass extinctions to evaluate whether commonalities exist. In general, the pace of ecosystem recovery depends on the degree of stability of the post-crisis marine environment.

Climatic reversals related to the Central Atlantic magmatic province caused the end-Triassic biotic crisis— Evidence from continental strata in Poland

Article

Full-text available

Sep 2014

Eight climatic events can be distinguished in the Triassic-Jurassic (ca. 201 Ma) continental strata of Poland. These events are distinguished by kaolinite/illite ratio, chemical index of alteration (CIA), color of sediments, and palynomorphs. The first transition to wetter climate, evidenced by a shift from smectite- to kaolinite-dominated mudrocks, coincides with the earlier ("precursor") Rhaetian negative δ13Corgexcursion, which means that the beginning of climate perturbations predates the oldest known Central Atlantic magmatic province flood basalts by some 100-200 k.y. The later global, late Rhaetian "initial" negative δ13Corgexcursion is divided into two subpeaks, each corresponding to hot and humid events, separated by a cooler and drier event. The upper subpeak is also associated with perturbation of the osmium isotope system (attributed to volcanic fallout), and darkened miospores, pointing to acid rains. Between the "initial" excursion and the Triassic-Jurassic boundary interval, five climatic fluctuations are inferred from the changing kaolinite/illite ratio, the last two of which are also associated with an Os isotope perturbation, polycyclic aromatic hydrocarbon (PAH) occurrences, a "spore peak," and darkened miospores. A series of periodic atmospheric loading events by CO2, CH4, or alternatively by SO2, sulfate aerosols, and toxic compounds, is inferred to have caused this series of rapid climatic reversals and resulting extinction of many less-adapted forms. Just above the palynofloral extinction level, appearance of new forms commenced Jurassic palynofloral recovery. Tetrapod evolution events in the end-Triassic-earliest Jurassic were related to the extinction of the Pseudosuchia, Dicynodontia, Capitosauroidea, Plagiosaroidea, and Rhynchosauria, while appearance of highly diversified tetrapod ichnofauna in the earliest Jurassic strata indicates a rapid recovery and refill of ecological niches by dinosaurs.

Climatic reversals related to the Central Atlantic magmatic province caused the end-Triassic biotic crisis--Evidence from continental strata in Poland

Article

Full-text available

Aug 2014

Eight climatic events have been distinguished in the Triassic–Jurassic continental sediments of Poland and their effect on the end-Triassic mass extinction has been assessed. The first climatic change predated the Central Atlantic magmatic province flood basalts by 100–200 k.y. and was followed by five further climatic fluctuations up to the Triassic-Jurassic boundary. Periodic atmospheric loading by CO2, CH4, or by SO2, sulfate aerosols, and toxic compounds is inferred to have caused this series of rapid climatic reversals and resulting extinctions. The appearance of highly diversifi ed tetrapod ichnofauna in the earliest Jurassic strata indicates a rapid recovery and refi ll of ecological niches by dinosaurs

Composition of Hettangian brachiopod communities in the Western Carpathians: implications for recovery after the end-Triassic mass extinction event

Article

The Lower–Middle Hettangian post-extinction brachiopods in the Western Carpathians occur in micrite-rich limestones with sponge spicules and peloids that represent carbonate-rich, mixed-bottom habitats below a maximum storm wave base. Lobothyris is the first brachiopod appearing in a succession and locally occurs in monospecific, autochthonous or parautochthonous shell beds. Lobothyris was less disarticulated and fragmented and attained a larger size in shell beds than in shell-poor beds. Uniform size modes of adults in shell beds indicate that the high shell density of Lobothyris was not a result of opportunistic bursts. The increase in shell density thus might be more related to a decrease in adult mortality rate and increase in mean adult size. The Lobothyris community was stratigraphically replaced by a community dominated by oysters, and higher by a community dominated by the terebratulid Zeilleria , the multi-costate rhynchonellid Jakubirhynchia and oysters. Compositionally, similar brachiopod communities dominated either by (1) Lobothyris or (2) Zeilleria and multicostate rhynchonellids inhabited also other western Tethyan regions during Hettangian. Lobothyris occupied shallower habitats or habitats more proximal to shoreline than Zeilleria and multicostate rhynchonellids. Distinct habitat preferences of Lobothyris , Zeilleria and rhynchonellids reflect an increase in between-habitat variation in composition of brachiopod communities in the western Tethys after the end-Triassic mass extinction. Jurassic, mass extinction, palaeoecology, taphonomy, Triassic, Western Carpathians. In spite of some discussion about duration of the end-Triassic mass extinction, i.e. whether it was stepwise or catastrophic (Hallam 2002), this event records genus and family extinction rates that were substantially higher than those typical of most other Phanerozoic stages (Sepkoski 1997). This event strongly affected distribution and abundance of brachiopods (Dagys 1990; Sandy 1995) and bivalves (McRoberts & Newton 1995; McRoberts et al . 1997; Hautmann 2004). An increase in predation and competition intensity is one of the explanations accounting for the general decrease in abundance and diversity of brachiopods through the Mesozoic (Vermeij 1987). Alternatively, effects of relatively sudden global or regional extrinsic disturbances might also govern this brachiopod decline, and can thus provide opposite or complementary expla-nations of their Mesozoic ecologic and evolutionary history (Jablonski 2001). Evaluating response of brachi-opods to extensive extrinsic disturbance at the end of the Triassic is thus essential for understanding their distribution pattern during the Mesozoic (Pálfy 2003). The recovery of Hettangian brachiopods in NW Europe was slow and characterized mainly by monospecific occurrences of the rhynchonellid Calcirhynchia calcaria Buckman (Hallam 1960; Alméras & Hanzo 1991). In contrast, Hettangian brachiopods were characterized by a higher taxonomic diversity in the Tethyan area (Dulai 2001). The aim of this study is to evaluate the composition and temporal replacement of Lower–Middle Hettangian brachiopod communities in the Western Carpathians, to assess whether bra-chiopod shell beds reflect bursts of post-extinction opportunists, and to compare them with other brachiopod communities known from Hettangian deposits of the western Tethys area. Although the presented data are derived from one section only, it is the only known site in the Western Carpathians where post-extinction Hettangian brachi-opods occur in high abundance. This site thus provides a unique opportunity to study the composition of post-extinction brachiopod communities in the Western Carpathians.

Latest Triassic-earliest Jurassic bivalves from the Germig Formation from Lanongla (Tibet, China)

Article

Full-text available

Jan 2006

The Germig Formation of the Tethyan Himalaya of southern Tibet contains an exceptionally abundant bivalve fauna which has been found in association with choristoceratid and psiloceratid ammonoids and spans the Triassic/Jurassic boundary. The bivalve fauna consists of 25 species, including four new species: Newaagia lanonglaensis, Persia hallami, Liostrea tibetica, and Ctenostreon newelli. The fauna comprises three biostratigraphically controlled bivalve assemblages: 1) an upper Rhaetian Palaeocardita-Krum- beckiella Assemblage including seven species; 2) a high diversity transitional Rhaetian-Hettangian Persia-Plagiostoma Assemblage with many as 19 species; and 3) a low diversity lower Hettangian Liostrea-Chlamys Assemblage containing three species. The tran- sitional Rhaetian-Hettangian Assemblage is dominated by cementing species and exhibits a high degree of endemism. A large proportion of lower latitude and cementing taxa from the lower two levels may indicate that they inhabited shallow subtidal tropic or subtropic paleoenvironments.

Astronomically-calibrated magnetostratigraphy of the Lower Jurassic marine successions at St. Audrie's Bay and East Quantoxhead (Hettangian–Sinemurian; Somerset, UK)

Article

Jun 2014
PALAEOGEOGR PALAEOCL

Extinction patterns among bivalves in South China during the Permian-Triassic crisis

Article

Apr 2014
PALAEOGEOGR PALAEOCL

Extent of the Upper Norian – Rhaetian Slatnik Formation in the Tolmin Nappe, eastern Southern Alps

Article

Full-text available

Dec 2013

In the Norian and Rhaetian the area of present-day Slovenia was divided into the Julian Carbonate Platform on in present north, the Dinaric Carbonate Platform in the present south and the intermediate Slovenian Basin. Main Dolomite or the Dachstein Limestone were deposited, on the platforms whereas the basin was characterized by the Bača Dolomite. The Upper Norian-Rhaetian succession was recently recognized in the northern part of the basin. It was studied in two sections and defined as the Slatnik Formation. Rich conodont and foraminiferal assemblages were additionally studied. Two new sections of the Slatnik Formation are presented in this paper, proving the existence of the formation across the entire northern segment of the basin. The Povdnar section is located in the continuous facies belt westward from the type-locality on Mt. Kobla. When compared to the type-locality and the other previously studied section at Mt. Slatnik, the Povdnar section exhibits more distal basinal development, where hemipelagic limestone prevails, whereas resedimented limestones occur only sporadically. For this reason, a coarsening and thickening upward trend that was recognized in previously investigated sections is poorly expressed in the Povdnar section. The second newly studied section is located on Mt. Javor where the most northwestern succession of the basin is found. In this section, the Slatnik Formation is composed solely of hemipelagic limestone.

Triassic/Jurassic bivalve biodiversity dynamics: Biotic versus abiotic factors

Article

Oct 2023

Based on the global occurrence dataset, the shift in taxonomic and functional diversity of bivalves at the Triassic/Jurassic transition was examined herein. There is a noticeable decline in diversity at many taxonomic levels (generic, family, and order) along the Triassic/Jurassic boundary. Test changes in the functional diversity (e.g., life habits, mobility levels, and feeding mode) revealed that the percentage of mobile exceeded stationary taxa after the end of the Triassic crisis, while no major changes were observed in the life habit or feeding mode. By the Sinemurian, diversity reached the pre-extinction levels. A significant difference was also found between survivors’ longevity and extinct taxa, where the Early Jurassic (Hettangian) fauna have a longer duration relative to those that became extinct. The Triassic/Jurassic boundary is marked by a marked sea-level fall and a decrease in the mean Sea Surface Temperature (SST), which is associated with increasing siliciclastic and decreasing carbonate rocks. The latter may also point to ocean acidification at the Triassic/Jurassic boundary. The geographic range size of bivalves is slightly changed by the end of the Triassic, where the taxa are slightly characterized by narrower ranges. Hence, the geographic range size, the result of ecophysiology, plays a major role in determining the extinction risk. The difference in the magnitude of the diversity loss (i.e., taxonomically vs. functionally) indicated that the shallower marine habitat destruction resulting from the sea-level fall is the primary cause of the Triassic/Jurassic mass extinction.

Evolution de la biosphère et événements géologiques

Book

Sep 2021

Francis Lethiers

An enormous sulfur isotope excursion indicates marine anoxia during the end-Triassic mass extinction

Article

Full-text available

Sep 2020

The role of ocean anoxia as a cause of the end-Triassic marine mass extinction is widely debated. Here, we present carbonate-associated sulfate d34S data from sections spanning the Late Triassic–Early Jurassic transition, which document synchronous large positive excursions on a global scale occurring in ~50 thousand years. Biogeochemical modeling demonstrates that this S isotope perturbation is best explained by a fivefold increase in global pyrite burial, consistent with large-scale development of marine anoxia on the Panthalassa margin and northwest European shelf. This pyrite burial event coincides with the loss of Triassic taxa seen in the studied sections. Modeling results also indicate that the pre-event ocean sulfate concentration was low (<1 millimolar), a common feature of many Phanerozoic deoxygenation events. We propose that sulfate scarcity preconditions oceans for the development of anoxia during rapid warming events by increasing the benthic methane flux and the resulting bottom-water oxygen demand.

A two-phase end-Triassic mass extinction

Article

Jul 2020

A two-phase end-Triassic mass extinction

Article

Jul 2020
EARTH-SCI REV

The end-Triassic mass extinction was one of the big five crises of the fossil record. It affected diverse marine groups, including bivalves, brachiopods, ostracods, calcareous algae, radiolarians, and tetrapods and coincided with major changes in palynological assemblages. The rapidity of the event has long been debated and here we show that it can be resolved into two distinct, short-lived extinction pulses separated by a several hundred-thousand-year interlude phase. Detailed collecting in the British Isles shows the first extinction in the lower Cotham Member eliminated many bivalves and ostracods. This event has been previously considered as the end-Triassic mass extinction horizon, however a second extinction is also seen at the top of the Langport Member after a phase of recovery marked by diversity increase. This younger crisis caused the loss of further bivalves, ostracods and the last of the conodonts. The two phases of marine extinctions coincide with marked turnovers amongst palynofloral assemblages with the interlude phase manifest as a fern spore-dominated interval (the Polypodiisporites polymicroforatus abundance interval). Correlation of Triassic-Jurassic boundary sections (and their associated extinction record) in Europe has been controversial. The most parsimonious correlation scheme assumes that a brief, high amplitude negative excursion of δ¹³Corg values, seen at the level of the first extinction phase in the UK, is manifest in other European sections in the same way. Alternative correlation schemes require complex scenarios with extinction occurring in some areas as recovery is happening elsewhere. In Europe, the first extinction coincides with regression whilst the second occurs at a flooding surface marked by the spread of anoxia. The extinction history of the terminal Triassic crisis is remarkably similar to that seen during other extinction events (end-Ordovician, Permo-Triassic, Toarcian) and suggests that, if the ultimate driver of these crises – large igneous province eruptions – is the same, then they show the same “double-punch” eruption history separated by a more benign interval of a few hundred-thousand-year duration.

The Late Triassic Extinction at the Norian/Rhaetian boundary: Biotic evidence and geochemical analysis

Article

Apr 2020
EARTH-SCI REV

The latest Triassic was an interval of prolonged biotic extinction culminating in the end-Triassic Extinction (ETE). The ETE is now associated with a perturbation of the global carbon cycle just before the end of the Triassic that has been attributed to the extensive volcanism of the Circum-Atlantic Magmatic Province (CAMP). However, we attribute the onset of declining latest Triassic diversity to an older perturbation of the carbon cycle (δ¹³Corg) of global extent at or very close to the Norian/Rhaetian boundary (NRB). The NRB appears to be the culmination of stepwise biotic turnovers that characterize the latest Triassic and includes global extinctions of significant marine and terrestrial fossil groups. These biotic events across the NRB have been largely under-appreciated, yet together with a coeval disturbance of the carbon cycle were pivotal in the history of the Late Triassic. Here, we present new and published δ¹³Corg data from widespread sections (Italy, Greece, Australia, New Zealand,USA, Canada). These sections document a previously unknown perturbation in the carbon cycle of global extent that spanned the NRB. The disturbance extended across the Panthalassa Ocean to both sides of the Pangaean supercontinent and is recorded in both the Northern and Southern Hemispheres. The onset of stepwise Late Triassic extinctions coincides with carbon perturbation (δ¹³Corg) at the NRB, indicating that a combination of climatic and environmental changes impacted biota at a global scale. The NRB event may have been triggered either by gas emissions from the eruption of a large igneous province pre-dating the NRB, by a bolide impact of significant size or by some alternative source of greenhouse gas emissions. As yet, it has not been possible to clearly determine which of these trigger scenarios was responsible; the evidence is insufficient to decisively identify the causal mechanism and merits further study.

Body size, sampling completeness, and extinction risk in the marine fossil record

Article

Jan 2020

Larger body size has long been assumed to correlate with greater risk of extinction, helping to shape body-size distributions across the tree of life, but a lack of comprehensive size data for fossil taxa has left this hypothesis untested for most higher taxa across the vast majority of evolutionary time. Here we assess the relationship between body size and extinction using a data set comprising the body sizes, stratigraphic ranges, and occurrence patterns of 9408 genera of fossil marine animals spanning eight Linnaean classes across the past 485 Myr. We find that preferential extinction of smaller-bodied genera within classes is substantially more common than expected due to chance and that there is little evidence for preferential extinction of larger-bodied genera. Using a capture–mark–recapture analysis, we find that this size bias of extinction persists even after accounting for a pervasive bias against the sampling of smaller-bodied genera within classes. The size bias in extinction also persists after including geographic range as an additional predictor of extinction, indicating that correlation between body size and geographic range does not provide a simple explanation for the association between size and extinction. Regardless of the underlying causes, the preferential extinction of smaller-bodied genera across many higher taxa and most of geologic time indicates that the selective loss of large-bodied animals is the exception, rather than the rule, in the evolution of marine animals.

The Missing Mass Extinction at the Triassic-Jurassic Boundary

Chapter

Nov 2018

The Late Triassic was a prolonged episode characterized by high rates of biotic turnover and discrete extinction events due to elevated extinction rates for some biotic groups and low origination rates for many. An end-Triassic mass extinction continues to be cited as one of the “big five” mass extinctions of the Phanerozoic. However, a detailed examination of the fossil record, especially by best-sections analysis, indicates that many of the groups usually claimed to have suffered catastrophic extinction at the end of the Triassic, such as ammonoids, marine bivalves, conodonts and tetrapod vertebrates, experienced multiple extinctions throughout the Late Triassic, not a single mass extinction at the end of the Period. Many other groups were relatively unaffected, whereas some other groups, such as reef communities, were subject to only regional effects. Indeed, the lack of evidence of a collapse of trophic networks in the sea and on land makes the case for an end-Triassic mass extinction untenable. Still, marked evolutionary turnover of radiolarians and ammonoids did occur across the Triassic-Jurassic boundary. The end of the Triassic encompassed temporary disruptions of the marine and terrestrial ecosystems, driven by the environmental effects of the eruption of the flood basalts of the Circum-Atlantic Magmatic Province (CAMP), through outgassing in particular, but these disruptions did not produce a global mass extinction.

Late Triassic Terrestrial Tetrapods: Biostratigraphy, Biochronology and Biotic Events

Chapter

Nov 2018

Spencer G. Lucas

The fossil record of Late Triassic tetrapods can be organized biostratigraphically and biochronologically into five, temporally successive land-vertebrate faunachrons (LVFs) that encompass Late Triassic time (in ascending order): Berdyankian, Otischalkian, Adamanian, Revueltian and Apachean. An up-to-date review of the age constraints on Late Triassic tetrapod fossil assemblages and correlation within the framework of the LVFs is presented. This makes possible a much more accurate evaluation of the timing of biotic events of Late Triassic tetrapod evolution, including: (1) Otischalkian, HO (highest occurrence) of almasaurids and chroniosuchians?, LOs (lowest occurrences) of crocodylomorphs and dinosaurs; (2) Adamanian, HO of mastodonsaurids and trematosaurids, LO of mammals; (3) Revueltian, HOs of capitosaurids, rhynchosaurs and dicynodonts; and (4) Apachean, HOs of metoposaurids, plagiosaurids and aetosaurs. The LO of turtles is Early Triassic or older, and the HO of phytosaurs is an Early Jurassic record. There is no compelling evidence of tetrapod mass extinctions at either the Carnian-Norian or the Triassic-Jurassic boundaries.

Nearing the End: Reef Building Corals and Bivalves in the Late Triassic and Comparing Corals and Bivalves before and after the end-Triassic Mass Extinction Using a Taxonomic Database

Thesis

Full-text available

Aug 2013

Hannah M E Shepherd

Biotic recovery after the end-Triassic extinction event: Evidence from marine bivalves of the Neuquén Basin, Argentina

Article

Aug 2017
PALAEOGEOGR PALAEOCL

We analyze the Late Triassic extinction and Early Jurassic recovery of bivalve faunas within marine environments in the Atuel River area of the Neuquén Basin, Argentina. Data were collected from a hundred samples with invertebrates in a well-exposed uppermost Triassic to lower Jurassic section in the Neuquén Basin (southern Mendoza Province, Argentina) and allow a high-resolution reconstruction of the local diversity dynamics. The nearly continuous presence of marine stenohaline major taxa such as cnidarians, rhynchonelliform brachiopods, echinoderms and cephalopods indicates normal salinity throughout. All bivalve species were identified, and each occurrence was recorded in meters above the base. To analyze the systematic diversity trends, diversity curves were calculated on the basis of the first and last occurrence data for each bivalve species, and both total diversity and boundary crossers diversity were used. As a result, four main phases were identified: a) Triassic equilibrium phase (Rhaetian), with relatively high origination and extinction rates; b) extinction phase (latest Rhaetian to earliest Hettangian), with high extinction rates and low origination rates; c) recovery phase (late Early to early Late Hettangian), with high origination rates and almost null extinction rates; and d) Jurassic equilibrium phase (Late Hettangian-Sinemurian), again with similar and relatively high origination and extinction rates. The extinction and recovery phases are separated by a gap of about 135. m without identifiable benthonic invertebrates but with early Hettangian ammonites. On the other hand, bivalve palaeoecologic diversity seems to have been more homogeneous along the section, being dominated by attached epifaunal species, though before the extinction epifaunal habits were slightly surpassed by infaunal ones. Slight differences observed include a) shallow burrowers were more diverse during the Rhaetian than during the earliest Jurassic and b) epifaunal free-lying and semi-infaunal attached bivalves were more diverse after the Rhaetian extinction.

Selective extinction of late Neogene bivalves on the temperate Pacific coast of South America

Article

Full-text available

Jun 2007

We assessed selective extinction patterns in bivalves during a late Neogene mass extinction event observed along the temperate Pacific coast of South America. The analysis of 99 late Neogene and Quaternary fossil sites (recorded from 7°S to 55°S), yielding ∼2800 occurrences and 118 species, revealed an abrupt decline in Lyellian percentages during the late Neogene–Pleistocene, suggesting the existence of a mass extinction that decimated ∼66% of the original assemblage. Using the late Neogene data set ( n = 59 species, 1346 occurrences), we tested whether the extinction was nonrandom according to taxonomic structure, life habit, geographic range, and body size. Our results showed that the number of higher taxa that went extinct was not different than expected by random. At first sight, extinction was selective only according to life habit and geographic range. Nevertheless, when phylogenetic effects were accounted for, body size also showed significant selectivity. In general, epifaunal, small-sized (after phylogenetic correction), and short-ranged species tended to have increased probability of extinction. This is verified by strong interactions between the variables herein analyzed, suggesting the existence of nonlinear effects on extinction chances. In the heavily decimated epifaunal forms, survival was not enhanced by widespread ranges or larger body sizes. Conversely, the widespread and large-sized infaunal forms tended to have lower probability of extinction. Overall, the ultimate extinction of late Neogene bivalve species along the Pacific coast of South America seems to have been determined by a complex interplay of ecological and historical (phylogenetic) effects.

Faunal succession of Norian (Late Triassic) level-bottom benthos in the Lombardian basin: Implications for the timing, rate, and nature of the early Mesozoic Marine Revolution

Article

Aug 2012

The recently expanded Norian stage now encompasses nearly half of the entire Triassic period, making it the longest single stage of the Phanerozoic. Very little is known about the paleoecological dynamics of shallow marine level-bottom benthos within the stage, however. Successive bulk samples from the Lombardian Alps, Italy, reveal gradual changes in dominant taxa throughout the Norian, and paleoecological transitions consistent with the Mesozoic Marine Revolution (MMR) hypothesis. At the expense of stationary epifauna, mobile infauna diversified and became dominant by the end of the Norian. In addition to increases in stationary semi-infauna, abundant mobile epifauna were perhaps early alternatives to increasing both mobility and infaunality during the middle Norian. The particular suite of trends observed suggests that an adaptive response to epifaunal and demersal predators was operating in this system, and is coincident with the known taxonomic radiations of shell-crushing predators from this interval (lobsters, fish). Thus, the MMR was gradually intensifying as early as 25 myr before the Triassic-Jurassic boundary.

Late Triassic extinction events

Article

Full-text available

Jan 2004

Norian-Rhaetian sedimentary evolution of the Slovenian Basin (eastern Southern Alps)

Article

Apr 2012

The Slovenian Basin represents a Mesozoic deep water sedimentary environment, during the Triassic situated on the southern passive continental margin of the Neotethys (Meliata) Ocean (cf. Schmid et al., 2008). The Norian-Rhaetian sedimentary evolution of the Slovenian Basin is reconstructed on the basis of five sections located in different parts of the Tolmin Nappe (Eastern Southern Alps, western Slovenia). The correlation of sections is based on conodont data and facies analysis. The Norian-Rhaetian interval is in the basin represented by the "Bača dolomite" (bedded dolostone with chert) and the Slatnik Formation (hemipelagic and allodapic limestones), while the bordering reef-rimmed carbonate platforms in inner areas record peritidal deposition (Main Dolomite, Dachstein Limestone). The transition from claystone and marly limestone dominated "Amphiclina beds" to the bedded "Bača dolomite" took place at the Carnian-Norian boundary. The change in facies can be attributed to the eustatic rise of sea-level and the subsequent retreat of terrigenous input. Intensive basin-wide slumping took place during the Early Norian and marks a short period of tectonic activity. Slump breccias are followed by bedded dolostones. An increase in terrigenous input in pyrite-enriched thin-bedded dolostones indicates a relative sea-level fall (cf. Haas, 2002) at the Early-Middle Norian boundary. The Middle-Late Norian sedimentation is dominated by bedded dolostones. The microfacies analysis of scarce non-dolomitized horizons indicates hemipelagic deposition and sedimentation from distal turbidites, with material derived from adjacent platform. An interval of slump breccias suggests that another tectonic pulse took place during the Middle Norian. The Late Norian in the northern part of the Tolmin Nappe already belongs to the Slatnik Formation, which spans the rest of the Triassic, while in other parts of the Basin the "Bača dolomite" continues up to the Triassic-Jurassic boundary. The Norian-Rhaetian boundary (based on Misikella posthernsteini) is marked by transition to more coarse grained, i.e. turbidity currents dominated sedimentation. Coarsening and thickening-upwards succession from packstones to boulder breccias is interpreted as a forced regressive wedge of the falling relative sea-level. The following thinning and fining-upwards succession marks the beginning of the sea-level rise and ends abruptly at the Rhaetian-Hettangian boundary with a few meters thick package of thin-bedded hemipelagic limestones. The lack of coarser platform material can be attributed to (A) the rising sea-level, or (B) to another fall of sea-level, coupled with a biocalcification crysis. Locally, extensional tectonics led to bottom differentiation. The Late Norian and Rhaetian tectonic activity was spatially limited to individual parts of the basin. Ooidal and peloidal allodapic limestones of the overlying Early Jurassic Krikov Formation mark renewal of carbonate production on the adjacent carbonate platform. The Norian-Rhaetian deposition in the Slovenian Basin was thus marked by eustatic changes and extensional tectonics. The later reflects the diminishing Neotethys rifting and the incipient opening of the Alpine Tethys area (Haas & Budai, 1999; Cozzi, 2000; Haas, 2002).

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

Article

Full-text available

Sep 2013
J Paleontol

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 stress.

Fades and geochemical evidence bearing on the end-Triassic disappearance of the Alpine reef ecosystem

Article

Full-text available

Jan 1990

A carbon and oxygen isotope profile is presented across the Triassic‐Jurassic boundary at the classic locality of Kendelbach, Austria. In conjunction with faciès data it lends no support to the claim that the spectacular disappearance of the reef ecosystem at the end of the Triassic was due to a sharp fall of seawater temperature. A model relating mass extinction to sea‐level change is preferred.

Quartz Grains With Planar Features in the Triassic-Jurassic Boundary Sediments From Northern Limestone Alps, Austria

Article

Full-text available

Feb 1987

Shocked Quartz at the Triassic-Jurassic Boundary in Italy

Article

Full-text available

Feb 1992

Quartz grains that appear to have been shock-metamorphosed occur within three closely spaced shale beds from the uppermost Triassic ("Rhaetian") Calcare a Rhaetavicula in the Northern Apennines of Italy. The upper shale coincides with the abrupt termination of the distinctive, uppermost Triassic Rhaetavicula fauna and is overlain by the Hettangian (Lower Jurassic) Calcare Massiccio; no extinctions appear to be associated with the two lower layers, which occur 1.2 and 2.4 meters below the boundary shale. Approximately 5 to 10% of the quartz grains within these layers exhibit one or more sets of planar deformational features whose orientations cluster around the rational crystallographic planes (basal, ω, and π) most commonly observed in shocked quartz. Textural and stratigraphic observations support an interpretation of at least three closely spaced impacts at the end of the Triassic.

Chapter 10. Marine Regressions and Mass Extinctions: A Test Using the Modern Biota

Chapter

Dec 1986

David Jablonski

Relation of shell form to life habits of the Bivalvia (Mollusca)

Article

S.M. Stanley

Population size, extinction, and speciation: the fission effect in Neogene Bivalvia

Article

Dec 1986

Steven M. Stanley

The extinction of a species represents reduction of both geographic range and population size to zero. Most workers have focused on geographic range as a variable strongly affecting the vulnerability of established species to extinction, but Lyellian percentages for Neogene bivalve faunas of California and Japan suggest that population size is a more important variable along continental shelves. The data employed to reach this conclusion are Lyellian percentages for latest Pliocene (∼2 ma old) bivalve faunas of California and Japan ( N = 245 species). These regions did not suffer heavy extinction during the recent Ice Age, and for each region the Lyellian percentage is 70%–71%. Discrepancies in population size appear to explain the following differences in survivorship to the Recent (Lyellian percentage) for three pairs of subgroups: (1) burrowing nonsiphonate species (42%) versus burrowing siphonate species (84%), which suffer less heavy predation; (2) burrowing nonsiphonate species of small size (73%) versus burrowing nonsiphonate species of large body size (96%); (3) Pectinacea (30%) versus other epifauna (71%), which suffer less heavy predation. During the Mesozoic Era, when predation was less effective in benthic settings, mean species duration for the Pectinacea was much greater (∼20 ma). Along the west coast of North and Central America, mean geographic range is greater for siphonate species of large body size than for siphonate species of small body size and greater still for pectinacean species. These ranges are inversely related to mean species longevity for the three groups, which indicates that geographic range is not of first-order importance in influencing species longevity. Species with nonplanktotrophic development neither exhibit narrow geographic ranges along the west coast of North and Central America nor have experienced high rates of extinction in California and Japan. Rates of extinction are so high for Neogene pectinaceans and nonsiphonate burrowers that without enjoying high rates of speciation these groups could not exist at the diversities they have maintained during the Neogene Period. They are apparently speciating rapidly because of the fission effect : the relatively frequent generation of new species from populations that are fragmented by heavy predation. Thus, ironically, there may be a tendency for high rates of speciation to be approximately offset by high rates of extinction. Only if mean population size for species in a particular group becomes extremely small is it likely to result in a high rate of extinction and a low rate of speciation—and hence a dramatic decline of the group. The fission effect may contribute to the general correlation in the animal world between rate of speciation and rate of extinction.

Physiological Energetics of Marine Molluscs

Chapter

Dec 1983

This chapter discusses the physiological energetics of marine molluscs. The measurement of the components of the energy balance equation for individual organisms—namely, ingestion, absorption, excretion, and respiration—allows the derivation of the energy available to the animal for growth and for reproduction. In this way, it is possible to analyze the relationships between growth and various endogenous and exogenous variables in terms of underlying physiological processes. The chapter discusses various physiological components of growth in marine molluscs (excluding the cephalopods) in relation to the major variables of body size, seasonal effects, temperature, oxygen concentration, and ration level. Studies on energy flow at the population level indicate the average rates and efficiencies that have been reported in the major trophic categories. Three efficiencies of energy transfer are commonly considered: (1) absorption efficiency (A/C); (2) gross growth efficiency (P/C); and (3) net growth efficiency (P/A). The concept of scope for growth, which was regarded as the difference between the energy of the food an animal consumes and all other utilizations and losses, has descriptive validity for a wide range of environmental variables and has been widely used in the study of physiological adaptation in molluscs. Recent advances in knowledge of the population genetics of marine molluscs pose a challenge to the whole-animal physiologist, and future research in either discipline must clearly take account of recent understanding that derives from the other.

Beiträge zur Paläontologie der nordalpinen Riffe. Die Fauna der Zlambach-Mergel der Fischerwiese bei Aussee, Steiermark (exkl. Coelenterata und Mikrofossilien)

Article

Jan 1967

H. Zapfe

The Alpine Kössen Formation, a key for European topmost Triassic correlations

Article

Jan 1990

R. Golebiowski

Response of marine plankton communities to a global atmospheric darkening

Article

Jan 1982

Two independent calculations suggest that temperate marine zooplankton would starve to death relatively quickly if phytoplankton photosynthesis were to cease. A sudden atmospheric darkening, blocking 99% of sunlight, as might accompany the impact of a large meteor, would be sufficient to stop global photosynthesis. An equation derived from basic principles, solved using North Sea plankton data, gives 9-41 days as the duration of the shortest atmospheric darkening needed to initiate a zooplankton starvation crisis during the spring season. An adaptation of a simple plankton model gives outer limits ranging from 104 days in January to 33 days in July and August for critical blackout durations. Such an event cannot be discounted as a cause of the widespread terminal Cretaceous plankton extinction. -from Authors

The first 2 million years after the Cretaceous-Tertiary boundary in east Texas: rate and paleoecology of the molluscan recovery

Article

Jan 1993

Analysis of molluscan collections from a 3+my interval around the Cretaceous-Tertiary (K-T) interval in east Texas suggests that molluscs suffered an extinction at or near the K-T boundary, followed by a prolonged period of stress which lasted through the P0 and P1a planktic foraminiferal zones. Species richness and the relative abundance of deposit feeders generally track the 13C depletion curve suggesting that the stress was caused by a lack of primary production. A stable, relatively diverse, suspension feeding molluscan community was reestablished less than two million years after the K-T boundary. -from Authors

Anatomy of a Regional Mass Extinction: Plio-Pleistocene Decimation of the Western Atlantic Bivalve Fauna

Article

Feb 1986

Steven M. Stanley

The Early Pliocene marine faunas of the southeastern United States were distinct from those of the Bahamas and Caribbean, apparently being separated from them by a zone of cool upwelling. Study of the fates of 361 Early Pliocene bivalve species reveals that a regional mass extinction occurred in the Eastern United States beginning in Late Pliocene time, when continental glaciers expanded, and continued into Early Pleistocene time, eliminating perhaps as many as 65% of the Early Pliocene species. Several observations oppose the hypothesis that Pleistocene regressions would have caused heavy extinction even in the absence of refrigeration. Among these are 1) the fact that in the Eastern Pacific Pleistocene extinction was weak even for species endemic to the temperate-warm temperate shelf, which was areally smaller than the shelf of the southeastern United States, and 2) the fact that even Western Atlantic species that were small, abundant, and adapted to muddy conditions suffered heavy losses. -from Author

Distribution, dynamics and palaeoecology of Kimmeridgian (Upper Jurassic) shelf anoxia in western Europe

Article

Dec 1991

Wolfgang Oschmann

Facies and related macrobenthic associations in the Kimmeridgian epeiric basin in Western Europe are arranged along an onshore-offshore gradient. It ranges from an intermediate-to-high-energy nearshore zone to a low-energy oxygen-controlled offshore environment. Anoxia in the Kimmeridgian epeiric basin was not a permanent feature and cannot be described by the classical models which define aerobic, dysaerobic and anaerobic facies zones. These models have been proposed for deep (slope and basin) environments, in which the oxygen values at a certain depth remain in general constant. In contrast, anoxia in the Kimmeridgian is more dynamic and resembles modern anoxia occurring in eutrophic shelf and epeiric basins (e.g. the coastal areas of Mid-Atlantic Bight, North Sea and Baltic Sea) and exhibit remarkable annual oxygen fluctuations. Therefore, in contrast to the classical models, a modified oxygen zonation for shelf environments is introduced, in order to explain the palaeoenvironment and dynamic alternation of Kimmeridgian anoxia. Both end members, the aerobic and the anaerobic environment, do occur as well. However, the short-term fluctuations prevent establishment of the dysaerobic zone. Instead, there is a seasonal anaerobic to anoxic environment, here defined as poikiloaerobic zone , which is colonized only by a few opportunists.

Biofacies, stratigraphic distribution and depositional models of British onshore Jurassic black shales

Article

Dec 1991

The majority of British Jurassic dysaerobic and anaerobic facies (black shales) accumulated in rapidly subsiding basinal areas. Exceptionally, during the earliest stages of transgression, organic-rich facies expanded their distribution into more marginal areas. The biofacies of the black shales display a range of species richness values which, when ranked, record an oxygen gradient that is also reflected by gradients in geochemical and sedimentological data. Truly anaerobic facies (no benthic taxa present) are very rare in the British Jurassic. More common are fissile organic-rich shales with discrete, low-diversity horizons of benthos here defined as lower dysaerobic biofacies. These are interpreted to have formed in a generally anoxic environment punctuated by benthic colonization events in response to ephemeral improvements of oxygen levels. Upper dysaerobic biofacies are characterized by slightly higher diversity faunas scattered throughout poorly fissile strata. The favoured depositional model for the British Jurassic black shales attributes the high preservational values of organic carbon to accumulation in oxygen-deficient waters trapped beneath a stratified water column in the deepest, basinal areas. We propose an ‘expanding puddle’ model for transgressive black shales. Deep water conditions are envisaged to become proportionally more extensive during early transgression due to the combined effects of subsidence, a rapid rate of sea-level rise and, unique to this portion of the sea-level curve, sediment starvation.

Comparison of Major Sequences of Organic-Rich Mud Deposition in the British Jurassic

Article

Apr 1980

K. A. Morris

The British Jurassic contains 3 major sequences of organic-rich shales: the Jet Rock Formation (Lower Toarcian), the Lower Oxford Clay (Callovian), and the Kimmeridge Clay (Kimmeridgian). In addition minor sequences are found in the Blue Lias Formation and the Shales-with-Beef Formation (Hettangian-Sinemurian). The Lower Oxford Clay has the lowest average organic carbon content and was deposited in mildly oxygenated bottom waters. The sediment profile consisted of a thin upper oxidizing layer, with reducing conditions occurring a few cm below the sediment surface. The Jet Rock Shales were laid down in very poorly oxygenated bottom waters. Here reducing conditions extended up to the sediment surface and this resulted in the preservation of a higher organic carbon content. The Kimmeridge Clay shows a much wider variation in organic carbon content than the other examples, indicating accumulation in an environment which periodically fluctuated between mildly oxygenated and totally anoxic.

Bivalve filter feeding: hydrodynamics, bioenergetics, physiology and ecology

Article

Oct 1992
J EXP MAR BIOL ECOL

Jeff Shimeta

Mass extinctions: Ecological selectivity and primary production

Article

Jan 1991
GEOLOGY

If mass extinctions were caused by reduced primary productivity, then extinctions should be concentrated among animals with starvation-susceptible feeding modes, active lifestyles, and high-energy budgets. The stratigraphic ranges (by stage) of 424 genera of bivalves and 309 genera of articulate brachiopods suggest that there was an unusual reduction of primary productivity at the Cretaceous/Tertiary (K/T) boundary extinction. For bivalves at the K/T, there were (1) selective extinction of suspension feeders and other susceptible trophic categories relative to deposit feeders and other resistant categories, and (2) among suspension feed-ers, selective extinction of bivalves with active locomotion. During the Permian-Triassic (P/Tr) extinction and Jurassic background time, extinction rates among suspension feeders were greater for articulate brachiopods than for bivalves. But during the K/T event, extinction rates of articulates and suspension-feeding bivalves equalized, possibly because the low-energy budgets of articulates gave them an advantage when food was scarce.

Article

Dec 1991

Recent studies of contemporary basins and ancient strata have provided a basis for expanding and refining early oxygen-related marine biofacies models. New observations permit higher resolution in palaeoecological, palaeoceanographic, and basin analyses. Five oxygen-related biofacies are currently recognized. (1) Anaerobic biofacies: well-laminated strata lacking in situ macro- and microbenthic body fossils and microbioturbation; may contain well-preserved remains of nektonic vertebrates, epiplanktonic or otherwise transported invertebrates, and faecal material of planktonic and/or nektonic origin. (2) Quasi-anaerobic biofacies: laminated strata, subtly disrupted by microbioturbation, containing microbenthic body fossils but lacking in situ macrobenthic body fossils; allochthonous body fossils and recognizable planktonic faecal material may be common. (3) Exaerobic biofacies: laminated strata similar to that of anaerobic or quasianaerobic biofacies but containing in situ epibenthic macroinvertebrate body fossils. (4) Dysaerobic biofacies: bioturbated strata characterized by low-diversity assemblages of relatively small, poorly calcified macrobenthic body fossils or absence of body fossils altogether. (5) Aerobic biofacies: bioturbated strata (where physical processes do not dominate) containing diverse assemblages of relatively large, heavily calcified macrobenthic body fossils. Recognition of these biofacies facilitates the recognition of relative palaeo-oxygenation gradients along the seafloor, vertically across the sediment-water interface, and through time. Application of sensitive trace-fossil models permits even more detailed reconstructions of benthic oxygenation histories for bioturbated strata, particularly those that fall within the previously defined dysaerobic realm.

A classification of Jurassic marine sequences and an example from the Toarcian (Lower Jurassic)of Great Britain

Article

Mar 1979
PALAEOGEOGR PALAEOCL

Keith A. Morris

A classification of Jurassic marine shales is proposed based on an analysis on the Toarcian (Upper Lias) sediments of the Lower Jurassic of Yorkshire, Great Britain. Using sedimentological, body-fossil and trace-fossil features, this sequence of apparently monotonous shales can be subdivided into three facies: 1.(a) Normal shale: a homogeneous bioturbated sediment often containing sideritic nodules or horizons. Trace-fossils are dominated by Chondrites; benthic body-fossils are abundant and diverse.2.(b) Restricted shale: consisting of poorly laminated sediment with scattered calcareous concretions. Bioturbation is generally sparse, with thin discrete pyritic burrows, while the benthic fauna is dominated by deposit feeding protobranch bivalves.3.(c) Bituminous shale: a finely laminated sediment with pyritic calcareous concretions, little or no bioturbation, and a benthic fauna which is sparse and entirely epifaunal.Each facies can be interpreted in terms of modern-day shelf mud environments and the balance between dissolved oxygen and hydrogen sulphide in the sediment column.

Is famine a common factor in marine mass extinctions? Geology

Article

Jan 1994
GEOLOGY

A comparison of biotic, sedimentary, and stable isotope patterns across the mass extinctions at the Cenomanian-Turonian and Cretaceous-Tertiary boundaries shows that despite differences in initial trigger, duration, and scale of the two events, reduction of marine primary productivity is a common factor. Our model predicts that zooplankton and suspension feeders will be most severely affected during marine mass extinctions, survivors will be small, and biotic turnover will be concentrated during significant delta13C excursions. The model is thus testable by using data from other mass extinctions.

The End-Triassic Mass Extinction Event

Article

Jan 1988

A. Hallam

The end-Triassic mass extinction event, one of the five biggest in the Phanerozoic, is clearly marked in the marine realm by the almost total extinction of the ammonites, final disappearance of the conodonts, collapse of the reef ecosystem, and substantial changes in other groups. In the terrestrial realm a contemporary mass extinction event among the tetrapods is clearly recorded in eastern North America, the site of the best stratigraphic record, and there was also a major floral turnover that has probably been hitherto underestimated. With regard to possible causes, there is no evidence in the stratigraphic sequence supporting bolide impact, such as shocked quartz or iridium anomalies, although such evidence has been sought, and no evidence of a significant climatic change across the Triassic/Jurassic boundary. There is, however, strong evidence of a sea-level change at the boundary in the form of a regressive-transgressive complet that appears to be associated with the inception of tensional tectonics and volcanicity in the central part of Pangaea. In the western Americas there is evidence of transgression-sea-Ievel rise at or close to the Triassic-Jurassic boundary but no evidence of preceding regression. Both in Europe and the Americas, transgressive deposits are characteristically anoxic or hypoxic. The underlying control is likely to be bound up with events in the mantle.

End Triassic Bivalve Extinction: Lombardian Alps, Italy

Article

Mar 1995

A major biotic crisis affecting virtually all major marine invertebrate clades occurred at the close of the Triassic. Species‐level data on bivalves from the Lombardian Alps of Italy record the extinction and suggest a possible causal mechanism. A significant decline in species richness is observed during the lower Rhaetian, where 51% of bivalve species, equally distributed among infaunal and epifaunal filter‐feeders, went extinct. The taxonomic loss at the middle Rhaetian was more severe, where 71% of the bivalve species were eliminated, including all infaunal and 50% of the epifaunal species. The data indicate that the extinction selectively eliminated infaunal bivalves. An initial loss of bivalve species richness during the middle and upper Rhaetian correlates with changes in sedimentary facies related to a fall in relative sea level. This sea level fall is marked by the onset of peritidal micrites and shifting ooid shoals which may have rendered substrates unsuitable for both epifaunal and infaunal bivalves. The possible influences of temperature and salinity fluctuations are difficult to assess, but they may also have had a deleterious effect on the local bivalve fauna. The loss due to peritidal conditions is not consistent with the selective survivorship of epifaunal taxa recurring in overlying Jurassic rocks. We propose that physiologic differences and selective resistance to physical stress are consistent with the pattern of selective extinction. Facies shifts associated with the marine regression are not sufficient to account for the extremely high magnitude of infaunal extinction. This selection against infaunal bivalves is probably caused by their decreased capacity to filter feed relative to their metabolic demands. A decrease in primary productivity could have selectively eliminated the infauna. Oceanographic processes or atmospheric darkening, perhaps caused by an extraterrestrial impact, could drastically limit food resources (primary productivity) and is consistent with the selective extinction at the end of the Triassic.

The exaerobic zone, a new oxygen-deficient marine biofacies

Article

May 1987

Classical biofacies models1,2 for reconstructing palaeoenvironments of strata deposited in oxygen-deficient marine settings define three principal facies: aerobic (> 1.0 ml 1−1 O2), dysaerobic (1.0 to 0.1 ml 1−1 O2) and anaerobic (<0.1 ml 1−1 O2) zones. These models have postulated a decrease in organism size and degree of calcification as well as a drastic reduction in the relative percentage of fauna possessing calcified skeletons as the dysaerobic/anaerobic boundary is approached. Through use of evidence independent of that provided by body fossils, we demonstrate here that in portions of the Monterey Formation (Miocene; California) the bivalve Anadara montereyana occurs in situ almost exclusively in strata deposited at the dysaerobic/anaerobic boundary. The occurrence of fossils of large well-calcified benthic macroinvertebrates at this redox boundary contradicts classical biofacies models1,2 and there-fore provides the basis for definition of a new oxygen-related biofacies, the 'exaerobic zone’. The exaerobic zone concept, when adjusted for differences in basin configuration and palaeoceano-graphic conditions, provides a potentially useful model for explain-ing occurrences of shelly benthic fossils within laminated, organic-rich strata of other Phanerozoic marine sequences.

The end-Triassic bivalve extinction event

Article

Dec 1981
PALAEOGEOGR PALAEOCL

A. Hallam

One of the most important episodes of mass extinction of animal groups in the whole of the Phanerozoic took place in the latter part of the Triassic, but the time of major faunal turnover of the vertebrates preceded that of marine invertebrates by several million years. As shown by ammonites, brachiopods and conodonts, decline from a Carnian—early Norian diversity peak was followed by a significant extinction episode at the end of the period. This pattern is confirmed at generic and subgeneric level by the bivalve molluscs, probably the most abundant and diverse macroinvertebrate group. This paper analyses the bivalves in detail and attempts to seek a relationship of the extinction event to environmental changes as recorded by late Triassic facies.

Salinity reduction of the end-Triassic sea from Alpine region into northwest Europe

Article

Oct 2007
Lethaia

A palaeoecological analysis of the Penarth Group (=‘Rhaetic’) of southern England and Wales is undertaken in terms of a species-richness comparison with the Zlambach and Kössen Beds of the Austrian Alps. The three groups studied, bivalves, foraminifers and ostracodes, comprise the most important invertebrate faunas occurring in the deposits cited. All show significant diversity from the Alps into northwest Europe. Coupled with the disappearance of stenohaline elements including ammonites, and taking into account other facies information, the evidence suggests a transgression of a shallow epicontinental sea in northwest Europe at the end of the Triassic. The salinity of this sea (˜25–30%□) was appreciably below that of the Tethyan ocean.

Alternative biofacies model for dysaerobic communities

Article

Oct 2007
Lethaia

An abundant calcareous fauna has been discovered in the oxygen minimum zone (OMZ; < 0.5 ml/l O2) off central California at oxygen concentrations considerably less than those predicted by previous ecological models. Analysis of box core samples and bottom photographs has revealed a distinct depth zonation of echinoderms. Asteroids and ophiuroids are most abundant along the upper and lower edges of the OMZ, respectively, whereas echinoids are found near the core of this zone where oxygen levels are as low as 0.3 ml/l O2. As these heart urchins are very abundant (14/m2), they represent a potentially significant component of the fossil record of OMZ's. Locally these urchins are capable of disturbing over 90% of near surface sediment. The core of the OMZ is inhabited by hermit crabs that actively transport and recycle gastropod shells. This ‘biotransport’ results in an accumulation of potentially preservable, non-endemic. hard-bodied organisms which may lead to misinterpretation of paleo-oxygenation conditions. We propose an alternative to the Rhoads & Morse (1971, Lethaia 4) biofacies model for open-ocean, dysaerobic environments which consists of: (1) a zone devoid of maeroinvertebrates. characterized by laminated sediments (<0.1 ml/l O2); (2) a zone dominated by small (1–2 mm) soft-bodied infauca which exhibits moderate disturbance of laminae due to bioturbation (0.1–0.3 ml/l O2); and (3) a zone inhabited by an abundant calcareous fauna characterized by highly bioturbated sediments (>0.3 ml/l O2).

Evolutionary and ecologic significance of oxygen-deficient basins

Article

Oct 2007
Lethaia

Benthic invertebrates living in low oxygen regions of the Black Sea, Gulf of California, and basins off Southern California form three major biofacies associated with the following concentrations of dissolved oxygen: (1) an azoic region (≤ 0.1 ml/1), (2) a low diversity, small, soft-bodied infauna (0.3–1.0 ml/1), and (3) a diverse calcareous fauna (2 1.0 ml/l). These biofacies recapitulate the chronologic appearance of Pre-Cambrian trace fossils followed by a diverse calcified fauna in the Cambrian. The basin model has been used to reconstruct a Lower Cambrian oxygen level of 0.1 P.A.L. (present atmospheric level). This value is ten-fold that proposed in the Berkner-Marshall hypothesis.

Comparative studies on the influence of oxygen deficiency and hydrogen sulfide on marine bottom invertebrates

Article

Aug 1973
Neth J Sea Res

H. Theede

Comparative measurements of the resistance of marine bottom invertebrates of macrofauna (polychaetes, lamellibranchs, gastropods, crustaceans, echinoderms) to oxygen deficiency and to H2S reveal correlations to the respiratory conditions of the biotopes, where the species naturally occur. High resistance to H2S parallels that to oxygen deficiency alone. This is valid on the organismic as well as on the tissue level. The resistance to H2S is strongly modified by some environmental factors; it is significantly higher at low temperatures and at reduced pH-values, whereas, in euryhaline species, salinity only has a small effect within a relatively broad range. In bivalves resistance to oxygen deficiency and to H2S is connected with a pronounced ability to reduce mechanical and metabolic activity by responses of the whole animals and by cellular reactions. Measurements of the dependency of oxygen consumption on oxygen tension in whole animals demonstrate different types of reaction dependent on the species and the states of activity.] Temporary increases of oxygen consumption at “normal” oxygen tensions after subjection to seawater deprived of oxygen indicate adaptations to oxygen deficiency.

The Triassic-Jurassic ecostratigraphic transition in the Lombardian Alps, Italy

Article

Jul 1994
PALAEOGEOGR PALAEOCL

Christopher A McRoberts

Three paleoenvironmental phases and two declines in diversity characterize the Late Triassic to Early Jurassic history of the Lombardian Platforms. The first phase, of Late Triassic time (?Choristoceras Zone), consists of 1–5 m thick shallowing-upward subtidal cycles of molluscan, coralline, and echinoderm wackestone and packstone of the Zu Limestone. Biotic and ecostratigraphic characteristics such as typical Rhaetavicula contorta fauna and facies allow correlation to the Kössen Formation of the Northern Calcareous Alps.The second phase, of latest Triassic time (?upper Choristoceras Zone), consists of shallow restricted marine or peritidal carbonates of the Chonchodon Formation dominated by barren lime mudstone and dolostone, algal laminites, and oolitic grainstone. The Zu-Conchodon transition predates the Triassic-Jurassic boundary and represents the first, and most severe, diversity decline for the Lombardian fauna corresponding to a fall in sea-level. Where observed, the upper and lower contacts of the Conchodon Formation are conformable and do not constitute sequence boundaries as suggested by some workers.The Lower Jurassic (?Psiloceras Zone) Sedrina Limestone marks the beginning of the third phase with the onset of transgression and return of normal marine conditions. Typical microfacies include molluscan, echinoderm, and sponge wackestone and packstone with abundant anomuran microcoprolites. The second diversity decline occurred at, or just above, the Triassic-Jurassic boundary at the Conchodon-Sedrina transition, where the remaining restricted marine forms disappeared with the transgression. Anoxia was not a factor in this decline in diversity, although other mechanisms in addition to sea-level change cannot be discounted.

Primary productivity and the Cretaceous/Tertiary boundary event in the oceans

Article

Mar 1987

Geochemical and paleontological evidence indicate that marine primary productivity decreased rapidly at the Cretaceous-Tertiary boundary resulting in the selective elimination of those organisms directly dependent upon the flux of organic matter as a food source (filter and suspension feeders). Detritus and deposit feeders, however, suffered relatively fewer extinctions, apparently utilizing the reservoir of organic matter stored within the sediments. Lower rates of oceanic productivity might have continued for at least 1.5 m.y. following the initial decrease despite the rapid evolution of fauna and flora during the early Paleocene. Although these results can be viewed as being compatible with the bolide impact hypothesis, the extended period of low productivity afterwards suggests some longer term effects on the biosphere than predicted by such a model.

Particle clearance and absorption of phytoplankton and detritus by the sea scallop Placopecten magellanicus (Gmelin)

Article

May 1990
J EXP MAR BIOL ECOL

Diets of cultured phytoplankton (Tahitian Isochrysis aff.galbana and Chaetoceros gracilis Schütt), fresh and “aged” kelp powder (Laminaria longicruris de la Pyl.) and resuspended sediment were fed to sea scallops (Placopecten magellanicus Gmelin) from Georges Bank. The majority of particles from each diet were within the size range effectively retained by sea scallops (>5/gmm). Based solely on net and gross absorption efficiency (AE) data as an index of nutritional quality, the following ranking was observed: “aged” kelp debris >C. gracilis = I. galbana >freshkelp >resuspended sediment. While only a small fraction of the total sediment organic matter was utilized (mean net AE = 9 %), an average of 50 % of available nitrogen was absorbed. Resuspended paniculate matter may play an important role in the energy gain and nitrogen demands of this species. Despite the ability of P. magellanicus to efficiently digest “aged” kelp debris, it was consumed at a much lower rate than phytoplankton and did not contribute significantly to the dietary requirements of the sea scallop. These results demonstrate the importance of phytoplankton as a diet for the sea scallop, but indicate that detrital particles can contribute to energy gain during periods when phytoplankton are less available to meet energy demands.

Comparative Physiology of Suspension Feeding

Article

Feb 1975

C. Barker Jørgensen

Patterns of generic extinction in the fossil record

Article

Feb 1988

Analysis of the stratigraphic records of 19,897 fossil genera indicates that most classes and orders show largely congruent rises and falls in extinction intensity throughout the Phanerozoic. Even an ecologically homogeneous sample of reef genera shows the same basic extinction profile. The most likely explanation for the congruence is that extinction is physically rather than biologically driven and that it is dominated by the effects of geographically widespread environmental perturbations influencing most habitats. Significant departures from the congruence are uncommon but important because they indicate physiological or habitat selectivity. The similarity of the extinction records of reef organisms and the marine biota as a whole confirms that reefs and other faunas are responding to the same history of environmental stress.

The Late Triassic–Hettangian bivalves turnover in Lombardy (Southern Alps): Rivista Italiana di Paleontologia e Stratigrafia

Jan 1992
97-431

Cited Allasinaz

CITED Allasinaz, A., 1992, The Late Triassic–Hettangian bivalves turnover in Lombardy (Southern Alps): Rivista Italiana di Paleontologia e Stratigrafia, v. 97, p. 431– 454.

Element concentrations at the Triassic-Jurassic boundary in the Kendelbachgraben section, Austria: International Geological Correlation Program Project 199, Rare Events in Geology, Abstracts of Lectures and Excursions Guide

Jan 1988
15-1

D D Badjukov
L D Barsukova
G M Kolesov
I V Nizhegoroda
M A Nazarov
H Lobitzer

Badjukov, D. D., Barsukova, L. D., Kolesov, G. M., Nizhegoroda, I. V., Nazarov, M. A., and Lobitzer, H., 1988, Element concentrations at the Triassic-Jurassic boundary in the Kendelbachgraben section, Austria: International Geological Correlation Program Project 199, Rare Events in Geology, Abstracts of Lectures and Excursions Guide, v. 15, p. 1–2.

Bivalvia: Les Cahiers de l

Jan 1990
55-60

A Hallam

Hallam, A., 1990b, Bivalvia: Les Cahiers de l'Université Catholique de Lyon, Série des Sciences, v. 3, p. 55– 60.

The timing and cause of Late Triassic marine invertebrate extinctions: Evidence from scallops and crinoids

Jan 1989
174-194

A L A Johnson
M J Simms

Johnson, A. L. A., and Simms, M. J., 1989, The timing and cause of Late Triassic marine invertebrate extinctions: Evidence from scallops and crinoids, in Donovan, S. K., ed., Mass extinctions: Processes and evidence: London, Bellhaven, p. 174–194.

Late Norian palaeoenvironments

Jan 1993

J Marcoux

Marcoux, J., and 11 others, 1993, Late Norian palaeoenvironments, in Dercourt, J., et al., eds., Atlas, Tethys Paleoenvironmental Maps and Explanatory Notes: Paris.

Lack of selective extinction among end-Cretaceous bivalves: Geological Society of America Abstracts with Programs

Jan 1994
394

D M Raup
D Jablonski

Raup, D. M., and Jablonski, D., 1994, Lack of selective extinction among end-Cretaceous bivalves: Geological Society of America Abstracts with Programs, v. 26, no. 7, p. A-394.

Black shales: Oxford Monographs on Geology and Geophysics 30

Jan 1994

P B Wignall

Wignall, P. B., 1994, Black shales: Oxford Monographs on Geology and Geophysics 30, 127 p.

Jan 1987
1-88

C L Griffiths
R J Griffiths

Griffiths, C. L., and Griffiths, R. J., 1987, Bivalvia, in Pandian, T. J., and Vernberg, F. J., eds., Animal energetics: London, Academic Press, p. 1– 88.

Selective extinction among end-Triassic European bivalves

Abstract

No full-text available

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Selective extinction among end-Triassic European bivalves